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SWRC Bulletin (Winter 2014)
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The SWRC Bulletin
Sound Science for Water Decisions

Winter 2014 

NASA satellite rainfall estimates

Long-term data from Walnut Gulch Experimental Watershed validates NASA satellite-based rainfall estimates. 

Water is a critical resource in rapidly developing arid and semiarid regions.  Accurate rainfall estimates are essential to effective management of agricultural production and associated water resources, but in many parts of the world, rugged terrain limits the deployment of rain gauges, while simultaneously blocking ground-based radar estimates of rainfall.  Working with colleagues from the National Aeronautics and Space Administration (NASA), ARS researchers in Tucson, Arizona, compared rain gauge observations from the densely instrumented ARS Walnut Gulch Experimental Watershed, with rainfall intensity estimates from the Tropical Rainfall Measurement Mission (TRMM) satellite for the period 1999 to 2010.  Results showed a very good agreement between the two sets  of rainfall rate estimates, an important finding because rainfall is not well measured over large parts of the globe, and the satellite design is the basis for NASA's new Global Precipitation Mission.  In addition to underscoring the importance of ARS long-term research sites and the data sets they enable, the validation presages success for the new NASA mission.  Among other benefits, the significance of quantifying precipitation worldwide has important implications for improving the world's capacity for food production in light of expected population growth and climatic uncertainty.


Amitai, E., Unkrich, C.L., Goodrich, D.C., Habib, E., Thill, B. 2012. Assessing Satellite-Based Rainfall Estimates in Semi-Arid Watersheds Using the USDA-ARS Walnut Gulch Gauge Network and TRMM-PR. Journal of Hydrometeorology. 13(5): 1579-1588.

Science Events:

WGEW 60th Anniversary! The USDA-ARS began conducting research and collecting hydrologic data at the Walnut Gulch Experimental Watershed in 1953 to better understand semi-arid soil and water processes and improve conservation science. We look forward to celebrating the 60th anniversary with a series of workshops, tours, and a banquet in Tombstone, AZ. We will highlight our research findings and introduce the Rangeland Hydrology and Erosion Model (RHEM), an erosion model developed specifically for rangelands, to Arizona's rangeland conservation community. There is no registration cost.  Activities include:

? Tours of the 58 square mile experimental watershed including instrumentation, rainfall simulation, evapotranspiration measurements, and rangeland conservation practices.

? Workshops introducing the new Rangeland Hydrology and Erosion Model that will include field visits to review measured erosion rates and collect data to run the model as well as hands-on sessions with the model.

? Field discussion of upland erosion control in semiarid watersheds.

We promise it will be a "watershed event". We hope to see you there!



Check out our two videos to learn about the important research and modeling at our research center, and to promote further collaboration with local landowners and ranchers, local government, university partners, and other state, federal and international scientists and agencies. 

••         One video offers a research overview of work at the USDA ARS Southwest Watershed Research Center in Tucson, AZ, to develop knowledge and technology to conserve water and soil in semi-arid lands. 

••         The second video celebrates the 60th anniversary of research and data collection at our instrumented outdoor laboratory, the Walnut Gulch Experimental Watershed (WGEW), near Tombstone, AZ.

Here's the SWRC Youtube channel:

Version 3.0 of AGWA - The Automated Geospatial Watershed Assessment tool was released in Nov. 2013.  AGWA was used by Burn Area Emergency Response (BAER) team for rapid post-fire watershed assessment on numerous wildfires in California, Washington, Idaho, and New Mexico during the 2013 fire season. The latest version of the software can be found at


We are approaching the 11th Annual Research Insights in Semiarid Environments (RISE) conference.  It will be scheduled for October 2014 at University of Arizona.  Announcements will be forthcoming, but you can check out last year's posters and presentations at


Latest Science Results (not yet published)

Modeling scale-dependent runoff generation in a small semi-arid watershed accounting for rainfall intensity and water depth

Changes in the functional response of U.S. grasslands to the Early 21st Century Drought

Coupling the Kinematic Erosion and Runoff (KINEROS) and hillslope-storage Boussinesq Soil Moisture (hsB-SM) Models for Operational Flash Flood Forecasting.

An overview of the water balance in the Brazilian Cerrado

Effect of check dams on runoff, sediment yield and retention on small semi-arid watersheds

Suspended sediment transport at the instantaneous and event time scales in semi-arid watersheds of southern Arizona, USA

Ecosystem CO2 exchange in response to nitrogen and phosphorus addition in a restored, temperate grassland

Key ecosystem services that are being disrupted by climate change in the United States

Using long-term datasets to study exotic plant invasions on rangelands in the western United States

Landscape and environmental controls over leaf and ecosystem carbon dioxide fluxes under woody plant expansion

Estimating riparian and agricultural evapotranspiration by reference evapotranspiration and MODIS Enhanced Vegetation Index

Mapping Impervious Surfaces Using Object-oriented Classification in a Semiarid Urban Region

Modeling evapotranspiration and its partitioning over a semiarid shrub ecosystem from satellite imagery: a multiple validation.

Investigating Historic Parcel Changes to Understand Land Use Trends: A Methodology and Application for the San Pedro River Watershed 

Developing a basin-wide evapotranspiration map of the Colorado River Basin at the LANDSAT scale for water use assessment

Nocturnal soil CO2 uptake and its relationship to sub-surface soil and ecosystem carbon fluxes in a Chihuahuan Desert shrubland

Investigating Historic Parcel Changes to Understand Land Use Trends: A Methodology and Application for the San Pedro River Watershed      

Projecting avian guild responses to restoration scenarios on a large dryland river (middle Rio Grande, New Mexico, U.S.A.)

Optimum irradiance level for detecting crop water deficit with chlorophyll fluorescence

Spaceborne Fluorescence Measurements Provide a Global Perspective on Agricultural Productivity

Measurement uncertainty in small watershed outlet-pond runoff

Curve Number estimation from rainfall-runoff data to the Brazilian Cerrado

Quantifying the time scales over which exogenous and endogenous conditions affect soil respiration

Land surface controls on afternoon precipitation diagnosed from observational data: Uncertainties, confounding factors and the possible role of vegetation interception

Summer soil moisture spatiotemporal variability in Southeastern Arizona

When vegetation change alters ecosystem water availability

Impact of prolonged drought on rainfall use efficiency across China in the early 21st century

Long-term decrease in satellite vegetation indices in response to environmental variables in an iconic desert riparian ecosystem: the Upper San Pedro, Arizona, USA

Papers Published in 2013:


Hamerlynck, E.P., Scott, R.L., Barron-Gafford, G.A. 2013. Consequences of cool-season drought induced plant mortality to Chihuahuan Desert grassland ecosystem and soil respiration dynamics. Ecosystems. 16: 1178-1191. DOI: 10.1007/s10021-013-9675-y (626 KB PDF)

Kennedy, J.R., Goodrich, D.C., Unkrich, C.L. 2013. Using the KINEROS2 Modeling Framework to Evaluate the Increase in Storm Runoff from Residential Development in a Semi-Arid Environment. J. Hydrologic Engineering. 18:698-706. (2.19 MB PDF)

Nichols, M.H., Nearing, M.A., Poyakov, V.O., Stone, J.J. 2013. A sediment budget for a small semiarid watershed in southeastern Arizona, USA. Geomorphology. 180-181:137-145. (1.75 MB PDF)

Poyakov, V., Nearing, M.A., Hawdon, A.A., Wilkinson, S.N., Nichols, M.H. 2013. A comparison of two stream gauging systems for measuring runoff and sediment yield on semi-arid watershed. Earth Surface Processes and Landforms. 38: 383-390. (429 KB PDF)

Cerd?, A., Brazier, R., Nearing, M.A., de Vente, J. 2013. Scales and Erosion. Catena. 102: 1-2. (117 KB PDF)

Guzm?n, G., Quinton, J., Nearing, M.A., Mabit, L., G?mez J.A. 2013. Sediment tracers in water erosion studies: Current approaches and challenges. Journal of Soils and Sediments. 13:816-833. (504 KB PDF)

Ponce Campos, G., Moran, M.S., Huete, A., Zhang, Y., Bresloff, C., Huxman, T.E., Eamus, D., Bosch, D., Buda, A.R., Gunter, S.A., Scalley, T.H., Kitchen, S.G., McClaran, M., McNab, W.H., Montoya, D.S., Morgan, J. A., Peters, D.C., Sadler, E.J., Seyfried, M.S., Starks, P.J. 2013. Ecosystem resilience despite large-scale altered hydro climatic conditions. Nature. 494: 349-352. (2.14 MB PDF)

Sanches Oliveira, P., Wendland, E., Nearing, M.A. 2013. Rainfall erosivity in Brazil: A Review. Catena 100:139-147. (858 KB PDF)

McGuire, L.A., Pelletier, J.D., Gomez, J., Nearing, M.A. 2013. Controls on the spacing and geometry of rill networks on hillslopes: Rainsplash detachment, initial hillslope roughness, and the competition between fluvial and colluvial transport. J Geoohysical Research: Earth Surface 118: 241-256. (3.0 MB PDF)

Zhang, Y., Moran, M.S., Nearing, M.A., Ponce Campos, G.E., Huete, A., Buda, A.R., Bosch, D.D., Gunter, S.A., Kitchen S.G., McNab, W.H., Morgan, J.A., McClaran, M.P., Montoua, D.S., Peters, D.C., Starks, P.J. 2013. Extreme precipitation patterns reduced terrestrial ecosystem production across biomes. Journal of Geophysical Research - Biogeosciences. 118: 148-157. doi: 10.1029/2012JG002136. (482 KB PDF)

Brown, M.E., Escobar, V., Moran, M.S., Entekhabi, D., O'Neil, P., Njoku, E.G., Doorn, B., Entin, J.K. 2013. NASA's Soil Moisture Active Passive (SMAP) Mission and opportunities for applications. Bulletin American Meteorolgical Society. 94:1125-1128. doi: (1.20 MB PDF)

Fehmi, J., Niu, G.Y., 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 (225 KB PDF)

Brand, A., Dixon, M.D., Fetz, T., Stewart, S., Brookshire, D., Stromberg, J.C., Goodrich., D.C., Graber, G., Benedict, K., Thacher, J., Broadbent, C. 2013. Projecting avian responses to landscape management along the middle Rio Grande, New Mexico. The Southwestern Naturalist. 58(2):150-162. 2013. (481 KB PDF)

Gao, P., Nearing, M.A., Commons, M. 2013. Suspended sediment transport at the instantaneous and event time scales in semi-arid watersheds of southeastern Arizona, USA. Water Resources Research. 49: 1-14. doi:10.1002/wrcr.20549 (.97 MB PDF)

Morris, C.E., Morris, L., Leffler, J.A., Holifield Collins, C., Forman, A.D., Weltz, M.A., Kitchen S.G. 2013. Using long-term datasets to study exotic plant invasions on rangelands in the western United States. Journal of Arid Environments. 95: 65-74. (921 KB PDF)

Barron Gafford, G.A., Scott, R.L., Jenerette, G.D., Hamerlynck, E.P., Huxman, T.E. 2013. Landscape and environmental controls over leaf and ecosystem carbon dioxide fluxes under woody plant expansion. Journal of Ecology. 101:1471-1483. doi: 10.1111/1365-2745.12161 (1 MB PDF)

Nagler, P.L., Glenn, E.P., Nguyen U., Scott, R.L., Doody, T. 2013. Estimating riparian and agricultural evapotranspiration by reference evapotranspiration and MODIS Enhanced Vegetation Index. Remote Sensing. 5: 3849-3871. doi:10.3390/rs5083849. (1.97 MB PDF)

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. 7: 1-16. doi: 10.1117/1.JRS.7.073495. (3 MB PDF)

Ascough II, J.C., Flanagan, D.C., Nearing, M.A., Engel, B.A. 2013. Sensitivity and first-order/Monte Carlo uncertainily analysis of the WEPP Hillslope Erosion Model. Transactions of the ASABE. 56(2): 437-452. (544 KB PDF)

Al-Hamdan, O., Pierson Jr., F.B., Nearing, M.A., Williams, C.J., Stone, J.J., Kormos, P.R., Boll, J., Weltz, M.A. 2013. Risk assessment of erosion from concentrated flow on rangelands using overland flow distribution and shear stress partitioning. Transactions of the ASABE. 56(2):539-548. (627 KB PDF)

Singh, R.K., Senay, G.B., Velpuri, N.M., Bohms, S., Scott, R.L., Verdin, J.P. 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: 233-256. doi: 74110.3390/rs6010233 (4.07 MB PDF)

Stillman.., Zeng, X., Shuttleworth, W.J., Goodrich, D.C., Unkrich, C.L., Zerda, M. 2013. Spatiotemporal Variability of Summer Precipitation in Southeastern Arizona. J. of Hydrometeorology. 14:1944-1951. doi: (854 KB PDF)

Cable, J.M., Ogle, K., Barron-Gafford, G.A., Bentley, L.P., Cable, W.L., Scott, R.L., Williams, D.G., Huxman, T.E. 2013. Antecedent conditions influence soil respiration differences in shrub and grass patches. Ecosystems. 16: 1230-1247. DOI: 10.1007/s10021-013-9679-7 (998 KB PDF)

Staff News:

Congratulations to SWRC Soil Scientist Dr. Chandra Holifield Collins.  We are happy to announce the arrival of little 4lb 14oz Vivyan Grace Collins on December 11, 2013.


New Hires and Retirements


Dr. Jeff Stone retired from the Southwest Watershed Research Center on January 11, 2013 after quarter century of federal service and a decade with the University of Arizona. Jeff was a Hydrologist whose work focused on understanding the processes controlling infiltration on uplands. One can quantify infiltration indirectly on experimental watersheds by measuring the precipitation input and runoff outflow. However, because watersheds integrate the effects of processes occurring across the watershed, it is much better to study these processes over smaller areas (plot scale) under controlled conditions. Jeff performed such studies, first with a rotating boom rainfall simulator and later with a variable intensity simulator, making improvements to both as research tools. Jeff studied the influence of soil and vegetation on infiltration, how the area contributing to runoff changes over the course of a rainfall event, as well as the impact of rainfall intensity on runoff and sediment yield. Jeff's understanding of infiltration and runoff processes was incorporated into the Water Erosion Prediction Project (WEPP) model, used by the Forest Service, and the Rangeland Hydrology and Erosion (RHEM) model. Jeff was unfailingly generous with his time, patiently explaining hydrologic concepts to generations of students, and scientists, working at the SWRC.


Our Ecologist Dr. Erik Hamerlynck was re-assigned to the ARS Range and Meadow Forage Management Research Unit in Burns Oregon in September 2013.  Erik brought a critical new dimension to research at SWRC.  Erik's expertise in dryland ecophysiology of plants helped to disentangle the biotic and abiotic components of water and carbon dioxide exchanges.  Erik was very versatile and creative in his research approach, whether it was with a ruler and tape measure to quantify changing patterns of native and invasive plants, chambers to clamp down on leaves and small plant-soil mesocosms to measure plant photosynthesis, or automated soil chambers to measure soil respiration next to drought-stricken plants.  He made many key contributions including understanding native vs. invasive grass productivity, effects of droughts and severe freezes on ecosystem fluxes, and the role of soil respiration in ecosystem carbon dioxide exchange.  Erik was passionate about desert ecosystems and graciously shared his enthusiasm and knowledge with the SWRC community.  Also, he was super productive as a researcher. Best of luck, Eric!  We will miss you.    


Dr. Russ Scott recently hired a new postdoctoral scientist at SWRC.  Welcome to Joel Biederman, recent Ph.D. from Arizona Department of Hydrology and Water Resources, who will be working with Russ on Ameriflux site studies.


Dr. Moran recently hired 3 bright young scientists to work on multi-location time-series ecohydrology:


Bhaskar Mitra, originally from Calcutta, India has a Mining Engineering background and has completed his PhD in Geography from State University of New York, Buffalo. His PhD research was about the role of plant hydraulics in regulating the spatial autocorrelation of soil respiration across the sagebrush steppe ecosystem in Wyoming. He has previously worked in the Critical Zone research group at University of Arizona on the Ecohydrology and Hydrologic Partitioning theme. 


Morgan Ross received her M.S. in Natural Resources at the University of Arizona with a focus in Watershed Management and Ecohydrology. With SWRC, she is studying the effects of prolonged droughts on grassland productivity. 


Mallory Barnes is a new biological technician at SWRC working for Dr. Susan Moran on a 180-day appointment. She recently received her MS from University of Hawaii in Natural Resource and Environmental Management. She will be looking at spatial patterns in vegetation response to climate variability in different ecosystems in the Southwest.




Congratulations to our recently graduating students!


Maria Pilar Cendrero Mateo completed her PhD program in the UA Dept. of Soil, Water and Environmental Science with advisors Dr. Susan Moran (SWRC) and Shirley Papuga (UA).  Her dissertation was entitled "Study of chlorophyll fluorescence response to water and nitrogen deficit" demonstrating that fluorescence is a reliable indicator of crop stress and has great potential as a tool for better understanding where, when, and how CO2 is exchanged between the land and atmosphere.  Dr. Cendrero Mateo has a postdoctoral position secured at the Forschungszentrum J?lich Research Center in Germany related to photosynthesis and water relations of plants with Dr. Uwe Rascher.   


Sapana Lohani finished her Ph.D. studies at the University of Arizona's School of Natural Resources and the Environment. Her dissertation was entitled "Linking Ecosystem Services

with State-and-Transition Models to Evaluate Rangeland Management Decisions" with Phil Heilman (SWRC) and Phil Guertin (UA) as advisors. Sapana developed a method to assess management practice impacts on vegetation communities and through to runoff and erosion effects on Loamy Upland and Sandyloam Upland sites of the Empire Ranch. She has since joined her husband, who is finishing a Ph.D. in Columbia, MO, and is expecting their first child.


Important Assignments and Visitors


Mark Nearing is serving as an expert on the Agriculture Indicators Technical Team to develop a prototype indicator system for the U.S. Global Change Research Program, National Climate Assessment.  The National Climate Assessment (NCA) is being conducted under the auspices of the U.S. Global Change Research Program (USGCRP), pursuant to the Global Change Research Act of 1990, Section 106, which requires a report to Congress every 4 years ( Part of the vision for the sustained NCA process is a system of indicators that communicate key aspects of the physical climate, climate impacts, vulnerabilities, and preparedness for the purpose of informing both decision makers and the public with scientifically valid information that is useful for decision-making. These indicators will be tracked as a part of ongoing assessment activities, with adjustments as necessary to adapt to changing conditions and understanding.


Dr. Nearing is currently collaborating with 4 visiting scientists from Brazil and China:


Paulo Tarso Sanches de Oliveira received a 9 month fellowship from the S?o Paulo Research Foundation (FAPESP) on "Dynamics of water balance and soil erosion in Cerrado".  He is a Ph.D. Student in Hydraulics and Sanitary Engineering at the S?o Carlos School of Engineering, University of S?o Paulo(EESC-USP), S?o Carlos - SP, Brazil. His research focuses on understanding and improving physical processes associated with the hydrology and soil erosion. He has worked with different scales (plots, hillslope, watershed and continent) and using data from experimental field, laboratory, and remote sensing.


Xiaowu He is a professor at Jiangxi Agricultural University in Nanchang, Jiangxi Province, China. His research area is soil erosion and conservation. He will be with us as a visiting scholar for 6 months. Financial assistance for this trip was provided by China Scholarship Council (CSC), which is a non-profit institution affiliated with the Ministry of Education of the P.R. China.  Xiaowu received his Ph.D. at Beijing Normal University.  He will be working on a project to test spatial and temporal downscling techinques and their impact on erosion prediciton.


Joanito de Andrade Oliveira is a professor of Cartography and Surveying at the Federal University of Bahia Reconcavo (UFRB) in Brazil. The Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES) and UFRB is funding his six month stay with us.  He is currently working on his Ph.D. on cartographic accuracy and its impact on soil erosion model results.

Feng Tengis a Ph.D. student at the Key Laboratory of Agro-ecological Processes in Subtropical Regions, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, China. Teng was awarded a scholarship by the China Scholarship Council for 8 months to work on her Ph.D. research project on soil erosion modeling in karst areas of the Guangxi Province in southern China.


Rainfall Report:

Walnut Gulch 2013 Precip

Santa Rita 2013 precip
Audubon Range 2013 precip

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




Mark Nearing and David Goodrich were part of the EPA Water Quality Climate Assessment Tools Team that was awarded an 2013 EPA Bronze Medal for developing tools, data products, reports and methods geared toward helping water resource managers respond to a changing climate.


David Goodrich was named as a Fellow to the American Geophysical Union in 2013 "For seminal advances in arid and semiarid hydrology and in ecohydrology, interdisciplinary leadership, and communication of science to elected officials."


Russ Scott's energy, carbon and water flux monitoring sites are now partially funded as Ameriflux Core Sites by the Dept. of Energy.  Funding will help offset maintenance costs, provide new equipment for additional field studies, and fund a post-doctoral appointment.


Susan Moran was selected for the NASA Soil Moisture Active Passive (SMAP) Science Team to provide guidance for calibration, validation and utilization of SMAP science data products in preparation for the SMAP launch in November 2014 .


Chandra Holifield Collins was granted funding by the Natural Resources Conservation Service (NRCS) to develop a protocol for using satellite imagery to measure woody vegetation cover throughout the western United States as part of the rangeland Conservation Effects Assessment Project (CEAP) effort to assess conservation practices.


Susan Moran was elected to the American Association for the Advancement of Science (AAAS) Electorate Nominating Committee (ENC) of the Section on Agriculture, Food and Renewable Resources, for a term running from 2013-2016.

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=53-42-45-00.



SWRC Mission:

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