| Drought is currently one of the most serious natural disasters in the world,and the occurrence of extreme events such as extreme droughts has a very serious impact on the social economy.Therefore,it is crucial to analyze the formation and evolution mechanism of extreme drought and evaluate the social and economic risks caused by extreme drought.This article takes the southwestern region of China,which is prone to frequent droughts,as the research object to explore the formation and evolution mechanism of typical regional extreme droughts,replaying the typical drought event of 2009,and focusing on analyzing the risks caused by this event to the agricultural system.The main content is to analyze the changes in the flow field from the troposphere to the near surface and various meteorological elements during the early stages of drought,and reveal the formation mechanism of extreme drought;Study the spatiotemporal variation characteristics of the land-atmosphere coupling index during the entire drought period and the impact of different soil depths on the land-atmosphere coupling index,and explore the evolution mechanism of extreme drought;Based on the WRF model,the 2009 severe drought event was replayed,and the coupled crop model was used to analyze the agricultural system risks caused by the severe drought.The research results can provide certain guidance for the precise identification of severe droughts and the prevention of severe droughts under current conditions.The main research content and achievements of this article include the following three parts:(1)In order to reveal the formation process of extreme drought,a complete process framework from the troposphere to the subsurface was established.The research shows that the southwest region was mainly controlled by the West Pacific subtropical high and the South Asia high at the beginning of the extreme drought.Under the control of the abnormal anticyclone,the water vapor of the extreme drought event in 2009 sharply decreased from the West Pacific Ocean and the Bay of Bengal,resulting in a continuous shortage of precipitation,which led to extreme drought;Under the control of abnormal anticyclone in the Bay of Bengal,the water vapor in the Bay of Bengal is difficult to transport to Yunnan in 2019,and the lack of precipitation and continuous high temperature are the main reasons for the formation of the extreme drought event.(2)Selecting land-atmosphere coupling atmospheric variables,land-atmosphere coupling intermediate variables,and land surface process state variables,the spatiotemporal distribution characteristics of the land-atmosphere coupling index were analyzed.It was found that during the major drought events of 2009 and 2019,soil moisture and soil temperature under the action of land-atmosphere can significantly increase the temperature by 2m and the height of uplift and condensation;In the middle stage of severe drought,the land atmosphere coupling index changes the most,and the feedback ability of surface soil to land atmosphere is significantly stronger than that of subsurface soil.Soil moisture,soil temperature,and latent heat flux are the main driving factors for drought evolution.(3)Based on WRF model,the effects of 2009 extreme drought event on the agricultural system of Chuxiong Prefecture in 2020 were analyzed by Aquacrop crop model.The results showed that compared with 2020,the decrease of corn and rice was 12.06 tons and 93,700 tons,respectively.A drought hazard risk assessment model was constructed in Chuxiong Prefecture.The results showed that the risk areas were high in the west and low in the east,high in the middle and low in the periphery.Chuxiong City and Lufeng County were the hot spots of drought risk... |
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