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The SWRC Bulletin
Sound Science for Watershed Decisions

Winter 2015

Walnut Gulch Precip Map

Bulletin Highlight of the Year

From Scott, R.L., Huxman, T.E., Barron-Gafford, G.A., Darrel Jenerette, G., Young, J.M. and Hamerlynck, E.P. 2014. When vegetation change alters ecosystem water availability. Global Change Biology, 20, 2198-2210. doi:10.1111/gcb.12511

Figure 1

Figure 1. (a) 2003-2007 16-day ensemble averages of MODIS Enhanced Vegetation Index (EVI), (b) net ecosystem production (NEP), (c) precipitation (P), and (d) evapotranspiration (ET). Error bars represent +/- 1 standard error. Precipitation is shown for just one site as the other sites had very similar magnitude and seasonality. The upland grassland is from the nearby Ameriflux Kendall Grassland, representing a more typical site in this region without access to groundwater.


The vegetation composition of many ecosystems around the world and in the U.S. is rapidly changing. The causes of these rapid changes are intimately connected with climate change and management practices, but the consequences of these shifts in composition and structure on the fundamental ecosystem services of water and carbon cycling are not well understood.For this study, we use 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 amongst three proximate ecosystems that are representative of varying degrees of mesquite tree invasion. We 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.Even as depth to groundwater increased from grassland to shrubland to woodland, the woodland had the highest evapotranspiration in excess of precipitation and the grassland was lowest. How the greater density of trees affected the amount of carbon taken in by an ecosystem was more complex. Woodland carbon sequestration was the largest but surprisingly similar to the less mature and dense shrubland, and both systems took in much more carbon than the grassland. 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.

Soil Moisture Validation Field Experiment

On January 31, 2015 the Soil Moisture Active Passive (SMAP) satellite was launched. Because of Walnut Gulch's dense raingage network, numerous soil moisture measuring instruments, and localized monsoon precipitation, the very first validation experiment of the SMAP sensor was performed here over the summer. Called the SMAP Validation EXperiment 2015, or SMAPVEX15, the experiment was held last August to see how well the satellite estimates moisture in the top 2 inches (5 cm) of soil.

Mike Cosh from the ARS Hydrology and Remote Sensing Lab in Beltsville led five separate crews sampling soil moisture near rain gauges on Walnut Gulch. Additional researchers came from the University of Arizona, USC, NASA's Jet Propulsion Laboratory, Texas A&M, the National Center for Atmospheric Research, and Princeton University to help with the field work as well as characterize vegetation, roughness, and test wireless sensor networks between overpasses. Two teams led by Chandra Holifield Collins sampled soil moisture on supplementary sites in the Santa Rita Experimental Range (SRER) and the Empire Ranch.


In the image below, the black lines are a 3km grid and the yellow points show locations of weighing rain gages with an associated soil moisture sensor, while the green points are tipping bucket gages managed by the Nature Conservancy on the Empire Ranch. The orange lines are flight lines for an aircraft with sensors similar to the SMAP satellite sensors.


Unfortunately, a problem was discovered with the active radar on the SMAP satellite. Consequently, the primary 9 km soil moisture product, which was to be calculated using a combination of the high resolution (~1-3 km) active radar and the low resolution (~40 km) passive sensor cannot be estimated. NASA is now exploring other ways to generate the 9 km product. More information on the SMAP Validation can be found at:

Awards and Recognition

Mark Nearing received the 2014 ASABE Superior Paper Award for the Paper: "Risk Assessment of Erosion From Concentrated Flow on Rangelands Using Overland Flow Distribution and Shear Stress Partitioning"


Mark Nearing received the 2014 Hugh Hammond Bennett Award from Soil and Water Conservation Society. The Hugh Hammond Bennett Award is the Society's most prestigious award and recognizes extraordinary national and international accomplishments in the conservation of soil, water, and related natural resources. "Because of his important contributions to the science of erosion modeling and his mentoring of scientists who carry on erosion research worldwide, Dr. Mark Nearing is fully deserving of the Hugh Hammond Bennett Award," said Rob Lawson, Chair of the SWCS Awards Committee.


Mark Nearing was named the 2015 Scientist of the Year from the ARS's Pacific West Area for innovative advances in modeling erosion processes and for integrating that research into science-based soil conservation decision making practices and polices.

Dave Goodrich and Mark Nearing
received the EPA Office of Research and Development Honor Award, Bronze medal, from the National Center for Environmental Assessment for Developing Water Quality Assessment Tools to assess climate change impacts on water resources.


David Goodrich was awarded a USDA/ARS headquarters funded postdoc entitled "Precipitation Extremes: Are Rainfall Intensities Increasing at Short Time Scales that are Critical in Determining Runoff, Erosion, and Design of Conservation and Storm Water Infrastructure?". He is in the process of hiring a postdoc for 2015, and the advertisement is currently posted on


Dave Goodrich and his collaborator Bill Kepner, of the Environmental Protection Agency (EPA), were awarded the EPA's Office of Research and Development Bronze Medal for their work on the Automated Geospatial Watershed Assessment (AGWA). The award was given in recognition of "superior performance in developing, applying, and providing innovative futures forecasting watershed analysis tools to the public, regulatory, and scientific communities." The Bronze Medal is the third highest formal honor award given by EPA.


David Goodrich made an invited keynote presentation to the 5th International Conference of Fire Effects on Soil Properties, 14th-17th July 2015 in Dublin, Ireland

John Hottenstein, our Space Grant Student, was selected as the 1st place poster presentation among student entries in the 28th Conference on Hydrology, last January 2014, in Atlanta, Georgia. His poster presentation was "Complex Response of Grassland Soil Moisture to Extreme Precipitation Patterns".


Congratulations to Mallory Barnes for winning the Grand Prize for her poster presentation at the 7th Annual "Phenology Research and Observations of Southwest Ecosystems (PROSE)" Symposium in Tucson, AZ October 2014, entitled "Spatial Patterns of Vegetation Response to Climate Variability in the American Southwest." Her poster presentation was rated the best of 12 entries.

New Hires and Retirements

Tim Keefer retired from the Southwest Watershed Research Center in January 2015 after nearly 30 years of federal service. Tim was a Hydrologist whose talents and expertise contributed to a wide array of research and the successful operation of the SWRC Walnut Gulch and Santa Rita Experimental Watersheds. His analysis of soil moisture observations, precipitation observations, and teleconnections significantly improved our understanding of semiarid hydrological processes. He is a true master of installation and testing of hydrometeorological instrumentation and subsequent quality control of observations from those instruments with a keen sense of the uncertainties associated with these observations. Consequently he made critical contributions to numerous interdisciplinary experimental campaigns and special projects conducted during his career. He was a key contributor to the SWRC Data Access Project (DAP) that made high-quality observations from our experimental watersheds internet accessible in addition to numerous papers in the 2008 Water Resources Research special issue on Walnut Gulch, DAP, and a variety of research conducted on Walnut Gulch. Whenever a student or colleague asked Tim for help or advice he always said yes! We are very pleased that Tim will continue to work with the SRWC on a part-time basis between his many planned travels.


In 2014, SWRC welcomed Abreeza Zegeer for a six-month appointment in concert with the University of Arizona School of Natural Resources and the Environment. A horticulture specialist with the Dept. of Ecology and Evolutionary Biology, Abreeza assisted SWRC hydrologist Joel Biederman with plant surveys, biomass sampling, and soils analysis. This work provided datasets needed to quantify whole-ecosystem carbon stocks at four eddy flux sites in Walnut Gulch Experimental Watershed and the Santa Rita Experimental Range, where SWRC lead scientist Russ Scott has been monitoring exchanges of water and carbon dioxide between semi-arid ecosystems and the atmosphere ( Abreeza's work was supported by a partnership between scientist Dr. Scott and the US Department of Energy's AmeriFlux program (


With joint support from the NASA Space Grant Consortium ( and AmeriFlux, University of Arizona undergraduate Theo Jones joined Joel Biederman as an intern focusing on spatial analysis of vegetation datasets at an eddy flux sites in the Santa Rita Experimental Range ( Using a combination of aerial photographs, airborne laser mapping, and ground-based vegetation datasets, Theo developed methodology for quantifying above-ground biomass across flux tower footprints and small watersheds. Using these in concert with multi-year observations of CO2 uptake by photosynthesis, Theo determined the mean carbon residence in this ecosystem is 25-35 years.


Joel Biederman was hired in 2014 to work with Russ Scott as an Associate Research Hydrologist. With support from the Department of Energy's Ameriflux Program, Dr. Biederman is working with eddy covariance datasets to improve understanding of the coupling between ecosystem water and carbon exchanges across the Southwest region.


Eleonora Demaria joined SWRC in May 2015 to work with Dave Goodrich as a Research Hydrologist-Meteorologist. Dr. Demaria is working with sub-daily precipitation data from the Long Term Agroecosystem Research (LTAR) network to evaluate the temporal changes in precipitation intensities across different hydro-climatic environments. Growing up in the flat and boring Argentine plans, Eleonora enjoys hiking and camping in the mountains of Arizona.


Enrique Perez Sanchez-Ca?ete (University of Granada, Spain) arrived in 2015 to work with Russ Scott and Greg Barron-Gafford (UofA) over the next two years. Enrique received a prestigious European Union Marie-Curie Fellowship to work on understanding the fundamental controls on soil respiration.


Ana Lopez Ballesteros, a Ph.D. student from the University of Granada, Spain, will be arriving for the summer of 2015 to work with Russ Scott on soil respiration and photo-degradation of litter and soil organic matter.


Li Li is newly arrived PhD student working with Mark Nearing at SWRC. He is from the city of Wuhan, which is located on the middle reach of the Yangtze River, China. Li Li got his bachelor degree at Southwest University in Chongqing City, 2011, majoring in Environment and Civil engineering, and his Master's degree in 2014 from Hohai University in Nanjing and the Yangtze River Scientific Research Institute in Wuhan, majoring in Disaster Protection engineering with an option in water and soil conservation. His previous research focused on soil erosion, water quality, soil environment and non-point pollutions. Li Li is now a PhD student in the School of Natural Resources and the Environment at the University of Arizona, working on soil erosion and watershed management. Soccer is his main entertainment. Hala Madrid! Country music is his favorite.


Ying Zhao is a new graduate student from Fujian, China working on a PhD. in the School of Natural Resources and the Environment, University of Arizona. Ying focused on GIS and remote sensing in her B.S. (2011) in Geographical Information Systems, School of Geography, Beijing Normal University. She participated in projects such as using the spatial analysis to assess the benefits of farmland rearrangement. She continued her Master's degree in Physical Geography and joined the soil erosion group in Beijing Normal University. She helped with the first Soil and Water Conservation Survey in China, including data management and design of the thematic maps. She is now studying for her PhD in the program of Watershed Management and Ecohydrology in the University of Arizona. Her research will be focusing on stochastic rainfall generator in soil erosion models. She works with Mark Nearing at SWRC.

Papers Published in 2014/5

Nichols, M.H,, Steven, J., Sargent, R., Dille, P., Schapiro, J. 2013. Very-high-resolution time-lapse photography for plant and ecosystems research. Applications in Plant Sciences 1(9):1300033.

Nelson, E., Kareiva, P., Ruckelshaus, M., Arkema, K., Geller, G., Girvetz, E., Goodrich, D.C., Matzek, V., Pinsky, M., Reid, W., Saunders, M., Semmens, D., Tallis, H. 2013. Climate change's impact on key ecosystem services and the human well-being they support in the US. Frontiers in Ecology and the Environment. 11(9): 483-493.

Hamerlynck, E.P., Scott, R.L., S?nchez-Ca?ete, 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.

Niu, G.Y., Troch, P.A., 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. DOI: 10.1002/eco.1405

Niu, G., Paniconi, C., Troch, P.A., 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. DOI: 10.1002/eco.1362

Flores Cervantes, J., Istanbulluoglu, E., Vivoni, E., Holifield Collins, C., Bras, R. 2014. A geomorphic perspective on terrain-modulated organization of vegetation productivity: Analysis in two semiarid grassland ecosystems in Southwestern United States. Ecohydrology. 7: 242-257.d

Langhans, C., Govers, G., Diels, J., Stone, J.J., Nearing, M.A. 2014. Modelling scale-dependent runoff generation in a small semi-arid watershed accounting for rainfall intensity and water depth. Advances in Water Resources. 69: 65-78.

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.P.C., Starks, P.J. 2014. Functional response of U.S. grasslands to the early 21st century drought. Ecology 95(8): 2121-2133.

Polyakov, V., Nichols, M., McClaran, M., Nearing, M.A. 2014. Effect of check dams on runoff, sediment yield and retention on small semi-arid watersheds. Journal of Soil and Water Conservation. 69:414-421.

Sugg, Z., Finke, T., Goodrich. D.C., Moran, M.S., Yool, S.R. 2014. Mapping Impervious Surfaces Using Object-oriented Classification in a Semiarid Urban Region. Photogrammetric Engineering & Remote Sensing. 80(4): 343-352.

Gaunter, L., Zhang, Y., Jung, M., Joiner, J., Voight, M., Berry, J., Frankenberg, C., Huete, A., Zarco-Trejada, P., Lee, J-E, Moran, M.S., once Campos, G., Beer, C., Camps-Valls, G., Buchmann, N., Gianelle, D., Klumpp K., Cescatti, A., Baker, J., Griffis, T. 2014. Global and time-resolved monitoring of crop photosynthesis with chlorophyll fluorescence. Proceedings of the National Academy of Sciences. Doi: 10.1073/pnas.1320008111

Nichols, M.H., Anson, E.L., Keefer, T.O. 2014. Uncertainty in measuring runoff from small watersheds using instrumented outlet-ponds. Transactions of the ASABE. 57(3): 851-859.

Barron-Gafford, G.A., Cable, J.M., Bentley, L.P., Scott, R.L., Huxman, T.E., Jenerette, G.D., Ogle, K. 2014. Quantifying the timescales over which exogenous and endogenous conditions affect soil respiration. New Phytologist. 202: 442-454. doi: 74310.1111/nph.12675

Stillman, S., Ninneman, J., Zeng, X., Franz, T., Scott, R.L., Shuttleworth, W.J., Cummins, K. 2014. Summer soil moisture spatiotmporal variability in Southeastern Arizona. Journal of Hydrometeorology. 15:1473-1485.

Scott, R.L., Huxman, T.E., Barron-Gafford, G., Jenerette, G.D., Young, J.M., Hamerlynck, E.P. 2014. When vegetation change alters ecosystem water availability. Global Change Biology. 20: 2198-2210.

Zhang, X., Moran, M.S., Zhao, X., Liu, S., Zhou, T., Ponce Campos, G.E. 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.

Weltz, M.A., Speath, K., Taylor, M.H., rollins, K., Pierson Jr., F.B., Jolley, L., Nearing, M.A., Goodrich, D.C., Hernandez, M., Nouywakpo, S., Rossi, C. 2014. Cheatgrass invasion and woody species encroachment in the Great Basin: benefits of conservation. Journal of Soil and Water Conservation. 69(2):39A-44A.

Templeton, R.D., Vivoni, E.R., Mendez-Barroso, L.A., Pierini, N.A., Anderson, C.A., Rango, A., Lalivberte, A.S., Scott, R.L. 2014. High-resolution characterization of a semiarid watershed: Implications on evapotranspiration estimates. Journal of Hydrology. 509, 306-319. doi: 73910.1016/j.jhydrol.2013.11.047

Al-Hamdan, O.Z., Hernandez, M., Pierson Jr., F.B., Nearing, M.A., Williams, C.J., Stone, J.J., Boll, J., Weltz, M.A. 2014. Rangeland Hydrology and Erosion Model (RHEM) enhancements for applications on disturbed rangelands. Hydological Processes. DOI: 10.1002/hyp.10167.

Xiao, J., Ollinger, S.., Frokling, S., Hurtt, G.C., Hollinger, Y., Davis, K.J., Pan, Y., Zhang, X.., Deng, F., Chen, J., Baldocchi, D.D., Law, B., Arain, M.A., Desai, A.R., Richardon, A.D., Sun, G., Amiro, B., Margolis, H., Gu, L., Scott, R.L., Blaken, P.D., Suyker, A.E. 2014. Data-driven diagnosticsof terrestrial carbon dynamics over North America. Agricultural and Forest Meteorology 197: 142-157.

Sanches Oliveira, P.T.S., Nearing, M.A., Moran, M.S., Goodrich, D.C., Wendland E., Gupta, H.V. 2014. Trends in water balance components across the Brazilian Cerrado. Water Resources Research. 50(9): 7100-7114.

Nguyen, U., Glenn, E., Nagler,P.L., Scott, R.L. 2014. Long-term decrease in satellite vegetation indices in response to environmental variables in an iconic desert riparian ecosystem: the Upper San Pedro, Arizona, USA. Ecohydrology. 8: 610-625

Garbrecht, J.D., Nearing, M.A., Shields Jr., F.D., Tomer, M.D., Sadler, E.J., Bonta, J.V., Baffaut, C. 2014. Impact of Weather and Climate Scenarios on Conservation Assessment Outcomes. J. Soil and Water Conservation. 69:374-392.

Guber, A.K., Pachepsky, Y.A., Yakirevich, A.M., 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.

Holifield Collins, C., Stone, J.J., Cratic III, L. 2015. Runoff and sediment yield relationships with soil aggregate stability for a state-and-transition model in southeastern Arizona. Journal of Arid Environments. 117: 96-103.

Hottenstein, J.D., Ponce-Campos, G.E., Yanes, J.M., Moran, M.S. 2015. Impact of varying storm intensity and consecutive dry days on grassland soil moisture. Journal of Hydrometeorology. 16:106-117.

Moran, M.S., Doorn, B., Escobar, V., Borwn, M. 2015. Connecting NASA science and engineering with earth science applications. Journal of Hydrometeorology. 16:473-483

Glenn, E., Scott, R.L., Nguyen, U., Nagler, P.L. 2015. Wide-area ratios of evapotranspiration to precipitation in monsoon-dependent semiarid vegetation communities. Journal of Arid Environments. 117: 84-95.

Norman, L.M., Brinkerhoff, F., Gwilliam, E., Guertin,D.P., Callegary, J., Goodrich, D.C., Goodrich, D.C., Nagler, P.L., Gray, F. 2015. Hydrologic response of streams restored with check dams in the Chiricahua Mountains. River Research and Applications. 1: 1-11.

Sanchez-Cohen, I., D?az-Padilla, G., Velasquez-Valle, M., Slack, D.C., Heilman, P., Pedroza-Sandoval, A. 2015. A decision support system for rainfed agricultural areas of Mexico. Computers and Electronics in Agriculture. 114:178-188.

Oliveira, P.T.S., 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.

Wagle, P., Xiao, X., Scott, R.L., Kolb, T.E., Cook, D.R., Brunsell, N., Baldocchi, D.D., Basara, J., Matamala, R., Zhou, Y., Bajgain, R. 2015. Biophysical controls on carbon and water vapor fluxes across a grassland climatic gradient in the United States. Agricultural and Forest Meteorology 214-215: 393-305

Polyakov, V.O., Nearing, M.A., Stone, J.J., Holifield Collins, C., Nichols, M.H. 2015. Quantifying decadal-scale erosion rates and their short-term variability on ecological sites in a semi-arid environment. Catena. 137:501-507.

Alexander .C., Autrey, B., DeMeester, J., Fritz, K., Goodrich, D.C., Kepner, W.G., Lane, C.R., LeDuc, S.D., Leibowitz,S.G., McManus, M., Pollard, A., Ridley, C.., Schofield, K., Wigington, P.J. 2015. Connectivity and effects of streams and wetlands on downstream waters: A review and synthesis of the scientific evidence. EPA/600-R-14/475F, 408 pp.

Garbrecht, J.D., Nearing, M.A., Shields Jr., F.D., Tomer, M.D., Sadler, E.J., Bonta, J.V., Baffaut, C. 2014. Impact of Weather and Climate Scenarios on Conservation Assessment Outcomes. J. Soil and Water Conservation. 69:374-392. doi:10.2489/jswc.69.5.374

Rainfall Report

Walnut Gulch Precip 2014
Santa Rita Precip 2014
Audubon Precip 2014
WGEW and SRER data can be downloaded from the web site at
Geographic locations of the three precipitation records can be found at/ARSUserFiles/20221000/images/sw_az3.jpg



SWRC Bulletin:

Contact the SWRC Research Leader, Dr. Phil Heilman at 520-647-9202 or Mailing address is USDA ARS SWRC, 2000 E. Allen Rd., Tucson, AZ 85719 and web address is The SWRC Bulletin is online at /News/News.htm?modecode=20-22-10-00.



SWRC Mission:

To develop knowledge and technology to conserve water and soil in semi-arid lands.

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