Measuring evapotranspiration by eddy covariance method and understanding its biophysical controls in moist deciduous forest of northwest Himalayan foothills of India

Forests play a pivotal role in carbon and water cycles by governing the exchanges of CO2 and H2O between the terrestrial biosphere and the atmosphere. The evapotranspiration (ET) is the variable, which links these cycles. The eddy covariance (EC) method provides direct, high-frequency observations of ET of an ecosystem. The present study was carried out in a moist deciduous plant functional type (PFT) of northwest Himalayan foothills of India to estimate ET using the EC flux tower measurements and to study its biophysical controls from 2016 to 2018. The variability of sensible (H) and latent (LE) heat fluxes was also studied. The mean diurnal variation in H was from − 1.31 to 109.35 Wm−2 whereas LE ranged from 4.47 to 186.89 Wm−2. The mean annual ET for 2016–2018 was found to be 693.67 ± 46.70 mm year−1. The highest diurnal variability in ET was witnessed during the post monsoon season followed by the monsoon, winter, and dry summer seasons. A relative weight analysis with multiple regression model was implemented to understand the control of biophysical variables on ET at an 8-day time scale. A combination of incoming solar radiation (Rg), leaf area index (LAI), vapour pressure deficit (VPD), air temperature (Tair), soil water content (SWC), and precipitation was able to explain 73% of the variability of ET at 8-day time scale. The analysis revealed that in the moist deciduous PFT the ET was limited by the availability of energy. The present study is the first-ever attempt to report the direct estimates of ET for an Indian forest.