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SWRC Bulletin (Winter 2013)
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The SWRC Bulletin

Sound Science for Water Decisions

Winter 2013 


Monthly Downloads Chart

For a number of years the Southwest Watershed Research Center publications have been available for download on our website. Since late 2006 we have been tracking the number of times each publication is downloaded (see figure). To prepare the figure, we removed the downloads from within the SWRC itself, as well as from locations that identified themselves as "spiders" with the goal of indexing websites, and a few spikes where a single location appeared to download all of our publications in a single day. The numbers in the figure are surprisingly high, apparently because our publications have been indexed by a number of search engines. The numbers in the figure probably overstate readership, as some publications may have been downloaded but not read, read for classwork, or downloaded multiple times by the same person. On the other hand, these numbers also understate readership, as most readers probably access papers through the original journal or that National Agricultural Library rather than our website. As of the end of 2012, we had 1312 publications (not including abstracts). Throughout 2012 the daily average of SWRC publicaitons downloaded was 1470, with 63% of the requests coming from outside the US. The five countries that downloaded the most publications are, in order: United States, India, China, United Kingdom, and Canada. The five most downloaded publications were primarily related to simulation models, as can be seen in the table below:


Titles and Authors of the 5 Most Downloaded SWRC Publications in 2012



1.) KINEROS, a Kinematic Runoff and Erosion Model; Woolhiser, Smith, Goodrich


2.) A Process-Based Soil Erosion Model for USDA-Water Erosion Prediction Project Technology;Nearing, Foster, Lane, Finkner


3.) RUSLE, Revised Universal Soil Loss Equation; Renard, Foster, Weesies, Porter


4.) Expected Climate Change Impacts on Soil Erosion Rates: A Review; Nearing, Pruski, O'Neal


5.) Normal Depth Calculations in Complex Channel Sections; Shirley, Lopes


Science highlight:

Moran, M.S., Scott, R.L., Hamerlynck, E.P., Green, K.N., Emmerich, W.E., Holifield Collins, C.D., 2009. Soil evaporation response to Lehmann lovegrass (Eragrostis lehmanniana) invasion in a semiarid watershed. Agric. For. Meteorol. 149, 2133-2142, doi:10.1016/j.agrformet.2009.03.018.

Polyakov, V.O., Nearing, M.A., Stone, J.J., Hamerlynck, E.P., Nichols, M.H., Holifield Collins, C.D., Scott, R.L., 2010. Runoff and erosional responses to a drought-induced shift in a desert grassland community composition. J. Geophys. Res. [Biogeo.] 115, G04027, doi:10.1029/2010JG001386

Scott, R.L., Hamerlynck, E.P., Jenerette, G.D., Moran, M.S., Barron-Gafford, G.A., 2010. Carbon dioxide exchange in a semidesert grassland through drought-induced vegetation change. J. Geophys. Res. 115, G03026, doi:10.1029/2010JG001348

Note of January Cold Snap

Scientists at SWRC are excited to see how the recent January 2013 cold snap will affect ecosystem processes in southern Arizona. Our last major cold snap, in February 2011, caused some remarkable changes out at our Kendall Watershed in Walnut Gulch Experimental Watershed.

In 2011, much of the semidesert grassland at Kendall was dominated by the exotic Lehmanns lovegrass, which became dominant across the Kendall watershed in 2007 after the protracted and extreme drought in the early 2000's. Lovegrass invasion had wide-spread ecohydrological consequences like 1) increased seasonal water loss via soil evaporation (Moran et al., 2009), 2) enhanced carbon uptake under dry conditions after Lehmanns established (Scott et al., 2010), and 3) high erosion and watershed sediment-yield during the transition from native to exotic grass dominance(Polyakov et al., 2010) that have been documented by SWRC scientists.

The cold snap of February 1 - 5, 2011 produced a record low of -16.2 deg C and two days below freezing (see figure). This event, coupled with very dry winter conditions, resulted in widespread lovegrass mortality across the watershed (77.5% of all lovegrass dead) with the remaining native bunchgrasses (mostly side oats grama, curly mesquite, and black grama) faring much better (40.9% mortality). Re-sampling of our long-term vegetation transects at rain gauge 82 reflected the decline of the exotic lovegrass, and showed a marked rebound in native bunchgrass contributions to total plant cover. Widespread grass mortality also resulted in enhanced decomposition, producing a respiratory efflux of carbon dioxide and a subsequent diminishment of summer growing season productivity that was detectable by our eddy covariance tower. These results are summarized from a manuscript by Erik Hamerlynck and others now in peer-review

The recent January 2013 cold snap wasn't as cold as in 2011, but lasted considerably longer (see figure). Scientists at SWRC will be eagerly watching (and measuring) to see what happens next. Who said watching the grass grow wasn't exciting?

Latest Science Results (not yet published)

Rainfall Erosivity in Brazil:  A Review

Loss of ecosystem resilience under large-scale altered hydroclimatic condition


Estimating crop biophysical properties from remote sensing data by inverting linked radiative transfer and ecophysiological models


Assimilating Remote Sensing Observations of Leaf Area Index and Soil Moisture for Wheat Yield Estimates: An Observing System Simulation Experiment


Time-Lapse Very High Resolution Photography in Rangeland Ecosystem Research


Response of terrestrial ecosystem production to extreme precipitation and temperature regimes across biomass


Controls on the spacing and geometry of rill networks on hillslopes: Rainsplash detachment, initial hillslope roughness, and the competition between fluvial and colluvial transport



Using remote sensing and eddy covariance data to determine evapotranspiration across a water-limitation gradient

KINEROS2/AGWA: Model Use, Calibration, and Validation

Assessing Satellite-Based Rainfall Estimates in Semi-Arid Watersheds Using the USDA-ARS Walnut Gulch Gauge Network and TRMM-PR

Uncertainties in the measurement of ecosystem carbon dioxide exchange due to differences in infrared gas analyzer response

Antecedent conditions influence soil respiration differences in shrub and grass patches

Evaluating the effect of rainfall variability on vegetation establishment in a semidesert grassland

Model enhancements for urban runoff predictions in the South-West United States 

Chapter 2: A synthesis framework for runoff predictions in ungauged basins

Consequences of cool-season drought induced plant mortality to Chihuahuan Desert grassland ecosystem and soil respiration dynamics

Water supply to the arid pastures of Kazakhstan's Balkhash region     


A geomorphic perspective on terrain-modulated organization of vegetation productivity:  Analysis in two semiarid grassland ecosystems in Southwestern United States

Assessing site-specific PRISM precipitation and temperature estimates for rangeland management in the Southwest


Runoff and sediment yield relationships with soil aggregate stability for a State - and- Transition model in Southeastern Arizona

Application of a rangeland soil erosion model using NRi data in southeastern Arizona

Papers Published in 2012:

Cable, J.M., Barron-Gafford, G.A., Ogle, K., Pavao-Zuckerman, M., Scott, R.L., Williams, D.G., Huxman, T.E. 2012. Shrub encroachment alters sensitivity of soil respiration to temperature and moisture. Journal of Geophysical Research. 117:1-11. (380 KB PDF)


Burba, G., Schmidt, A., Scott, R.L., Nakai, T., Kathilankal, J., Fratini, G., Hanson, C., Law, B., McDermitt, D.K., Eckles, R., Furtaw, M., Velgersdyk, M. 2012. Calculating CO2 and H2O eddy covariance fluxes from an enclosed gas analyzer using an instantaneous mixing ratio. Global Change Biology. 18:385-399. (1.27 MB PDF)


Heilman, P., Malone, R.W., Ma, L., Hatfield, J., Ahuja, L., Boyle, K., Kanwar, R. 2012. Extending results from agricultural fields with intensively monitored data to surrounding areas for water quality management. Agricultural Systems. 106:59-71. (938 KB PDF)


Krishnan, P., Meyers, T., Scott, R.L., Kennedy, L., Heuer, M. 2012. Energy exchange and evapotranspiration over two temperate semi-arid grasslands in North America. Agricultural and Forest Meteorology. 153:31-44. (1008 KB PDF)


Guber, A.K., Pachepsky, v., Yakirevich, A., Shelton, D.R., Sadeghi, A.M., Goodrich, D.C., Unkrich, C.L. 2011. Uncertainty in modelling of faecal coliform overland transport associated with manure application in Maryland. Hydrological Processes. 25:2393-2404. (319 KB PDF)


Barron-Gafford, G.A.1, Scott, R.L., Jennerette, G.D., Hamerlynck, E.P., Huxman, T.E. 2012. Temperature and precipitation controls over leaf- and ecosystem--level CO2 flux along a woody plant encroachment gradient. Global Change Biology, 18, 1389-1400. (313 KB PDF)


Ross, I., Mission, L., Ramnbal, S., Arneth, A., Scott, R.L., Carrara, A., Cescatti, A., Genesio, L. 2012. How do variations in the temporal distribution of rainfall events affect ecosystem fluxes in seasonally water-limited Northern Hemisphere shrublands and forests?. Biogeosciences, 9, 1007-1024. doi:10.5194/bg-9-1007-2012. (1.50 MB PDF)


Nearing, G.S., Moran, M.S., Scott, R.L. 2012. Coupling diffusion and maximum entropy models to estimate thermal inertia. Remote Sensing of Environment. 119:222-231. (2.80 MB PDF)


Wilcox, B.P., Turnbul, L., Young, M.H., Williams, J., Ravi, S., Seyfried, M.S., Bowling, D.R., Scott, R.L., Germino, M.J., Caldwell, T., Wainwright, J. 2012. Invasion of shrubands by exotic grasses: Ecohydrological consequences in cold vs. warm deserts. Ecohydrology. 5:160-173. (452 KB PDF)


Miller, G.R., Cable, J.M., McDonald, A.K., Bond, B., Franz, T.E., Wang, L., Gou, S., Tyler, A.P., Zou, C.B., Scott, R.L. 2012. Understanding ecohydrological connectivity in savannas: A system dynamics modelling approach. Ecohydrology. 5: 200-220. (1.88 MB PDF)


Scott, R.L., Serrano-Ortiz, P., Domingo F., Hamerlynck, E.P., Kowalski, A.S. 2012. Commonalities of carbon dioxide exchange in semiarid regions with monsoon and Mediterranean climates. J. of Arid Enviroments. 84:71-79. (1.14 MB PDF)


Thorp, K.R., Wang, G., Westg, A.L., Moran, M.S., Bronson, K.F., White, J.W., Mon, J. 2012. Estimating crop biophysical properties from remote sensing data by inverting linked radiative transfer and ecophysiological models. Remote Sensing of Environment. 124:224-233. (1.01 MB PDF)


Hutton, C., Brazier, R., Nicholas, A., Nearing, M.A. 2012. On the effects of improved cross-section representation in one dimensional flow routing models applied to ephemeral rivers. Water Resources Research. 48: 1-11. (923 KB PDF)


Al-Hamdan, O.Z., Pierson Jr., F., Nearing, M.A., Stone, J.J., Williams, C., Moffet, C.A., Kormos, P.R., Boll, J., Weltz, M.A. 2012. Characteristics of concentrated flow hydraulics for rangeland ecosystems: implications for hydrologic modeling. Earth Surface Processes and Landforms. 37(2): 157-168. (927 KB PDF)


Yan, H., Wang, S.Q., Billesbach, D., Oechel, W., Zhang, J., Meyers, T., Martin, T.A., Matamala, R., Baldocchi, D., Bohrer, G., Dragoni, D., Scott, R.L. 2012. Global estimation of evapotranspiration using a leaf area index-based surface energy and water balance model. Remote Sensing of Environment 124: 581-595. (2.07 MB PDF)


Wei, H., Heilman, P., Qi, J., Nearing, M.A., Zhihui, G., Zhang, Y. 2012. Assessing phenological change in China from 1982 to 2006 using AVHRR imagery. Frontiers of Earth Science. 6(3): 227-236. DOI 10.1007/s11707-012-0321-3 (10.1 MB PDF)


Lebed, L., Qi, J., Heilman, P. 2012. An ecological assessment of pasturelands in the Balkhash area of Kazakhstan with remote sensing and models. Environmental Research Letters. 7: 1-8. (1.92 MB PDF)


Kareiva, P., Ruckelshaus, M., Arkema, K., Geller, G., Girvetz, E., Goodrich, D.C., Nelson, E., Matzek, V., Pinsky, M., Reid, W., Saundersm M., Semmens, D., Tallis, H. 2012. Impacts of Climate Change on Ecosystem Services. Impacts of Climate Change on Biodiversity, Ecosystems, and Ecosystem Services: Technical Input to the 2013 National Climate Assessment. Cooperative Report to the 2013 National Climate Assessment. 296 p. (9.93 MB PDF)


Hagen, S.C., Heilman, P., Marsett, R., Torbick, N., Saas, W., Ravensway, J., Qi, J. 2012. Mapping Total Vegetation Cover Across Western Rangelands With Moderate-Resolution Imaging Spectroradiometer Data. Rangeland Ecology & Management. 65(5): 456-467. (979 KB PDF)


Nichols, M.H., McReynolds, K., Reed, C. 2012. Short-term variations in rangeland soil moisture in response to low-tech erosion control structures. Catena. 98: 104-109. (494 KB 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)


Reike-Zapp, D., Nichols, M.H. 2011. Headcut retreat in a semiarid watershed in the southwestern United States since 1935. Catena. 87: 1-10. (2.14 MB PDF)


Goodrich, D.C., Unkrich, C.L., Smith, R.E., Guertin, D.P., Hernandez, M., Burns, I.A., Massart, J., Levick, L., Miller, S.N., Semmens, D., Kepner,W.G. 2010. THE AGWA - KINEROS suite of modeling tools. American Society of Civil Engineers Water Resources Conference Proceedings. (1.90 MB PDF)

SWRC News:

We have started a review of the SWRC publication list to better understand, from a long-term perspective, what our most significant contributions have been. The original thought was to identify the most significant 1% of our publications, but as we got into the list, it seemed that many of the publications were of incomparable types, and it was difficult to settle on just 1% of the over 1300 publications. Consequently, we revised our objective to select the top 15 publications in each of 3 categories. The top 15 Manuals, Reports, and Bulletins published by the SWRC are shown via this LINK. The list includes a diverse mix through time and provides a feel for the research topics we have addressed. The other two lists will include first, Books, Handbooks and Conference Proceedings, and second, individual papers.

One of those user manuals is for AGWA, the Automated Geospatial Watershed Assessment tool developed by the SWRC in cooperation with the EPA Office of Research and Development Landscape Ecology Branch.  AGWA uses widely available standardized spatial datasets that can be obtained via the internet. The data are used to develop input parameter files for two watershed runoff and erosion models: KINEROS2 and SWAT. Using digital data in combination with the automated functionality of AGWA greatly reduces the time required to use these two watershed models.  AGWA is publicly available for download from our site: There were over 7,000 visitors to the website just in the last year!


Rainfall Report:

Walnut Gulch rainfall report 2012

Santa Rita rainfall report 2012
Audubon rainfall report 2012

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




Hydraulic Engineer Ken Renard, who retired from the ARS Southwest Watershed Research Center, Tucson, AZ, is being recognized by the Soil and Water Conservation Society (SWCS) with its highest honor, the Hugh Hammond Bennett Award.  In addition, Ken received the Royce J. Tipton Award from the American Society of Civil Engineers, its most prestigious award in water resources.  The award citation reads: "For significant contributions to the advancement of soil and water managemnet in arid regions through research, technology transfer and public service." Congratulations Ken, you deserve this recognition!

We are also happy to report that Carl Unkrich was recognized as the 2012 Support Scientist of the Year in the Pacific West Area!

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.