Increase in aerodynamic impedance and energy uptake in response to grazing prohibition in semi-arid grasslands during the beginning of the growing season

Abstract

In Inner Mongolia, China, semi-arid grasslands have strong winds and radiation in spring, but it is unclear how grazing management influences the connections between aerodynamic and energy balance during this time. During spring, we conducted measurements of radiation, wind speed, and air temperature, for both grazed and grazing-prohibited grasslands. From these results it was found that the temperature gradient differential (ΔT = T0.4m-T2m) between the ground level (T0.4m) and the high height (T2m) is normally negative at night and positive during the day. Grazed grassland was found to have very few negative ΔT values. Albedo and ΔT were higher on the grazed grasslands, while net radiation and aerodynamic roughness (Z0) were lower on the grazed grasslands. According to structural equation modeling (SEM), the grazing prohibited and grazed had no effect on the relationship between surface albedo, air temperature, and humidity. Z0 in grazed grassland exhibited a substantial positive correlation with net radiation (Rn), but was not correlated with albedo. The Z0 of the grazing-prohibited grassland exhibited a substantial negative correlation with albedo, but not with Rn, and Z0 had a significant negative correlation with air temperature. These findings explain how grazing measures affect the vertical variations of surface heat in air.