Quantifying Baseflow Changes Due to Irrigation Expansion Using SWAT+gwflow

Baseflow, the portion of streamflow sustained by groundwater discharge, is crucial for maintaining river ecosystems. Irrigation practices could influence baseflow, with varying impacts depending on the irrigation practices. This study evaluates the impact of irrigation expansion on baseflows, accounting for weather-driven irrigation demand. The SWAT+gwflow model was applied to the San Antonio Catchment (225 km²) in Uruguay, a region dominated by intensive horticulture and citrus farming reliant on groundwater. Irrigation expansion involves extending irrigated areas from 6,193 to 8,561 hectares, in-creasing average groundwater use from 2,247 to 2,835 hm³/yr. Model results predict that this expansion could cause annual groundwater depletion of up to 1.2 m and a 2% reduction in annual baseflow over a 30 year. Increased summer extractions lead to a delayed impact on winter baseflows, with monthly baseflow reductions of 90% during dry years, especially in heavily irrigated areas. These results have implications for water management. Current regulations ignore groundwater-surface water interactions and fail to account for variable irrigation water demand in high variable weather conditions. This ap-proach provides a tool to anticipate the environmental effects of irrigation expansion and supports the development of adaptive regulations that better align with hydrological realities.