Temporal And Spatial Variation Characteristics And Influencing Factors Of Actual Evapotranspiration In Arid Region Of Northwest China

Hydrological change and water cycle in different regions are easily affected by global climate change,particularly in arid areas with extremely fragile ecological environment.As an important component of land water cycle and energy flow,actual evapotranspiration can reflect the amount directly involved in the hydrological cycle.The study on evapotranspiration is of great significance not only for understanding climate change and its impact on arid areas,but also for understanding the influence of climate change on arid areas.The accurate estimation also has important guiding significance for rational utilization of water resources,ecological environment restoration and future sustainable development in arid area.In this paper,the arid region of Northwest China was taken as the study area.Based on the 1960-2019 daily data of 54 meteorological observation stations in the study region,the actual evapotranspiration of the study area was estimated by using three complementary evapotranspiration theoretical models of AA,CRAE,and GG.And the data set of land evapotranspiration and total primary productivity(PML?V2)was taken as the standard.The three actual evapotranspiration models were simulated and tested to screen out the actual evapotranspiration model with good simulation effect.The selected actual evapotranspiration model was used to estimate the actual evapotranspiration in the arid region of Northwest China during 1960-2019,and the spatiotemporal variation characteristics of the actual evapotranspiration in the arid region of Northwest China were analyzed.In addition,the spatiotemporal variation characteristics of five meteorological factors such as air temperature,relative humidity,sunshine duration,wind speed and precipitation in the arid region of Northwest China were also analyzed,and the effects of meteorological factors on actual evapotranspiration were also analyzed.The main research results were as follows:(1)The annual monthly actual evapotranspiration of the arid region of Northwest China from August 2002 to August 2019 was estimated by three actual evapotranspiration models(AA,CRAE and GG).Based on the PML?V2 global evapotranspiration and gross primary production,the results of three models were tested.The analysis found that the ET_aestimated by the three models all showed a unimodal trend,high in su mmer and low in winter,with a peak in July.All three models overestimated ET_ato a certain extent,the CRAE model had the most obvious overestimation and its relative average error was also the largest,while the GG model had the best correlation with the data set,and its relative average error was the smallest.Therefore,GG model in this paper was selected to estimate the actual evapotranspiration and analyze its temporal and spatial variation characteristics.(2)Based on the GG model,the actual evapotranspiration in the arid region of Northwest China was estimated from 1960 to 2019.The annual average value of the actual evapotranspiration in the arid region of Northwest China in the past 60 years was between 482.93-720.25 mm,and the annual average value was 586.90 mm.The ET_aof four seasons was showen that summer>spring>autumn>winter,with the ET_aof272.24 mm,184.93 mm,93.64 mm and 36.14 mm,accounting for 46%,32%,16%and 6%of the whole year respectively.The average actual evapotranspiration change rate was 0.24 mm/10a,showing a slight upward trend.(3)From 1960 to 2019,the spatial distribution of ET_ain the arid region of Northwest China showed a trend of high in the east and west,low in the middle,and low in the south and low in the north.ET_awas higher in the Taklimakan Desert and Tengger Desert,and lower in the Tianshan,Altai,Junggar and Turpan basins.In four subregions,69.23%,50%and 66.67%of the sites in northern Xinjiang,Tianshan and southern Xinjiang showed an increasing trend,respectively,while 78.57%of the stations in Hexi-Alxa region showed a decreasing trend.(4)From 1960 to 2019,the annual average temperature in the arid region of Northwest China was 8.13?,and its change rate was 0.34?/10a,showing an upward trend.The seasonal performance of ET_awas summer>spring>autumn>winter,and the spatial performance was southern Xinjiang>Hexi-Alxa>Northern Xinjiang>Tianshan.The annual average relative humidity was 50.75%,the change rate was-0.27%/10a,showing a downward trend.The seasonal performance of relative humidity was winter>autumn>summer>spring,and the spatial performance was northern Xinjiang>Tianshan>Hexi-Alxa>Southern Xinjiang.The annual average sunshine duration was 7.99 h,and the change rate was-0.04 h/10a,showing a downward trend.The seasonal performance of sunshine duration was summer>spring>autumn>winter,and the spatial performance was Tianshan>Hexi-Alxa>Southern Xinjiang>Northern Xinjiang.The average annual wind speed was 2.51 m·s^-1,the change rate was-0.12m·s^-1/10a,showing a downward trend.The seasonal performance of wind speed was spring>summer>autumn>winter,and the spatial performance was Tianshan>Northern Xinjiang>Hexi-Alxa>Southern Xinjiang.The average annual precipitation was 133.51 mm,its change rate was 6.39 mm/10a,showing an increasing trend.The seasonal performance of precipitation was summer>spring>autumn>winter,and the spatial performance was Tianshan>Northern Xinjiang>Hexi-Alxa>Southern Xinjiang.(5)In the past 60 years,the annual actual evapotranspiration in the arid area of Northwest China had a positive correlation with average temperature and relative humidity,and a negative correlation with wind speed.The correlation between actual evapotranspiration and meteorological elements was different in different seasons.ET_awas positively correlated with temperature and sunshine duration in spring,and negatively correlated with wind speed.In summer,ET_ahad a very significant positive correlation with relative humidity and sunshine duration,and a significant negative correlation with wind speed.In autumn,ET_ahad a significant positive correlation with average temperature and relative humidity,and a significant negative correlation with wind speed.In winter,ET_ahad a very significant positive correlation with the average temperature,and had no obvious correlation with other meteorological elements.(6)The meteorological factors that affected actual evapotranspiration were different in different regions.The main interfering factors of actual evapotranspiration in the arid area of Northwestern China were temperature and wind speed.The main influencing factors of ET_ain northern Xinjiang and Tianshan were temperature and wind speed;the main influencing factors of ET_ain southern Xinjiang were relative humidity,wind speed and precipitation;the main influencing factors of ET_ain Hexi-Alxa area were temperature and relative humidity.