The Response Of Land-Atmosphere Interaction To Precipitation In The Semi-Arid Area

By utilizing turbulence observations and conventional observations of collaborative experimental observation in arid and semi-arid regions over the northern in summer and autumn (from July to September) observed in Yuzhong station of the temperate continental monsoon semi-arid climate and Miyun station of the warm temperate monsoon continental semi-arid climate, firstly, the short-term response of surface albedo and soil volumetric water content to precipitation and the threshold and the lag of response of soil volumetric water content to precipitation are systematically analyzed in each climate zone. Secondly, the short-term response of sensible heat flux and latent heat flux to precipitation and the hierarchy and the lag of the response of latent heat flux to precipitation are explored in each climate zone. Finally, the threshold of short-term response of CO2flux to precipitation and the impact of precipitation on CO2exchange are research in each climate zone by normalization method. The main following conclusions are obtained:(1)In the temperate semi-arid climate zone and the warm temperate semi-arid climate zone, the surface albedo in non-precipitation days is0.2and0.14respectively. When precipitation events occur, the surface albedo decrease, with the continuing impact of precipitation, surface albedo remains unchanged, after the end of precipitation, the surface albedo increase. The range of variation of the surface albedo under the influence of precipitation is-0.04～0.04、-0.01～0.01respectively.(2)In the temperate semi-arid climate zone, the response of surface and deep soil volumetric water content to precipitation events less than5mm does not exist. In the period of dry soil, soil volumetric water content in5cm has a weak response to precipitation events exceeded5mm. In the period of humid soil, soil volumetric water content from5cm to40cm has a response to precipitation events exceeded10mm and soil volumetric water content from5cm to20cm has a response to precipitation process of total precipitation more than10mm, and the response of soil volumetric water content in80cm to all precipitation events does not exist.the response of soil volumetric water content from5cm to20cm and soil volumetric water content in40cm to precipitation events exceeded10mm have the lag of1～2days and6～7days respectively.In the warm temperate semi-arid climate zone, soil volumetric water content from5cm to40cm response weakly to precipitation evens exceeded20mm, soil volumetric water in5cm response weakly to precipitation process of total precipitation exceeded20mm, the response of soil volumetric water content in100cm to all precipitation events does not exist, and the response of soil volumetric water content in40cm to precipitation events exceeded20mm has the lag of3～4days.The response of soil volumetric water content to precipitation in the warm temperate semi-arid climate zone is lower than in the temperate semi-arid climate zone.(3)In the temperate semi-arid climate zone and the warm temperate semi-arid climate zone, the sensible heat flux response to precipitation events and even small precipitation events. When precipitation events occurred during the day, the sensible heat flux decreases, and the sensible heat flux increases after the end of the precipitation events, relative to precipitation process. The sensible heat flux increases during the night or early morning due to insulation effect of the increased thicker clouds, but clouds insulation effect in the warm temperate semi-arid climate zone is more obvious. In the temperate semi-arid climate zone, the response of high sensible heat flux to precipitation is more significant.(4)In the temperate semi-arid climate zone, the latent heat flux response to precipitation events exceeded5mm significantly, and the maximum response to precipitation is the lag of2-3days. During the precipitation process, the latent heat flux increase after precipitation events exceeded5mm, the latent heat flux decrease after precipitation events less than5mm.The latent heat flux increase after precipitation process.In the warm temperate semi-arid climate zone, the response of latent heat flux to precipitation events and even small precipitation events is exist, the maximum response of latent heat flux to precipitation events exceeded5mm is the lag of3days, the maximum response of latent heat flux to less than5mm is the lag of1～2days, and compared to the temperate semi-arid climate zone, the response of latent heat flux to precipitation events is more significant. The latent heat flux decreases with beginning days of precipitation, with the continuous precipitation, the latent heat flux may increase or decrease, the latent heat flux increased after precipitation.(5)In the temperate semi-arid climate, the lower threshold of response of CO2flux to precipitation is5mm, the response appeared in4～5days after the end of the precipitation events; In the warm temperate semi-arid climate,CO2flux response to precipitation events even minor precipitation events is exist, the response appeared in1～2days after the end of the precipitation events due to precipitation events and even small precipitation events restrain the soil respiration because of the larger soil moisture,resulting in the amount of absorbing CO2relatively increase in1to2days after precipitation.