Assessing the impact of irrigation on water storage dynamics in a Mediterranean catchment using land surface modelling

Anthropogenic land use can strongly affect regional water stocks and fluxes. Irrigation, for instance, greatly influences soil moisture, which in turn acts as a mediator between water storage compartments. There has been a growing effort to represent these processes in land surface models (LSMs), and thus better simulate the impact of global changes on water resources. An accurate representation of irrigation practices and associated processes is therefore crucial in LSMs when quantifying water storage dynamics and associated fluxes. However, the ability of LSMs to represent irrigation management and thus investigate its role in the water cycle within complex catchments has not yet been explored in sufficient detail.This study attempts to quantify the influence of irrigation on water storage dynamics of the Pinios Hydrological Observatory (PHO), a small Mediterranean catchment in central Greece, taking the Community Land Model version 5 (CLM5) as an example. For this, CLM5 was first applied and tested in two highly instrumented irrigated apple orchards within the PHO by using available information on local climate, soil, crop management and phenology for model set-up and calibration. Model results were compared to observed apple yield, sap flow, soil matric potential, and soil moisture. The latter two were obtained from a distributed sensor network measuring at three depths (12 locations per field). CLM5 was able to accurately reproduce the soil moisture response to irrigation in one of the fields whereas some bias was apparent in the second field. In a next step, CLM5 was applied to the entire PHO using regional land use and soil information. Utilising this model setup, one full and two deficit irrigation scenarios were implemented over a 7-year period using local climate data to analyse the impact of irrigation on soil water storage and groundwater interactions at the catchment scale. We will demonstrate how the findings of this study can contribute to understand the effects of irrigated agriculture on catchment water storage dynamics and aid in the management of regional water resources