Comparative Analysis Of Dryer Or Wetter In Semi-arid Regions Between China And The United States At The Same Latitude

Various extreme weather and climate events brought about by the dry and wet change of climate has affected our daily life seriously.Especially in arid and semi-arid areas,the ecological deterioration caused by continuous drought has threatened the sustainable development of human society.However,we still lack the understanding of regional dry and wet change law and its mechanism from a global perspective.In this paper,the soil moisture,precipitation,potential evaporation,sensible heat flux,latent heat flux have been choused as the climatic elements mainly representing the degree of dryness and wetness,and the global land surface dryness and wetness in semi-arid regions between China and the United States at the same latitude has been comprehensively analyzed based on the reanalysis data of NCEP R-2 dataset from 1979 to 2018.The results show that:the trends of soil moisture,potential evaporation,sensible heat flux,latent heat flux and precipitation all indicate that the most of global continent presents a trend of "dry gets drier,wet gets wetter".In particular the "dry becomes drier" phenomenon in the Sahara desert of the Northern Africa,the Arabian Peninsula in Western Asia and Central Asia,and the "wet gets wetter"phenomenon in Central North America and Western South America are more significant,which is consistent with the viewpoint proposed in IPCC AR5.However,in the arid and semi-arid areas,there is a tendency of "dry to wetter,wet to drier".For example,the eastern part of Northwest China,the western part of Australia and the eastern side of the Andes in South America show a significant trend of "dry to wetter".the southern part of Balkhash,the eastern part of Australia,the East African Rift Valley in Africa,the eastern side of South America and the western end of North America show a significant trend of "wet to drier".We believe that the reversion of "dry to wetter" and "wet to drier" may have a great impact on the ecological changes in the mainland,and the reasons for its formation are worthy of futher study.Therefore,we use the methods of wavelet analysis and catastrophe test to analyze the dry and wet change law and possible causes between two typical regions of Northwest China and southwest America.It is found that the soil moisture in both regions changed from dry to wet at the beginning of the 21st century,and the change period of dry and wet is 2-10 years.The precipitation in Northwest China has a periodic oscillation of 2-5 years,and the first significant period of precipitation in southwest America is 4 years.There is a downward trend of potential evaporation in Northwest China,and the downward trend of potential evaporation in southwest America is not significant.The change cycle of potential evaporation in both regions is 2-10 years.The sensible heat flux showed a downward trend and had a change cycle of more than 50 years.The sensible heat flux in Northwest China mutated around 2005 and that in southwest America occurred around 2008.The latent heat flux shows an upward trend,and the upward trend in Northwest China is more significant after 2009,and that in southwest America is more significant after 2004.There are 2-10-year periodic oscillations in both regions.In general,the reversal of "dry to wet" and"wet to dry" may have a great impact on the ecological changes of the mainland,and its causes are worthy of in-depth study.