Untangling the eco-hydro-geomorphic knot: Insights from an experiment seeking to explain patterns, processes, and feedbacks at the catchment scale

In recent years much has been advanced in the understanding of landscape patterns and processes by means of ever more complex modeling exercises coupling biological and physical mechanisms. Although meaningful, the outcomes of such models are frequently limited and undermined by the lack of proper datasets on which these results can be tested and verified. In this work we provide a summary of findings based on the observation of the ecologic-hydrologic-geomorphic interactions of a semiarid catchment with clear vegetation and geomorphic contrasts. Through various years of data from a network of hydrologic sensors deployed on and along the catchment slopes we were able to decouple the effect of vegetation, terrain properties and energy fluxes on the hydrologic dynamics of two coexisting but opposing ecosystems; a Juniper-savanna on a north facing slope (NFS) and a creosote shrubland on a south facing slope (SFS). Our analyses show that: 1) topographic modulated energy loads exert a first order control on the dynamics of evapotranspiration and soil moisture residence times in the catchment, with vegetation imposing a second order control at the onset of the growing season; 2) the soils exhibit a characteristic progression of moisture and temperature along the slope aspect continuum that is preserved throughout the year, going from a wetter and cooler NFS to a drier and warmer SFS; 3) there is remarkably distinct rainfall-runoff dynamics between the catchment slopes, where a much smaller precipitation threshold on the SFS triggers larger runoff peaks with more variable time lags in runoff initiation than at its NFS counterpart; 4) seasonal water balances of the NFS and SFS follow opposite trajectories in the year and point to distinct soil water pools for ET demands, where the NFS ET is mainly supported by shallow soil moisture while SFS ET may come from deeper soil moisture tapped by the roots of creosote shrubs. Preliminary results on the contribution of transpiration to total ET support these findings. Taken together, the results of this study have important implications for the understanding of the potential causes and effects of landscape changes in areas of complex topography under current and future climatic scenarios. The work provides a conceptual framework for the systematic study of different vegetation-terrain-hydrologic interactions that is currently being explored on an experimental catchment with distinct climatic properties in the southern hemisphere.