Ecohydrological coupling and episodic hydrological connectivity in the Edwards Plateau

Abstract. In semiarid karst systems, the hydrologic budget is regulated by strong interactions among the water fluxes of precipitation, soil water dynamics, evapotranspiration, runoff, and groundwater recharge. In this study, we evaluated the temporal coupling among these fluxes in the Edwards Plateau Balcones Fault Zone (Texas, USA) using five years (2021–2025) of daily observations of precipitation (P), soil water content (SWC), evapotranspiration (ET), runoff (Rf), and groundwater (GW). Soil water content responses to precipitation exhibited threshold-dependent behavior under both dry and wet antecedent conditions, with breakpoints at 66.9 and 32.6 mm, respectively. Evapotranspiration dynamics were jointly controlled by SWC and temperature, with strong limitations under dry soil conditions and maximum ET values occurring only under warm and wet conditions. In contrast, Rf and GW responses were highly episodic and associated with the relatively rare large precipitation events. Although both fluxes increased rapidly following rainfall inputs, Rf responses were short-lived whereas GW responses persisted for several weeks to months. Groundwater recharge exhibited a clear threshold response, occurring only after precipitation events greater than 78 mm and never following events smaller than 62 mm. On the basis of these findings, we have developed a conceptual model for semiarid karst ecosystems whereby hydrological connectivity is activated during short-lived windows created only when precipitation pulses exceed both atmospheric demand and internal storage thresholds.