Groundwater Recharge Variability in Semi-Arid Watersheds Under Changing Precipitation Patterns

Résumé

Groundwater recharge in semi-arid watersheds is highly sensitive to shifts in precipitation timing and intensity, yet recharge estimation methods often rely on long-term average precipitation inputs that obscure the episodic character of recharge events characteristic of these systems. This study examines groundwater recharge variability across a semi-arid watershed using a combination of soil moisture monitoring, isotopic tracing, and event-based precipitation records collected over multiple hydrological years with contrasting rainfall patterns. Rather than modeling recharge as a continuous seasonal process, the analysis identifies discrete high-intensity precipitation events as the dominant recharge mechanism, with the majority of annual recharge attributable to a small number of events exceeding a threshold intensity. We examine how observed shifts toward more variable and episodic precipitation, relative to historical patterns, correspond with changes in recharge timing and magnitude at the site, finding that recharge has become increasingly concentrated in fewer, more intense events. These findings suggest that water resource planning models relying on smoothed average recharge estimates may increasingly misrepresent actual aquifer replenishment dynamics under evolving precipitation regimes. We discuss implications for groundwater management strategies in semi-arid regions facing similar precipitation pattern shifts.