Research Broad Themes

Why Focus on Vegetation?

The amount and fate of precipitation are controlled by four factors: topography, aspect, soil properties, and vegetation. Of these vegetation is the most dynamic, changing on a human timescale. Thus "ecohydrology", the study of the mutual controls and feedbacks between available water and vegetation communities represents a critical knowledge gap needed to evaluate potential for changes in water resources.

Over the last several decades vegetation change in the Southwest has occurred in the form of shrub invasion of grasslands, expansion of pinyon-juniper and mesquite ranges, the thickening of ponderosa pine forests, and different land uses. More recently, drought-related fires and bark beetle infestations have caused large-scale vegetation change.

While it is widely perceived that such changes have reduced water resources available for human use, research documenting the actual effects of vegetation change on the basin-scale water balance is lacking. SAHRA seeks to understand the role of vegetation type and structure in the partitioning of rain and snow into evaporation, runoff, and infiltration, and how moisture stored in the soil is distributed among transpiration, recharge, and streamflow.