| Flash drought is a drought event that occurs rapidly and is characterized by high temperature and a shortage of soil moisture content.Under the background of global warming,the frequent and increasing drought in recent years poses a serious threat to food and agricultural security and the health of ecological environment.Southwest China is affected by the drought disaster,and the drought research result is fruitful,but the research on the flash drought is still insufficient.Focusing on the characteristics of spatio-temporal changes,processes and prediction of flash drought in ecologically fragile areas and climate sensitive areas can not only help to understand the law of climate change,but also has far-reaching significance for ensuring the security of food and water resources and promoting the sustainable development of ecological environment.Therefore,this study takes southwest region as the research object,studies the spatio-temporal characteristics of flash drought,analyzes its evolution process and explores its future development trend,which can put forward the adaptive countermeasures of flash drought for the research area and improve the early warning ability.Based on the data,such as maximum temperature,precipitation,soil moisture content and evapotranspiration,define and identify the events of flash drought and rainfall shortage from1989 to 2019,explore the frequency,average duration and area,quantitatively analyze the characteristics of flash drought in recent years,and finally used the mainstream prediction model to estimate the future trend of short-term flash drought in the southwest.The main study conclusions are summarized as follows:(1)From 1989 to 2019,there were significant differences in the spatial distribution of the total frequency,total phenology,frequency,and average duration of two types of flash droughts in the southwest.The total frequency,total phenology,and spatial distribution of flash droughts caused by high temperature heat waves show little difference,with an overall pattern of "less in the south and more in the north" and an average duration of "shorter in the south and longer in the north";The spatial distribution characteristics of flash droughts caused by rainfall shortage are basically opposite to those caused by high temperature heat waves,showing a pattern of "more in the south and less in the north" and "shorter in the south and longer in the north".The total number,total number,frequency,average duration,and area of two types of flash droughts have shown an overall increasing trend in time series changes,with more concentrated outbreaks from 2006 to 2015.The flash drought events occurring in the research area are mainly characterized by relatively long periods of high temperature heat wave flash drought,accompanied by shorter periods of rainfall shortage flash drought.From the perspective of flash droughts caused by high temperatures and heatwaves in various provinces,Chongqing is the most severe,followed by Guizhou;Sichuan has the longest average duration and fastest growth rate.The situation in Yunnan and Guangxi is relatively mild.From the perspective of flash drought caused by rainfall shortage in various provinces,Yunnan is the most severe;Various indicators in Sichuan show a fluctuating upward trend;The situation in Guizhou and Chongqing is relatively mild;The fluctuation of various indicators in Guangxi has slowly decreased.(2)From 1989 to 2019,the evolution trend of two types of flash droughts in the southwest region passed the significance test,with the mutation time mainly concentrated in 1997 to 2003.The total number,total number,frequency,and area of high-temperature heat wave type flash droughts increased significantly compared to rainfall shortage type flash droughts,while the average duration of the upward trend was less significant.The frequency,duration,and area of flash droughts caused by high temperature heatwaves in Sichuan,Yunnan,and Chongqing show a significant upward trend;The frequency,duration,and area of flash droughts caused by high temperature heatwaves in Guizhou and Guangxi have increased significantly;The average duration of flash droughts caused by high temperature heatwaves in Sichuan and Yunnan has increased significantly;The average duration of flash droughts caused by high temperature waves in Chongqing shows a significant upward trend,while the average duration of flash droughts caused by high temperature waves in Guizhou and Guangxi shows an insignificant upward trend.The number,frequency,duration,average duration,and area growth trend of flash droughts caused by rainfall shortage in Sichuan and Yunnan are extremely significant;The frequency and frequency of flash droughts caused by rainfall shortage in Chongqing have a significant increasing trend,while the number and area of droughts have a significant increasing trend,and the average duration has no significant shortening trend;The decreasing trend of the number and frequency of flash droughts caused by rainfall shortage in Guangxi is not significant,while the decreasing trend of the number and area of droughts is significant,and the decreasing trend of the average duration is extremely significant;The increasing trend of the number and frequency,duration,and area of flash droughts caused by rainfall shortage in Guizhou is not significant,and the decreasing trend of average duration is not significant.(3)From the perspective of high temperature heat wave flash drought in various provinces,Chongqing has the highest annual average grid point occurrence frequency,maximum occurrence area,and fastest growth rate;The average number of grid occurrences and the average number of grid occurrences in Guizhou are second to those in Chongqing,and the average duration and growth rate are the slowest;Sichuan has the longest average duration and fastest growth rate.Yunnan and Guangxi are low incidence areas,with similar average grid occurrence frequency,average grid occurrence number,and average duration,but significant differences in growth rates.The increase in average grid occurrence number in Yunnan is stronger,and the occurrence area is the smallest.From the perspective of flash droughts caused by rainfall shortage in various provinces,the average occurrence frequency,occurrence frequency,duration,and area of grid points in Yunnan and Sichuan provinces show a fluctuating upward trend.Among them,Yunnan has the highest annual average occurrence frequency and occurrence frequency among the five provinces;The average grid occurrence frequency,average grid occurrence frequency,and area growth rate in Guizhou and Chongqing are slow,and the average duration dynamically decreases;The average occurrence frequency,number of occurrences,frequency,duration,and area of grid points in Guangxi fluctuated slowly and decreased.(3)The common type of regional flash drought in the southwest region is the regional high temperature heat wave flash drought event.Four periods before the occurrence of a high temperature heat wave flash drought event,the highest temperature began to rise sharply,and evapotranspiration and soil moisture content changed synergistically.The rapid increase in evapotranspiration and decrease in soil moisture content accelerated the occurrence of the event.After the event occurred,all elements gradually returned to normal.The coverage of flash droughts caused by regional rainfall shortage is not high,so the changes in various meteorological elements are not very significant.In the first period of the event,significant changes occur in each element,while in the second period after the event,the recovery of precipitation and evapotranspiration is slower,and the recovery of maximum temperature and soil moisture is faster.(4)From 2020 to 2025,the overall pattern of flash droughts in the southwest region has not changed much.High temperature heat wave flash drought is still the main type of flash drought in the region.The total frequency and duration of two types of flash droughts show an increasing trend,which is closely related to the dynamic increase of annual maximum temperature,fluctuation decrease of precipitation,increase of annual evapotranspiration,and decrease of soil moisture content in Southwest China from 1989 to 2025.In the future work of preventing and reducing flash drought disasters,effective defense measures should be taken,such as improving meteorological monitoring and forecasting mechanisms,constructing early warning mechanisms for flash drought disaster prevention and reduction,and increasing the research and development of modern artificial precipitation methods. |
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