Impacts Of Climate Change And Human Activities On Dryness And Wetness In Different Sub-regions Of China

Drought is one of the most severe and destructive natural disasters.With the warming of global climate and the development of social economy,the impacts of climate change and human activities on drought and its driving factors have gradually become the focus of scientific research.In order to monitor and forecast drought,it is important to analyze the driving factors of drought.The meteorological elements,circulation index,socio-economic indicators and greenhouse gases data were used to analyze the impact of climate change and human activities on drought.Based on the water deficit/surplus(D),the temporal and spatial variation of drought for different regions of China was revealed,the modified Mann-Kendall method(MMK)were used to test the trend of D;The circulation index were selected by collinearity analysis and Pearson correlation analysis and its significance;The multiple linear regression(MLR)model of D and circulation fators were established to make short-term drought forecast for different sub-regions in China.In addition,based on socio-economic indicators,The selected 525 sites were divided into 6 different socio-economical levels to explore the impact of socio-economic and human activities on extreme wet and drought events under different socio-economical levels,the contribution of climate change(represented by circulation factors)and human activities(represented by greenhouse climate)to drought was determined from different sites,different sub-regions and different socio-economical levels by using the uncertainty analysis method.The main conclusions are as follows:(1)The temporal and spatial of D in seven different sub-regions was analyzed.China is divided into seven sub-regions,and D was different in seven sub-regions from 1961to 2020,to be specifically,Temperate and warm-temperate northwestern China desert(sub-region I),Temperate grassland of Inner Mongolia(sub-region II)and Qinghai-Tibetan Plateau(sub-region III)were in a state of drought,and the Northwest China is the most severe in May and June,while Subtropical humid central and southern China(sub-region VI)and Tropic humid southern China(sub-region VII)were wet.The southeast region had the highest degree of moisture and the highest degree of moisture from May to August.The results of annual D variation trend showed that the number of stations with increasing trend of D was greater than that with decreasing trend except for sub-region II and V,and the phenomenon was most obvious in subregion VI.During the study period,the northwest,east and southeast of China showed a trend of wetness,while the central region showed a trend of aridity.(2)The key driving circulation factors of drought in different sub-regions were selected.For the results of collinearity analysis,Pearson correlation and its significance,the occurrence of drought is the result of the concurrence of multiple circulation factors;Drought in different sub-regions and even the whole country was influence by circulation index.In addition,the influence of circulation factors on drought under climate change is cyclical,with a period of about 12 months,and there is a lag time,which is basically with0-12 months.Among numerous circulation factors,atmospheric circulation factors played a dominant role on drought,for example,the number of drought circulation driving factors is the largest in the northwest region,and the degree of influence is the highest,the correlation coefficient between drought and PPVI without Hysteresis is as high as 0.88,and the correlation coefficient between drought and SSRP with lagged 10 months is-0.86.(3)Quantitative analysis and prediction of drought based on key circulation factors.The multiple linear regression model show that,the Pearson correlation coefficient(r)were higher and normalized root mean square error(n RMSE)were lower in calibration period(1961-2020),but both of them indicate that the model in calibration period was better.No matter in calibration or validation period,the model has the best performance in the northwest region(sub-region I).The model performance effects of the same region with different lag times are different.In validation period,the simulation effect of subregion I is the best and the lag time is the 5 month,and r and n RMSE are 0.96 and 8.2%,respectively.In validation period,the simulation effect of sub-region VI was the best and the lag time was1 month,and r and n RMSE were 0.58 and 15.3%,respectively.In addition,The D of each month in 2021 will be negative in Temperate and warm-temperate northwestern China desert(sub-region I),Temperate grassland of Inner Mongolia(sub-region II),Temperate humid and sub-humid northeastern China(sub-region IV),Warm-temperate humid and sub-humid northern China(sub-region V),which indicate that these region will be in a state of drought,and the drought in sub-region II is the most serious in June 2021,The D value is-144.1 mm;D in sub-reigno VI and VII is mostly greater than 0,indicating that these region will be in a humid state in 2021,and subregion VII is the highest degree of moisture with D value of113.3mm.According to the evaluation of the prediction model,the drought degree in sub-region II in 2021 will be more severe than before(<40%),we should pay more attention to it and take measures to prevent and deal with drought in advance.Sub-region VII will be more wet than ever in 2021(>60%),some measures should be taken to prevent flooding risk in advance for the region.(4)The impact of socio-economical conditions on extreme drought and wet events.The selected total 525 sites were divided into 6 socio-economical levels by socio-economic indicators(Population and GDP)in 2018.The population and GDP of each level tended to increase,especially in big cities such as Beijng,Shanghai,Guangzhou,Shenzhen which belonged to socio-economical level 6 and located mostly in developed eastern China.Extreme wet events denoted by SPEI?MAX have become worse and extreme drought events denoted by SPEI?MIN turned to be milder over time.The years 2016 with averaged SPEI?MAX of SPEI_12-monthof 1.83 and 2011 with averaged SPEI?MIN of SPEI_12-monthof-1.58 were found to be extremely wet and extremely dry years in China,respectively.There were general increasing trends in SPEI?MAX and decreasing trends in SPEI?MIN as the socio-economical levels increased,but the rate of increase or decrease varied were different.The extreme wet events were more severe in developed cities at high levels and the extreme drought events were more severe in less developed sites at low levels.(5)Contribution of climate change and human activities to drought.In terms of time,the four greenhouse gases concentration(CH₄,CO₂,N₂O SO₂)were increasing over time.With the improvement of socio-economical level,its also gradually increased.In terms of space,spatial distribution of four greenhouse gas concentrations in China had a certain regional,and gradually increased from west to east.The contribution of climate change to drought was greater than that of human activities at different sites,different subregions and different socio-economic levels.Under different sites,the contribution of climate change to drought ranges from 30%to 99.2%,and the contribution of human activities to drought ranged from 0 to 70%.Meanwhile,the contribution of human activities to drought increased gradually from west to east in China.Under different sub-regions,the contribution of climate change to drought in the Qinghai-Tibet Plateau(sub-region III)is the highest,which is 82.7%.The contribution of human activities to drought is 37.4%in Temperate grassland of Inner Mongolia(sub-region II).The contribution of climate change to drought decreased with increased socio-economical level,while the contribution of human activities to drought gradually increased with increased socio-economic level.