Method and system for calculating time-varying runoff coefficient reflecting urbanization underlying surface regulation and storage

Abstract

The application discloses a time-varying runoff coefficient calculation method and system reflecting urbanization underlying surface regulation and storage, and steps are as follows: S1, obtaining rainfall data of a city research area, drawing a column chart and a curve chart of a rainfall process, and extracting high-precision digital surface model data by using high spatial resolution satellite stereo image pair data; S2, performing grid processing on the high-precision digital surface model data, constructing a grid type, and performing land utilization division and extraction analysis; S3, calculating hydrological parameters including a basin water content parameter, vegetation interception, a filling and depression parameter and a infiltration parameter; S4, calculating building roof runoff, effective impervious area, non-effective impervious area, pervious area and water area based on the rainfall process, the land utilization division and the hydrological parameters; and S5, calculating a time-varying runoff coefficient. The application can accurately evaluate the availability of rainfall water resources, provide scientific guidance for urban rainwater collection and utilization, and provide a more reliable basis for urban flood forecasting and drainage system design.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of time-varying analysis of runoff coefficient in urbanized areas, and particularly relates to a time-varying runoff coefficient calculation method and system reflecting the storage of urbanized underlying surface. BACKGROUND

[0002] The hydrological response of urbanized areas is significantly different from that of non-urbanized areas, mainly reflected in the increase of surface runoff and the decrease of groundwater recharge. This change poses new challenges to urban drainage system design and flood management. In the past few decades, in order to better understand and simulate the hydrological processes in urbanized areas, researchers have developed various hydrological models, such as SWMM (Storm Water Management Model) and SCS (Soil Conservation Service) model. The SWMM model can simulate the total runoff under rainfall events, but it mainly provides a comprehensive runoff coefficient, i.e. the ratio of total runoff to total precipitation, which cannot reflect the time-varying characteristics of runoff coefficient during the rainfall event process. The SCS model estimates the total runoff of a rainfall event through the Curve Number (CN). This method assumes that the runoff coefficient is related to factors such as land cover, soil type and moisture conditions, but does not consider the rainfall intensity or the specific temporal and spatial distribution of rainfall events, and is not sensitive enough for dynamic evaluation of runoff changes in urbanized areas.

[0003] Runoff coefficient refers to the ratio of runoff to rainfall under certain conditions, which is an important parameter for evaluating the absorption and loss of rainfall water by the ground. In urbanized areas, due to the increase of impervious surface area, the surface runoff increases and the precipitation infiltration capacity decreases, so the runoff coefficient will increase with the increase of urbanization degree. However, both the comprehensive runoff coefficient and the runoff coefficient calculated by the SCS through the Curve Number cannot accurately reflect the runoff characteristics at different time periods in a rainfall event, and have obvious limitations in the face of the current demand for fine management of urban water resources and flood control and disaster reduction. SUMMARY

[0004] In view of the limitations of the prior art, the present application provides a time-varying runoff coefficient calculation method and system reflecting the storage of urbanized underlying surface, which aims to analyze the runoff process of building roofs, non-effective impervious areas (NEIA), effective impervious areas (EIA), pervious underlying surfaces (PA), and water areas according to rainfall data and high-precision digital surface model data at different time periods in a rainfall event, and to calculate time-varying runoff coefficients, including instantaneous time-varying runoff coefficients and cumulative time-varying runoff coefficients. This provides a more detailed perspective for analyzing and simulating runoff responses under rainfall events. By calculating time-varying runoff coefficients and cumulative time-varying runoff coefficients based on urban area study areas, the real-time changes of runoff coefficients in the rainfall runoff process can be reflected, and the time dimension analysis capability is introduced into the hydrological model. Time-varying runoff coefficients will help to more accurately assess the availability of rainfall water resources, provide scientific guidance for urban rainwater collection and utilization, and provide more reliable basis for urban flood forecasting and drainage system design, to solve the complexity of the change of runoff coefficients with time which is usually ignored or simplified by traditional models.

[0005] In the calculation of time-varying runoff coefficients in urbanized areas, it is crucial to distinguish between effective impervious areas (EIA) and non-effective impervious areas (NEIA), because the contributions of these two types of impervious surfaces to runoff are significantly different, directly affecting the accurate calculation of time-varying runoff coefficients and their application in urban hydrological analysis. By distinguishing whether the impervious area is effective or not, the storage capacity of the pipe network can be considered.

[0006] Definition: Effective impervious area (EIA) refers to urban impervious surfaces directly connected to drainage systems or urban water areas; while the part of the runoff that flows through the pervious area before entering the pipe network is the non-effective impervious area (NEIA); the sum of the two is the total impervious area (TIA); the underlying surface of the permeable water flow is the pervious underlying area (PA).

[0007] To achieve the above purpose, the specific schemes of the present application are as follows:

[0008] A time-varying runoff coefficient calculation method reflecting the storage of urbanized underlying surface, comprising the following steps:

[0009] S1, obtain fine rainfall data of the urban study area, draw a column chart and a curve chart of the rainfall process, and extract high-precision digital surface model data by using high-spatial-resolution satellite stereo image data;

[0010] S2, process the high-precision digital surface model data extracted in step S1 to remove house and vegetation information to obtain high-precision digital elevation model data, perform raster processing on the high-precision digital surface model data to construct a grid type, and perform land use division to obtain a city land use data layer to distinguish the types of various underlying surfaces, such as building roofs, effective impervious areas, non-effective impervious areas, pervious areas, and water areas;

[0011] S3, calculate hydrological parameters based on the grid type constructed in step S2, the hydrological parameters including watershed water content parameters, vegetation interception, depression storage parameters, and infiltration parameters;

[0012] S4, calculate building roof runoff and runoff of effective impervious areas, non-effective impervious areas, pervious areas, and water areas based on the rainfall process, land use division, and hydrological parameters obtained in steps S1, S2, and S3;

[0013] S5, calculate time-varying runoff coefficients based on the curve chart in step S1 and the building roof runoff and runoff of effective impervious areas, non-effective impervious areas, pervious areas, and water areas calculated in step S4.

[0014] Further, the land use division in step S2 includes the following steps:

[0015] S21, import the city land use data layer, the high-precision digital elevation model data, and relevant vector layers of all data layers in the rainwater collection system into ArcGIS Pro software;

[0016] S22, rasterize all data layers in step S21, and convert the entrance position vector layer and conveying elements of the rainwater collection system into a raster format, ensure that all data layers in step S22 are converted into a consistent coordinate system, and perform cutting according to watershed boundaries; the conveying elements include curb opening entrances, open channels, ponds, drainage ditches, and drainage pipe networks;

[0017] S23, resample all data layers in step S22 to make the data layers have consistent resolutions;

[0018] S24, depression storage: perform depression storage processing on the high-precision digital elevation model data in step S21 by using ArcGIS Pro software to remove all depressions, identify depression positions by subtracting the high-precision digital elevation model data in step S21 from the high-precision digital elevation model data after depression storage processing and searching for non-zero values, and determine the depression storage area of the watershed;

[0019] S25, determining the water flow direction of the impervious area surface, using a weighted interpolation method to adjust the high-precision digital elevation model data to eliminate flat areas;

[0020] S26, after determining the water flow direction, classifying each grid cell in the urban land use data layer according to the runoff characteristics, and finally obtaining a grid composed of building roofs and effective impervious areas, non-effective impervious areas, pervious areas, and water areas.

[0021] Further, the step of classifying each grid cell in the urban land use data layer in step S26 is as follows:

[0022] S261, checking the land cover type of each grid cell;

[0023] S262, for each asphalt / concrete cell, checking each downstream cell along the water flow path, if the downstream cell is also asphalt / concrete and there is a rainwater collection system, then the cell is classified as an effective impervious area;

[0024] S263, if the downstream cell is green, the original cell is considered a non-effective impervious area.

[0025] Further, the pre-precipitation water content of the watershed in step S3 is obtained by satellite remote sensing data or measured data;

[0026] The continuity equation for the amount of water intercepted by vegetation is as follows:

[0027] dS tree = (i-w tree )dt

[0028] In the formula, dS 屋顶 is the water storage depth of vegetation per unit time dt, mm; i is the rainfall intensity corresponding to dt, mm / min; w s is the drainage rate of rainwater through vegetation to the ground, mm / min.

[0029] Further, the calculation of building roof runoff in step S4 is as follows:

[0030] The building roof runoff is the time from the generation of roof rainwater runoff to the flow to the ground, and its calculation formula is as follows:

[0031] T 屋顶 = τ + t0 + t s

[0032] In the formula, T EIA is the time from the generation of roof rainwater runoff to the flow to the ground T; τ is the roof concentration time, min; t0 is the roof runoff response time, min; ts Time for roof rainwater to fall to the ground from the rainwater pipe, min;

[0033] The runoff of the effective impervious area is expressed by instantaneous runoff, and the calculation formula is as follows:

[0034] dR EIA =(i-u EIA )dt

[0035] In the formula, dR EIA is the runoff of the effective impervious area per unit time dt, mm; i is the rainfall intensity corresponding to dt, mm / min; u EIA is the depression rate of the underlying surface of the effective impervious area corresponding to dt, mm / min, u EIA =u EIA (t).

[0036] The runoff of the non-effective impervious area is expressed by instantaneous runoff, and the calculation formula is as follows:

[0037] dR NEIA =(i-u NEIA )dt

[0038] In the formula, dR NEIA is the runoff of the non-effective impervious area per unit time dt, mm; i is the rainfall intensity corresponding to dt, mm / min; u NEIA is the depression rate of the underlying surface of the non-effective impervious area corresponding to dt, mm / min, u NEIA =u NEIA (t).

[0039] The runoff of the underlying surface of the permeable area is expressed by instantaneous runoff, and the infiltration capacity is considered at the same time. When the rainfall intensity i PA of the underlying surface of the permeable area is less than the initial infiltration capacity f0, the underlying surface first satisfies the infiltration and then the depression. When the infiltration rate f i =i PA at the i-th moment, the underlying surface starts to be depressed. When the rainfall intensity i PA of the underlying surface of the permeable area is less than the initial infiltration capacity f0, the runoff formula is as follows:

[0040]

[0041] When the rainfall intensity i PA of the underlying surface of the permeable area is greater than or equal to the initial infiltration capacity f0, the runoff formula of the underlying surface simultaneously performing depression and infiltration is as follows:

[0042] dR PA =(i PA -f p -u PA )dt

[0043] wherein dR PA is the runoff of the underlying surface of the water-permeable area in the unit time dt, mm; i PA is the rainfall intensity on the underlying surface of the water-permeable area, mm / min; f p is the infiltration rate of the watershed at the time t, mm / min; u PA is the depression rate of the underlying surface of the water-permeable area corresponding to the time dt, mm / min;

[0044] The runoff of the water area is calculated by using the Muskingum method evolution formula, and the formula is as follows:

[0045] O2 = C1I1 + C2I2 + C3O1

[0046] C1 = (Kx + Δt / 2) / C0

[0047] C2 = (-Kx + Δt / 2) / C0

[0048] C3 = (K - Kx - Δt / 2) / C0

[0049] C0 = K - Kx + Δt / 2

[0050] wherein I and O are the inflow and outflow of the river section respectively; the subscripts 1 and 2 represent the initial and final time; x is the relative proportion of the inflow and outflow to the influence of the slot storage; K is the storage parameter; C1, C2 and C3 are coefficients determined according to the Muskingum parameters K, x and the time period Δt, and their sum is equal to 1.0; K and x are determined according to the hydraulic characteristics and flow characteristics of the research river section, and are assumed to be constant, which can be determined by using the trial and error method, the least square method, the analysis method, the matrix method, the cumulative method or the direct optimization method according to the inflow and outflow data; wherein the trial and error method is to calculate the best x value which can make the storage-flow relationship curve on the rectangular coordinate paper close to the single value relationship, and the x value range is 0-0.5; K is the slope when the single value curve is assumed to be a straight line.

[0051] Further, the time-varying runoff coefficient in step S5 includes an instantaneous time-varying runoff coefficient and a cumulative time-varying runoff coefficient, the instantaneous time-varying runoff coefficient is calculated according to the instantaneous rainfall dP at each time read from the rainfall curve in step S1, and the calculation formula of the time-varying runoff coefficient through the instantaneous runoff dR is as follows:

[0052]

[0053] wherein: C i is the time-varying runoff coefficient; dR is the runoff change amount in the time dt; dP is the rainfall change amount in the time dt, i is the rainfall intensity corresponding to the unit time dt, mm / min; s tree is the vegetation water storage rate, mm / min; uEIA is the filling rate of the effective impervious underlying surface per unit time dt, mm / min; u NEIA is the filling rate of the non-effective impervious underlying surface per unit time dt, mm / min; u PA is the filling rate of the permeable underlying surface per unit time dt, mm / min; f P is the infiltration rate per unit time dt, mm / min; s w is the time-varying water storage per unit time dt, mm / min;

[0054] or

[0055]

[0056] In the formula, C i is the time-varying runoff coefficient; P(i) is the cumulative rainfall amount corresponding to i moment, mm; dR roof is the building roof yield flow, mm; dR EIA is the runoff of the effective impervious underlying surface per unit time dt corresponding to i moment, mm; dR PA is the runoff of the permeable underlying surface per unit time dt corresponding to i moment, mm; S(i) is the water storage per unit time, mm; F p (i) is the infiltration per unit time of the water area, mm;

[0057] The calculation formula of the cumulative time-varying runoff coefficient is as follows:

[0058]

[0059] In the formula, P(t) is the cumulative rainfall at t moment, m 3 ; S tree (t) is the cumulative vegetation interception amount at t moment, m 3 ; U all (t) is the cumulative filling of the building roof, effective impervious underlying surface, non-effective impervious underlying surface and permeable underlying surface at t moment, m 3 ; F p (t) is the cumulative infiltration amount at t moment, m 3 ; S(t) is the cumulative water storage of the water area at t moment, m 3 .

[0060] A system for implementing the time-varying runoff coefficient calculation method, the system comprising:

[0061] a data acquisition module for acquiring rainfall data and high-precision digital surface model data;

[0062] a filling processing module for determining the filling area of the watershed;

[0063] a land use analysis module for analyzing runoff processes of building roof, effective impervious area, non-effective impervious area, pervious area and water area;

[0064] a grid processing module for processing high-precision digital surface model data and performing land use division and extraction analysis;

[0065] an EIA classification module for classifying each grid cell in the urban land use data layer according to runoff characteristics after determining the water flow direction;

[0066] a hydrological parameter calculation module for calculating hydrological parameters of watershed water content, vegetation interception, infiltration and depression process;

[0067] a water area regulation simulation module for simulating the regulation process of urban water area;

[0068] a runoff and runoff calculation module for calculating building roof runoff and runoff of effective impervious area, non-effective impervious area, pervious area and water area according to rainfall process, land use classification and hydrological parameters;

[0069] a time-varying runoff coefficient calculation module for calculating instantaneous time-varying runoff coefficient and cumulative time-varying runoff coefficient.

[0070] A computer program product, the product comprising a storage medium and computer readable instructions stored on the medium, which, when executed by a computer, implement the computing method.

[0071] Advantages of the present application

[0072] The time-varying runoff coefficient calculation method and system reflecting urbanization underlying surface regulation of the present application can analyze the runoff processes of roof, non-effective impervious area (NEIA), effective impervious area (EIA), pervious area (PA) and water area according to rainfall data and digital elevation and surface data in different time periods of rainfall events, calculate instantaneous time-varying runoff coefficient, and thus more accurately describe the change of runoff coefficient in the rainfall process, and also calculate cumulative time-varying runoff coefficient, i.e. the change characteristics of runoff coefficient accumulated over time, which provides a more detailed perspective for analyzing and simulating runoff response under rainfall events. Through the calculation of time-varying runoff coefficient and cumulative time-varying runoff coefficient based on urban area research area, the real-time change of runoff coefficient in the rainfall runoff process can be reflected, the time dimension analysis capability is introduced into the hydrological model, and the time-varying runoff coefficient will help to more accurately evaluate the availability of rainfall water resources, provide scientific guidance for urban rainwater collection and utilization, and provide more reliable basis for urban flood forecasting and drainage system design, so as to solve the complexity of the change of runoff coefficient with time which is usually ignored or simplified by traditional models. BRIEF DESCRIPTION OF DRAWINGS

[0073] Figure 1 Flow chart of the method for calculating time-varying runoff coefficient reflecting urbanization underlying surface regulation and storage.

[0074] Figure 2 Satellite remote sensing image (a), digital elevation DEM map (b), land use distribution map (c), and land use reclassification map (d).

[0075] Figure 3 Schematic diagram of runoff flow of the present application.

[0076] Figure 4 Rainfall process distribution map of ten-year Chicago rain type of the present application.

[0077] Figure 5 Roof runoff process map of the present application.

[0078] Figure 6 Runoff process map of effective impervious area EIA / non-effective impervious area NEIA of the present application.

[0079] Figure 7 Horton infiltration curve and cumulative infiltration amount map of the present application.

[0080] Figure 8 Permeable area PA runoff process map of the present application.

[0081] Figure 9 Water area regulation and storage process map of the present application.

[0082] Figure 10 Instantaneous rainfall runoff process and time-varying runoff coefficient C i of the present application.

[0083] Figure 11 Cumulative rainfall runoff process and cumulative time-varying runoff coefficient C t of the present application.

[0084] Figure 12 Working principle diagram of the system for calculating time-varying runoff coefficient reflecting urbanization underlying surface regulation and storage of the present application. DETAILED DESCRIPTION

[0085] The present application will be further explained and described with reference to the accompanying drawings and specific embodiments, and it should be noted that the specific embodiments are not used to limit the scope of the present application.

[0086] As Figure 1 , Figure 2 (a)、 Figure 2 (b)、 Figure 2 (c)、 Figure 2 (d) to Figure 12As shown, the specific embodiment provides a time-varying runoff coefficient calculation method and system reflecting urbanization underlying surface regulation and storage, comprising the following steps:

[0087] S1, obtain fine rainfall data of a substorm process in a city research area, draw a column chart and a curve chart i = i(t) of the rainfall process, and use high spatial resolution satellite stereo image data to extract high-precision digital surface model data (hereinafter referred to as: DSM data);

[0088] This embodiment uses ten-year rainfall data, and the total rainfall is 107.6977mm. The city research area is Zhupaihong watershed in Qingxiu district of Nanning city in Guangxi Zhuang Autonomous Region. According to the mask extraction satellite image and DEM data Figure 2 (a)、 Figure 2 (b). Obtain fine rainfall data of a substorm process, then draw a rainfall cumulative process column chart P = P(t) and a curve chart i = i(t), use Chicago rain type to distribute the rainfall process, and draw a ten-year Chicago rain type distribution rainfall process chart of the research area, that is Figure 4 .

[0089] S2, process the high-precision DSM data extracted in step S1 to remove house, vegetation and other information to obtain high-precision digital elevation model data (hereinafter referred to as: DEM data). The DSM data is processed by grid to construct grid type, and GE and Arcgis Pro are used to divide the land use of the DSM data to obtain the land use distribution map, as shown in Figure 2 (c), and the land use is redivided by the steps of S21-S24 to obtain the division of each part of the underlying surface, as shown in Figure 2 (d) divides the types of each part of the underlying surface into building roof, effective impervious area, non-effective impervious area, permeable area and water area. The flow path of each underlying surface type is as shown in Figure 3 .

[0090] The specific steps are as follows:

[0091] S21, divide two basic types of impervious area: roof and traffic system (such as parking lot, road), and import the impervious area data layer (hereinafter referred to as: TIA data layer) in the city land use data layer, fine resolution DEM data and all data layers related to the vector layer of the rainwater collection system into ArcGIS Pro.

[0092] S22, rasterize all data layers, convert the inlet location vector layer and conveyance elements (e.g. curb opening inlets, open channels, ponds, swales, drainage pipe network, etc.) of the stormwater collection system into raster format. Ensure that the TIA data layer, DEM data, and rasterized stormwater collection system data layer are all converted into a consistent coordinate system. Then, clip them according to the watershed boundary so that only the area required for analysis is included. This step is to ensure that all data layers can be integrated and processed within the same analytical framework.

[0093] S23, resample: resample all data layers from step S22 to have a consistent resolution (m). This step ensures compatibility between data layers and the accuracy of the analysis.

[0094] S24, fill depression: use ArcGIS Pro software to fully fill the original DEM to remove all depressions. Then, identify the depression locations by subtracting the original DEM data from the filled DEM data and searching for non-zero values. Non-zero pixels indicate differences, and spatially connected groups of non-zero pixels are considered a depression.

[0095] Depression area: the watershed area of a depression is the sum of the depression area plus its upslope contributing area. Use the D8 algorithm or an elevation difference-based strategy to determine the upslope contributing area to identify and calculate the depression area. For larger watersheds, the fill threshold can be determined by the sink

[0096] S25, determine the flow direction of impervious areas: the flow direction between raster cells is assumed to be from high points to low points, following the slope gradient path. In some cases, consecutive pixels in the DEM data may show the same elevation, making it impossible to determine the flow direction. To solve this problem, a weighted interpolation method is used to adjust the DEM data to eliminate these flat areas, making it possible to determine the flow path.

[0097] S26, after determining the flow direction, the next step is to classify each raster cell in the TIA data layer as an effective impervious area (EIA classification).

[0098] First, check the land cover type of each raster cell (e.g. asphalt / concrete, building roof, green space, or water body). Building roof, water body, and green space cells usually do not directly participate in runoff generation, so they are skipped during the EIA classification process.

[0099] Processing of asphalt / concrete cells: for each asphalt / concrete cell, check each downstream cell along the flow path. If the downstream cell is also asphalt / concrete and there is a stormwater collection system, then the cell is classified as an effective impervious area (EIA) meaning it will have a direct impact on urban runoff.

[0100] If the downstream unit is green land, the original unit is regarded as non-effective impervious area (hereinafter referred to as NEIA) because green land can absorb or slow down water flow and reduce runoff. The final obtained grid is a data layer composed of EIA, NEIA, PA, water area and building roof categories. The area of each type is shown in Table 1.

[0101] Table 1 Land use classification (unit: m 2 )

[0102]

[0103] Note: The pervious area (PA) includes forest land, grassland and bare land.

[0104] Table 2 Impervious area (TIA) classification (unit: m 2 )

[0105] Type Effective impervious area (EIA) Non-effective impervious area (NEIA) Area (m 2 ) 6931.318 70929.182

[0106] S3, calculate hydrological parameters based on the grid type constructed in step S2, the hydrological parameters including watershed water content parameters, vegetation interception, depression parameter and infiltration parameter; the watershed water content parameters including watershed pre- stage water content, watershed maximum water content, watershed water quantity relationship empirical coefficient; the depression parameter including watershed initial infiltration rate f0 and watershed stable infiltration rate f c ; the infiltration parameter including EIA / NEIA maximum depression, PA maximum depression and impervious roof maximum depression. The value results of the hydrological parameters are shown in Table 3:

[0107] Table 3 Hydrological parameters

[0108]

[0109] The specific steps are as follows:

[0110] S31, obtain the watershed soil water content by satellite remote sensing data or measured data, and the watershed soil water content is the watershed pre-stage water content W0; for the evaporation, the evaporation of single rainstorm process is small and can be ignored.

[0111] S32, in the embodiment, the vegetation interception of the secondary rainstorm process is small and can be ignored.

[0112] Vegetation interception: the vegetation is assumed to be a simple water storage reservoir, the reservoir is filled with water by rainfall, and the drainage includes two parts, one is the evaporation of the water storage based on the wet canopy evaporation, and the other is the drainage when the water storage capacity exceeds the maximum water storage capacity S tree,max . The continuity equation of vegetation interception water quantity is as follows:

[0113] dS tree = (i-w tree)dt (1)

[0114] In formula (1) : dS tree is the water storage depth of vegetation in unit time dt, mm; i is the rainfall intensity corresponding to dt, mm / min; w tree is the drainage rate of rainwater through vegetation to the ground surface, mm / min.

[0115] w tree It can be expressed by the following formula:

[0116]

[0117] In formula (2) : S tree,max is the critical value of allowing the water storage capacity to drain downward, that is, the maximum water storage capacity, mm; S tree (t) is the cumulative water storage capacity of plant at time t; a tree is the drainage coefficient. Wherein

[0118]

[0119] In formula (3) : NDVI can be obtained from remote sensing data; b tree , c tree is the relationship coefficient; e represents the exponential function with real number as base, that is, e≈2.71828.

[0120] The calculation formulas of formulas (1) to (3) are used to simulate the interception effect of vegetation in the rainfall process, calculate the water amount that can be intercepted by vegetation and the drainage amount after exceeding the water storage capacity.

[0121] S4, based on the rainfall process, land use division and hydrological parameter calculation obtained in steps S1, S2 and S3, the runoff of building roof and effective impervious area, non-effective impervious area, pervious area and water area is calculated; through this step, the instantaneous runoff curve and the per-minute cumulative runoff bar chart of building roof ( Figure 5 ), effective / non-effective impervious area EIA / NEIA ( Figure 6 ), pervious area PA ( Figure 8 ) and water area ( Figure 9 ) are obtained, and the Horton infiltration curve and cumulative infiltration amount of pervious area PA ( Figure 7 ) are obtained. The runoff path conditions of building roof, EIA / NEIA, PA and water area are shown in Figure 3 .

[0122] The specific steps are as follows:

[0123] S41, Calculation of building roof runoff: Due to the different ways of rainwater drainage, the building needs to be divided into high-rise buildings and low-rise buildings. According to the General Rules for Design of Civil Buildings (GB50352-2005), residential buildings of ten floors or above or other civil buildings with a height of more than 24m are high-rise buildings. The roof rainwater drainage of high-rise buildings is generally first collected into a rainwater tank, and then directly discharged into the underground pipe network system through a vertical pipe or a rainwater pipe. Low-rise buildings will discharge rainwater to the surrounding underlying surface through a rainwater pipe.

[0124] Considering that the roof area is relatively small, the hydrological response is fast and relatively simple, the Nash model can effectively simulate the roof runoff with fewer parameters.

[0125] The Nash instantaneous unit line mathematical expression is adopted:

[0126]

[0127] In formula (4), u(0, t) is the instantaneous unit line, t is the time, K is the linear reservoir regulation parameter, and e represents the exponential function with real number as base, that is, e≈2.71828.

[0128] The instantaneous unit line is converted into a discrete period unit line form by S integral transformation:

[0129] q(Δt, n) = (e -Δt / K ) n-1 (1-e -Δt / K ) (5)

[0130] In formula (5), q(Δt, n) is the period unit line, Δt is the unit line period, and n is the period number.

[0131] The corresponding outlet section flow process is:

[0132]

[0133] In formula (6), dR roof is the outlet section flow, which is converted into the runoff depth per unit time (flow divided by catchment area), mm / min; n is the outflow time; m is the calculation period number; and i(m) is the net rain intensity, mm / min.

[0134] The linear reservoir regulation parameter K in formula (4) is equal to the roof slope flow concentration time τ:

[0135]

[0136] In formula (7), τ is the slope flow concentration time, s; L is the slope length, m; and V is the average flow velocity of slope water flow, m / s. In this example, K is calculated as 16.6667s.

[0137] Research shows that the average flow velocity V of slope flow is affected by many factors, including slope, roughness, rainfall intensity, etc., and the influencing mechanism is very complex. It can be approximately estimated by Eagleson-Bra formula:

[0138]

[0139] In formula (8), J is the slope gradient; n is the roughness; A is the slope area, km 2 ; B is the slope width, m; i is the average rainfall intensity, mm / h.

[0140] The starting time of roof runoff is determined by comparing the cumulative rainfall and the loss of filling. For an impermeable roof in a certain rainfall, when the current water demand is zero, the change process of the filling depth with rainfall can be approximately calculated according to the Linsley formula:

[0141] Δ = Δ max (1-e -kP ) (9)

[0142] In formula (9), Δ is the impermeable roof filling depth loss, mm; Δ max is the maximum impermeable roof surface filling depth loss, mm; k is the change rate, k = 1 / Δ max ; P is the rainfall, mm.

[0143] The maximum impermeable roof surface filling depth loss Δ max is smaller than the ground filling amount, which is calculated by the formula proposed by British Kidd and lowring, that is:

[0144]

[0145] In formula (10), k is a coefficient related to the type of ground surface, mm, and the impermeable ground surface takes 0.07 and the permeable ground surface takes 0.28; s is the ground slope. In this embodiment, k takes 0.07 and s takes 0.02, and Δ max is calculated to be 0.495 mm.

[0146] S42, the roof filling time (t r ) is obtained by time step iteration, and in this example, t r = 2.0359 min;

[0147] S43, from the start of rainfall to the time (t s ) when the roof rainwater falls to the ground from the rainwater pipe, it can be approximately solved by the physical free-fall motion equation:

[0148]

[0149] In formula (11), H is the height of the pipe; g is the acceleration of gravity. In this example, t s = 2.4743 s.

[0150] The building roof runoff is the time from the generation of roof rainwater runoff to the flow to the ground, and the final roof rainwater runoff from the generation to the flow to the ground T 屋顶 : T 屋顶 = τ + t0 + t s . Wherein τ is the roof concentration time, min; t0 is the roof runoff response time, min; t s is the time for roof rainwater to fall from the rainwater pipe to the ground, min. In this example, t0 = 2 min, the roof from the runoff to the ground T 屋顶 = 2.319 min.

[0151] S44, Effective Impervious Area (EIA) runoff, considering the variability of runoff over time, using instantaneous runoff, then:

[0152] dR EIA = (i - u EIA ) dt (12)

[0153] In formula (12), dR EIA is the runoff of the effective impervious area (EIA) per unit time dt, mm; i is the rainfall intensity corresponding to dt time, mm / min; u EIA is the depression rate of the effective impervious underlying surface EIA corresponding to dt time, mm / min, u EIA = u EIA (t).

[0154] S45, Non-effective Impervious Area (NEIA) runoff, also using instantaneous runoff, then:

[0155] dR NEIA = (i - u NEIA ) dt (13)

[0156] In formula (13), dR NEIA is the runoff of the non-effective impervious area (NEIA) per unit time dt, mm; i is the rainfall intensity corresponding to dt time, mm / min; u NEIA is the depression rate of the non-effective impervious underlying surface NEIA corresponding to dt time, mm / min, u NEIA = u NEIA (t).

[0157] S46, runoff of the permeable area (PA) is expressed by the instantaneous runoff, and the infiltration is considered by the widely used Horton infiltration formula. In this process, the green land is calculated as the permeable underlying surface.

[0158] The rainfall on the permeable underlying surface should include the runoff from the effective impervious underlying surface NEIA (here, according to the idea of rainwater disconnection, it is considered that the runoff from the effective impervious underlying surface NEIA all flows into the permeable area PA, and the part exceeding the storage capacity of the permeable area is calculated as the runoff of the permeable area)

[0159]

[0160] In formula (14), i PA is the rainfall intensity on the permeable underlying surface, mm / min; dR NEIA is the inflow rate of the runoff from the effective impervious underlying surface NEIA, mm / min; dR roof is the inflow rate of the runoff from the impervious roof, mm / min; S NEIA is the area of the effective impervious underlying surface NEIA, m 2 ; S roof is the area of the impervious roof, m 2 ; S PA is the area of the permeable underlying surface PA, m 2 .

[0161] The initial infiltration capacity f0 of the permeable underlying surface is:

[0162] f0 = λ (W m -W0) (15)

[0163] In formula (15), f0 is the initial infiltration rate of the watershed, mm / min; λ is the empirical coefficient of the water content relationship of the watershed, min -1 ; W m is the maximum water content of the watershed, mm; and W0 is the initial water content of the watershed, mm

[0164] The infiltration relationship curve is drawn as:

[0165] f p = f c +(f0-f c )e -kt (16)

[0166] In formula (17), f p is the infiltration rate of the watershed corresponding to the time t, mm / min; f0 is the initial infiltration rate of the watershed, mm / min; f c is the stable infiltration rate of the watershed, mm / min; and k is an empirical constant.

[0167] Infiltration rate F at time i p (i)(mm) is the area of ​​the curvilinear trapezoid formed by t=i and the infiltration curve at that moment.

[0168] When the rainfall intensity of the permeable underlying surface is i PA When the initial infiltration capacity is f0, the underlying surface first satisfies the infiltration requirement and then fills the depression. When the infiltration rate f at time i... i =Rainfall intensity i PA At that time, the underlying surface begins to fill depressions, and when the rainfall intensity on the underlying surface of the permeable zone is i PA The formula for the flow generation when the initial infiltration capacity is f0 is as follows:

[0169]

[0170] In equation (17): dR PA The permeable surface area (PA) runoff per unit time dt, expressed in mm; u PA The value represents the depression filling rate of the permeable subsurface PA at time dt, expressed in mm / min; the meanings of other symbols are the same as above.

[0171] When the rainfall intensity of the permeable underlying surface is i PA When the initial infiltration capacity f0 is greater than or equal to the initial infiltration capacity, the runoff generation formula for simultaneous depression filling and infiltration on the underlying surface is as follows:

[0172] dR PA =(i PA -f p -u PA )dt (18)

[0173] In the formula, dR PA i represents the runoff volume of the permeable surface under the permeable zone within a unit time dt, in mm. PA The rainfall intensity on the underlying surface of the permeable zone, in mm / min; f p The infiltration rate of the watershed at time t is expressed in mm / min; u PA The depression filling rate of the underlying surface of the permeable zone at time dt, in mm / min;

[0174] Iterative process of filling depressions with time step:

[0175] The quantitative relationship between rainfall and the amount of depression filling in the watershed is represented by a watershed depression distribution curve, dynamically simulating the depression filling process:

[0176]

[0177] In formula (19): U is the watershed filling volume, mm; U max P represents the maximum amount of depression filling in the basin, in mm; P represents the rainfall in the basin, in mm.

[0178] The change of the amount of water in the depression during the rainfall process is simulated using time steps (e.g., every minute). For each time step, the increase of the amount of water in the depression is calculated, and the current amount of water in the depression (U_current) is updated. When the amount of water in the depression (U_current) reaches its maximum capacity (U_max), the depression filling is completed and a curve of the relationship between the amount of depression filling (mm) and time (min) is obtained. The slope of this curve can be calculated to read the depression filling intensity u (mm / min) at any minute of this process.

[0179] S47, urban water body regulation

[0180] Urban water body regulation: for the water body in the city where the underwater topographic data is lacking, the topological network relationship of the water flow direction is determined based on the numerical river network system, the water storage and transport process is simulated by using the Muskingum equation to obtain the regulation curve (in this example, the Muskingum method coefficient K = 0.2, x = 0.38), and the cumulative water storage S(t) (mm) and the time-varying water storage s w (mm / min) of the water body at the t time are read. w w .

[0181] Where the water area rain intensity is:

[0182] i w = i + dR PA (20)

[0183] In formula (20), i w is the water area rain intensity; dR PA is the runoff of the water-permeable underlying surface (PA) in the unit time dt; i is the rainfall intensity corresponding to dt; and dR PA is the runoff of the water-permeable surface (PA) in the unit time dt.

[0184] The runoff of the water body is calculated by using the Muskingum method, and the formula is as follows:

[0185] It is assumed that at any time, the river section storage (S) and the upstream and downstream section flow are in a linear relationship, that is,

[0186] S = KQ' = K[xI + (1-x)O] (21)

[0187] and the water balance equation

[0188]

[0189] Solve the two equations to obtain the Muskingum evolution formula as follows:

[0190] O2 = C1I1 + C2I2 + C3O1 (23)

[0191] ​C1 = (Kx + At / 2) / Co (24)

[0192] C2 = (-Kx + At / 2) / Co (25)

[0193] C3 = (K - Kx - At / 2) / Co (26)

[0194] Co = K - Kx + At / 2 (27)

[0195] In formula (21) to (27), I, O, S are the inflow, outflow and storage of the river section respectively; the subscripts 1, 2 represent the initial and final time; Q' is the apparent storage flow, which is the sum of the weighted flow of the inflow and outflow; x is the relative proportion of the inflow and outflow to the tank storage; K is the storage parameter; C1, C2, C3 are coefficients determined by the parameters K, x and the time interval (At), and their sum is equal to 1.0; K, x are determined according to the hydraulic characteristics and flow characteristics of the research river section, and are assumed to be constant, which can be determined by the least squares method, analysis method, matrix method, cumulative method or direct optimization according to the inflow and outflow data. Among them, the trial and error method is to calculate the best x value (generally in the range of 0 to 0.5) that can make the storage-apparent storage flow relationship curve on the rectangular coordinate paper close to a single value relationship by trial calculation; K is the slope when the assumed single value curve becomes a straight line.

[0196] S5, according to the curve in step S1 and the building roof runoff and effective impervious area, non-effective impervious area, pervious area, water area calculated in step S4, calculate the time-varying runoff coefficient, which includes the instantaneous time-varying runoff coefficient and the cumulative time-varying runoff coefficient. The rainfall process is plotted together with the calculation results of the time-varying runoff coefficient, the instantaneous rainfall runoff process and the instantaneous time-varying runoff coefficient C i The curve is shown in the accompanying Figure 10 The cumulative rainfall runoff process and the cumulative time-varying runoff coefficient C t The curve is shown in the accompanying Figure 11

[0197] Instantaneous time-varying runoff coefficient: read the instantaneous rainfall dP at each time according to the rainfall curve in step S1, and calculate the instantaneous runoff dR by the following formula to calculate the time-varying runoff coefficient (C i ):

[0198]

[0199] In formula (28), dR is the runoff change amount in time dt; dP is the rainfall change amount in time dt, i is the rainfall intensity corresponding to unit time dt, mm / min; s tree is the water storage rate of vegetation, mm / min; u EIA is the puddling rate of effective impervious underlying surface EIA corresponding to unit time dt, mm / min; u​NEIA is the filling rate of non-effective impervious underlying surface (NEIA) per unit time dt, mm / min; u PA is the filling rate of pervious underlying surface (PA) per unit time dt, mm / min; f P is the infiltration rate per unit time dt, mm / min; s w is the time-varying water storage per unit time dt, mm / min.

[0200] or

[0201]

[0202] In formula (29), P(i) is the cumulative rainfall at i moment, mm; dR roof is the runoff of building roof, mm; dR EIA is the runoff of effective impervious underlying surface (EIA) per unit time dt at i moment, mm; dR PA is the runoff of pervious underlying surface (PA) per unit time dt at i moment, mm; S(i) is the water storage per unit time, mm. p (i) is the infiltration per unit time, mm.

[0203] The cumulative time-varying runoff coefficient is:

[0204]

[0205] In formula (30), P(t) is the cumulative rainfall at t moment, m 3 ; S tree (t) is the cumulative interception of vegetation at t moment, m 3 ; U all (t) is the cumulative filling of high-rise and low-rise buildings, effective impervious surface (EIA), non-effective impervious surface (NEIA), and pervious surface (PA) at t moment, m 3 ; F p (t) is the cumulative infiltration at t moment, m 3 ; S(t) is the cumulative water storage of water area at t moment, m 3 .

[0206] In this process, the curve of the cumulative time-varying runoff coefficient can be obtained according to the calculation.

[0207] The obtained runoff coefficient result is compared with the comprehensive runoff coefficient obtained by SWMM simulation, and the infiltration amount and yield obtained by the process are compared and analyzed with those obtained by the SWMM model. The simulation result in SWMM is that the precipitation is 107.58 mm, the total evaporation is 0 mm, the total infiltration is 35.99 mm, the total runoff is 92.55 mm, and the comprehensive runoff coefficient (equal to the ratio of total runoff to total precipitation in SWMM) is 0.8603. In this example, the calculated precipitation is 107.6977 mm, the total evaporation is 0 mm, the total infiltration is 35.1518 mm, the total runoff is 91.9249 mm, and the comprehensive runoff coefficient is 0.8755, which is close to the simulation result of SWMM.

[0208] A system for implementing the above time-varying runoff coefficient calculation method, the system comprising:

[0209] A data acquisition module for acquiring rainfall data and high-precision digital surface model data;

[0210] A depression filling processing module for determining the depression filling area of the watershed;

[0211] A land use analysis module for analyzing the runoff process of building roof, effective impervious area, non-effective impervious area, pervious area and water area;

[0212] A grid processing module for processing high-precision digital surface model data and performing land use division and extraction analysis;

[0213] An EIA classification module for classifying each grid cell in the urban land use data layer as effective impervious area;

[0214] A hydrological parameter calculation module for calculating the hydrological parameters of watershed water content, vegetation interception, infiltration and depression process;

[0215] A water area regulation and storage simulation module for simulating the regulation and storage process of urban water area;

[0216] A runoff and yield calculation module for calculating the runoff of building roof and the yield of effective impervious area, non-effective impervious area, pervious area and water area according to rainfall process, land use classification and hydrological parameters;

[0217] A time-varying runoff coefficient calculation module for calculating instantaneous time-varying runoff coefficient and cumulative time-varying runoff coefficient.

[0218] A computer program product, the product comprising a storage medium and computer readable instructions stored on the medium, which, when executed by a computer, implement the above calculation method.

Claims

1. A method for calculating time-varying runoff coefficient reflecting urbanization underlying surface regulation and storage, characterized in that, Comprise the following steps: S1, obtain the fine rainfall data of the urban study area, draw the column chart and curve chart of the rainfall process, and extract high-precision digital surface model data using high spatial resolution satellite stereo image data; S2, process the high-precision digital surface model data extracted in step S1 to remove house and vegetation information to obtain high-precision digital elevation model data, perform raster processing on the high-precision digital surface model data to construct a grid type, and perform land use division to obtain a city land use data layer to distinguish the types of each part of the underlying surface as building roof, effective impervious area, non-effective impervious area, pervious area and water area; S3, calculate hydrological parameters based on the grid type constructed in step S2, the hydrological parameters including watershed water content parameters, vegetation interception, depression parameters and infiltration parameters; S4, calculate building roof runoff and runoff yield of effective impervious area, non-effective impervious area, pervious area and water area based on the rainfall process, land use division and hydrological parameters obtained in steps S1, S2 and S3; S5, calculate the time-varying runoff coefficient according to the curve chart in step S1 and the building roof runoff and runoff yield of effective impervious area, non-effective impervious area, pervious area and water area calculated in step S4; The time-varying runoff coefficient includes instantaneous time-varying runoff coefficient and cumulative time-varying runoff coefficient, the instantaneous time-varying runoff coefficient is calculated according to the instantaneous rainfall dP at each time obtained from the rainfall curve in step S1, and the calculation formula of the time-varying runoff coefficient through instantaneous runoff dR is as follows: ， where: C i is the time-varying runoff coefficient; dR is the runoff change amount within dt; dP is the rainfall change amount within dt; i is the rainfall intensity corresponding to dt; s tree is the vegetation water storage rate; is the depression storage rate of the effective impervious underlying surface corresponding to dt; is the depression storage rate of the non-effective impervious underlying surface corresponding to dt; is the depression storage rate of the pervious underlying surface corresponding to dt; f P is the infiltration rate corresponding to dt; s w is the time-varying water storage amount corresponding to dt; dP, i, s tree , , , , f P , s w The units of dP, i, s Or ， wherein: P(i) is the cumulative rainfall amount corresponding to the i time; dR roof is the building roof yield flow; dR EIA is the runoff of the effective impervious area underlying surface within dt corresponding to the i time; dR PA is the runoff of the pervious area underlying surface within dt corresponding to the i time; S(i) is the water storage amount per unit time of the water area; F p (i) is the infiltration amount per unit time of the water area; P(i), dR roof , dR EIA , dR PA , S(i), F p (i) are all in mm; The calculation formula of the cumulative time-varying runoff coefficient is as follows: ， In the formula, P(t) is the accumulated rainfall at time t; S tree (t) is the accumulated interception of vegetation at time t; U all (t) is the accumulated filling of the building roof, the effective impervious area, the non-effective impervious area and the pervious area at time t; F p (t) is the accumulated infiltration at time t; S(t) is the accumulated water storage of the water area at time t, P(t), S tree (t), U all (t), F p (t) and S(t) are all in the unit of m 3 .

2. The computational method of claim 1, wherein, The land use division in step S2 comprises the following steps: S21, import the city land use data layer, high-precision digital elevation model data and related vector layers of all data layers in the rainwater collection system into the ArcGIS Pro software; S22, rasterize all data layers in step S21, and convert the entrance position vector layer and conveying elements of the rainwater collection system into raster format, ensure that all data layers in step S22 are converted into a consistent coordinate system, and are cut according to the watershed boundary, the conveying elements including curb opening entrance, open channel, pond, drainage ditch and drainage pipe network; S23, resample all data layers in step S22 to make the data layers have consistent resolution; S24, use the ArcGIS Pro software to perform depression processing on the high-precision digital elevation model data in step S21 to remove all depressions, identify the depression positions by subtracting the high-precision digital elevation model data in step S21 from the high-precision digital elevation model data after depression processing and searching for non-zero values therein to determine the depression area of the watershed; S25, determine the water flow direction of the impervious surface, and adjust the digital elevation model data using a weighted interpolation method to eliminate flat areas; S26, after determining the water flow direction, classify each grid cell in the city land use data layer according to the runoff yield characteristics to obtain a data layer composed of building roof runoff and runoff yield of effective impervious area, non-effective impervious area, pervious area and water area.

3. The computational method of claim 2, wherein, The step of classifying each grid cell in the urban land use data layer according to the runoff characteristics in step S26 is as follows: S261, checking the land cover type of each grid cell; S262, for each asphalt or concrete cell, checking each downstream cell along the water flow path, if the downstream cell is also asphalt or concrete and there is a rainwater collection system, the asphalt or concrete cell is classified as an effective impervious area; S263, if the downstream cell is green land, the original cell is regarded as a non-effective impervious area.

4. The computational method of claim 1, wherein, The watershed water content parameter in step S3 is obtained by satellite remote sensing data or measured data; The continuity equation of the water intercepted by the vegetation is as follows: ， wherein dS tree is the water storage depth of vegetation in unit time dt, in mm; i is the rainfall intensity corresponding to dt; w tree is the drainage rate of rainwater through vegetation to the ground surface, i, w tree both in mm / min.

5. The computational method of claim 1, wherein, The calculation of the building roof runoff in step S4 is as follows: The building roof runoff is the time for the roof rainwater runoff to flow to the ground from generation, and its calculation formula is as follows: ， In the formula, T 屋顶 is the time for roof runoff to go from generation to ground; τ is the roof runoff concentration time; t0 is the roof runoff response time; t s τ, t 0、 t s in min; The runoff of the effective impervious area is represented by the instantaneous runoff, and its calculation formula is as follows: ， where: dR EIA is the runoff from the effective impervious area for dt, in mm; i is the rainfall intensity corresponding to dt; is the depression storage for the underlying surface of the effective impervious area for dt, in mm; i and are the units of mm / min, ; The runoff of the non-effective impervious area is represented by the instantaneous runoff, and its calculation formula is as follows: ， where: dR NEIA is the runoff from the non-effective impervious area in dt, in mm; i is the rainfall intensity corresponding to dt; is the depression storage of the underlying surface of the non-effective impervious area corresponding to dt, i and have units of mm / min, ; The water permeable area underlying surface runoff is expressed by instantaneous runoff, and the infiltration capacity is considered when the rainfall intensity of the water permeable area underlying surface When the initial infiltration capacity f0, the underlying surface first meets the infiltration and then fills the depression, and when the infiltration rate f i = rainfall intensity When the rainfall intensity of the water permeable area underlying surface The runoff formula when the initial infiltration capacity f0is as follows: ， When the rainfall intensity of the pervious zone underlying surface ≥ initial infiltration capacity f0, the underlying surface simultaneously carries out the filling of the depression and the infiltration, and the runoff formula is as follows: ， where dR PA is the runoff of the underlying surface of the water permeable area in dt, with the unit of mm; is the rainfall intensity on the underlying surface of the water permeable area; f p is the infiltration rate of the watershed at the time t; is the filling rate of the underlying surface of the water permeable area corresponding to dt, , f p , the units of which are mm / min; The runoff of the water area is calculated by using the Muskingum method evolution formula, and the formula is as follows: ， ， ， ， ， In the formula, I and O are the inflow and outflow of the river section respectively; subscripts 1 and 2 represent the initial and final times; x is the relative proportion of the inflow and outflow to the influence of the slot storage; K is the storage parameter; C1, C2 and C3 are coefficients determined according to K, x and the time interval Δt, and their sum is equal to 1.0; K and x are determined according to the hydraulic characteristics and flow characteristics of the research river section, and are assumed to be constant, and are determined by using the trial and error method, the least square method, the analysis method, the matrix method, the cumulative method or the direct optimization method according to the inflow and outflow data; wherein the trial and error method is to calculate the best x value that can make the storage-discharge relationship curve on the rectangular coordinate paper close to the single value relationship by trial calculation, and the x value range is 0-0.

5.

6. A system for implementing the time-varying draw coefficient calculation method of any one of claims 1 to 5, characterized in that, The system comprises: a data acquisition module for acquiring rainfall data and high-precision digital surface model data; a depression filling processing module for determining the depression filling area of the watershed; a land use analysis module for analyzing the runoff processes of building roofs, effective impervious areas, non-effective impervious areas, pervious areas and water areas; a grid processing module for processing high-precision digital surface model data and performing land use division and extraction analysis; an EIA classification module for classifying each grid cell in the urban land use data layer according to the runoff characteristics after determining the water flow direction; a hydrological parameter calculation module for calculating the watershed water content parameter, the hydrological parameters of vegetation interception, infiltration and depression filling process; a water area regulation and storage simulation module for simulating the regulation and storage process of urban water areas; a runoff and runoff calculation module for calculating the building roof runoff and the runoff of effective impervious areas, non-effective impervious areas, pervious areas and water areas according to the rainfall process, land use classification and hydrological parameters; a time-varying runoff coefficient calculation module for calculating the instantaneous time-varying runoff coefficient and the cumulative time-varying runoff coefficient.

7. A computer program product, characterised in that, The product comprises a storage medium and computer readable instructions stored on the medium, which, when executed by a computer, implement the calculation method of any one of claims 1-5. The product comprises a storage medium and computer readable instructions stored on the medium, which, when executed by a computer, implement the calculation method of any one of claims 1-5.

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