Skip to main content
ARS Home » Pacific West Area » Tucson, Arizona » SWRC » Research » Research Project #422899

Research Project: Ecohydrological Processes, Scale, Climate Variability, and Watershed Management

Location: Southwest Watershed Research Center

2015 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. 4. As part of the LTAR network, and in concert with similar long-term, land-based research infrastructure in Southwestern U.S., use the WGEW LTAR to improve the observational capabilities and data accessibility of the LTAR network, to support research to sustain or enhance agricultural production and environmental quality in agroecosystems characteristic of the Southwestern U.S., as per the LTAR site responsibilities and other information outlined in the 2011 USDA Long- LTAR Network Request for Information (RFI) to which the location successfully responded, and 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.

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. Multiple methods and techniques will be employed to improve the prediction of plant-water soil dynamics under objective one. They include data assimilation techniques to incorporate both in-situ and remotely sensed measurements into simulation models. In addition, algorithms for enhanced retrieval of watershed characteristics and state variables will be developed. Results from this research are critical for extension of results to large-areas using remote sensing and critical for improved inputs and parameter estimates for the models addressed under objective three. Research undertaken to address objective two more closely focuses on ecohydrology and determining changes in the cycling of energy, water and carbon as well as changes in the composition of plant communities across a wide range of time scales. This includes global change impacts on ecohydrologic processes (including water, nutrient and energy cycles) that underpin ecosystem structure and function. Thus, objective two also focuses on the relationship between global change, ecohydrology and watershed response, which will allow the evaluation of the combined impacts of climate change, intensive land use and species invasions on ecohydrological processes that are critical to maintaining ecosystems. It includes three Multi-Location Projects (MLPs) led or co-led by scientists in this research unit, which will examine observations across decadal and continental scales using observations from USDA’s national network of experimental watersheds, ranges and forests. To address objective three we will develop tools and methods to enhance watershed and rangeland management through wider accessibility of databases from our long-term experimental watersheds, and by development and testing of watershed and decision support models which can assimilate remotely sensed data and incorporate economic and ecosystem service information.

3. Progress Report:
This project is carried out under National Program 211 - Water Availability & Watershed Management. The first objective of this project is associated with National Action Plan Components 1 and 4; the second objective with Component 4, the third objective with Components 3 and 4; and the fourth objective with Components 2, 3, and 4. This report summarizes progress through FY15 corresponding to the 48th month milestones listed in the five-year project plan. Progress on Objective 1 was made using remotely sensed data coupled with in-situ observations and models to more accurately predict soil and plant water dynamics. An intensive field experiment Soil Moisture Active Passive (SMAP) Validation Experiment 2015, SMAPVEX15, was undertaken in collaboration with National Aeronautics and Space Administration (NASA), the Hydrology and Remote Sensing Laboratory, and numerous university collaborators. Airborne SMAP instruments were flown concurrently with the SMAP overpass and soil moisture measurements were taken with both manual and automated methods across southeastern Arizona, but with most sampling occurring on the Walnut Gulch Experimental Watershed. Soil and vegetation characteristics and surface roughness were sampled as well. An experiment is underway in the summer 2015 at the Institute of Bio- and Geosciences in Jülich, Germany to test the Decision Support System for Agrotechnology Transfer - Cropping System Model (DSSAT-CSM) fluorescence submodel. This will result in a better understanding of the effect of soil moisture on the chlorophyll fluorescence spectrum to improve crop yield prediction. Substantial progress was made on Objective 2. Analysis of land-atmosphere carbon dioxide (CO2) and water exchange data from a network of eddy covariance sites across southern Arizona was made to determine the role of interannual fluctuations in precipitation and evapotranspiration on net CO2 exchange, providing an improved understanding how El Nino/La Nina induced alterations in precipitation in the southwest U.S. affect CO2 exchange in the semiarid Southwest. ARS scientists used soil moisture data at nine grassland sites in California, Arizona, Nevada, New Mexico, Oklahoma, Mississippi and Georgia and found fundamental differences in how Desert and Plains grasslands responded to the early 21st century drought. Several studies on how changes in land use and climate will affect semiarid watersheds were conducted. As part of a multi-location project, bias corrected and statistically downscaled climate projections were made for seven ARS Experimental Watershed locations. This effort was led by the El Reno, Oklahoma, management unit. Historical climate observations in and around the Walnut Gulch Experimental Watershed (WGEW) area operated by the Southwest Watershed Research Center were used to test the downscaling procedure. Three emissions scenarios were examined. Downscaled Global Climate Model (GCM) climate projections indicated that annual precipitation for the WGEW is not expected to change much over the 21st century. Trends in projected monthly precipitation were not statistically significant in most cases. Only the December to June seasonal trend in precipitation for the high green house gas scenario had a statistically significant decreasing trend. However, annual air temperature for the WGEW was expected to increase over the 21st century for all three emissions scenarios. The time scales of these projections (monthly) are too coarse to address storm intensification, which is currently being investigated, but higher projected temperatures will add to plant stress. The primary progress made toward Objective 3 involved continued improvements to the Automated Geospatial Watershed Assessment (AGWA) tool and the KINematic runoff and EROSion model (KINEROS2) rainfall-runoff-erosion model. These included improved prediction of fate and transport of microbes in lands with applied or deposited animal waste. This work was conducted in cooperation with ARS scientists from Beltsville, Maryland, and verified that nationally available soil survey data can provide good estimates of the water retention-related infiltration parameter that is a critical for predicting the fate and transport of microbes from animal waste. In addition, a Green Infrastructure (GI) module was added to AGWA/KINEROS2 to provide a better representation of the effects of GI best management practices such as porous pavement, bio-retention cell, and rainwater harvesting to reduce the impacts of off-site storm water. Objective 4 was added in Fiscal Year 2014 as a result of increased funding for the Walnut Gulch Experimental Watershed Long Term Agroecosystem Research site. Progress this year was primarily to: 1) locate and hire a postdoctoral scientist to better understand the short and long-term impacts of brush management on runoff and erosion, and a second postdoctoral scientist to analyze WGEW precipitaiton data: 2) expand the instrumentation power, wireless connectivity, and rangage network infrastructure at Walnut Gulch Experimental Watershed and the watersheds on the Santa Rita Experimental Range; 3) improve measurements of soil CO2 respiration; 4) collect and analyze high resolution digital elevation data; and, 5) co-chair the meteorological observations committee to provide guidelines to other Long Term Agricultural Research (LTAR) locations on instrumentation and co-chair the data committee to develop procedures for transmitting meteorological observations and phenocam images from LTAR sites to the National Agricultural Library.

4. Accomplishments
1. Documenting the importance of ephemeral streams for the physical, chemical, and biological integrity of the Nation's waters. Following the 2006 Rapanos Supreme Court decision there was significant uncertainty about which wetlands and tributaries are considered to be Waters of the U.S. (WOTUS) and consequently subject to the Clean Water Act. In May, 2015, the Environmental Protection Agency/Corps of Engineers more specifically defined the WOTUS based on a national report summarizing the scientific literature (Connectivity of Streams & Wetlands to Downstream Waters: A Review & Synthesis of the Scientific Evidence). The portion of the report covering ephemeral and intermittent streams in the southwest was written by an ARS scientist in Tucson, Arizona, and substantially based on research conducted by the ARS in the Walnut Gulch Experimental Watershed and the larger San Pedro Basin. The physical, chemical, and biological integrity of downstream waters in the southwest was found to depend on the tributary ephemeral and intermittent streams. The new definition of WOTUS ensures that waters protected under the Clean Water Act are more precisely defined and predictably determined, while providing additional protection to the one-in-three Americans dependent on ephemeral and intermittent streams for their drinking water.

2. Regional understanding of the impact of precipitation patterns on grassland soil moisture status. In the early 21st century, grassland regions of the U.S. have experienced prolonged warm drought and a shift to larger, more infrequent storms. This has raised the question: How will these new storm patterns affect our grasslands? ARS scientists in Tucson in collaboration with the University of Arizona used the USDA/NRCS soil climate analysis network (SCAN) measurements of soil moisture at nine grassland sites in California, Arizona, Nevada, New Mexico, Oklahoma, Mississippi and Georgia and found a fundamental difference in Desert and Plains grasslands. That is, soil moisture in the wetter Plains grasslands decreased with an increase of high-intensity storms, whereas the drier Desert grasslands were not responsive to storm size, but instead, soil moisture decreased as storms became more infrequent. This improved ability to predict soil moisture and plant growth with changing hydro-climatic conditions will result in more efficient resource management and better informed policy decisions.

3. Preparation for SMAP soil moisture products. The Soil Moisture Active Passive (SMAP) satellite will provide global measurements of soil moisture for weather prediction, drought and flood forecasting, agricultural management, and national security. An ARS researcher in Tucson, Arizona, in collaboration with the National Aeronautics and Space Administration (NASA) Headquarters, involved potential users in mission planning through the SMAP Applications Working Group. The result has been an unprecedented pre-launch preparation for SMAP applications and critical feedback to improve the mission, providing direction for all upcoming NASA earth observation missions and setting the context for the future of earth observation. This work also led to a 5-year NASA-USDA agreement signed by the USDA Under-Secretary and NASA Deputy Administrator “to improve agricultural and Earth science research, technology, agricultural management, and the application of science data, models, and technology in agricultural decision-making”.

4. Improved prediction of fate and transport of microbes in land applied or deposited animal waste. Runoff of microorganisms from field-applied manure and animal waste is dependent on how rainfall or irrigation water is partitioned between overland flow and infiltration into the soil. Infiltration depends on both the ability of soil to transmit water and to retain water. ARS scientists from Beltsville, Maryland, and Tucson, Arizona, compared three methods to evaluate the effect of soil water retention and found that soil survey data can provide a good estimate of the water retention-related infiltration parameter when used with an ensemble of predictive relationships. These results are useful for predicting the fate and transport of microbes from animal waste as well as demonstrating the feasibility of using soil survey data to improving these predictions.

Review Publications
Pierini, N., Vivoni, E., Robles-Morusa, A., Scott, R.L., Nearing, M.A. 2014. Using observations and a distributed hydrologic model to explore runoff thresholds linked with mesquite encroachment in the Sonoran Desert. Water Resources Research. 50:8191-8215.
Glenn, E., Scott, R.L., Nguyen, U., Nagler, P. 2015. Wide-area ratios of evapotranspiration to precipitation in monsoon dependent semiarid vegetation communities. Journal of Arid Environments. 117:84-95.
Norman, L., Brinkerhoff, F., Gwilliam, E., Guertin, D., Callegary, J., Goodrich, D.C., Nagler, P., Gray, F. 2015. Hydrologic response of streams restored with check dams in the Chiricahua Mountains. River Research and Applications. 1:1-11.
Sanches Oliveira, P., Wendland, E., Nearing, M.A., Scott, R.L., Rosolem, R., Da Rocha, H. 2015. The water balance components of undisturbed tropical woodlands in the Brazilian cerrado. Hydrology and Earth System Sciences. 19:2899-2910.
Stillman, S., Ninneman, J., Zeng, X., Franz, T., Scott, R.L., Shuttleworth, W., Cummins, K. 2014. Summer soil moisture spatiotemporal variability in southeastern Arizona. Journal of Hydrometeorology. 15:1473-1485.
Sanches Oliveira, P., Nearing, M.A., Moran, M.S., Goodrich, D.C., Wendland, E., Gupta, H. 2014. Trends in water balance components across the Brazilian Cerrado. Water Resources Research. 50:7100-7114.
Guber, A., Pachepsky, Y.A., Yakirevich, A., Shelton, D.R., Whelan, G., Goodrich, D.C., Unkrich, C.L. 2014. Modeling runoff and microbial overland transport with KINEROS2/STWIR model: Accuracy and uncertainty as affected by source of infiltration parameters. Journal of Hydrology: 519.644-655.
Moran, M.S., Doorn, B., Escobar, V., Brown, M. 2015. Connecting NASA science and engineering with earth science applications. Journal of Hydrometeorology. 16:473-483.
Hottenstein, J., Ponce-Campos, G., Yanes, J., Moran, M.S. 2015. Impact of varying storm intensity and consecutive dry days on grassland soil moisture. Journal of Hydrometeorology. 16:106-117.
Xiao, J., Ollinger, S., Frolking, S., Hurtt, G., Hollinger, D., Davis, K., Pan, Y., Zhang, X., Deng, F., Chen, J., Baldocchi, A., Law, B., Arain, M., Desai, A., Richardson, A., Sun, G., Amiro, B., Margolis, H., Gu, L., Scott, R.L., Blaken, P., Suyker, A. 2014. Data-driven diagnostics of terrestrial carbon dynamics over North America. Agricultural and Forest Meteorology. 197:142-157.