| The Tibetan Plateau(TP)is known as the “Asian water tower”.The water vapor transport and budget over the TP not only determine spatial distribution and changes of water resources,but also exert profound impacts on the Asian hydroclimate.Investigating the multiscale variabilities and water vapor balance characteristics of water vapor budget of the TP is helpful to fully understand the changes of water vapor transport and budget over the TP and is of great significance for improving the understanding of water resources and water cycle conditions of the "Asian water tower",and deepening the understanding of the impact of the TP water vapor on Asia at different timescales.Therefore,using ERA-Interim and ERA5 reanalysis datasets,the net water vapor budget(Bt)of the TP is calculated based on the refined boundary of the TP.Then,this paper explored multiscale variation characteristics of the TP Bt in different seasons,including the climatology,diurnal variation,interannual and interdecadal variations.The relationship between Bt and precipitation and quantitative contribution of the transient water vapor transport to Bt were also investigated.In addition,from the perspective of multiple satellites and observed precipitation data fusion,and validation of different estimation methods of evapotranspiration,atmospheric water vapor balance characteristics over the TP region is preliminary studied.The main conclusions are as follows.(1)The TP is a water vapor sink throughout the year.The TP Bt is the largest in summer,followed by spring and autumn.And the TP Bt is the smallest in winter.The seasonal variation of Bt is closely related to water vapor budgets at the southern(Bs)and western(Bw)boundaries.Except for winter,the meridional water vapor transport dominates the southern boundary and water vapor input is concentrated below 500 h Pa in the eastern-central part of the boundary(83°-96° E),where the seasonal variation of Bs is also evident.Bs gradually decreases with height.The zonal water vapor transport is stable at the western boundary with small seasonal variation,while the meridional component shows obvious seasonal variation.At the western boundary,the strongest water vapor transport is in the middle level of the troposphere(550-500 h Pa)except for summer.At the eastern and northern boundaries,the vertical structure of water vapor transport always shows water vapor “inflow in lower level-outflow in the middle and upper levels” in the troposphere in four seasons.Besides,the low-level westward water vapor transport belt to the south of 32 ° N over the eastern slope of the TP shows a significant seasonal variation in the source and intensity of the water vapor transport.On the northern boundary,the summer water vapor budget is slightly larger than other seasons and water vapor mainly enters the TP from the 91°-94° E region below 650 h Pa.(2)The TP Bt shows a distinct diurnal variation with a single peak in four seasons.Bt tends to arrive at a minimum in the early morning(0500-0900 BJT)and peaks in the afternoon(1600-1700 BJT).The diurnal variation of Bt is the strongest in summer,while the intensities of diurnal variations in Bt in spring and autumn are less than half of that in summer.In summer,the growths in four boundary water vapor budgets of the TP from the early morning to the afternoon contribute to the diurnal variation of the TP Bt.In spring and autumn,the diurnal cycle of Bt is determined by that of Bs and Bw.The intensity of diurnal variation is weak in winter.Due to the influence of the low-level wind field,water vapor transport over the TP also ehxibits distinct diurnal variability,manifesting the water vapor flux vector rotating clockwise within a day,and water vapor convergence(divergence)occuring over the inner TP during the daytime(nighttime).The latter is the predominant reason for diurnal variations in Bt and boundary water vapor budgets of the TP,which is essentially regulated by the changes in the orographic thermodynamic effect.Specially,the rapid and strong warming on the TP slopes generates anomalous water vapor inputs(outputs)by anomalous upslope(downslope)flows during the daytime(nighttime),thus resulting in a rise(drop)of water vapor budget at the boundary.In addition,to the south of the TP,the diurnal variation of low-level southerly flows also contributes to the diurnal variations of Bs and Bw.In addition,the largest amount of precipitation over the TP occurs 2–3 h after the Bt peak in summer.(3)At the interannual timescale,the variation of Bt is mainly determined by anomalous water vapor transports at the western and southern boundaries.The Bay of Bengal,the North Arabian Sea,and mid-latitude West Asia are the main sources of excessive water vapor for a wetter TP.Moreover,the variability of the TP Bt is closely associated with precipitation over the central-southern and southeastern parts of the TP in summer and winter,which is attributed to the combined effect of the stationary and transient water vapor transports.At the interdecadal time scale,Bt displays a clear increasing trend in spring,summer and autumn,with significant mutations in the mid-1990 s in spring and summer.(4)The transient water vapor transport is quasi-meridional in the mid-and high-latitude areas and plays a leading role in winter Bt but contributes little in other seasons.By adjusting the water vapor supply anomalies at the southern and western boundaries,the transient water vapor budget regulates one-third to four-fifths of Bt anomalies at the interannal time scale.In addition,the transient water vapor transport can also effectively regulate the variability of precipitation over the central-southern and eastsouthern parts of the TP in summer and winter.The stationary water vapor budget based on monthly data may underestimate the link between the TP Bt and local precipitation.When considered the effect of the transient water vapor transport,the linkage between the TP Bt and local precipitation is tighter.The interdecadal variability and and long-term trend of Bt is mainly dominated by the stationary water vapor transport in summer.(5)On an annual average scale,the annual precipitation,annual evapotranspiration,and annual accumulated water vapor income of the TP are 17980 trillion tons,7140 trillion tons,and 11540 trillion tons,respectively.Evapotranspiration produced by Maximum entropy production model generally maintains the atmospheric water vapor balance over the TP. |
