Location: Southwest Watershed Research Center2017 Annual Report
1a. Objectives (from AD-416):
1:As part of the LTAR network, and in concert with similar long-term, land-based research infrastructure in the region, use the Walnut Gulch LTAR site to improve the observational capabilities and data accessibility of the LTAR network and support research to sustain or enhance agricultural production and environmental quality in agroecosystems characteristic of the semiarid Southwest region. Research and data collection are planned and implemented based on the LTAR site application and in accordance with the responsibilities outlined in the LTAR Shared Research Strategy, a living document that serves as a roadmap for LTAR implementation. Participation in the LTAR network includes research and data management in support of the ARS GRACEnet and/or Livestock GRACEnet projects. 1.1:Improve & continue long-term measurements & analysis of water budgets on WGEW & Santa Rita Experimental Range (SRER) watersheds. 1.2:Expand variables measured on WGEW & SRER watersheds based on recommendations of the LTAR Meteorology, Hydrology, CO2, Non-CO2 Gas, Soil, Biology, & Wind Erosion Committees. 1.3:Develop a long-term monitoring program. 1.4:Implement an experiment on the SRER watersheds to quantify the effects of brush management on a set of ecosystem services. 1.5:Compute trends in sub-daily & daily precipitation intensity across LTAR sites. 1.6:Evaluate National Weather Service dual pole radar precipitation data & its ability to improve flash flood forecasting. 2:Quantify how seasonal, annual, and decadal-scale variations in climate, plant community composition, and management impact processes controlling the cycling of water, energy, and carbon in semiarid rangelands 2.1:Determine how changes in vegetation structure & climate affect ecosystem-atmosphere water vapor & CO2 exchange using long-term flux tower observations. 2.2:Use isotopes in pond deposition sediments to understand & quantify erosion & sediment yields in semiarid landscapes as a function of ecological sites. 2.3:Quantify the impact of erosion control structures on runoff & sediment transfers in semiarid landscapes. 2.4:Estimate annual production & minimum total foliar cover using Landsat & MODIS satellite. 2.5:Develop methods to assess climate impacts on rangeland vegetation composition & production across the West. 3:Develop a new conceptual framework and corresponding experimental methods to understand and model the dynamics of semiarid upland and channel erosion processes. 3.1:Conduct experiments to quantify the effects of surface condition. 3.2:Conduct experiments to develop a remote sensing method to estimate hydraulic roughness. 4:Improve hillslope (RHEM) and AGWA/KINEROS2 watershed models and develop methods to incorporate new remotely sensed, meteorologic, & land surface information. 4.1:Complete development & post-disturbance testing of the RHEM for application in Western rangelands. 4.2:Develop a mechanism to extend the findings from the Walnut Gulch LTAR site across Arizona & New Mexico & support collaborative vegetation management of public lands to improve watershed function. 4.3:Incorporate a variety of KINEROS2 (K2) / AGWA model enhancements.
1b. Approach (from AD-416):
Objective 1: 1. Use co-located rain gauges to quantify uncertainties in long-term precipitation datasets. 2. Use radar stage measurements to test remote methods to measure runoff stage 3. Deploy mobile x-band Doppler radar and compare with Dual Pole radar rainfall rain-gauge observations, and runoff observations on the WGEW. 4. Meet LTAR objectives by: a) using observational datasets to quantify the individual components of the watershed water balance in Walnut Gulch Experimental Watershed WGEW), b) using satellite and ground measurements of vegetation to document changes in watershed vegetation, c) determining trends and magnitude of precipitation intensities and precipitation extremes across the continental US, and d) implementing the LTAR common experiment to assess the effects of brush management on a set of ecosystem services. Objective 2: 1. Use long-term flux tower observations to determine how changes in vegetation structure and climate affect ecosystem-atmosphere water vapor and carbon dioxide exchange. 2. Use 210Pb pond stratigraphy to determine erosion rates and their historical dynamics on small watersheds over the past 50-100 years. 3. Quantify runoff and sediment yields on watersheds to quantify the impact of erosion control structures on runoff and sediment transfers. 4. Use satellite, climate, site productivity and management data to estimate annual production and minimum total foliar cover. 5. Use LiDAR, point cloud, and new satellite datasets to construct canopy height models to assess climate impacts on rangeland vegetation composition and production. Objective 3: 1. Use rainfall simulator experiments to quantify the effects of surface condition on infiltration, runoff, concentrated flow dynamics, sediment transport processes, and surface evolution. 2. Use radar backscatter roughness and hydraulic roughness at a laboratory, rainfall simulator, and small watershed scales using airborne and satellite active radar imagery to develop a remote sensing methods to estimate hydraulic roughness. Objective 4: 1. Complete development and post-disturbance testing of the Rangeland Hydrology and Erosion Model (RHEM) for application in Western rangelands. 2. Create a web interface to identify problem areas in watersheds, compare across watersheds, and assess trends in time prior to KINEROS2 modeling. 3. Incorporate RHEM, improved process model representations, and higher-resolution, model inputs, sub-surface and variable width routing, and interstorm processes into KINEROS2.
3. Progress Report:
This newly initiated project began on 01/30/2017 and continues to expand upon the research of two expiring projects that have been combined to form one project. See the reports for the previous projects, "Ecohydrological Processes, Scale, Climate Variability, and Watershed Management, 2022-13610-011-00D, and, "Soil Erosion, Sediment Yield, and Decision Support Systems for Improved Land Management on Semiarid Rangeland Watersheds", 2022-12660-005-00D for additional information. Substantial progress has been made towards beginning to address all four main objectives. Under Objective 1, improvements were made in the observational capacities of Walnut Gulch Long-Term Agroecosystem Research (LTAR) with the deployment of radars to measure stream stage and cloud precipitation processes, and new LTAR objectives were met with the development of water budgets, drafting a new vegetation monitoring program, and the continuation of the brush management experiment. Under Objective 2, we have begun analyses of flux tower observations and isotopes in pond deposition sediments, and we are developing new methods for assessing climate impacts on rangeland vegetation. For Objective 3, we have conducted some rainfall simulator experiments to quantify the effect of surface conditions on runoff and erosion. Under Objective 4, further improvements for the Rangeland Hydrology and Erosion Model (RHEM) and Automated Geospatial Watershed Assessment (AGWA) have continued.
1. Validation of the recently launched Soil Moisture Active Passive (SMAP) satellite products. National Aeronautics and Space Administration (NASA) global measurements of soil moisture are important in agriculture, hydrology, drought and famine warnings as well as forecasting agricultural yields. The critical need for soil moisture estimates led NASA and international partners to develop and launch the SMAP mission. Confidence in satellite derived soil moisture measurements requires ground-based validation in well understood and well instrumented locations. ARS scientists from Tucson, Arizona, and Beltsville, Maryland, and other researchers, conducted a field validation experiment on the Walnut Gulch Long-Term Agroecosystem Research (LTAR) site, along with a number of other LTAR study areas serving as core SMAP validation sites in 2015. Subsequent analysis of the collected data for validation indicate that the SMAP soil moisture data product meets its expected performance of 0.04 volumetric soil moisture. The core validation sites will continue to be monitored by SMAP to further improve its data products to provide ongoing confidence in globally distributed soil moisture measurements.
2. Incorporating ephemeral channel transmission losses is important for flash flood hazard mapping in arid and semiarid regions. The goal of this research was to couple hydrological and 2D hydraulic model treatments of channel transmission losses, to show the impact of not taking transmission losses on flood hazard mapping into consideration. ARS scientists in Tucson, Arizona, tested the stream reach between flumes 2 and 1 in the Walnut Gulch Experimental Watershed. Two hydraulics models were set up, the first did not incorporate channel transmission and the second did, with transmission losses as boundary conditions. The error in volume and peak runoff rate between the observed and simulated data ranges was in the order of –4.5 – 34.4 percent for runoff volume and –16.4 – 9.6 percent for peak runoff rate. There were also important differences in flow depths at the peak runoff rate between the two flood maps, with 0.68 meters maximum and 0 meters minimum indicating that if transmission losses are ignored, the inundated area will be underestimated.
3. A new, very high-resolution photographic method to monitor riparian area grazing. Traditional methods to assess riparian grazing impacts typically focus on vegetation without distinguishing between wildlife and livestock use and provide no information on actual animal presence or behavior. ARS scientists in Tucson, Arizona, and scientists at the University of Arizona, deployed an automated, high resolution camera to capture images every 30 seconds for 38 days and created high resolution, zoomable videos of riparian area use by elk and cattle in Arizona. Elk exhibited the unique behavior of standing in and traveling within the stream channel while grazing, and grazed while lying down. The system is being used to quantify the impacts of wild horses at sites in Arizona where horses compete with cattle, wildlife, and humans for scarce riparian resources. This new photographic tool can document direct grazing impacts on public lands between cattle, large wild ungulates and wild horses at much lower cost than was previously possible across the western U.S.
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