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 this interaction, with varying impacts depending on the irrigation practices. This study evaluates the impact of irrigation expansion on baseflows, considering the influence of weather-driven irrigation demand. The SWAT+gwflow model is applied to the San Antonio Catchment (225 km²) in Uruguay, a region dominated by intensive horticulture and citrus farming reliant on groundwater pumping. Irrigation expansion involves increasing the irrigated area from 6,193 to 8,561 hectares, which leads to an increase in average groundwater use from 2,247 to 2,835 hm³/yr. Model results predict that this expansion could cause annual groundwa-ter depletion of up to 1.2 m and a 2% reduction in annual baseflow. In addition, increased summer extractions lead to a delayed impact on winter baseflows, with monthly baseflow reductions of 90% during dry years, particularly in locations with high irrigation. These findings have implications for water management and policy, as current regulations overlook the interactions between groundwater and surface water and fail to account for variable irrigation water demand in high variable weather conditions.