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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

2014 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 with Component 4, the third with Components 3, and 4; and the fourth with Components 2, 3, and 4. This report summarizes progress through FY14 corresponding to the 36th month milestones listed in the five-year project plan. Progress on Objective 1 was made on several fronts using remotely sensed data coupled with in-situ observations. As part of the AgriSAR (Agricultural bio/geophysical retrieval from frequent repeat pass Synthetic Aperture Radar (SAR) and optical imaging) effort, SAR imagery was used with in-situ measurement in Canada, Spain and the Netherlands to improve estimates of soil moisture and plant phenology. In the United States remote and field measurements were used to assess public land ranch management on allotments in southeastern Arizona using estimates of plant production from the Landsat (30 meter) and MODerate resolution Imaging Spectroradiometer (MODIS, 250 meter) sensors. We used multiple imagery products to estimate plant production throughout the growing season as well as pre- and post-monsoon total vegetative cover. For each unit of analysis (pixel), we modeled the vegetation production or cover as a function of climate, management, and GIS-based physical attributes to identify how the observed vegetation differed for each pixel compared to what the model predicted at that pixel. Substantial progress occurred toward meeting Objective 2. Results indicated grassland mortality in the early 21st-century drought in the southwestern United States was compounded due to higher ambient temperatures than in past equally dry droughts. Another study was first to comprehensively establish the mechanisms and role of nocturnal soil CO2 uptake and inorganic carbon dynamics in aridland ecosystem showing that non-biologically mediated carbon dynamics are the dominant feature in ecosystem gas exchange during annually re-occurring drought periods. Another important result found significant differences as to where shrubs were able to conduct photosynthesis across a broader temperature range than co-occurring grasses during dry periods. This has important implications for the conversion of many grasslands to shrublands that is being observed worldwide. A study across China determined that the water use of plants across ecosystems from grassland to forest is affected by not only the current drought conditions, but also the drought conditions of the previous year. The primary progress made toward Objective 3 involved improvements to the Automated Geospatial Watershed Assessment (AGWA) tool and the KINEROS2 rainfall-runoff-erosion model. The Rangeland Hydrology and Erosion Model (RHEM), developed primarily under the management unit’s companion CRIS project, was incorporated into KINEROS2. In addition, a method to represent curvilinear hillslope shapes derived from digital elevation data was implemented in AGWA. Both were tested as part of a Western Conservation Effects Assessment (CEAP) Pilot Project on the Cienega Creek Watershed. Findings from this pilot project were also incorporated into a report fulfilling an Annual Performance Goal (APG) for the USDA Water Team led by the USDA Deputy Under Secretary of Natural Resources and Environment. Objective 4 is new to the project in this year as a result of increased funding. Progress this year was primarily to plan field experiments and purchase/build equipment to better understand the short and long-term impacts of brush management on runoff and erosion, expand the precipitation gauge network, upgrade the automated reporting capabilities of Walnut Gulch Experimental Watershed and small watersheds on the Santa Rita Experimental Range, refurbish stock tanks, build additional flumes, improve measurements of ET, CO2, and Cs-137, capture high resolution digital elevation data, and expand data processing capabilities to scale gridded climate data across the West.

4. Accomplishments
1. U.S. grassland mortality increased by the early 21st-century drought. In this study, ARS researchers in Tucson, Arizona, found that the early 21st century drought in the southwestern United States resulted in an exceptional decrease in grassland growth, and the replacement of native grasses with less-nutritious and more-fire-prone invasive grasses. This study was based on in-situ measurements of surface soil moisture and precipitation, and satellite estimates of above-ground net primary production (ANPP) for six USDA experimental grasslands in Utah, New Mexico, Arizona, Colorado and Oklahoma. This is a first report of how U.S. grasslands will respond to the regional drying and warming predicted with climate change. This analysis has two important implications: first, it provides ranchers with new information for managing grasslands under predicted climate change to lower fire risk, minimize loss of forage, and retain ecosystem services; and second, the aberrant behavior reported here suggests that grasslands can serve as an early indicator of impending climate change. These compelling results in a natural setting at the regional scale should play a role in future grassland research, management and policy.

2. Non-biological carbon dioxide uptake in desert soils. Soils play a huge role in global carbon cycle, but this exchange of carbon dioxide between the land and atmosphere is thought to be non-existent when soils are dry and plants are dormant. ARS researchers in Tucson, Arizona, in collaboration with University of Arizona and University of Granada scientists, discovered that dry soils in the Chihuahuan desert of the Southwest U.S. absorb atmospheric carbon dioxide at night. These results show that non-biologically mediated carbon dynamics are the dominant feature in ecosystem gas exchange during annually re-occurring drought periods and these will likely respond strongly to continued atmospheric carbon dioxide increases, as well as the warmer and drier early summer periods predicted across the Southwest U.S. This work also demonstrated that plant canopy cover affected the soil temperature gradients that drove soil CO2 uptake, showing plant cover influences soil carbon processes in dryland systems. This research is the first to comprehensively establish the mechanisms and role of nocturnal soil CO2 uptake and inorganic carbon dynamics in aridland ecosystem-level CO2 fluxes.

3. Vegetation change alters water availability. The vegetation composition of many ecosystems around the world and in the U.S. is rapidly changing, causing unknown changes in the way these ecosystems cycle carbon and water. ARS researchers in Tucson, Arizona, in collaboration with scientists from the University of California-Irvine, the University of Arizona, the University of California-Riverside, and the University of Alaska, used multi-year hydrological and meteorological data to evaluate how soil water accessibility affects the magnitude and variability of the biosphere-atmosphere exchanges of water and carbon dioxide across three ecosystems that are representative of varying degrees of mesquite tree invasion. They found that groundwater access increased in ecosystems with greater amounts of trees rather than grasses, and that groundwater accessibility led to significant changes in magnitude and variability in ecosystem water and carbon cycling. Vegetation change in areas where the accessibility to deeper soil water increases will likely increase carbon sequestration but at the expense of higher water use.

4. The importance of “where” for determining impact of shrub expansion into grasslands. The conversion of many grasslands to shrublands worldwide has the potential to alter how ecosystems respond to future climate because grasses and woody plants have different responses to environmental conditions. ARS scientists in Tucson, Arizona, along with scientists from the University of California-Irvine, the University of Arizona, and the University of California-Riverside, found significant differences where shrubs were able to conduct photosynthesis across a broader temperature range than co-occurring grasses during dry periods, but with grasses outperforming shrubs during the wetter summer rainy season within a pair of semiarid shrublands in Arizona that had undergone shrub expansion. Importantly, they found that the shrubland landscape position modulated these temperature sensitivities, as the range of functional temperatures and maximum rates of photosynthesis were much larger in dry times at the site closer to a river due to greater availability of shallow groundwater. Given projections of more variable precipitation and increased temperatures, the different responses of grasses and shrubs are likely to drive patterns of ecosystem carbon cycling.

5. Cost effective method to map impervious surfaces with high-resolution satellite imagery. Mapping the expansion of impervious surfaces is important for understanding the hydrologic impacts of land development but is difficult in arid and semiarid environments due to the sparse coverage of contrasting vegetation. In this study, ARS researchers in Tucson, Arizona, in collaboration with scientists from the University of Arizona, developed a cost-effective, semi-automated approach for mapping impervious surfaces using object-oriented classification of high-resolution QuickBird satellite imagery. Application of the approach over a 1,179 square kilometer region produced maps of impervious surfaces with a mean overall accuracy of 88.1 percent. This study demonstrates the ability to operationally monitor urban growth in arid lands at different spatial scales to improve water capture and flood control.

6. Prolonged drought decreases vegetation production across China. ARS researchers in Tucson, Arizona, in collaboration with scientists from Beijing Normal University and the University of Arizona, determined that the water use of plants across ecosystems from grassland to forest is affected by not only the current drought conditions, but also the drought conditions of the previous year. This behavior was modeled to provide managers with a tool to plan for the impact of predicted climate change on valuable natural resources, especially if prolonged drought continues in the future. This was attributed to the legacy effect of precipitation changes in both wet and dry years, and to the resilience of the biomes in the dry years. This model is particularly useful at the landscape scale because it is based on accessible satellite data and available meteorological data and the results have been tested across four major biomes in China.

Review Publications
Yang, Y., Scott, R.L., Shang, S. 2013. Modeling evapotranspiration and its partitioning over a semiarid shrub ecosystem from satellite imagery: a multiple validation. Journal of Applied Remote Sensing (JARS). 7:1-16.
Singh, R., Seney, G., Velpuri, N., Bohms, S., Scott, R.L., Verdin, J. 2013. Actual evapotranspiration (water use) assessment of the Colorado River Basin at the Landsat resolution using the operational Simplified Surface Energy Balance Model. Remote Sensing. 6:223-256.
Barron-Gafford, G., Cable, J., Bentley, L., Scott, R.L., Huxman, T., Jenerette, G., Ogle, K. 2014. Quantifying the time scales over which exogenous and endogenous conditions affect soil respiration. New Phytologist. 202:442-454.
Niu, G., Paniconi, C., Troch, P., Scott, R.L., Durcik, M., Zeng, X., Huxman, T., Goodrich, D.C. 2014. An integrated modelling framework of catchment-scale ecohydrological processes: 1. Model description and tests over an energy-limited watershed. Ecohydrology. 7:427-439.
Niu, G., Troch, P., Paniconi, C., Scott, R.L., Durcik, M., Zeng, X., Huxman, T., Goodrich, D.C., Pelletier, J. 2014. An integrated modelling framework of catchment-scale ecohydrological processes: 2. The role of water subsidy by overland flow on vegetation dynamics in a semi-arid catchment. Ecohydrology. 7:815-827.
Cable, J., Ogle, K., Barron-Gafford, G., Bentley, L., Cable, W., Scott, R.L., Williams, D., Huxman, T. 2013. Antecedent conditions influence soil respiration differences in shrub and grass patches. Ecosystems. 16:1230-1247. DOI: 10.1007/s10021-013-9679-7.
Brown, M., Escobar, V., Moran, M.S., Entekhabi, D., O'Neill, P., Njoku, E., Doorn, B., Entin, J. 2013. NASA’s Soil Moisture Active Passive (SMAP) mission and opportunities for applications users. Bulletin of the American Meterological Society. 94:1125–1128. https//
Fehmi, J., Nie, G., Scott, R.L., Mathias, A. 2013. Evaluating the effect of rainfall variability on vegetation establishment in a semidesert grassland . Environmental Monitoring and Assessment. 186:395-406. DOI: 10.1007/s10661-013-3384-z.
Nagler, P., Glenn, E., Nguyen, U., Scott, R.L., Doody, T. 2013. Estimating riparian and agricultural actual evapotranspiration by reference evapotranspiration and MODIS Enhanced Vegetation Index. Remote Sensing. 5:3849-3871.
Brand, A., Dixon, M., Fetz, T., Stromberg, J., Stewart, S., Graber, G., Goodrich, D.C., Brookshire, D., Broadbent, C., Benedict, K. 2013. Projecting avian responses to landscape management along the Middle Rio Grande, New Mexico. The Southwestern Naturalist. 58(2):150–162.
Zhang, X., Moran, M.S., Zhao, X., Liu, S., Zhou, T., Ponce Campos, G. 2014. Impact of prolonged drought on rainfall use efficiency using MODIS data across China in the early 21st century. Remote Sensing of Environment. 150:188-197.
Scott, R.L., Huxman, T., Barron Gafford, B., Jenerette, G., Young, J., Hamerlynck, E.P. 2014. When vegetation change alters ecosystem water availability. Global Change Biology. 20:2198-2210.
Templeton, R.D., Vivoni, E.R., Mendez-Barroso, L.A., Pierini, N.A., Anderson, C.A., Rango, A., Laliberte, A.S., Scott, R.L. 2014. High-resolution characterization of a semiarid watershed: Implications on evapotranspiration estimates. Journal of Hydrology. 509:306-319.
Hamerlynck, E.P., Scott, R.L., Sánchez-Cañete, E.P., Barron-Gafford, G.A. 2013. Nocturnal soil CO2 uptake and its relationship to sub-surface soil and ecosystem carbon fluxes in a Chihuahuan Desert shrubland. Journal of Geophysical Research-Biogeosciences. 118:1593–1603. DOI :10.1002/2013JG002495.
Gaunter, L., Zhang, Y., Jung, M., Joiner, J., Voight, M., Berry, J., Frankenberg, C., Huete, A., Zarco-Trejada, P., Lee, J., Moran, M.S., Ponce Campos, G., Beer, C., Camps-Vall, G., Buchmann, N., Gianelle, D., Klumpp, K., Cescatti, A., Baker, J.M., Griggis, T. 2014. Global and time-resolved monitoring of crop photosynthesis with chlorophyll fluorescence. Proceedings of the National Academy of Sciences. 111(14):E1327-E1333.
Sugg, Z., Finke, T., Goodrich, D.C., Moran, M.S., Yool, S. 2014. Mapping impervious surfaces using object-oriented classification in a semiarid urban region. Photogrammetric Engineering and Remote Sensing. 80:343-352. DOI: 10.14358/PERS.80.4.343.
Broxton, P., Troch, P.A., Schaffner, M., Unkrich, C.L., Goodrich, D.C. 2014. All-season flash flood forecasting system for real-time operations. Bulletin of the American Meterological Society. 95:399–407.
Moran, M.S., Ponce Campos, G., Huete, A., Mcclaran, M., Zhang, Y., Hamerlynck, E.P., Augustine, D.J., Gunter, S.A., Kitchen, S.G., Peters, D.C., Starks, P.J., Hernandez, M. 2014. Functional response of U.S. grasslands to the early 21st century drought. Ecology. 95:2121-2133.
Barron-Gafford, G., Scott, R.L., Jenerette, G., Hamerlynck, E.P., Huxman, T. 2013. Landscape and environmental controls over leaf and ecosystem carbon dioxide fluxes under woody plant expansion. Journal of Ecology. 101:1471-1483.
Stillman, S., Zeng, X., Shuttleworth, W., Goodrich, D.C., Unkrich, C.L., Zerda, M. 2013. Spatiotemporal variability of summer precipitation in southeastern Arizona. Journal of Hydrometeorology. 14:1944-1951.