Irrigation parameterization for the ICON model

Abstract

Irrigation is an agricultural practice that keeps an ideal soil moisture for crop growth. Aside from this, the Earth system community also recognized the irrigation impact on different components of the Earth system. Therefore, the aim of the study was to develop an irrigation parameterization for the ICOsahedral Nonhydrostatic model (ICON) in order to quantify the long-term impact of irrigation on surface and atmospheric variables over the EURO-CORDEX domain using convection-permitting simulations that cover a period of 12 years. The ICON model was developed by the German Weather Service (DWD) and the Max Planck Institute for Meteorology (MPI-M). ICON is currently used operationally at the Deutscher Wetterdienst (DWD) for weather forecasting. Moreover, ICON is now open source (https://www.icon-model.org/) and the modules related to the parameterization are: the interface modules and the land surface scheme (TERRA). We found appropriate to add this parameterization to the interface between the atmosphere and the land surface since ICON can also be coupled with another land surface model. The parameterization includes irrigation water into the grid-scale precipitation variable. It is an adaptation from Valmassoi et. al (2020), irrigation parameterization for the Weather Research and Forecasting Model (WRF). However, in our study, the daily irrigation volume is equal to the readily available water (RAW), which is the portion of the total available water (TAW) that a crop can absorb from the root zone without experiencing water stress. To calculate RAW, we also use a constant depletion fraction and root depth in milimeters. For the TAW calculation, we use soil information, field capacity and permanent wilting point from a specific soil type of a given grid-cell. Our results reveal that irrigation has an effect on surface variables such as temperature 2-m, energy fluxes, evapotranspiration and even radiation variables. We found an irrigation cooling effect in irrigated areas, an increase of latent heat flux and evapotranspiration. As a result, sensible heat flux values decrease.