Vegetation-Soil-Aspect Modulated Hydrologic Dynamics on Semiarid Hillslopes of Central New Mexico

Topographic modulated microclimate on a semiarid catchment in central New Mexico has led to distinct vegetation cover and pedogenic properties of north, south and east facing slopes. The combination of different vegetation, soil and aspect results in characteristic hydrologic dynamics for each hillslope within this catchment. This study illustrates the role played by slope position, soil properties and vegetation on soil moisture dynamics, runoff production and evapotranspiration by means of modeling and field data analysis. Our results evidence a strong control of vegetation, slope position and soil properties on soil moisture dynamics both, in the short term in response to single rainfall events and in the long term in response to normal seasonal and interannual rainfall variability. Actual evapotranspiration fluxes on the opposing north and south facing hillslopes were obtained through a 1D vadose zone model. Modelling results illustrate the strong control of soil properties and vegetation in root zone water fluxes. To complement these analyses and to address the impacts of the characteristic hydrologic dynamics of each hillslope on the geomorphic properties of the basin, we investigated the feedbacks among hydrologic, terrain and vegetation characteristics of the study basin. We assessed the role played by trees and topographic sheltering on the annual incoming solar radiation using high resolution topographic data. Remarkable differences in incoming radiation are found between north and south facing slopes and these are then related to terrain and vegetation attributes. These analyses are used to explore potential causes for vegetation patterns at the study site and their subsequent impact on pedogenic and hydrogeomorphic processes via modification of runoff-erosion mechanisms. In summary, we found that variations in water fluxes and soil moisture dynamics at each site under the current climate conditions are in agreement with the observed vegetation patterns, soils and hillslope properties in the study catchment.