Effect of irrigation in simulating long-term evapotranspiration climatology in a human-dominated river basin system

Evapotranspiration (ET) is highly variable in space and time and its quantification using observations or land surface models aids in irrigation and water management. Using the Noah land surface model, long-term trends of ET and surface energy balance were studied within the Snake River basin for the past 30 years spanning between 1980 and 2010. In this study, changes only due to meteorological factors were considered to capture the patterns of change in surface energy balance components. We employed an irrigation scheme in this simulation study since the agricultural lands in the river basin is irrigated almost entirely. This investigation has implications for water management, hydrology, and sustainability of this ecosystem. Uncoupled land surface modeling showed that the energy budget was altered due to anthropogenic activities in the basin with increased latent heat flux and reduced sensible heat flux. ET generally increased over a thirty year period due to warming climate and boundary layer meteorological variables indicated cooling induced by irrigation.