Aquifer recharge estimation and its origins in intensive irrigated agriculture

Intensive agriculture often occurs in water-scarce regions, relying on diverse water sources such as imported non-local water–water transfers, treated wastewater, desalination, and groundwater. Efficient water use is crucial to minimize aquifer losses and fertilizer leachates. Understanding the contributions of these sources to both irrigation and aquifer recharge is essential due to differences in volume, quality, and cost. This study presents a methodology combining: i) a spatially distributed approach using the water-table-fluctuation (WTF) method to estimate total aquifer recharge and ii) an experimental assessment of precipitation and irrigation water contributions via mixing calculations. The method is validated through unsaturated flow and stable water isotope transport modeling, applied to the Campo de Cartagena aquifer (SE Spain). Findings reveal that irrigated area contributes ∼ 30 % of total recharge — ∼ 26 % in wet years and ∼ 41 % in dry years— primarily from annual row crops. Groundwater supplies 49 ± 13 % of crop water needs. Recharge contributions from different sources within the irrigated area include precipitation (16 %), Water Transfer (29 %), shallow aquifer (26 %), and the underlying confined aquifer (29 %). These results underscore the importance of quantifying individual water source contributions to irrigation and aquifer recharge, especially if the aquifer is one more water source, for improved water resource management at the catchment scale.