Spatial-temporal Variation And Projection Of Drought In The Arid Regions Of Northwestern China

The arid region of Northwestern China is the main arid climate distribution area in China.The geographical location of the arid region of Northwestern China and the complex topography of high mountains and basins have made water shortages and continuous drought the main limiting factors for the sustainable development of the region.Severe drought disasters will have a huge impact on agricultural production,ecosystem functions,water sources,and socio-economic aspects.Research on the temporal and spatial changes of drought is of great significance to the arid region of Northwestern China.Therefore,this study uses temperature and precipitation data to calculate the standardized precipitation evapotranspiration index(SPEI)as an indicator of drought detection,and the vegetation normalized index(NDVI)as an indicator of vegetation change,combined with climate tendency rate and Mann-Kendall non-parametric test,correlation analysis,and other methods have analyzed the spatio-temporal changes of temperature,precipitation,SPEI and NDVI in the northwest arid region from 1961 to 2015.The Weather Research and Forecasting Modell(WRF)was used to predict the climate,drought and vegetation changes in the arid region of Northwestern China from 2016 to 2100 under two typical concentration paths of RCP2.6 and RCP8.5.and using regional climate models to predict the climate,drought and vegetation changes in the arid region of northwest China from 2016 to 2100 under two representative path concentration(RCP2.6 and RCP8.5).The conclusions as below:(1)From 1961 to 2015,the temperature in the arid region of Northwestern China showed a significant warming trend,with a warming rate of 0.303°C/10a(P<0.05).The Hexi-Alxa subregion had the fastest warming rate.The temperature in the four seasons has a significant growth trend,and the temperature in winter has the fastest growth rate,which is 0.373?/10a(P<0.05).The spatial distribution of temperature has the regularity of high temperature in plains and basins,and low temperature in mountainous and surrounding areas.The precipitation increase rate is 5.217mm/10a(P<0.05).The precipitation increase rate in the Tianshan subregion is the largest,and the precipitation increase rate in the southern Xinjiang subregion is relatively the smallest.The increase rate of precipitation in spring is not significant,and the precipitation in other seasons increases significantly.The spatial distribution of precipitation has a pattern of high precipitation in mountainous areas and less precipitation in deserts and plains.(2)In the past 55 years,the temporal change of SPEI in the arid region of Northwestern China has shown a significant decreasing trend,with a rate of change of-0.186/10a,and the SPEI of each subregion has also shown a decreasing trend.On a seasonal scale,SPEI increased significantly in winter with a rate of change of 0.061/10a,SPEI decreased significantly in spring,summer,and autumn,and SPEI decreased at the highest rate in autumn.Northe Xinjiang subregion and Tianshan Mountains subregion have high frequency of light drought and moderate drought,while South Xinjiang subregion and Hexi-Alxa subregion have severe drought.The frequency of extreme drought is higher,and the drought in the south of the arid region of Northwestern China is more severe than that in the north.(3)From 1982 to 2015,the interannual and seasonal NDVI in the arid region of Northwestern China showed an increasing trend,and the NDVI increase rate was the largest in summer,which was 0.004/10a.Most areas covered by vegetation show an increasing trend of NDVI,and the areas showing a trend of vegetation degradation are mainly concentrated in the central part of the northern Xinjiang subregion.Vegetation changes in the arid region of Northwestern China are mainly positively correlated with temperature,precipitation,and SPEI.The vegetation in the Tianshan Mountains subregion and the South Xinjiang subregion have a high response to temperature,while the vegetation in the Hexi-Alxa subregion has a high response to precipitation.The North Xinjiang subregion has the highest response to SPEI.The NDVI area affected by temperature is relatively large in the arid region of Northwestern China.(4)The future temperature and precipitation changes under different greenhouse gas concentration emission scenarios are different.Under the RCP2.6 scenario,the temperature showed an insignificant decreasing trend,and the temperature decline rate was-0.013?/10a.Under the RCP8.5 scenario,the inter-annual and seasonal temperature both increased,and the inter-annual temperature increase rate was0.63?/10a(P<0.05),continuous warming in different periods of the 21st century.The change in precipitation is the same as the temperature.The precipitation under the RCP2.6 scenario shows an insignificant downward trend,while the precipitation under the RCP8.5 scenario rises significantly.The decreasing rate of precipitation in the RCP2.6 scenario is-0.022mm/10a,and in the RCP8.5 scenario,the precipitation increasing rate is 1.137mm/10a(P<0.05),and the average precipitation at the end of the21st century is 245mm.(5)The SPEI under the RCP2.6 scenario is only show an insignificant increasing trend,and the increase rate is 0.003/10a.In the RCP8.5 scenario,SPEI shows a significant downward trend,and the extent of the decline is very large,with the reduction rate of SPEI is-0.274/10a.The frequency of drought under the RCP2.6scenario does not change much.With the increase of greenhouse gas emission concentration,the frequency of drought in the early,middle and late 21st century under the RCP8.5 scenario increases.Under the influence of climate change,the NDVI under the RCP2.6 scenario shows an insignificant increase trend,with an increase rate of10^-5/10a,and the NDVI under the RCP8.5 scenario shows a significant increase trend,with an increase rate of 0.003/10a.This study conducts a systematic analysis of the historical and future temporal and spatial changes of temperature,precipitation,SPEI and NDVI in the arid region of Northwest China.The results of the study are helpful to understand the evolution characteristics of the climate and drought in the arid region of Northwest China.The application capabilities of forecasting future climate change in the northwest arid zone are expected to provide scientific support for the future use of water resources in the northwest arid zone,drought monitoring,evaluation,prediction,and research on the impact of drought on agriculture,hydrology and ecology.