Quantifying the Effect of Irrigation on Non-local Aspects of the Atmosphere

Irrigation is an important resource for agricultural practices worldwide, predominately in arid regions. The added water supplements farmland that receives low precipitation during the growing season. The direct alteration of the land-surface by human-induced irrigation creates perturbed land surfaces that modify the local atmosphere through changes in the surface energy fluxes. Across the irrigated area, the sensible heat flux is reduced and the latent heat flux is increased, forming a boundary that can create a local circulation where water vapor is transported and the nearby cloud distribution is modified. More generally, such changes can contribute to deep, moist convection with sufficient soil moisture and atmospheric instability.

The current study hypothesizes land surface moisture input into the atmosphere above irrigated farmland can modify the atmospheric state on larger scales well downstream. The sensitivity of irrigation effects from the southern Texas Panhandle on the downstream atmospheric state is investigated here with the Advanced Research (ARW) Weather Research and Forecasting Model (WRF). Three domains of 10, 2 km and 400 m are employed with ensemble members to study the effects of planetary boundary layer (PBL) parameterization schemes on the atmospheric state as well as the magnitude and area of added soil water. Different flow regimes (e.g. frontal, dryline) are utilized for case studies to understand the particular perturbation growth mechanisms that might be responsible for inadvertent weather modification, and the frequency with which they occur.