Three stakeholder-relevant questions give focus to SAHRA’s efforts to generate new hydrological understanding and encourage its application to improved water resources management and public policy in semiarid regions. SAHRA selected these questions because they are or will soon become critical for the wise management of water resources in semiarid regions, and because they can only be addressed by researchers operating in center mode through the consistent deployment of integrated, multidisciplinary science.

What is the Impact of Vegetation Change on the Basin Scale Water Balance?

Vegetation change is a common feature of the Southwestern landscape, particularly in the form of shrub invasion of grasslands, expansion of pinyon-juniper, and the thickening of ponderosa pine forests. While a widespread perception exists that such changes have reduced water resources available for human use, scant research documents the actual changes on the basin-scale water balance. SAHRA seeks to understand the role of vegetation type and structure in the partitioning of rain and snow into evaporation/sublimation, runoff, and infiltration, and how moisture stored in the soil is shared between transpiration, recharge, and streamflow. SAHRA’s approach involves: (i) intensive field measurements at selected plot- to hillslope-scale sites, in order to investigate vegetation controls on partitioning and to aid the development of methods to model and scale these processes; (ii) exploring the use of remotely sensed data to determine key hydrologic variables across basins; and (iii) integrated modeling, to evaluate the effect of vegetation change.

What are the Costs and Benefits of Riparian Restoration and Preservation?

In the semiarid Southwest, most human settlements, irrigated agriculture, and regional biodiversity are located in riparian corridors. These riparian systems integrate the hydrologic and biogeochemical processes that occur within a basin. Consequently, water resource management decisions may impact river systems not only through changes in streamflow, but also through unforeseen changes in water quality, the socioeconomic value of the river system, and the structure and diversity of the riparian ecosystem. A complete evaluation of the costs and benefits of important management decisions regarding riparian preservation and restoration therefore requires an integrated, multidisciplinary understanding. SAHRA research on this question has focused on developing fundamental, process-level understanding in three areas: (i) determining the water balance of riparian systems, (ii) evaluating ecosystem dynamics and values, and (iii) understanding nutrient and solute sources and cycling. The resulting understanding will further the development of integrated river system models that stakeholders can use to evaluate the costs and benefits of potential restoration or preservation efforts.

Are Water Markets and Water Banking Feasible?

In the Southwest, water markets and water banking are increasingly viewed as potentially effective mechanisms for allocating water resources, providing maximum economic benefit and avoiding potential conflicts associated with water scarcity. For these mechanisms to be truly effective, detailed knowledge of the available water supply and the factors that affect water demand is critical. To this end, SAHRA is developing remote sensing products to better estimate precipitation rates and snow pack volumes at the basin scale. SAHRA is also improving understanding of the factors that determine residential, industrial, and agricultural demand for water, using approaches such as experimental economics and water use micrologging to disaggregate demand. These products and knowledge will then be integrated into a model that allows water resource managers to evaluate the potential of market-based mechanisms to better allocate water resources through consideration of the trading of water rights and third party impacts.