A Study On The Change Of Dryness And Humidity In The Northern Arid Region And The Evolution Of Future Climate Divisions

Drying and wetting trends in the background of global warming are key issues in global climate change research,but there are still large uncertainties.The northern drylands(including arid and semi-arid areas)are important ecological restoration areas and ecological engineering construction areas in China.The climate evolution characteristics of this area and the study of drying and wetting trends are of great significance.Therefore,this paper chooses the arid area in northern China as the research area based on Eco geographical regionalization.This paper uses temperature,precipitation and potential evapotranspiration based on observations of the sites and GLEAM surface and root zone soil moisture data,Palmer Drought Index(PDSI),SelfCalibrating Palmer Drought Severity Index(sc PDSI)and the Standard Precipitation Evapotranspiration Index(SPEI)at time-scale of one month,six month,and twelve month.Based on the same characteristics of the results of multiple indices,the 1982-2012 Regional drying and wetting trends were obtained.At the same time,this paper explores the drought index driven by different precipitation data,compares and analyzes the regional dry and wet changes,and explores the impact of precipitation data differences on the study of dry and wet changes.It is of great significance to explore the future climate change in the arid area of northern China.Therefore,based on the results of CMIP6 multi-mode ensemble,this paper analyzes the climate evolution trend of each climate area in the middle and end of the 21 st century based on Cobain climate classification.The main conclusions are follows:(1)From 1982 to 2012,both temperature and potential evapotranspiration showed an upward trend,precipitation and soil moisture also showed an upward trend;PDSI and sc PDSI showed a downward trend in the entire study area,while SPEI01,SPEI06 and SPEI12 showed an upward trend.However,from the perspective of spatial distribution characteristics,based on each index,we can get the trends characteristics of the eastern part of the study area becoming dry and the western part becoming wetter.In the semi-arid area,precipitation,surface soil moisture and root zone soil moisture,as well as various drought indexes all declined significantly,that is,a consistent drying trend.In the arid zone,all indexes showed a significant upward trend,that is,a consistent trend of wetting.This shows that although the various indexes themselves are different,each index shows that the semi-arid area of the northern arid area becomes dry and the arid area becomes wet.(2)Based on the CMA precipitation data,it is verified that the CRU precipitation data has applicability problems in the northern drylands of China.From the multi-year average value,the spatial heterogeneity of CMA precipitation data is stronger.Both sets of precipitation data show that there is a significant upward trend in precipitation in the northern drylands,but the upward trend in the CMA precipitation data is stronger than the CRU result.From the perspective of the spatial distribution of the trends in dryness and wetness,in the results of the SPEI index over time on each time scale calculated based on the CMA precipitation data,the wetting area in the northern arid area is larger than the result calculated based on the CRU data,and the drying area is smaller than the one based on the CRU.From the perspective of time series,the fluctuation characteristics and trends of SPEI at each scale calculated based on different precipitation data sets are basically the same,but there are significant differences in their values,the specific manifestations are the SPEI01,SPEI06,and SPEI12 calculated based on the CMA precipitation data set.The multi-year trend values are all greater than the multiyear trend of SPEI01,SPEI06,and SPEI12 calculated based on the CRU precipitation data set in the entire study area.(3)The CMIP6 multi-model ensemble average result can reasonably reproduce the spatial distribution characteristics of the average precipitation and temperature in the northern drylands of China during the historical period and obtain the K(?)ppen climate zone based on the CMA observation data.CMA observation data show that the precipitation in the vicinity of the Tianshan Mountains and semi-arid areas from 1982 to 2012 was significantly higher than that of other areas in the study area,and the spatial distribution of temperature was more consistent.Only in the vicinity of the Tianshan Mountains and the semi-arid northern part,the annual average temperature was lower.The temperature in other areas is above 7°C,and the average results of the CMIP6 multi-mode set during the same period are also consistent with it.Under the SSP2-4.5 and SSP5-8.5 scenarios,the arid climate zone in the region still accounted for more than 60% in the middle and end of the 21 st century.As the global temperature continues to rise in the future,the cold arid climate zone will gradually transform into a hot drought,the warm summer climate in the cold temperate climate zone will gradually transform into a hot summer climate,and the cold summer climate will transform into a warm summer climate.