Asymmetric warming of grassland and its effect on evapotranspiration in cold and arid region

In this study, observations from meteorological stations in and around the Hailar River basin from 1981 to 2020 were selected and combined with hydrological data to estimate regional evapotranspiration using the BTOP distributed hydrological model applicable to sparsely vegetated substrates, and then to analyze its influence characteristics on evapotranspiration under the influence of asymmetric warming phenomena. The results show that the asymmetric warming phenomenon in the basin from 1981 to 2020 is significant, mainly due to the diurnal asymmetric warming dominated by a larger increase in nighttime temperature and the asymmetric warming of ground air dominated by a larger increase in surface temperature. The main meteorological factors affecting evapotranspiration were relative humidity, wind speed, ground temperature difference and diurnal temperature difference, and relative humidity, diurnal temperature difference and ground temperature difference had the opposite trend of evapotranspiration, among which relative humidity and wind speed had a stable interannual variation, while temperature factor had an increasing intensity year by year. And the influence of asymmetric warming on basin evapotranspiration increases year by year, and the enhancement of surface warming rate is the main reason for the asymmetric warming of ground gas, under which the regional evapotranspiration shows a decreasing trend, so the temperature difference change cannot be ignored when exploring the reasons for the change of evapotranspiration.