Plants vs. streams: Many aces under their sleeves
Far from following a simple predictable partition of rainfall inputs into evapotranspiration and streamflow, the El Morro catchment has shown over the last decades a rapidly switching balance between them. After an early stage in which mechanism 1 has kept the system free of streamflow (and streams), away from the expected water yield suggested by global empirical models (Zhang et al., 2001), the expansion of cultivation, aided by a relatively rainy period, has brought the system to a new stage of higher groundwater storage. Saturated water consumption (Mechanisms 2 and 3) in this new stage had increased evapotranspiration locally but was unable to prevent stream formation (Mechanism 4) and the onset of a stable water yield that approaches empirical global predictions. Sapping erosion is still taking away water from plants in the catchment, yet its long-term outcome is hard to predict. Climate fluctuations, but more importantly, land use changes and spontaneous vegetations shifts can twist it. Acknowledging the non-additive and non-linear effects of vegetation and streams on groundwater is crucial to develop more successful hydrological models for dry sedimentary catchments. The peculiarities of the El Morro catchment may cast light on overlooked (and not so peculiar) hydrological mechanisms.