Evaluation And Projects Of Seasonal Drought In Northwest China Under The Climate Change

As a major arid and semi-arid climate zone in China,five provinces in Northwest China often experience persistent seasonal droughts,which have great impacts on local agriculture,production and life,etc.It is of great importance to study the spatial and temporal variations of seasonal droughts and their possible future scenarios in Northwest China.In this paper,we calculate the standardized precipitation evapotranspiration index(SPEI)using meteorological elements such as temperature and precipitation,and analyze the spatial and temporal variability of seasonal drought in Northwest China from 1961 to 201 7 by combining Mann-Kendall nonparametric test.Finally,the high-resolution smallscale numerical model was used to predict the seasonal drought variation in Northwest China from 2018 to 2100 under two different typical emission scenarios(SSP2-4.5 and SSP5-8.5).The main research results are as follows:(1)The overall trend of seasonal drought succession intensity(rate of change-0.28/10a)and extent(rate of change-3.1%/10a,)for the whole Northwest region from 1961-2017 is weakening.The seasonal drought series turned in 1993,and the intensity and extent of the drought series changed from significantly weakened to non-significantly increased from 1994 to 2017.The extent and intensity of the drought series starting in spring were the largest,with an overall trend of significant weakening,followed by the second largest in summer and the smallest in autumn.In terms of spatial distribution,from 1961 to 2017,the extent and intensity of consecutive droughts showed a trend of increasing from west to east and weakening from north to south.Among the five provinces,the overall extent and intensity of continuous drought in Qinghai and Xinjiang decreased,while the intensity and extent of continuous drought in Shaanxi and Ningxia showed a non-significant increasing trend,and the intensity and frequency of continuous drought in the whole region showed an overall trend from west to east and from north to south.(2)There was an overall non-significant increasing trend of precipitation(P)with spring and summer season in the northwest during 1961-2017,while potential evapotranspiration(ET0)showed a weak decreasing trend.Precipitation(P)was significantly and positively correlated with SPEI,while potential evapotranspiration(ET0)was significantly and negatively correlated with SPEI.The seasonal drought was most influenced by potential evapotranspiration(ET0),while precipitation(P)contributed less to it.The non-significant increase in precipitation(P)and the weakening of potential evapotranspiration(ET0)jointly led to the weakening trend of intra-annual and spring-summer seasonal drought intensity and extent from 1 961 to 2017.The dominant factor for intra-annual potential evapotranspiration(ET0)is wind speed(WS),while the dominant factor for spring-summer season potential evapotranspiration(ET0)is sunshine hours(SH),and the variance contributions of maximum temperature(Tmax),minimum temperature(Tmin),and mean temperature(Tmean)to potential evapotranspiration(ET0)are low.(3)The optimal model applicable to Northwest China was selected from nine global climate models using the rank scoring method,among which the GFDL-ESM4 model was the best,and the model was spatially downscaled,and the seasonal-scale SPEI index was calculated using the output meteorological data to predict the spatial and temporal evolution patterns of seasonal successive droughts in Northwest China from 2018 to 2100 under two different scenarios.Overall,the extent of seasonal successive droughts under the two different scenarios from 2018 to 2100 shows an increasing trend,and the overall change trend of successive drought intensity is not obvious,and the extent and intensity of successive droughts increase relative to the base period.From 2018 to 2060,the seasonal drought extent decreases significantly,while from 2061 to 2100,the drought extent increases significantly under both scenarios,and the incremental rate increases compared to the whole period.The extent and intensity of drought starts in spring,followed by summer and autumn.The extent and intensity of consecutive droughts in two and four seasons are more extensive,and the extent and intensity of consecutive droughts in three seasons are less.The spatial distribution of the annual drought frequency in Northwest China under the two scenarios is consistent,with the eastern region being higher than the western region,and the frequency of drought in both two and four seasons being higher,while the frequency of drought in three seasons is lower.