SAHRA frames its science and stakeholder activities in a river basin context. Basin-focused science yields a synergy of activities that helps to drive science integration and, because stakeholder issues are tied to river basins, also helps to drive the application of research results. SAHRA’s primary geographical focus is on two river basins (Figure 1): the Rio Grande/Rio Bravo and the Upper San Pedro, although we maintain interest and some activity in the Salt-Verde and Rio Conchos basins.

Three stakeholder-relevant integrating questions (Table 1) is being used to further focus SAHRA scientific research in these two river basins. All of these questions are or will soon become critical for the wise management of water resources in semiarid and arid regions and can be addressed only by researchers operating in center mode through the consistent deployment of integrated, multidisciplinary science. The three questions, which are broad-based and capable of engendering and crosscutting many related topics of inquiry, touch on scenarios that are of prime interest in this region: land use changes, population growth, and climate variability.

RIPARIAN QUESTION: 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 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 consequently focuses on developing fundamental, process-level understanding in three areas: 1) determining the water balance of riparian systems, 2) evaluating ecosystem dynamics and values, and 3) 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 costs and benefits of potential restoration or preservation efforts.

WATER MARKETS QUESTION: Under what conditions 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 economic benefits 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 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 micro-logging to disaggregate demand. These products and knowledge will then be integrated into a model that allows water resource managers to consider the trading of water rights and third party impacts in evaluating the potential of market-based mechanisms to allocate water resources effectively.

VEGETATION QUESTION: What are the impacts of vegetation change on the basin-scale water balance?

Vegetation change is a common feature of the Southwestern landscape. Over the last several decades this has occurred in the form of shrub invasion of grasslands, expansion of pinyon-juniper, thickening of ponderosa pine forests, and anthropogenic land-use changes. More recently drought related fires and bark beetle infestations are resulting in large-scale vegetation change. While a widespread perception exists that such changes have reduced water resources available for human use, research that documents the actual changes 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/sublimation, runoff, and infiltration, and how moisture stored in the soil is shared between transpiration, recharge, and streamflow. SAHRA’s approach involves: 1) intensive field measurements at selected plot- to hillslope-scale sites to investigate vegetation controls on partitioning and guide development of methods to model and scale these processes; 2) exploring the use of remotely sensed data to determine key hydrologic variables across basins; and 3) integrated modeling to evaluate the effects of vegetation change.