Analysis On The Variation Characteristics And Causes Of Evaporation In Northwest China

Evaporation is an important part of water cycle and an important way to reallocate water resources.The arid climate in northwest China makes water supply the main factor restricting evaporation.Based on GLEAM(AE_GLEAM),six reanalysis datasets(AE_reanalyses),and its complementary relationship with the evaporation dataset(AE_CR),the evaporation trend in northwest China is evaluated.During 1981-2017,both AE_GLEAM and AE_reanalyses increased significantly(p<0.001).AE_CR also increased to a certain extent,but at a slower rate.In general,the increasing trend of evaporation is mainly concentrated in the Altai Mountains,Tianshan Mountains,Karakoram Mountains,Kunlun Mountains,Altun Mountains and Qilian Mountains.For these regions,evaporation is even higher than precipitation in terms of climatic averages and linear trends.This suggests that the amount of water stored on land can provide a supplementary supply for evaporation.Therefore,we extend the Budyko framework to assess the effect of terrestrial water storage on evaporation.Taking landscape parameter n=1.8 as reference,the contribution ratio of land water storage to evaporation is about 27%.Land-based water storage appears to be the main contributor to the increasing evaporation in the Altai,Tianshan,Qilian and Altun Mountains.Precipitation is the main source of evaporation in the western Tianshan-Karakoram region,and potential evaporation is also the main reason for the increase of evaporation.For different n values,the contribution of land-based water storage varies from-16.9%to 8.5%.The model provides an opportunity to assess the effect of evaporation on terrestrial water storage in the absence of observational data.Evaporation observation data are scarce,but there are a lot of reanalysis and model estimation data,and the study of these data will bring uncertainty error.Therefore,the wavelet transform decomposition and reconstruction method is used to integrate GLEAM,reanalysis data set,data set based on complementary relationship and data set based on land-surface model.The spatial distribution of climate average and trend of the fusion data is basically consistent with the spatial distribution of most data sets,and the fusion data has the ability to integrate the main features of most data.Compared with AE_AVE,NCEP/NCAR overestimated evaporation in spatial distribution.Using the fusion data,we evaluated the evaporation trend in the northwest China and compared it with other data.From 1982 to 2013,the evaporation trend increased significantly and was mainly concentrated in the Altai,Tianshan,Kunlun,and Qilian Mountains.While ERA Interim and other data showed an inverse trend in the mountain region.According to the water balance equation,evaporation in basins and deserts is highly dependent on precipitation,while evaporation in mountainous areas is regulated by precipitation,runoff,land storage and other uncertain factors.