Analysis Of Climatic Characteristics Of Soil Moisture During Warm Periods On Tibetan Plateau

This paper uses the observation data of the soil moisture automatic stations of the third Tibetan Plateau Atmospheric Science Experiment(TIPEX-III)during 2015-2016and the hourly precipitation data of the automatic rainfall stations of my country to analyze the characteristics of the temporal and spatial changes of soil moisture and dynamic characteristics of summer soil moisture on the Tibetan Plateau.Combined with daily soil temperature data from surface meteorological stations,evaluate multiple sets of soil moisture products(ERA5,ERA-Interim,MERRA-2,CFSv2 and NOAH2.1)during warm periods(April to October)on the Tibetan Plateau.The main conclusions are as follows:(1)The soil moisture is arid in the western part and humid in the eastern part of the Tibetan Plateau.The average annual soil moisture in the western plateau is in the range of 0.03?0.088)~3/8)~3,while the average soil moisture in the eastern plateau is in the range of 0.07?0.218)~3/8)~3.The soil moisture in the eastern plateau is about twice that of the western plateau,and the standard deviation of the soil moisture in the eastern plateau is much larger than that in the western plateau.Affected by climatic factors(precipitation,radiation,etc.)and geographical factors(river,topography,soil quality,etc.),the distribution of soil moisture in the eastern Plateau is more complicated,and individual arid soil moisture sites appear in the humid spatial distribution.The monthly variation characteristics of soil moisture in different areas of the Tibetan Plateau are different,but they are all significantly affected by precipitation.(2)The dynamic characteristics of summer soil moisture are obviously different in the eastern and western parts of the Tibetan Plateau.The proportions of precipitation stored in the soil decrease exponentially over time,and the proportions of precipitation stored in the soil in the western plateau are always higher than that in the eastern plateau.The time for soil moisture to return to normal after a precipitation event(sustainability of soil moisture)increases with the increase of soil depth.In the 0-10cm soil layer,the soil moisture persistences(7.90 days)in the western plateau are less than that in the eastern plateau(11.23 days),but in the 20-30cm soil layer,the soil moisture persistences(23.45 days)in the western plateau are more than that in the eastern plateau(19.88 days).(3)ERA5,ERA-Interim,MERRA-2,CFSv2 and NOAH2.1 can reflect the characteristics of dryness in the western part and wetness in the eastern part of the Tibetan Plateau.In the western Plateau,the correlations of soil moisture between observational and model products are higher than that in the eastern plateau;after eliminating the influence of monthly changes,the correlations of soil moisture in the eastern plateau are higher than that in the western plateau.This may be due to the fact that the soil moisture in the western plateau is greatly affected by monthly change factors such as precipitation and soil temperature,making the time sequence of soil moisture changes in the western plateau easier to be described by models.The correlations of ERA5 are the best,especially in the western plateau,where the correlations coefficient of most sites are above 0.8,but ERA5 performs the worst in the unbiased root mean square error;ERA-Interim performs the best in the unbiased root mean square error,but the correlations of it lag behind ERA5.In addition,the five sets of model products obviously overestimate the soil moisture,which may be related to the high precipitation and low soil temperature of the five sets of model products.(4)In the western Plateau,the proportions of stored precipitation in soil of ERA5and CFSv2 are greater than that of observation,and the proportions of stored precipitation in soil of ERA-Interim are less than that of observation.In the eastern plateau,the proportions of precipitation stored in soil of observation are greater than that of ERA5,ERA-Interim,MERRA-2,CFSv2 and NOAH2.1.The persistences of soil moisture in ERA-Interim are less than that in observation.The persistences of soil moisture in MERRA-2 and NOAH2.1 are higher than that in observationn.ERA5underestimates the persistences of soil moisture in the western plateau.The persistences of soil moisture in CFSV2 are more consistent with the observation.