Human-induced modifications to land surface fluxes and their implications on water management under past and future climate change conditions

Abstract

We used a coupled land-atmospheric simulation framework to quantify the feedback impacts of water resources in a changing climate. The simulations dynamically downscaled data from the North American Regional Reanalysis (NARR) data, Climate Forecast System (CFS) Version 2 and the North American Regional Climate Change Assessment Program (NARCCAP), to investigate irrigation effects on temperatures and surface fluxes under current and future scenarios in Southern Idaho. This study implements irrigation schemes within the Noah Land Surface Model (LSM) coupled with the Weather Research and Forecast (WRF) 3.4 at a 4-km resolution to diagnose irrigation-induced changes to surface energy fluxes and boundary layer properties. Our results suggest that induced cooling via evaporation causes a decrease of 0.8°C to the air temperature over April − October, a decrease of up to 90m of the planetary boundary layer depth and an increase of 2.0°C in the dew point over the irrigated areas. On average, the growing season start date trends 0.46days/year earlier and the growing season termination date trends 0.60days/year later. A decrease in precipitation with time is also seen at all elevation ranges from the year 2040–2070, with the lowest elevation levels seeing a bigger decrease than the higher levels. Thus, irrigation-induced increases in growing degree days and modifications to surface fluxes are shown in the basin and it is critical to consider when planning both crop and water management.