Study on Water Consumption Law of Typical Alpine Meadow and Alpine Swamp Wetland Vegetation in Qinghai-Xizang Plateau

Abstract

In order to reveal the water consumption characteristics of typical alpine meadow and alpine swamp wetland on the Qinghai-Xizang Plateau， taking alpine meadow in Maqin area and alpine swamp wetland in Yushu Longbao area of Qinghai-Xizang Plateau as observation stations， the actual evapotranspiration was taken as the research object.The eddy correlation system was used to preprocess the original observation data by eddy correlation theory.The changes of actual evapotranspiration in different time scales and different underlying surfaces were analyzed， and the influence of typical environmental factors on actual evapotranspiration was explored.In the process of flux observation， the observation data will be abnormal and missing due to instrument failure， weather conditions， atmospheric stability， and power supply system failure.Therefore， data elimination and interpolation are needed to obtain a complete flux time series.In this study， combined with meteorological and hydrological factors （ net radiation， temperature， relative humidity， soil heat flux， wind speed， soil moisture content ）， Random Forest （ RF ） method was used to interpolate monthly evapotranspiration， and the interpolation accuracy was higher ［R2=0.80~0.91， RMSE=0.05~0.08 mm·（30min）-1， MAE=0.03~0.04 mm·（30min）-1］.The results showed that： （1） Evapotranspiration of alpine meadow and alpine swamp wetland mainly concentrated in May to September.The monthly average evapotranspiration of alpine meadow was 123.46 mm， and the highest evapotranspiration was 160.88 mm in July.The average monthly evapotranspiration of alpine swamp wetland was146.76 mm.Evapotranspiration peaked in August at 168.41 mm.Evapotranspiration peaked at 14-15 hours a day.The trend of daily evapotranspiration and monthly evapotranspiration was similar， and evapotranspiration was mainly concentrated in the growing season.（2） For different underlying surfaces， the correlation between evapotranspiration and meteorological factors is different.Among them， the correlation between evapotranspiration and meteorological factors in alpine meadow ranked the first three as net radiation， temperature， and relative humidity， indicating that radiation energy budget is the most critical factor affecting evapotranspiration in Maqin area.Soil heat flux， net radiation and relative humidity are the main factors of alpine swamp wetness.According to the importance estimation method in random forest model， the contribution of net radiation to evapotranspiration in alpine meadow is the most prominent， and the soil heat flux is low， while the contribution of soil heat flux to evapotranspiration in alpine swamp wetland is the largest， followed by net radiation， indicating that soil heat flux is the key factor affecting the evapotranspiration process when the underlying surface is alpine swamp wetland.（3） Analysis of variation characteristics of water consumption （IETP） of different underlying surfaces shows that the underlying surfaces of Maqin alpine meadow and Longbao alpine swamp wetland are dominated by water consumption， accounting for 69% and 80% respectively.Through understanding the actual evapotranspiration characteristics of alpine meadow and alpine wetland ecosystems， it provides reference and data support for the study of water cycle of alpine meadow and alpine wetland in Qinghai-Xizang Plateau.

Keywords

• alpine meadow
• alpine swamp wetland
• actual evapotranspiration
• meteorological factors