Method for predicting summer drought in northwest region

Abstract

The invention discloses a northwest region summer drought prediction method, and relates to the technical field of regional drought prediction, and the method comprises the steps: 1, building a northwest region summer drought prediction weather dynamics conceptual model under the synergistic effect of multiple factors; 2, establishing a rainfall dynamic-statistical forecasting model based on CFSv2 forecasting data under the multi-factor synergistic effect; 3, forecasting technology research of the next season extension period under the multi-factor synergistic effect is carried out; according to the method for predicting the summer drought in the northwest region, large-scale circulation and sea temperature in spring are gradually influenced through heat-sensitive heating and air-sea interaction from front winter foreign aid forcing factor change and mutual influence, and then direct influence factors of the summer drought in the northwest region are influenced through high-low altitude configuration adjustment and air-sea interaction; and finally, a weather dynamics conceptual model influencing drought and flood in northwest summer improves the predictability of drought events, and realizes the comprehensive prediction capability of full-time-scale drought.

Description

Technical Field

[0001] The invention relates to the technical field of regional drought prediction, and in particular to a method for predicting summer drought in northwest China. Background Art

[0002] Northwest China is one of the main components of the arid zone in Asia. It is located in the hinterland of the continent and belongs to the arid continental climate zone. From the perspective of climate, the eastern part of the Northwest is located on the northeast side of the Qinghai-Tibet Plateau. It is generally an edge area affected by the southeast monsoon, and is also affected by the westerly circulation, plateau monsoon and plateau weather system; the western part of the Northwest is mainly affected by the westerly system and the plateau. Arid and semi-arid are the basic climatic characteristics of the Northwest.

[0003] Since Northwest China is a sensitive area to climate change, the non-uniformity of spatial and temporal distribution of precipitation is the main and most direct cause of drought. A large number of research results have been made on the causes of drought in Northwest China, including strong signals of drought in Northwest China, drought circulation background field, evolution characteristics of regional precipitation, and the relationship between water cycle changes and drought. In order to improve the predictability of drought events and achieve comprehensive prediction capabilities for droughts on all time scales, a prediction method for summer drought in Northwest China is proposed. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a method for predicting summer drought in the northwest region, which solves the problems raised in the above-mentioned background technology.

[0005] To achieve the above purpose, the present invention is implemented by the following technical scheme: a method for predicting summer drought in Northwest China, comprising the following steps:

[0006] Step 1: Establish a conceptual model of weather dynamics for summer drought prediction in Northwest China under the synergistic effect of multiple factors;

[0007] Step 2: Establish a precipitation dynamic-statistical forecast model based on CFSv2 forecast data under the synergistic effect of multiple factors;

[0008] Step 3: Conduct research on the forecast technology of the next seasonal extended period with the synergistic effect of multiple factors.

[0009] Optionally, the step one is: establishing a conceptual weather dynamics model for predicting summer drought in the northwest region under the synergistic effect of multiple factors, based on the actual conditions of plateau heat source, snow cover, and sea temperature in the previous winter, combined with the performance of various factors during the transition period from winter to spring, predicting the characteristics of spring influencing factors, and judging the status of summer northwest drought influencing factors.

[0010] Among them, I i =W i w iSubscript i represents the i-th component, w is the apparent vertical migration speed of water, there is a water-heat coupling effect between the soil and the atmosphere, I i That is the combined effect; D hW It is the horizontal flow convergence, such as runoff, water vapor convergence in the air, and moisture exchange between vegetation and air; D hI It is the horizontal flow flux convergence, such as the water vapor flux divergence in the air; D hQ is the horizontal heat flux convergence; Q i W is an exogenous term for heat, such as work done, dissipation, conversion and radiation of kinetic energy, etc.; Δ represents the spatial scale change of the actual component; p is the pressure on the water at the upper and lower ends of the component; S is other forms of source and sink terms, such as the water consumption or replenishment of the component itself; l is the linear scale of the component, g is the acceleration of gravity, and t is time. thres is the critical value of water content, including the saturation value and the minimum value. It is a function of time t, temperature T, water content, component mass M (such as biomass) and other factors O (for organisms, such as sunlight, nutrients, growth rate and respiration rate, etc.); in the atmosphere, W thres It is only related to temperature. i =W thres,i When the moisture content of the component reaches saturation or minimum, if W thres As time goes by, the relationship in equation (4) will constrain equation (1).

[0011] Optionally, the step three: conduct multi-factor synergistic research on the key areas affecting my country's mid- and high-latitudes, as well as some key areas affecting my country's mid-latitudes, and the 500hPa height field has a quasi-30-pentad period that can pass the test of 0.01-0.10 confidence, that is, the atmospheric circulation situation will reappear after every 30 pentads. On this basis, the physical field of the previous 30 pentads is used to make extended-term forecasts, for example, the 500hPa height field of the first pentad in January is used to make a forecast for the first pentad in June, and the 500hPa height field of the second pentad in January is used to make a forecast for the second pentad in June, and so on.

[0012] Optionally, the step two: establishing a precipitation dynamic-statistical forecast model based on CFSv2 forecast data under the synergistic effect of multiple factors to study the role of the synergistic effect of EU wave trains and El Niño on drought prediction: the study found that a strong El Niño does not mean that extreme summer drought will occur in northern my country. The positive teleconnection pattern (EU type) in the mid-latitudes of Eurasia is the key to the occurrence of summer drought in northern my country. The dynamic prediction model of sea-atmosphere coupling can only predict extreme drought events in northern my country if it can better capture the positive phase EU type.

[0013] The present invention provides a method for predicting summer drought in Northwest China, which has the following beneficial effects:

[0014] 1. The prediction method of summer drought in Northwest China is based on the establishment of a conceptual model of weather dynamics of summer drought in Northwest China under the synergistic effect of multiple factors: it starts with the changes in external forcing factors in the previous winter and their mutual influence, gradually affects the large-scale circulation and sea temperature in spring through sensible heat heating and sea-air interaction, and then affects the direct influencing factors of summer drought in Northwest China through the adjustment of high and low air configuration and sea-air interaction, and finally affects the weather dynamics conceptual model of summer drought and flood in Northwest China, which improves the predictability of drought events and realizes the comprehensive prediction capability of drought on the entire time scale.

[0015] 2. The prediction method for summer drought in Northwest China found that the water vapor flux input by the southern branch of the water vapor pathway was significantly reduced, which was the main water vapor influence mode leading to major summer drought events in the eastern part of Northwest China. A set of drought moisture thermodynamic equations based on a loop system that reflects the synergistic effect of multiple factors was constructed, and the movement law of water in the loop system composed of soil, vegetation and air was analyzed; a set of thermodynamic equations that describe drought and waterlogging was established, which can quantitatively describe and predict drought and waterlogging.

[0016] 3. The prediction method for summer drought in Northwest China proposed a multi-factor synergistic forecast technology for the next seasonal extended period. It was found that the 500hPa height field affecting the key areas of Northwest China has a 28-34 pentad period. Four circulation situation fields corresponding to the strong cold air in spring were selected, and a similar method was used to predict the period of occurrence of strong cold air in spring on a sub-seasonal scale. The evaluation results showed that the accuracy of the forecast was significantly improved compared with that of a single situation field, and the false alarm rate and missed alarm rate were also greatly reduced, providing a new way to predict important weather processes on a sub-seasonal scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the step structure of the present invention;

[0018] Figure 2 The present invention is a drought level monitoring result diagram of the SPEI index in the eastern part of the northwest region in 1929, 1986, 1997, the spring of 1995, the summer of 1997 and the autumn of 1956;

[0019] Figure 3 The figure is the effect of temperature change on drought in the eastern part of the northwest region of the present invention;

[0020] Figure 4 This is a graph showing the annual changes in summer drought in the northwest region of the present invention;

[0021] Figure 5 This is a spatial variation diagram of the tendency rate of the number of days of continuous dryness in Northwest China from 1961 to 2011;

[0022] Figure 6It is a percentage diagram of the difference in water vapor budget at each boundary in the extreme drought event of the present invention;

[0023] Figure 7 This is a conceptual model diagram of the causes of drought and flood in Northwest China in the present invention;

[0024] Figure 8 This is a weather dynamic diagram of the synergistic effect of the South Asian High and the Western Pacific Subtropical High in the present invention;

[0025] Fig. 9 This is a conceptual model diagram of weather dynamics for predicting summer drought in Northwest China under the synergistic effect of multiple factors of the present invention; DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] See also Figures 1 to 9 The present invention provides a technical solution: a method for predicting summer drought in the northwest region, comprising the following steps:

[0028] Step 1: Establish a conceptual model of weather dynamics for summer drought prediction in Northwest China under the synergistic effect of multiple factors;

[0029] Based on the actual conditions of plateau heat source, snow cover and sea temperature in the previous winter, combined with the performance of various factors during the transition period from winter to spring, the characteristics of spring influencing factors are predicted, and the status of factors affecting drought in the northwest in summer is judged. Compared with the existing prediction models for the northwest region, this model takes into account the interaction between factors, regional differences in factor influence, and the performance of factors during the seasonal transition period, so that the model can obtain the final result in a dynamic prediction environment.

[0030] Step 2: Establish a precipitation dynamic-statistical forecast model based on CFSv2 forecast data under the synergistic effect of multiple factors;

[0031] Study on the role of EU wave train and El Niño synergy in drought prediction:

[0032] The study found that a strong El Niño does not mean that extreme summer drought will occur in northern my country. The positive teleconnection pattern (EU pattern) in the Eurasian mid-latitudes is the key to the occurrence of summer drought in northern my country. The dynamic forecast model of sea-atmosphere coupling can only predict extreme drought events in northern my country if it can capture the positive phase EU pattern. The dynamic-statistical forecast model established by considering the sea temperature in the central and eastern Pacific and the spring Eurasian snow cover is better than the dynamic model CFSv2 when the forecast period is longer.

[0033] Example

[0034] Taking the extreme drought event and the strong El Nino event in northern my country in 2015 as the starting point, the causes and predictability of drought in northern my country are deeply discussed based on observations and the results of the NCEP / CFSv2 seasonal forecast model. In the summer of 2015, the western Pacific subtropical high was stronger and located more eastward than usual. Only a small amount of warm and humid air flow penetrated northward, resulting in a long-term and large-scale drought in northern summer. At the same time, the vertical motion field in the summer of 2015 also showed obvious anomalies: the ascending motion in the area south of 30°N was significantly enhanced, and the sinking motion in the area north of 30°N was significantly enhanced, which also suppressed the precipitation in the north to a certain extent. From the distribution of 500hPa potential height anomalies, it can be found that there is a "negative-positive-negative" wave train in the middle and high latitudes of Eurasia - significant low pressure anomalies appeared in the Ural Mountains and eastern East Asia, and significant high pressure anomalies appeared in the Lake Baikal area - similar to the positive phase of Eurasian teleconnection. Under the circulation configuration of the Lake Baikal high-pressure anticyclone and the eastern East Asian low-pressure cyclone, most of northern my country is under the control of the abnormal north, and the summer monsoon is weak, which explains why the warm and humid air currents from the ocean are difficult to reach northern my country.

[0035] Based on the precipitation anomaly of 1 standard deviation, there were 7 extreme drought events in northern my country during the 37 years from 1979 to 2015, namely 1991, 1999, 2001, 2002, 2006, 2014 and 2015. The study found that during the occurrence of these 7 extreme drought events, the mid-latitude Eurasian region showed a positive Eurasian teleconnection pattern. At the same time, based on the average results of the 24 member ensembles of the NCEP / CFSv2 seasonal forecast model, it was found that the CFSv2 model can better predict the drought in northern my country with a lead time of 0.5 months (0.5-lead-month), but the intensity is weaker than the observation. This is because the model better captures the El Niño signal and the "negative positive negative" circulation pattern. In addition, the 4 best and worst performing member ensembles were selected, and the comparative analysis further verified that the CFSv2 model can better predict extreme drought events in northern my country only if it better captures the positive phase Eurasian teleconnection pattern;

[0036] Verify whether the dynamic-statistical forecast of multi-factor synergy is better than the CFSv2 model;

[0037] The tropical central and eastern Pacific SST and Eurasian snow cover stimulate the Eurasian teleconnection through the sea-air and land-air interactions. From the lead-lag correlation analysis, it can be found that the Nino3.4 index in July and the Eurasian snow cover in March are closely related to the Eurasian teleconnection. The seven extreme drought events in northern my country all occurred in El Niño years or years with low Eurasian snow cover. When the tropical central and eastern Pacific SST is abnormally high or the Eurasian snow cover is abnormally low, it can stimulate positive Eurasian teleconnection patterns, thereby causing summer droughts in northern my country. In addition, a simple dynamic statistical forecast model for summer precipitation in northern my country was established using the Eurasian snow cover observed in March and the July Nino3.4 index reported by the CFSv2 seasonal model from March. The results show that the CFSv2 seasonal forecast model has a better effect in reporting summer precipitation 0.5 months in advance, but when it is 3 months in advance, the dynamic-statistical forecast is better than the CFSv2 model;

[0038] Step 3: Conduct research on the forecast technology of the next seasonal extended period with the synergistic effect of multiple factors;

[0039] As shown in Table 1: Through periodic testing, it was found that the key areas affecting my country's mid- and high-latitudes, such as the Ural Mountains, Lake Baikal, and the Sea of ​​Okhotsk, as well as some key areas affecting my country's mid-latitudes, such as the Xinjiang region and the Qinghai-Tibet Plateau region, have a quasi-30-pentad period in the 500hPa height field that can pass the test of 0.01-0.10 confidence level, that is, the atmospheric circulation situation will reappear every 30 pentads. Therefore, the physical field of the previous 30 pentads is used to make extended-term forecasts, such as using the 500hPa height field of the first pentad in January to make a forecast for the first pentad in June, and using the 500hPa height field of the second pentad in January to make a forecast for the second pentad in June, and so on. It was found that the 500hPa height field affecting the key areas of the Northwest region has 28-34 cycles. Four circulation situation fields corresponding to the strong cold air in spring were selected, and a similar method was used to predict the period of occurrence of strong cold air in spring on a sub-seasonal scale. The evaluation results showed that the forecast accuracy was significantly improved compared with that of a single situation field, and the false alarm rate and missed alarm rate were also greatly reduced, providing a new way to predict important weather processes on a sub-seasonal scale.

[0040] Table 1 Comparison of typical field superposition forecast effects

[0041]

[0042] Furthermore, the forcing factors of the former East include the difference in ground-air temperature on the plateau, more (less) snow on the plateau, high (low) Pacific Ocean temperature, low (high) Indian Ocean temperature and strong (weak) Kuroshio Current; the influencing factors in spring include the early (late) arrival of the South Asian high pressure on the plateau, high (low) Pacific Ocean temperature, low (high) Indian Ocean temperature, positive (negative) position of the EU wave train, and El Niño (La Niña) phenomenon; the direct influencing factors in summer include weak (strong) downward flow on the north side of the plateau, the South Asian high pressure being stronger (weak) and more easterly (westerly), the position of the Western Pacific Subtropical High being more northerly (southward) and more intense (weak), the number of typhoons affecting my country being more (fewer), the synergistic effect of the South Asian high pressure and the Western Pacific Subtropical High being stronger (weak), and the axis of the high-altitude jet stream being more northerly (southward) and its exit being more westerly (eastward).

[0043] Example:

[0044] Comprehensive research on external forcing factors and direct factors affecting drought in Northwest China, using dynamic-statistical methods to analyze the synergy between key factors and the impact of synergy on regional differences in drought in Northwest China;

[0045] 1. Study the temporal and spatial evolution and characteristics of arid climate in Northwest China

[0046] 1.1 Reconstruction of the drought climate series in the eastern part of Northwest China from 1901 to 2011

[0047] The SPEI index has good applicability in the eastern part of the northwest region ( Figure 2 ): From the analysis of the intensity and range of drought events, the SPEI index has good applicability in the eastern part of the Northwest region. The fluctuations of SPEI and SPI are consistent at different time scales. The short time scale mainly shows annual or seasonal characteristics, while the long time scale focuses on interannual and interdecadal characteristics. The study area was divided into the eastern plateau and southern Shaanxi for analysis. From 1901 to 2012, there were 4 dry periods in the eastern plateau and 5 dry periods in southern Shaanxi. The impact of temperature change on drought in the eastern part of the Northwest region and the comparison with the SPI index show that the contribution of high temperature to drought cannot be ignored ( Figure 3 ).

[0048] 1.2 Multi-temporal evolution patterns and characteristics of arid climate in Northwest China

[0049] Study on the interannual variation of summer drought in Northwest China: Severe drought does not occur frequently in Northwest China, but the frequency has increased significantly since 2000, especially during 2005-2010, when severe drought occurred at all stations except 2007. In 1997, the most severe drought stations occurred in Northwest China, with 14 stations experiencing severe drought in the summer of that year. Moderate drought has weakened relatively, while mild drought has increased. In other words, extreme events have occurred frequently in the past decade, and the characteristics of mild drought in summer in Northwest China have also increased year by year against the background of a decrease in overall summer precipitation in Northwest China.

[0050] The linear change trends of drought on different time scales were studied: the eastern part of Northwest China, the eastern part of Southwest China and parts of the middle and lower reaches of the Yangtze River tended to drought in spring mainly because these areas tended to drought significantly in April. In addition, the eastern part of Southwest China and parts of the middle and lower reaches of the Yangtze River also tended to drought in May; the summer drought in Northeast China, North China and the Huanghuai region was mainly due to the significant drought in July and August, while the summer drought in the southern part of Southwest China was mainly caused by the drought in August; in autumn, all drought-prone regions in China became significantly dry in September; in winter, the northern part of Northeast China, northern Xinjiang and the middle and lower reaches of the Yangtze River tended to be humid mainly because the precipitation in January in recent years was significantly higher than normal, and the area became significantly humid. The precipitation in December in the northern part of Northeast China and northern Xinjiang was also significantly higher than normal, and they tended to be humid.

[0051] Study the detailed characteristics of the dry-wet evolution in various regions of China: Based on the number of drought years in each decade counted by SPI360, the frequency of drought in each decade was calculated, and the interdecadal transfer characteristics of China's drought-prone areas were analyzed. In the 1960s, drought-prone areas (frequency greater than 50%) were mainly located in the central and western parts of the Northwest and parts of the middle and lower reaches of the Yangtze River; in the 1970s, it was "drought at both ends", that is, the western part of the Northwest and the Northeast were high-incidence areas of drought; in the 1980s, drought-prone areas were mainly located in North China, Huanghuai, central and western Inner Mongolia, and eastern Southwest China; in the 1990s, drought-prone areas shifted to the central part, and southeastern Northwest China, North China, Huanghuai, Jianghuai, and Jianghan were high-incidence areas of drought; after entering the 21st century, drought-prone areas are mainly located in the area east of 100°E, and drought is high in parts of Northeast China, eastern Inner Mongolia, eastern Northwest China, eastern Southwest China, and parts of the middle and lower reaches of the Yangtze River.

[0052] 1.3 Study on the multi-spatial evolution of drought climate in Northwest China and its characteristics The interdecadal and spatial variation trends of the number of days of continuous dryness are different in different natural areas: Figure 5 As shown in the figure, the number of days with continuous dry periods in spring and winter in the whole Northwest has shown a significant downward trend in the past 51 years, while the trend in summer and autumn is not obvious. In terms of spatial distribution, the trend of change in the number of days with continuous dry periods in most areas of the region is decreasing in spring, and the trend in different regions is different in summer; in autumn, the western part of the Northwest shows a decreasing trend, while the eastern part of the Northwest shows an increasing trend; in winter, except for the Guanzhong Plain and Qinba Mountains in southern Shaanxi, most other areas show a decreasing trend.

[0053] The study shows that summer precipitation in Northwest China shows obvious regional differences: from 1981 to 2012, summer precipitation in Northwest China showed an overall decreasing trend, while Qinghai Province was the main area with increased summer precipitation at relatively few stations.

[0054] Distribution characteristics of drought periods of ≥10 days and ≥20 days since 1981: During the 32 years from 1981 to 2012, there were 17 years with drought periods of ≥10 days, and a total of 20 drought periods, including 5 periods in the 1980s, 9 periods in the 1990s, and 6 periods in the 2000s. From the perspective of seasonal distribution, there were 11 periods in spring, 4 periods in summer, and 5 periods in autumn, which shows that the frequency of spring drought is significantly higher than that in other seasons. There were 3 drought periods from June to October 1997; the longest drought period could reach 68 days, which occurred from May 10 to July 16, 1995, which was a typical cross-season drought. There were also 15 years in which there was no obvious large-scale drought period in the eastern part of the Northwest. Among the above 20 drought periods, there were 8 drought periods of ≥20 days, which mainly occurred from the mid-to-late 1990s to the beginning of the new century. Among them, the drought periods in the mid-to-late 1990s mainly occurred in midsummer and early autumn, while the new century was mainly drought in late spring and early summer. In terms of duration, the drought lasted the longest from late spring to midsummer in 1995. In terms of the average range of drought, 1995 was also the year with the largest drought.

[0055] 1.4 Study on inter-seasonal drought events in Northwest China

[0056] Characteristics of interseasonal drought events in Northwest China in the past 50 years: There were 42 interseasonal drought events in Northwest China from 1961 to 2010, including 10 interseasonal severe drought events (duration greater than or equal to 90 days). These interseasonal severe drought events have obvious regional characteristics: in addition to the Northwest region, the occurrence areas are often accompanied by droughts in adjacent areas, such as North China and Inner Mongolia, and sometimes even extend to the Northeast region; from the Northwest region itself, the most prone to interseasonal severe droughts are the eastern part of the Northwest region (a total of 8 times), followed by the central part of the Northwest region (twice). The annual frequency of drought events generally shows an upward trend, accompanied by clear interdecadal changes. There were significantly fewer drought events in the 1960s, and more drought events from the 1980s to the early 21st century. In Northwest China, spring and summer are the seasons with more severe drought events.

[0057] 1.5 Study the water vapor characteristics that affect the arid climate in Northwest China:

[0058] The sources of water vapor in the Northwest region are: the Mediterranean Sea, the Black Sea and the Caspian Sea, the Indian Ocean, the Bay of Bengal, the South China Sea and the mid- and high-latitude continents. In the winter half of the year, the water vapor transport from the Mediterranean Sea, the Black Sea and the Caspian Sea, and the Indian Ocean is the main source, and the water vapor transport from the mid- and high-latitudes is supplementary; in autumn, the Bay of Bengal and the South China Sea are the main sources; in summer, all four water vapor sources contribute, forming convergence in the Northwest region. In summer (June to August), there are three water vapor channels in the eastern part of the Northwest region: the main water vapor channel is water vapor from the Indian Ocean and the Bay of Bengal, which goes northward through Tibet and the Sichuan Basin to the eastern part of the Northwest region; the second water vapor comes from the western Pacific Ocean, which is transported northward by the Indian Ocean monsoon to the eastern part of the Northwest region; the third water vapor comes from the northwest airflow in the mid- and high-latitudes. The third water vapor forms convergence in the eastern part of the Northwest region in August, forming the strongest rainy season in the eastern part of the Northwest region.

[0059] like Figure 6 As shown in the figure, the influence of water vapor during extreme drought is studied: in extreme drought events, the abnormal water vapor flux at the southern boundary has the greatest impact on the occurrence of extreme drought events; the water vapor in the eastern part of the northwest mainly comes from the westerly belt and the southeast coastal monsoon system. The water vapor at the northern boundary supplements the western and southern boundaries. Therefore, the westerly belt circulation and monsoon anomalies are one of the main reasons for the occurrence of extreme drought events in the eastern part of the northwest.

[0060] Research on the factors affecting summer drought in Northwest China:

[0061] like Figure 7 As shown in the figure, the causes of summer drought in Northwest China are studied: the difference in surface-air temperature on the plateau approximately reflects the sensible heat conditions on the plateau. Through the relationship between the surface-air temperature difference and the South Asian High Pressure, it is found that if the sensible heat on the plateau is strong in spring, the South Asian High Pressure will be established earlier in that year, and generally, the South Asian High Pressure will be stronger in that year. The westward and strong South Asian High Pressure in summer is conducive to more precipitation in Northwest China in summer. When the exit of the 200hPa high-altitude jet is located near 105°E, the divergence and convergence fields formed by the strong northerly axis of the South Asian High Pressure and the convergence field in front of the right side of the high-altitude jet form a pair of mesoscale circulation circles. These two circulations play a key role in maintaining the heavy precipitation rain belt, making it easy for large-scale heavy precipitation to occur in the eastern part of Northwest China. The strong vertical airflow sinking area on the north side of the plateau is mainly located in the north of the Qilian Mountains, which makes the region less precipitated in summer. When the South Asian High Pressure and the exit of the high-altitude jet are in the right position, heavy precipitation can alleviate the overall less precipitation situation. The water vapor path in the western part of Northwest China is mainly the Aral Sea and Caspian Sea path, while the eastern part is the water vapor path around the plateau. When a strong high-pressure area appears in the 500hPa height field over the plateau in summer, drought and little rain will occur in the eastern part of the Northwest China. At this time, the Western Pacific Subtropical High is biased to the south and east, which is not conducive to precipitation in the Northwest China.

[0062] The study found that the synergistic effect of the Western Pacific Subtropical High and the South Asian High mainly affects the central and eastern parts of the Northwest, typhoons mainly affect the southeastern part of the Northwest, downward airflow on the north side of the plateau mainly affects the central and western parts of the Northwest, and the position of the high-altitude jet stream exit and the jet stream axis mainly affect the central and eastern parts of the Northwest.

[0063] 3. Study the possible interaction modes of key influencing factors of summer drought in Northwest China

[0064] like Figure 8 As shown, the South Asian High and the Western Pacific Subtropical High work synergistically: the eastward extension of the South Asian High enables the Western Pacific Subtropical High to develop and westward, and precipitation to develop, which in turn causes the uneven distribution of non-adiabatic heating in the vertical direction. The thermal effect strengthens the southwesterly wind along the west side of the subtropical high, causing the Western Pacific Subtropical High to strengthen and move westward, thereby intensifying the occurrence of heavy rain. The sinking and warming of air under the control of the Western Pacific Subtropical High and the radiation heating under clear sky conditions cause the temperature to remain abnormally high.

[0065] The impact of sea surface temperature and plateau sensible heat on the synergistic effect between the South Asian High and the Western Pacific Subtropical High: The seesaw effect of sea surface temperature between the Indian Ocean and the Pacific Ocean promotes the occurrence and development of the synergistic effect between the South Asian High and the Western Pacific Subtropical High. The more obvious the seesaw phenomenon is, the stronger the synergistic effect is, that is, the more frequent the phenomenon of "moving towards each other and repelling each other" between the South Asian High and the Western Pacific Subtropical High is.

[0066] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for predicting summer drought in Northwest China, characterized in that: The following steps are involved: Step 1: Establish a conceptual model of weather dynamics for summer drought prediction in Northwest China under the synergistic effect of multiple factors; Step 2: Establish a precipitation dynamic-statistical forecast model based on CFSv2 forecast data under the synergistic effect of multiple factors; Step 3: Conduct research on the forecast technology of the next seasonal extended period with the synergistic effect of multiple factors.

2. A method for predicting summer drought in Northwest China according to claim 1, characterized in that: The first step is to establish a weather dynamics conceptual model for predicting summer drought in the northwest region under the synergistic effect of multiple factors, based on the actual conditions of plateau heat source, snow cover, and sea temperature in the previous winter, combined with the performance of various factors during the transition period between winter and spring, predict the characteristics of spring influencing factors, and judge the status of summer drought influencing factors in the northwest.

3. The method for predicting summer drought in Northwest China according to claim 1, characterized in that: The aforementioned external forcing factors of the former east include the difference in ground-air temperature on the plateau, more (less) snow on the plateau, high (low) Pacific Ocean temperature, low (high) Indian Ocean temperature and strong (weak) Kuroshio Current; the influencing factors in spring include the early (late) arrival of the South Asian High on the plateau, high (low) Pacific Ocean temperature, low (high) Indian Ocean temperature, positive (negative) direction of EU wave train, El Niño (La Niña) phenomenon; the direct influencing factors in summer include weak (strong) downward flow on the north side of the plateau, the South Asian High being stronger (weak) and more easterly (westerly), the Western Pacific Subtropical High being more northerly (southern) in position and more (weak) in intensity, many (few) typhoons affecting my country, the strong (weak) synergistic effect of the South Asian High and the Western Pacific Subtropical High, the northerly (southern) exit of the high-altitude jet stream being more westerly (easterly).

4. The method for predicting summer drought in Northwest China according to claim 1, characterized in that: The step three is to conduct multi-factor synergistic research on the key areas affecting my country's mid- and high-latitudes, as well as some key areas affecting my country's mid-latitudes. The 500hPa height field has a quasi-30-pentad period that can pass the test of 0.01-0.10 confidence, that is, the atmospheric circulation situation will reappear after every 30 pentads. On this basis, the physical field of the previous 30 pentads is used to make extended-term forecasts. For example, the 500hPa height field of the first pentad in January is used to make a forecast for the first pentad in June, and the 500hPa height field of the second pentad in January is used to make a forecast for the second pentad in June, and so on.

5. The method for predicting summer drought in Northwest China according to claim 1, characterized in that: The second step is to establish a precipitation dynamic-statistical forecast model based on CFSv2 forecast data under the synergistic effect of multiple factors to study the role of the synergistic effect of EU wave trains and El Niño in drought prediction: the study found that a strong El Niño does not mean that extreme summer drought will occur in northern my country. The positive teleconnection pattern (EU type) in the mid-latitudes of Eurasia is the key to the occurrence of summer drought in northern my country. The dynamic prediction model of sea-atmosphere coupling can only predict extreme drought events in northern my country if it can better capture the positive phase EU type.

Images