Detection Of Highly Sensitive Areas In China Based On Multi-source Soil Moisture Data

In the past 50 years,extreme climate events have become more frequent along with global warming.There are regional differences in response to climate change.In order to adapt to and mitigate the climate change,the highly sensitive areas in China need to be identified.Soil moisture is a key variable of the land surface which controls the exchange and circulation of water and energy.Soil moisture can also directly monitor drought events.In this paper,firstly,several long-term soil moisture products are evaluated in comparison to in-situ measurements in China,then the product with highest quality is selected to explore the location and evolution of the highly sensitive areas in China from the perspective of soil moisture drought events and flash drought events in the past 40 years.Due to their accessibility,the evaluation of the soil moisture products is conducted at both point scale and regional scale from 1992 to 2013.According to the Brunke ranking method,the soil moisture products of different datasets rank from excellent to poor are ESA CCI,ERA-Interim,NCEP/DOE-R2 and NOAA/CIRES-20CR,respectively.Among them,ESA CCI soil moisture can better reflect the spatial distribution with the highest spatial resolution.This product both has the smallest bias and the highest correlation,as well as the most accurate monthly variation simulation.The simulation of inter-annual variation of all products needs to be improved,and controlling the bias is a method which is worth investigation.In addition,the ERA5 soil moisture product has a good spatial correlation and better reflection of inter-monthly and inter-annual variations.However,the relatively small variation is over-corrected in ERA5 based on ERA-Interim,thus its accuracy need to be further improved.Based on the evaluation of the datasets,soil moisture drought(SD)events were defined using ESA CCI soil moisture data following the definition of heat wave.SD events show the sensitivity of semi-arid and semi-humid area,where SD events occurred frequently with significant,constant growth since 1987.The development of SD events changes between seasons,and the growth of the frequency and duration in the Eastern plateau in summer are particularly significant.In the past 20 years,the frequency of SD has increased more than 3 times compared to previous 19 years.The duration has increased to more than 6 times.Compared with Southern China and the plateau,Northeast and Northwest China have more frequent and more continuous SD events.The highly sensitive areas of the extreme event of temperature,heat wave,are concentrated in part of the plateau and Southwest China,while the highly sensitive areas of soil moisture extreme event lies in the climate transition zone,especially in the semi-arid areas.Moreover,the agriculture,economy,natural resources and natural disasters of provinces in China's arid and semi-arid regions are proved sensitive to soil moisture.Flash drought(FD)is an extreme event that comprehensively reflects the characteristics of drought and heat wave.One type of flash drought(high-T driven FD)is mainly driven by a sudden increase in temperature and the other type(low-SM driven FD)is mainly driven by soil water shortage.The soil water shortage may result from a long-term lack of precipitation before the occurrence o.f the latter type.A case study indicates that flash drought may help forecast seasonal drought.Research based on soil moisture data shows that,the frequency of high-T driven FD increased by 145%,while low-SM driven FD increased by 1 15%from 1979 to 2014.Both types occur frequently in July.The first type is likely to occur in wet and semi-humid areas,and its growth is evident in semi-humid areas,while the highly sensitive areas of the latter type are in arid and semi-arid areas.The latter type is generally more frequent and more sustainable than the first type in their own highly sensitive areas.Based on the composite evaluation of five datasets,this study selected a suitable soil moisture product for the long-term research of climate change and regional response in China,and identified the highly sensitive areas from the perspectives of soil moisture drought,flash drought and the evaluation of social-economic impacts of soil moisture,providing some scientific basis for the mechanism of regional response to climate change and the solution to it in China.