| Under the background of climate change,drought disasters occur frequently all over the world,especially in arid and semi-arid areas.Gansu Province is located at the intersection of different climatic regions in northwest China,and spans several different climatic zones,making it an ecologically fragile and climate-sensitive terrain region in China.It is deeply affected by drought disaster,which seriously hindering the socio-economic development of Gansu Province.Therefore,it is of great significance to study the potential evapotranspiration and the spatio-temporal evolution of drought in this region.Based on the data of meteorological stations in and outside Gansu Province,the Penman-Monteith formula was used to calculate the annual and seasonal potential evapotranspiration and standardized precipitation evapotranspiration index(SPEI)of different climate regions during 1961-2020.Then,partial correlation analysis,wavelet periodicity analysis and cross wavelet analysis were used to explore the correlation between potential evapotranspiration and drought index and the drought characteristics of different climatic regions in Gansu Province.Finally,combined with the scenario data of SSP126,SSP245 and SSP585 of the sixth phase of the International Coupled Comparison Program(CMIP6),the temporal and spatial evolution of drought in Gansu Province during 2021-2099 was predicted.The main conclusions are as follows:(1)In the past 60 years,the average annual temperature in Gansu Province increased significantly,and the temperature growth rate in arid climate region was higher than that in humid climate region.In terms of time,the seasonal temperature growth rate was ranked as spring > winter > summer > autumn.In terms of spatial distribution,the temperature rise trend in spring and summer is similar,showing a downward trend from northwest to southeast.In terms of spatial distribution,the temperature rise trend in autumn and winter shows that the temperature increase rate in the central climate region of Gansu Province is higher than that in the eastern and western climate regions of Gansu Province.In the temporal variation of precipitation,precipitation in autumn showed an insignificant decreasing trend in the past 60 years,while precipitation in other seasons showed an increasing trend,and the contribution of precipitation in summer was the largest.In terms of spatial variation,the distribution of precipitation in spring,autumn and winter in humid climate area showed a decreasing trend.(2)In terms of time,the annual and seasonal variation of potential evapotranspiration in different climate zones in Gansu Province showed an increasing trend except for the arid warm temperate zone in western Hexi,and the seasonal growth rate of potential evapotranspiration was the highest in spring,followed by summer and the lowest in autumn.Spatially,the spatial distribution of annual mean evapotranspiration showed that the potential evapotranspiration in spring,summer and autumn was in the high value area of potential evapotranspiration in arid climate region,while the potential evapotranspiration in winter was in the high level of the whole province in humid climate region.The spatial distribution characteristics of the change trend of spring and summer potential evapotranspiration in Gansu Province were similar.Through partial correlation analysis of potential evapotranspiration and meteorological factors,it is concluded that the positive correlation between air temperature,wind speed,sunshine duration and potential evapotranspiration is relatively high,and this high correlation is more obvious in arid climate regions.(3)In terms of SPEI12 time variation trend,in the past 60 years,except for the warm temperate arid zone in western Hexi and the alpine and semi-arid zone in Qilian Mountains,the whole Gansu Province and other climatic zones showed a trend of dryness.On the seasonal scale,the drought in summer was alleviated,and the trend of dryness in other seasons was spring > autumn > winter.From the perspective of SPEI12 trend spatial distribution,the annual scale drought in Gansu Province shows that most of the climate regions are developing toward dryness,while the warm temperate arid zone in western Hexi and the cold temperate semi-arid zone in western Gansu are wetting.The spatial distribution of the four seasons drought trend shows that the dryness trend in northwest arid zone is higher than that in southeast humid climate zone.In terms of the spatial distribution of drought frequency in Gansu Province,the drought frequency is higher in the cold temperate semi-arid area in northern Gansu Province,the temperate sub-humid area in southern Gansu Province and the warm temperate humid area in northern Gansu Province.In the four seasons of drought frequency,the area with high drought frequency in winter is larger than that in other seasons.In terms of time,the ratio of drought stations to annual drought,spring drought,autumn drought and winter drought has increased in the past 60 years,and the occurrence range of drought has expanded.Through wavelet series analysis,the SPEI12 cycle changes in Gansu Province and other climate regions are obvious,and SPEI12 has a high negative correlation with potential evapotranspiration.(4)Temperature,precipitation and potential evapotranspiration will all show consistent increase changes under different CMIP6 development scenarios in the future 2021-2099,that is,high emissions will bring more significant increase in temperature,precipitation and potential evapotranspiration.However,the changes of temperature,precipitation and potential evapotranspiration in four seasons are different under different emission scenarios.Under low emission scenario,summer temperature increases obviously,while under high emission scenario,autumn temperature increases faster than other seasons,and a warm autumn phenomenon will appear in the future.The spatial distribution of temperature,precipitation and potential evapotranspiration under the emission scenarios of SSP126,SSP245 and SSP585 shows that the temperature rising trend in the cold temperate semi-arid region in northern central Gansu is higher than that in other climate regions,and the precipitation change in the humid climate region is more significant than that in the arid climate region.The spatial distribution of potential evapotranspiration under SSP245 and SSP585 was similar,but it was different under SSP126,and the trend of potential evapotranspiration in arid climate zone was higher than that in humid climate zone.(5)With different emission scenarios,the future drought trend in Gansu Province will be different.Under the low emission scenarios of SSP126 and SSP245,the trend of drought is mainly concentrated in the period of 2021-2060.However,under the SSP585 high emission scenario,Gansu Province will maintain an obvious drought trend in the next 79 a,and the SPEI12 drought index decline tendency rate is-0.23/10 a.According to the spatial distribution of SPEI12 drought index trend,the spatial distribution pattern of the three scenarios was similar,and the trend of aridity was accelerated from the southeast humid area to the northwest arid area.In addition,with the increase of emission scenario,the range of high-value frequency areas of drought in Gansu Province becomes more and more extensive.Under the high-emission scenario of SSP585 in the future 79 a,the frequency of drought in83.3% sites is between 31.6% and 39.2%. |
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