Near-surface atmospheric response to irrigation over the United States: A model based simulation with a regional atmospheric model coupled to a land surface model and an irrigation model

The present work builds upon an earlier study (Ozdogan et al 2010) where surface water and energy balances are studied under the influence of irrigation over the continental United States. In that study, a new methodology is developed to construct a 1-km grid global land cover map together with a irrigation model (IRM) which introduces realistic irrigation daily practices and an array of crop types. This information is used to modify the land cover of the Noah land surface model (LSM) which uses NLDAS data at a horizontal resolution of 0.125⁰ as meteorological forcing. It is demonstrated that added higher resolution information can improve on the estimate of energy fluxes at the land surface. This study further explores the impact of irrigation on boundary layer development using the regional atmospheric model WRF version 3.0 coupled with the Noah LSM and the IRM within the NASA Land Information System (LIS) protocol. The coupling between WRF, LSM and IRM is achieved using the Earth System Modeling System (ESMF) interfaces to fit WRF 15 km grid size computational domain over the continental US. The atmospheric sensitivity to the coupling of the models and to irrigation is tested with a set of uncoupled runs in which WRF is forced with the fluxes produced by the LSM with and without the IRM for a full year. A second set of experiments is performed with the fully coupled suite of models: WRF, LSM and IRM. Preliminary results indicate that the footprint of irrigation is not localized only to the irrigated region and that its influence is felt much farther west in the central US in the form of changes in precipitation, specific humidity and potential temperature. The magnitude of the response is significantly modified by the feedbacks introduced by the interactions among the models.