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Science Results (Winter 2015)
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Impact of varying storm intensity and consecutive dry days on grassland soil moisture

Hottenstein, J.D.                     University of Arizona

Ponce-Campos, G.E.               University of Arizona

Yanes, J.M.                             University of Arizona

Moran, M.S.                            Southwest Watershed Research Center


Climates across the world are undergoing unprecedented changes. In the early 21st century, grassland regions of the United States 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?  For nine grassland sites across the southern United States, we found a fundamental difference in Desert and Plains grasslands. Soil moisture in the wetter Plains grasslands decreased with an increase of high-intensity storms.  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.

Precipitation legacy effects on dryland ecosystem carbon balance: A simulation analysis on the direction, magnitude and biogeochemical carryovers at annual to decadal timescales

Shen W.                          South China Botanical Garden, Chinese Academy of Sciences
Jenerette, G.D.
                UC Riverside

Hui, D.                            University of Tennessee

Scott, R.L.                       Southwest Watershed Research Center


The legacy of past precipitation patterns has been recognized as an important factor in shaping the way plants respond to current precipitation. However, the precipitation legacy effects on total ecosystem carbon fluxes of which plants uptake of carbon by photosynthesis is only a part has rarely been quantitatively assessed.  We adjusted an ecosystem-level water and carbon cycling simulation model to match observations made at a semiarid mesquite savanna ecosystem in southwestern United States and conducted simulation experiments to assess the PPT legacy effects.  We found that total ecosystem uptake of carbon increased when the past precipitation legacy was dry and decreased when the past legacy was wet.  In general, the dry legacy effect was due to a more vigorous plant response which was stimulated by increased soil nitrogen, and the wet legacy effect was due to the stimulation of soil respiration (carbon loss) due to the increase in carbon substrate for microbes. These results suggest that precipitation-induced biogeochemical carryovers can impose substantial legacy impacts on ecosystem carbon balance that should be taken into account when predicting the response of carbon fluxes to current and future climate.     


Editorial-Moving beyond science and engineering with NASA earth science applications

Moran, M.S.                            Southwest Watershed Research Center

Doorn, B.                                NASA Headquarters, Washington, DC

Escobar, V.                             NASA Goddard Space Flight Center

Brown, M.                               NASA Goddard Space Flight Center


NASA will launch a new satellite on November 5, 2014 - the Soil Moisture Active Passive (SMAP) mission - which will provide global measurements of soil moisture for weather prediction, drought and flood forecasting, agricultural management, and national security.  The SMAP Project has taken extraordinary steps to include potential users in SMAP mission planning.  The result has been an unprecedented pre-launch preparation for SMAP applications and critical feedback to improve the mission.  The results presented in this Editorial provide direction for upcoming NASA missions and set some context for the future of Earth observation.

Quantifying extreme precipitation events and their hydrologic response in Southeastern Arizona


Keefer, T.O.                            Southwest Watershed Research Center

Renard, K.G.                          Retired ARS

Goodrich, D.C.                       Southwest Watershed Research Center

Heilman, P.                             Southwest Watershed Research Center

Unkrich, C.L.                          Southwest Watershed Research Center


Civil engineers need good estimates of extreme rainfall and runoff amounts and intensities to properly design the size of drainage and flood control structures such as highway culverts and bridges.  It is common to use the storm information provided by the National Weather Service for such design problems.  The National Weather Service collects and analyzes rainfall data from around the country to calculate and publish the rainfall amounts for different locations in a format that the design engineers can use.  This format is referred to as "intensity-duration-frequency".  That is a certain rainfall intensity (in inches per hour), for a certain duration (in minutes from 5, 10, 15, 30, 60,...), has a certain frequency of recurring (in years from 5, 10, 25, 50 to 100).  For the Southwestern US, the rain gauges are spaced much farther apart than rain gauges in more populated areas and very few of them record data at time scales less than a day.  Thus, the National Weather Service must estimate the intensities of sub-daily durations. In this study we compare observations of the intensity-duration-frequency derived from a network of rain gauges on an area of about 50 square miles in southeastern Arizona.  The network is called the Walnut Gulch Experimental Watershed and is operated by the US Dept. of Agriculture, Agricultural Research Service, Southwest Watershed Research Center.  We find that our results and those of the National Weather Service are similar.  We also show that many events that have a frequency of recurrence of 1 in 1000 years have been observed in the network over the last 53 years and that the impacts of these types of extreme rainfall can be large floods over small areas.  The significance is that as the southwest US continues to grow in population because of more people moving to this area of the country, these flood events will cause more damage and potential hazards.

Using observations and a distributed hydrologic model to explore runoff thresholds linked with mesquite encroachment in the Sonoran Desert     


Pierini, N.A.                            Arizona State University

Ivoni, E.R.                              Arizona State University

Robles-Morusa, A.                  Instituto Tecnol?gico de Sonora

Scott, R.L.                              Southwest Watershed Research Center

Nearing, M.A.                         Southwest Watershed Research Center


The proliferation of shrubs in grasslands has transformed semiarid landscapes worldwide over the past century.  In this study, we use runoff observations from two paired watersheds in southern Arizona documented to have undergone the encroachment of mesquite shrubs, and where one watershed had mesquite removed in 1974, to understand how shrub proliferation affects the amount of runoff produced by a watershed. Forty years of runoff observations from the watersheds exhibit changes in runoff production over time, such that the watershed with more woody plants currently leads to less runoff for small rainfall events, more runoff for larger events, and a larger overall runoff coefficient.  To explain this observation, we first test the hydrologic model against data from an environmental sensor network (e.g., soil temperatures and water content, landscape evaporation, etc.) and runoff data. We find good agreement between the model and observations and then use it to identify that the relative amounts of grass and bare soil covering the watershed determine the observed runoff response. These mechanisms help to explain how woody plants have different effects on watershed runoff depending on rainfall amounts.

Intra-storm temporal patterns of rainfall in China using Huff curves

Yin, S.Q.                                Beijing Normal University

Xie, Y.                                    Beijing Normal University

Nearing, M.A.                         Southwest Watershed Research Center

Guo, Wen-Ii                            Beijing Climate Center, Beijing Meteorology Bureau


The temporal patterns of precipitation within a storm event are important to hydrologic and soil erosion processes.  The mathematical curves that describe temporal patterns of precipitation within a storm event are called hyetographs.  A convenient and established method for characterizing precipitation hyetographs is with the use of Huff curves, which are basically mathematically normalized versions of the hyetograph.  The reason that normalized curves are used is so that results found in one location or during one time of rainfall record can often more easily be extrapolated to other locations and other time periods.  In this study, hyetographs from 11,801 erosive rainfall events with a time-resolution of one minute were collected over 30-40 years from 18 weather stations located across the central and eastern parts of China.  Then the data were analyzed to produce Huff curves.  Our results showed that nearly 40% of the events had peak rainfall intensities in the first quarter of the storm, with 65% having the peak intensity in the first half of the storm.  These early peaking events also tended to be more intense and erosive.  The erosivity index (power to cause soil erosion) was 71% greater, on average, for storms with the peak rainfall in the first quarter of the storm compare to the storms with peak intensity in the last quarter.  The higher intensity events generally arise from convective thunderstorm processes in summer.  Statistical testing showed that differences of Huff curves for the 18 stations, spreading across much of China, were minor.  The Huff curves developed in this study shared similar distributional characteristics with those reported for Illinois in the USA, Malaysia, and the Santa Catarina of Brazil, which may lead to important techniques for characterizing temporal patterns of rainfall in many areas of the world.

Missing input for dry land decomposition: rain- and wind driven sediment deposition onto litter as drivers of soil litter mixing

Logie, C.J.                                           University of Arizona

Law, D.J.                                            University of Arizona

Field, J.P.                                            University of Arizona

Reynoso, E.D.                                     University of Texas

Bojorquez, O.M.                                 Universidad Estatal de Sonora

Breshears, D.                                       University of Arizona

Archer, S.R.                                        University of Arizona

Polyakov, V.O.                                   University of Arizona


The rate of sediment deposition on different type of litter (grass, leaves, and twigs) was investigated. This process is affected by the type of event (rainfall or wind) and its duration and intensity.



Controls on slope erosion rates in the Mojave Desert


Crouvi, O.                                           Geological Survey of Israel

Polyakov, V.O.                                   University of Arizona

Pelletier, J.D.                                       University of Arizona

Rasmussen, C.                                     University of Arizona


Erosion rates on slopes in Mojave Desert were estimated using Cs-137 tracer. These rates were correlated with slope shape and steepness, and surface rock cover.

Evaluation of an extreme-condition-inverse calibration remote sensing model for mapping energy balance fluxes in arid riparian areas

Hong, S.                                  Murray  State University

Hendrickx, J.M.H.                  New Mexico Tech

Kleissl, J.                                 U C San Diego

Allen, R.G.                              University of Idaho

Bastiaanssen, W.G.M.              Delft University of Technology

Scott, R.L.                              Southwest Watershed Research Center

Steinwand, A.L.                     Inyo County, California


Accurate information on the evaporation from arid riparian areas is needed for sustainable management of water resources as well as for a better understanding of water and energy exchange processes between the land surface and the atmosphere. Since estimating evaporation over long river reaches is difficult to determine from ground measurements alone, their prediction from satellite data is very attractive. In this study a remote sensing approach was used to estimate evaporation and other aspects of the surface-atmosphere energy exchange in the arid riparian areas of the Middle Rio Grande Basin (New Mexico), San Pedro Basin (Arizona), and Owens Valley (California). We found good comparisons between estimated exchanges derived from satellite images and surface-based measurements. This study shows the potential for this algorithm to yield reliable estimates for evaporation and other energy exchanges in riparian areas in the southwestern United States.   Such estimates should prove cost-effective and valuable to water and river resource managers in this region.

Assessing hydrologic impacts of future land cover change scenarios in the South Platte River Basin (CO, WY, & NE)


Barlow, J.                    University of Arizona

Burns, I.S.                   University of Arizona

Kepner, W.G.              US EPA

Goodrich, D.C.           Southwest Watershed Research Center

Sidman, G.                  University of Arizona

Guertin, D.P.               University of Arizona

McCarthy, J.S.            US EPA


Long-term land-use and land cover change and their associated impacts pose critical challenges to sustaining vital human and environmental benefits provided by healthy watersheds. In this study a method was developed to estimate hydrologic impacts from future growth. Future growth is represented by housing density maps generated every 10 years from 2010 to 2100. These datasets were produced by the U.S. Environmental Protection Agency Integrated Climate and Land-Use Scenarios (ICLUS) project. This project developed future housing density maps by adapting the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) based on social, economic, and demographic storylines for the United States. To estimate hydrologic impacts from future growth, the housing density maps were converted into land cover and land use maps that could be input into the USDA-ARS SWAT (Soil and Water Assessment Tool) watershed model using the Automated Geospatial Watershed Assessment (AGWA) tool. This method was applied the South Platte Basin that encompasses the greater Denver Colorado area and much of the rapidly developing front range. The method developed provides environmental protection managers and practitioners with an ability to assess the cumulative hydrologic impacts of future growth



A coupled modeling approach to assess the impact of fuel treatments on post-wildfire runoff and erosion

Sidman, G.                  University of Arizona

Guertin, D.P.               University of Arizona

Goodrich, D.C.           Southwest Watershed Research Center

Thoma, D.                   National Park Service

Falk, D.                       University of Arizona

Burns, I.S.                   University of Arizona


The hydrological consequences of wildfires are some of the most significant and long-lasting effects. Since wildfire severity impacts post-fire watershed response, reducing excess woody fuels can be a useful tool for land managers to moderate the severity of future wildfire. However, current computer simulation models of post-wildfire watershed response focus on only one aspect of the fire-watershed linkage (fuel treatments, fire behavior, fire severity, or watershed responses). This study outlines a modeling approach that combines three models to sequentially to allow forest managers to model the effects of fuel treatments on post-fire hydrological impacts. Case studies involving a planned prescribed fire to remove excess fuels at Zion National Park and a planned mechanical removal of excess fuels at Bryce Canyon National Park were used to demonstrate the approach. The resulting linked application of these models could help managers estimate the impact of planned fuel treatments on wildfire severity and post-wildfire runoff/erosion, and compare various fuel treatment to and maximize post-wildfire mitigation results.

A paired watershed experiment to investigate the hydrology of check dams in an Arizona Sky Alliance                  


Norman, L.M.             U.S.G.S.

Brinkerhoff, F.            U.S.G.S.

Gwilliam, E.                National Park Service

Nagler, P.L.                 U.S.G.S.

Guertin, D.P.               University of Arizona

Callegary, J.                U.S.G.S.

Goodrich, D.C.           Southwest Watershed Research Center

Gray, F.                       U.S.G.S.         


In this study, the effectiveness of in-channel rock-detention structures (check dams) was evaluated using paired watersheds during a summer monsoon season in southeast Arizona. The effects of using check dams to treat watersheds for mitigation of high flows were explored along with their potential for assisting in long-term maintenance of near stream vegetation. We analyzed two adjacent watersheds in the West Turkey Creek area of the Chiricahua Mountains during June-October of 2013: One had a series of check dams over the past 30 years and one had no check dams. Our goal was to develop a method to systematically evaluate how these watersheds response to monsoon storms without investing large amounts of time and money in instruments to measure rainfall, runoff, evaporation and plant water use. Three types of non-traditional data are coupled to develop results: 1) Field data are collected from the installation of a simple runoff estimation procedure that measures the depth of water a two locations and the stream slope between them and several existing rain gages, 2) Satellite data are used in deriving estimates of evapotranspiration, and 3) Hydrologic models are applied to calculate local water budgets and rainfall-runoff ratios.  Observations document the inflow to and outflow from both watersheds. Results show that the treated watershed with check dams has a lower runoff response to precipitation, most notably in measurements of peak flow, yet sustain low flows longer after periods of rain than the untreated watershed. We surmise that check dams are a useful management tool for maintaining forested riparian ecosystems.

Ecohydrology in the ecological site description concept


Wiliams, C.J.                           USDA-ARS

Pierson Jr., F.B.                       USDA-ARS

Spaeth, K.E.                            NRCS

Brown, J.R.                             NRCS

Al-Hamdan, O.Z.                    University of Idaho

Weltz, M.A.                            USDA-ARs

Nearing, M.A.                         Southwest Watershed Research Center

Herrick, J.E.                            USDA-ARS

Boll, J.                                     University of Idaho

Robichaud, P.R.                      USFS

Goodrich, D.C.                       Southwest Watershed Research Center

Heilman, P.                             Southwest Watershed Research Center

Guertin, D.P.                           University of Arizona

Hernandez, M.                         University of Arizona

Wei, H.                                    University of Arizona

Hardegree, S.P.                       USDA-ARS

Strand, E.K.                            University of Idaho

Metz, L.J.                                NRCS

Nichols, M.H.                         Southwest Watershed Research Center



Ecological Sites (ES) and their descriptions (Ecological Sites Descriptions,ESDs) are the primary basis by which rangeland managers and management agencies evaluate ecosystem health, develop management objectives, target conservation practices, and communicate regarding ecosystem responses to management.  However, ESDs seldom include ecohydrologic relationships that strongly regulate overall ecosystem health and responses to disturbances and management.  This study developed a framework and methodology for integration of key ecohydrologic data and relationships within the ESD structure.  The results include application of USDA developed rangeland hydrologic and erosion prediction technologies to the development and enhancement of ESDs.  The integration of this new technology and framework on ecohydrologic relations expands the ecological foundation of the overall ESD concept for management of US rangelands.  The proposed enhancement of ESDs will improve communication between private land owners and resource managers and researchers across multiple disciplines in the field of rangeland management.    



Temporal and elevation trends in rainfall erosivity on a 149 km2 watershed in a semi-arid region of the American Southwest


Nearing, M.A.                         Southwest Watershed Research Center

Unkrich, C.L                           Southwest Watershed Research Center

Goodrich, D.C.                       Southwest Watershed Research Center

Nichols, M.H.                         Southwest Watershed Research Center

Keefer, T.O.                            Southwest Watershed Research Center


Rainfall erosivity is the term used to describe the power or capability for rain storms to cause soil erosion.  Scientific studies have shown that the amount of soil erosion caused by a storm is a function of the total energy of a storm and its intensity, given conditions on the ground surface, such as soil type, topography, and vegetation, being equal.  The energy of a storm is related to the size of raindrops, how fast they fall, and how long the storm lasts.  The intensity is defined and calculated by the maximum amount of rain that falls during any 30 minute period of the storm.  With climate change there is an expectation that rainfall erosivity is changing.  Generally across the world scientists have observed an increase in the number of extreme rainfall events, which means we are seeing more storms with more energy and probably also higher intensity for a longer period of time during the event.  In this study we used data from our ARS watershed in Tombstone Arizona to look at the rainfall erosivity and how it may have changed over the past 50 years.   We can do this at our ARS watershed, called Walnut Gulch, because at this site we have a very long record of highly detailed rainfall information from many raingages.  This gives us the long record needed for finding temporal trends in the data, as well as the very high resolution of data needed to accurately calculate erosivity.  An added bonus, and very important for the study from a statistical standpoint, is that we have there more than 80 raingages spread across the watershed.  It is a highly replicated set of data.  The results of the study did not show any temporal trends in the rainfall erosivity. For this particular location the rainfall patterns do not seem to have significantly changed, at least in a way that has caused a significant change in rainfall erosivity. We did find a spatial trend in the data, showing that higher elevations tended to slightly increasing erosivity.  This was due to something called the orographic effect, which basically results in the fact that more rainfall comes in higher elevations. This was true even though the maximum elevation difference in the Walnut Gulch watershed was only of the order 1300 feet.  The study provides a basis and methodology that can be used at other ARS watersheds to determine if trends exist in other parts of the country.  

Green infrastructure management techniques in arid and semi-arid regions:  Software implementation and demonstration using the AGWA/KINEROS2 Watershed Model

Korgaonkar, Y.           University of Arizona

Burns, I.S.                   University of Arizona

Guertin, D.P.               University of Arizona

Goodrich, D.C.           Southwest Watershed Research Center

Unkrich, C.L.              Southwest Watershed Research Center

Barlow, J.E.                University of Arizona

Kepner, W.G.              US EPA


Green Infrastructure (GI) are features added to sub-divisions and urban developments to capture and hold rainfall and runoff on the developed area to reduce downstream storm water runoff. However, Geographic Information System (GIS)-based watershed modeling tools that operate from the lot-to-subdivision-to-watershed level for rapid planning assessments are lacking. The Automated Geospatial Watershed Assessment (AGWA) computer tool was modified to simulate several GI practices within the USDA-ARS KINEROS2 rainfall-runoff computer model. The resulting software provides a GI assessment framework that is capable of manipulating GI features and simulating urban hydrology at the lot scale within a graphical interface to conveniently view and compare simulation results. The AGWA GI software was then tested at the lot level with and without GI features to ensure programming integrity and hydrologically sound results. Successful testing of the tool was conducted at the subdivision level using observed rainfall-runoff observations from a subdivision in Sierra Vista, Arizona. A set of case study simulations was then conducted for the Sierra Vista subdivision with various combinations of the implemented GI features. Results indicate that the resulting software worked well at the lot, subdivision, and small watershed level and it can realistically represent and simulate storm runoff responses for several GI features.


Modeling flash flood events in an ungaged semi-arid basin using a real-time distributed model: Fish Creek near Anza Borrego, California

Goodrich, D.C.           Southwest Watershed Research Center

Kustas, W.P.               USDA-ARS

Cosh, W.H.                 USDA-ARS

Moran, M.S.                Southwest Watershed Research Center

Marks. D.G.                USDA-ARS

Jackson,T.J.                 USDA-ARS

Bosch, D.D.                USDA-ARS

Rango,A.                     USDA-ARS

Seyfried, M.S.             USDA-ARS

Scott, R.L.                  Southwest Watershed Research Center

Fast responding headwater basins and canyons pose a significant threat to life and property throughout the semi-arid western United States. The National Weather Service (NWS) of the National Oceanographic and Atmospheric Administration (NOAA) is responsible for providing flash flood warnings to the public.  This paper presents the results from the application of the real-time distributed model KINematic runoff and EROsin model (KINEROS2) to the complex terrain of the Fish Creek basin located at the southern end of the Vallecito Mountains and the Carrizo Badlands. In operations, KINEROS2 uses real-time radar-rainfall data to produce a forecast hydrograph. Due to inherent uncertainties with forecasting for ungaged locations, the forecast will be qualitative in nature (no flooding, minor flooding, moderate flooding, major flooding, or record flooding). The model was calibrated using a series of rainfall events representing a full range of flow outcomes from below flood stage up to record flood. Calibration was successful in reproducing all flows regardless of magnitude. A simple calibration scheme of one calibration for low flows through low-end major flooding and another for higher end major floods through record flooding was employed. The timing and magnitude of the peak flow is useful information currently not available using current NOAA/NWS flash flood forecasting methodologies available at the Weather Forecast Office.

Curve number estimation from Brazilian Cerrado rainfall and runoff data


Sanches Oliveira                     University of S?o Paulo

Nearing, M.A.                         Southwest Watershed Research Center

Stone, J.                                  Southwest Watershed Research Center

Hawkins, P.                             University of Arizona

Rodrigues, D.B.B.                  University of S?o Paulo

Panachuki, E.                          State University of Mato Grosso do Sul

Wendland, E.                          University of S?o Paulo


Brazil has a large region of savannah, called the Cerrado, that is rich in biological diversity and freshwater resources. It is also being rapidly converted to agricultural use for production of both row crops and livestock.  The Brazilian Cerrado is one of the most important Brazilian biomes, covering ~22% of the total area of Brazil. The vegetation of the Cerrado varies from grassland to savanna to forest. Because of its highly diverse plant and vertebrate species, this biome has been classified as one of the 25 global biodiversity hotspots.  Despite the importance of the Brazilian Cerrado, knowledge of the hydrology associated with the change from native cover to grassland and cropland is still limited. In this study, we measured infiltration and runoff rates and amounts on plots with native Cerrado vegetation and the main crops found in the region.  From the resulting data we derived widely used hydrologic modeling parameters, called curve numbers, that both help us to characterize the differences between the native and introduced vegetation and to model a part of the water cycle across wider area of the biome.  We found that runoff was very different, and much greater, on the agricultural lands as compared to the native vegetation. In fact, we found that the Curve Number method was not suitable to estimate runoff under undisturbed Cerrado, bare coarse soils with high infiltration rates, pasture, and millet.  These results are important for better understanding how to manage change in Brazil as more and more land is being converted to agricultural use.

Hydrological processes in the Brazilian Cerrado

Sanches Oliveira, P.                University of S?o Paulo

Wendland, E.                          University of S?o Paulo

Nearing, M.A.                         Southwest Watershed Research Center

Scott, R.L.                              Southwest Watershed Research Center

Rosolem R.                             University of Bristol

De Rocha, H.R.                      University of S?o Paulo


The tropical forests, savannas, biological diversity and freshwater resources of Brazil are among the world's largest. The Brazilian Cerrado is considered one of the most important Brazilian biomes, covering an area of 2 million km2, and is the second largest biome in South America after the Amazon. The physiognomies of the Cerrado vary from grassland to savanna to forest. Because of its endemic plant and vertebrate species, this biome has been classified as one of the 25 global biodiversity hotspots.  Despite the importance of the Brazilian Cerrado, knowledge of hydrological processes and water budget dynamics associated with the change from native cover to grassland and cropland is still limited. In this study, we measured components of the water budget on a native Cerrado and bare soil site.  We found that runoff increases and infiltration decreases on agricultural lands as compared to the native vegetation. These results are important for better understanding how to manage change in Brazil as more and more land is being converted to agricultural use.


Analysis of vegetation fragmentation in Southeast Arizona across scalar space

MItram B.                   University of Arizona

Moran, M.S.                Southwest Watershed Research Center

Holifield Collins, C.       Southwest Watershed Research Center

Ponce-Campos, G.      Southwest Watershed Research Center

Kautz, M.                    University of Arizona

Ross, M.                      University of Arizona


Across the vast rangelands in the Southwest USA, landscape conservation is highly dependent upon the uniform distribution of grasses.  Our analysis found a significant increase in vegetation patchiness across a rangeland ecosystem in southeast Arizona over a 30-year period from 1984-2013.  This increase was related to extreme climate events as well as a decrease in precipitation, thereby highlighting the important impact of climate change on vegetation dynamics.  Such an increase in vegetation patches has important implications for ecosystem services such as forage quality and carbon storage in a rangeland ecosystem.



A GIS-based procedure for automatically calculating soil loss from the Universal Soil Loss Equation: GISus-M

Oliveira, Joanito de Andrade              Institute of Geosciences, Federal University of Bahia

Dominguez, Jos? Maria Landim         Institute of Geosciences, Federal University of Bahia

Nearing, M.A.                                     Southwest Watershed Research Center

Oliveira, Paulo Tarso Sanches           University of S?o Paulo


The Universal Soil Loss Equation (USLE), developed by USDA scientists, is the world's most widely used tool for calculating soil erosion rates by water.  The equation calculates estimated soil loss rates as a function of rainfall erosivity, soil erodibility, the effect of vegetation cover and management, and the steepness and lengths of hill slopes.  Geographical Information Systems are used routinely now to conduct analyses and representation of many different types of spatially distributed characteristics of the landscape.  The work represented in this article is a plug-in module for the most commonly used GIS software, ArcGIS Desktop, which allows the user to apply the USLE across large areas.  The tool allows the user to construct the data bases and automatically make the calculations necessary for building the layers, which are the spatial maps of information used in the equation, and then calculating estimated soil erosion rates over the area of interest.  It also allows the user to map and visualize results.  Information for vegetation cover is generated from readily available remotely sensed satellite data, and factors of slope steepness and length are derived from available topographic information.  Soil and rainfall erosivity information may be incorporated from many sources.  The tool provides a variety of options for making calculations of input values for the equation, dependent on the environment being assessed.  This tool is easy to use and readily available, and would be valuable for a wide variety of applications associated with soil conservation and land management.