Location: Southwest Watershed Research2012 Annual Report
1a. Objectives (from AD-416):
1. Improve watershed management by developing the capacity to more accurately predict soil and plant water dynamics utilizing a combination of remote sensing, modeling and in-situ measurements. 2. Quantify how seasonal, annual, and decadal-scale variations in climate (including climate forecasts) and plant community composition impact the cycling of energy, water and carbon in semiarid rangelands. 3. Develop improved watershed model components and decision support systems that more fully utilize and assimilate economic and remotely sensed data for parameterization, calibration and model state adjustment.
1b. Approach (from AD-416):
Methods of investigation include field and laboratory experimentation, as well as the development and use of state-of-the-science watershed models and the use of remote sensing for watershed characterization. Satellite derived rainfall will be evaluated using raingages for large area rainfall estimation, the enhancement of recharge due to urbanization will be examined in adjacent, well instrumented, natural and residentially developed catchments. High-resolution remotely sensing and rainfall simulator experiments will be used to evaluate the capability to remote estimate infiltration rates on compacted and constructed surfaces common to development at the urban-rural interface. Remote spectral surface responses will be combined with energy balance models and radiative transfer theory to estimate surface water, carbon and energy fluxes based on observations from a network of five eddy-covariance and two Bowen ratio towers. A number of modeling components for the Automated Geospatial Watershed Assessment (AGWA) will be developed or enhanced to enable a more realistic representation of watershed processes and best management practices. AGWA will be migrated to both the internet and ARCGIS platforms to enhance usability and access. In addition we will quantify the physical mechanisms and component fluxes that are responsible for the observed ecosystem-scale water and CO2 fluxes. Scientists will carry out this research at sites located across both a riparian and an upland woody plant encroachment gradient. Continue existing research under objective #3, and add activities to develop methods and techniques to quantify and predict water budgets under current and projected climate scenarios through direct measurements of evaporation and plant transpiration, and predict water savings by removal of invasive mesquite vegetation.
3. Progress Report:
This is a new project that was initiated on Jan. 30, 2012. It expands upon research from the prior project entitled “Hydrologic Processes, Scale, Climate Variability, and Water Resources for Semiarid Watershed Management” (Project Number: 5342-13610-011-00D). All of the research conducted in this project is directed toward NP 211 – Water Availability and Watershed Management, Action Plan Component 4 – Improving Watershed Management and Ecosystem Services in Agricultural Landscapes. An important aspect of this new project is the MU’s leadership and involvement in 6 Multi-Location Projects (MLPs). During action plan and project plan development a concerted effort was made to develop MLPs to leverage ARS’s long-term experimental and observational assets (i.e. Experimental Watersheds and Ranges) with a goal of conducting regional and continental scale research on watershed and ecosystem response to a more variable and changing climate. The three MLPs being led or co-led by scientists in this MU are: 1) Discover “convergence” of eco-hydrologic patterns within multi-location, time-series, eco-hydrologic data that could allow generalization to other locations; 2) Utility of the ARS Watershed Network for Quantifying the Extent and Magnitude of Climate Change and its Impacts on Watershed Response Across the Agricultural Regions of the United States & North America; and, 3) Continental-scale synthesis of high-resolution observations from and trends of future climate at ARS and USDA experimental watersheds, ranges, and forests, to quantify the impacts of climate variability and change on regional water availability and agro-ecosystems. Good progress was made on each of these efforts. For Objective 1 a number of new experiments and analyses of remotely sensed imagery to improve watershed management through more accurate prediction of soil and plant water dynamics were successfully initiated. For Objective 2 a significant number of instruments have been installed as part or our effort quantify climate interactions on the cycling of energy, water and carbon in semiarid rangelands. The MLPs discussed above also fall under this objective. In comparative analysis between semiarid systems in Arizona and Spain we found that precipitation strength and timing dominated carbon exchange, but temperature also played an important role in regulating plant growth and net carbon uptake which may provide an important contribution to future global climate modeling efforts as these carbon dioxide exchanges across summer versus winter precipitation dominated environments can be accounted for by modeling the same physical ecosystem processes. For Objective 3 the KINEROS2 watershed model developed and maintained by the MU was improved for flash-flood forecasting in cooperation with the National Weather Service. In addition, rangeland state and transition model information is being developed for the ecosites in the Empire Ranch in southeastern Arizona. This research also directly supports our cooperative efforts with the Natural Resources Conservation Service (NRCS) for the Congressionally mandated rangeland CEAP (Conservation Effects Assessment Program) effort.
1. Commonalities in semiarid ecosystem functioning across ecosystems in summer versus winter dominated rainfall regimes. Although semiarid regions occupy a vast amount of the global land surface, it is not known whether ecosystems in these regions take in and release carbon dioxide differently depending on the seasonality of rainfall. ARS researchers in Tucson, Arizona, and scientists in southern Spain measured and analyzed carbon fluxes of semiarid ecosystems that were dominated by either summer or winter precipitation to understand how precipitation seasonality influences patterns of photosynthesis and net carbon dioxide flux. They found that precipitation strength and timing were the dominant controls of carbon exchange, but temperature also played an important role in regulating plant growth and net carbon uptake. The commonalities found across these contrasting climates will impact later global climate modeling efforts in that these exchanges of carbon dioxide can be accounted for by modeling the same physical ecosystem processes.
Barron-Gafford, G., Scott, R.L., Jenerette, G., Hamerlynck, E.P., Huxman, T. 2012. Temperature and precipitation controls over leaf- and ecosystem-level CO2 flux along a woody plant encroachment gradient. Global Change Biology. 18;1389-1400. doi:10.5194/bg-9-1007-2012.