The effect of time scales on the distribution of evapotranspiration and driving factors in desert grasslands

Promoting the reasonable allocation of evaporation (E) and transpiration (T) at a certain time scale is important for controlling the grassland desertification. Nevertheless, evapotranspiration (ET) and its components on a single time scale often cannot guarantee the dynamic and reasonable distribution of E and T. This study quantified ET and its component distribution in different time scales of the plant-growing season in desert grassland ecosystems to address this contradiction. Further the main driving factors of ET and its components at different time scales were clarified under multi-factor coupling. Results indicated that E was the leading component of ET in the ecosystem, with an average T/ET of 39.64%. The dominant factors of T/ET on different time scales were air temperature (Ta) and surface temperature (Ts), which showed significant negative correlations (p < 0.05). ET and its components showed obvious unimodal changes at the hourly scale. The peaks occurred at 12:00–14:00, and they all increased with increasing radiation (Ra), Ts, Ta, and saturated water vapor pressure difference (VPD). Ta was the dominant factor with a correlation coefficient of 0.76, followed by VPD> Ra>Ts. At the daily scale, ET and its components showed clear seasonal changes, ET was 1.94 mm d-1and T was 0.77 mm d-1. The dominant factors were soil moisture content (SWC) of the 0–10 cm soil layer and Ts. The dominant factors affecting ET and its components in the early, middle, and late stages of growth were relative humidity (RH), SWC, and Ts. At the monthly scale, the cumulative values of ET and its components were the largest in August and the lowest in October, mainly regulated by precipitation (P), whereas, T/ET had no significant correlation with P. The results from this study can provide a scientific basis for vegetation restoration and environmental protection in desert grassland ecological function areas.