Integration of remote sensing, field observations and modelling for ecohydrological studies in Sonora, Mexico

Ecohydrological responses to rainfall in the North American monsoon (NAM) region lead to complex surface-atmosphere interactions. In early summer, it is expected that soil properties and topography act as primary controls in hydrologic processes. Under the presence of strongly dynamic ecosystems, catchment hydrology is expected to vary substantially in comparison to other semiarid areas, affecting our understanding of ecohydrological processes and the parameterization of predictive models. A large impediment toward making progress in this field is the lack of spatially extensive observational data. As a result, it is critical to integrate numerical models, remote sensing observations and ground data to understand and predict ecohydrological dynamics in space and time, including soil moisture, evapotranspiration and runoff generation dynamics. In this thesis, a set of novel ecohydrological simulations that integrate remote sensing and ground observations were conducted at three spatial scales in a semiarid river basin in northern Sonora, Mexico. First, single site simulations spanning several summers were carried out in two contrasting mountain ecosystems to predict evapotranspiration partitioning. Second, a catchment-scale simulation was conducted to evaluate the effects of spatially-variable soil thickness and textural properties on water fluxes and states during one monsoon season. Finally, a river basin modeling effort spanning seven years was applied to understand interannual variability in ecohydrological dynamics. Results indicated that ecohydrological simulations with a dynamic representation of vegetation greening tracked well the seasonal evolution of observed evapotranspiration and soil moisture at two measurement locations. A switch in the dominant component of evapotranspiration from soil evaporation to plant transpiration was observed for each ecosystem, depending on the timing and magnitude of vegetation greening. Furthermore, spatially variable soil thickness affects subsurface flow while soil texture controls patterns of surface soil moisture and evapotranspiration during the transition from dry to wet conditions. Finally, the ratio of transformation of precipitation into evapotranspiration (ET/P) and run off (Q/P) changed in space and time as summer monsoon progresses. The results of this research improve the understanding of the ecohydrology of NAM region, which can be useful for developing sustainable watershed management plans in the face of anticipated land cover and climate changes.