Providing environmental flows is challenging in the middle portion of the Rio Grande/Bravo Basin (between Elephant Butte Reservoir in New Mexico and Presidio, Texas) where water demand has continued to increase over time despite limited river water and dropping groundwater levels. Riparian ecosystems in this agriculture-dominated desert environment will likely become more vulnerable as competition over scarce water increases in the face of growing demand and dwindling supply. Little to no water is allocated to riparian ecosystems unless water or water rights are purchased or transferred to sustain those systems. Ongoing debates about providing environmental flows for riparian forest galleries in this water-scarce region have not been backed by quantitative modeling results of potential impacts on surface water and groundwater availability. We quantify water requirements to provide a menu of options for environmental flow allocation to establish cottonwood forest galleries. We apply hydrologic modeling under a projected warm-dry future to determine the frequency of river water availability for providing minimum environmental flows, and to evaluate water budget tradeoffs associated with environmental flow allocations in this region. Results inform water resources management decisions that support riparian habitats.

The USDA-ARS Grazinglands Research Laboratory (GRL) operates four research watersheds at three spatial scales representing a gamut of topographic, physiographic, vegetative, or agricultural conditions characteristic of the Southern Great Plains (SGP). The mission of GRL is to address “agricultural sustainability, climate change, ecosystem services, and conservation of natural resources at the watershed or landscape scale”— a primary objective of the USDA-ARS Conservation Effects Assessment Project (CEAP) and the Long-Term Agro-Ecosystem Research (LTAR) network. Assessment of the impacts of conservation practices in agricultural watersheds requires long-term research sites of varying size due to differences in scales required to codify and evaluate the collection of water and soil data. The two larger (> 600 km2) watersheds provide primarily observational data collected for use in hydrologic modeling and large-scale investigations. Modeling is used to quantify benefits of conservation and best management practices to meet selected environmental endpoints. The Little Washita River (LWREW) and Fort Cobb Reservoir (FCREW) experimental watersheds are located in southwestern Oklahoma, USA, and have been part of the GRL research catchment portfolio since 1961 and 2004, respectively. The two smaller catchment areas are located on the grounds of the GRL in Central Oklahoma and are a collection of eight plot-scale watersheds, The Water Research and Erosion Units (WRE) and ten farm-scale watersheds the Grazinglands Research agroEcosystems and the ENvironment (GREEN) Farm that allow replicated manipulative and/or process-based investigations. The WRE, established in 1976, consists of eight contiguous 1.6 ha sized plots. The GREEN Farm comprises 162 ha. Both catchments contain alternative agricultural systems that are evaluated for intensification, sustainability, resiliency, minimization of environmental impact, and profitability in anticipation of climate shifts and extremes. Measurements collected across the four watersheds includes but are not limited to components of water balance, soil erosion, runoff, water quality, nutrient and water use efficiency and soil health.