Impact of Spatial Extension of Irrigation in the ICON-nwp Model

Irrigation plays a crucial role in maintaining an ideal soil moisture level for an optimal crop development. This practice is nowadays indispensable for farmers as a method to adapt to the challenges posed by climate change. The Earth science community has recognized additional effects of irrigation beyond its impact on soil moisture and plant growth. Various studies have revealed that irrigation can influence atmospheric variables such as 2-meter temperature, relative humidity, and even precipitation. Furthermore, researchers have investigated the impact of irrigation on the Earth's system across different timeframes, geographic regions, and using diverse climate and land surface models. Nevertheless, the number of studies that have simulated the effects of irrigation at higher resolutions on a regional level are scarce. Therefore, the aim of this study is to include the representation of irrigation processes in the operational ICON-nwp in Limited Area Mode on the EURO-CORDEX domain at 3km resolution. The implementation of the current irrigation parameterization in ICON-nwp coupled with TERRA is an adaptation of the CHANNEL scheme developed by Valmassoi et al. (2020). Since there are more than one land surface model coupled with ICON, we found suitable to include this scheme in the land surface and atmosphere interface of the icon-nwp-2.6.6-nwp0 version. 

The current investigation includes two irrigation maps: the default map from the operational ICON-nwp (from GlobCover2009) and the Digital Global Map of Irrigation Areas (Siebert, et al. 2013). For the first irrigation map, the study comprises five sensitivity experiments involving varying irrigation water amounts: 2.6 mmd-1, 6.7 mmd-1, 11.1 mmd-1, and two fixed soil moisture levels (field capacity and saturation). Regarding the second irrigation map, currently we have three experiments with the irrigation amounts:  2.6 mmd-1, 11.1 mmd-1, and soil moisture set to field capacity. All experiments have the same irrigation frequency (1 day), length (24 hours), and simulation period (May to August). The results from the difference between experiments and the control run demonstrate that ICON captures the irrigation effect on land surface atmospheric variables. As expected, soil moisture content increases resulted in an average cooling effect of 1.4 K across all experiments. Likewise, energy fluxes were sensible to the different irrigation quantities. In addition, we present a validation of selected irrigation experiments with a reanalysis dataset and observations from meteorological stations used in the operational DWD model equivalent cycle. Preliminary results indicate that when comparing the biases of the first guess with those of the field capacity experiment concerning observations in Spain, the  temperature bias decreases from an average of -0.20 to -0.08 across  twelve stations.