| The Tibetan Plateau(TP)is known as the “Asian Water Tower” and has an important impact on the regional and global hydrological cycle and climate change.In this paper,ERA-Interim reanalysis data,station observation data provided by China Meteorological Administration(CMA),and Global Land Surface Data Assimilation System(GLDAS-2.0)data,multiple precipitation grid data,historical data and estimated experimental data of CMIP5 model are used to analyze the variation of water vapor content over TP during the summer period from 1979-2010,the net water vapor transport from outside region to the TP,and the evapotranspiration of the underlying surface,the water vapor transport of the eastern boundary of the TP in the summer during 1979-2016,the spatial and temporal characteristics of summer precipitation,as well as the relationship between water vapor transport of the TP and precipitation in Northern China(32-43°N,100-115°E)and the influence of near-surface specific humidity on local temperature over the TP.The main conclusions are as follows :(1)Using ERA-Interim reanalysis data,station observation data provided by CMA and GLDAS-2.0 data,the water vapor content in the atmosphere over the TP,the net water vapor transport from outside region to the TP and the variation of the amount of evapotranspiration of the underlying surface during the summer period from 1979-2010 are studied in this paper.The analysis finds that the water vapor content over the TP increases before and after 1998.After 1980,the water vapor transported to the TP decreases year by year,the spacial characteristics of the net water vapor transport volume trend is significantly different in the southeast part over the TP in comparison with that before 1998.Afterwards,due to the significant weakening of the southwest monsoon,the net water vapor transport from the outsideregion to the TP decreases significantly,resulting in a significant decrease in the net water vapor transport on the southeast part of the TP.After 1998,there is a significant increase in the surface evapotranspiration of the TP.Comprehensive analysis of the relationship between evapotranspiration,net water vapor transport and atmospheric water vapor content shows that after 1998,the significant increase in surface evapotranspiration over the TP is the main reason for the significant increase of atmospheric water vapor content.(2)The water vapor in the atmosphere plays an important role in adjusting climate of the TP and is an important factor affecting the sustainable development of the TP.Water vapor is an important greenhouse gas in the atmosphere.The water vapor in the upper part of the troposphere is of great significance to climate change.It can change the climate by absorbing short-wave radiation from the sun and long-wave radiation from the ground.Since the near-surface specific humidity data is more common than the entire layer of water vapor in the atmosphere,which is more convenient,more accurate than the latter.Therefore,in this paper,we analyzes the influence of the change of near-surface specific humidity on local temperature over the TP in the summer from 1979-2016 with near-surface specific humidity data and temperature data,and predict near-surface specific humidity impact on the local temperature during 2017-2100 over the TP for different scenarios(RCP4.5(8.5))in order to provide a basis for the study of the TP in the context of global warming with equal weighted integration average results of 16 CMIP5 models.The results show that during 1979-2016,there are differences in the trend of near-surface specific humidity and temperature in different altitudes over the TP.For the near-surface specific humidity,as the decreases of altitude,the near-surface specific humidity over the TP changes year by year with an increasing rate,which is gradually weakened.For the temperature over the TP,as the altitude decreases,the temperature changes gradually year by year,and during this period,the influence of the near-surface specific humidity on the local temperature gradually increases.The maximum temperature of the near-surface specific humidity sensitivity ? in the 2000-3000 m of the TP causes the highest temperature increasing rate in this region.In the scenario of RCP4.5,the influence of near-surface specific humidity over the TP in 2017-2100 is weakened year by year.In addition,the weakening trend is most obvious in the area where the altitude of the TP is 2000-3000 m.In the scenario of RCP8.5,the near-surface specific humidity and temperature changes in different altitudes over the TP in 2017-2100 areconsistent,and the temperature and near-surface specific humidity increase whilst altitude of the TP decreases.The increasing rate is faster than that in the scenario of RCP4.5.Over the TP where altitude is greater than 4000 m,the contribution of near-surface specific humidity to temperature in 2017-2100 is smaller than that in other regions;while in the 3000-4000 m over the TP,the near-surface specific humidity has the largest contribution to the local temperature.Under the scenario of RCP8.5,the influence of near-surface specific humidity over the TP is increasing year by year.In addition,the contribution of near-surface specific humidity to temperature is most obvious in the area where the altitude of the TP is 3000-4000 m.(3)Based on ERA-Interim reanalysis data and multiple precipitation grid data,the water vapor transport and precipitation spatial and temporal characteristics of the humidity over the TP above 500 hPa and the water transport from the eastern boundary of the TP to Northern China in the summer of 1979-2016,as well as the relationship between water vapor transport and precipitation over North China(32-43°N,100-115°E)are studied.The results show that under the context of global warming,compared with other regions of the same latitude,the TP is the center of the high special humidity value above 500 hPa in the atmosphere,which is the well-renown as the "wet island".The humidity over the TP increases year by year,and in summer,the TP provides water vapor for the surrounding area.During the period of 1979-2016,the water vapor transport from the eastern boundary of the TP is significantly positively correlated with the summer precipitation in Northern China.Over the TP and Northern China,precipitation is mainly concentrated in the summer,especially in July.In the summer of 1979-2016,the water vapor flows from the TP to the Northern China,the humidity advection in Northern China is negative,and the contribution to the water vapor flux convergence there is positive,resulting in water vapor convergence in Northern China.The contribution of the humidity advection in Northern China to the convergence of the entire layer of water vapor exceeds the contribution of the wind field to the convergence of water vapor.Therefore,in Northern China,the divergence of the summer water vapor transport flux mainly depends on the humidity advection.There is a significant positive correlation between summer precipitation in Northern China and water vapor transport at the eastern boundary of the TP.During the period of 1979-2016,the average water vapor flux on the eastern boundary of the TP tends to decline slightly,resulting in a slight decrease in precipitation over Northern China during this period.During the period of1979-1998,the water vapor flux on the eastern boundary of the plateau shows a downward trend;however,during the period of 1999-2016,the water vapor flux at the eastern boundary of the TP increases significantly at a rate of +0.182 kg/s per year,causing a significant increase the summer precipitation in Northern China after 1998. |
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