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- Research Overview
- Most Important Manuals/Reports/Bulletins from the SWRC
- Science Results
- Experimental Watersheds

| Science Results (Winter 2008) |
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**Assessing hillslope heterogeneity for rainfall-runoff modeling:  KINEROS 2 case study
 
Bulygina, N.S.                          University of Arizona
Goodrich, D.C.                        SouthwestWatershedResearchCenter
Guertin, D.P.                            University of Arizona
Gupta, H.V.                             University of Arizona
 
Computer models that represent the hydrologic behavior watersheds are an important tool in managing the nation's water resources. A challenge in applying these models is determining when a portion of the watershed is sufficiently different enough that it should be treated as a separate computer model element with distinct hydrologic properties.  A procedure is developed determine when the watershed should be further subdivided based on the watershed soils and climate characteristics of runoff producing storms.  Using this procedure will enable computer watershed models to more realistically represent watershed response and thus improve our management of our water resources. 

 
**Event to Multi-decadal Persistence in Spatial Rainfall and Rainfall and Runoff as a Function of Spatial and Temporal Scales 
 
Goodrich, D.C.                        SouthwestWatershedResearchCenter
Unkrich, C.L.                           SouthwestWatershedResearchCenter
Keefer, T.O.                            SouthwestWatershedResearchCenter
Nichols, M.H.                          SouthwestWatershedResearchCenter
Stone, J.J.                                SouthwestWatershedResearchCenter
Levick, L.                                 University of Arizona
Scott, R.L.                               SouthwestWatershedResearchCenter
 
Arid and semi-arid regions account for approximately one-third of the land mass of earth.  These regions are experiencing continued pressure from population growth in many parts of the world.  Water is a critical resource in these regions and is often in short supply.  Detailed study of water resources and the hydrology of semi-arid regions is important if we are to continue to populate and use these regions.  This paper analyzed the highly detailed long-term rainfall and runoff records from the USDA-ARS Walnut Gulch Experimental Watershed (WGEW) near Tombstone, Arizona.  The major findings of this study are that the spatial variability of precipitation decreases rapidly (exponentially) as the time over which it is summed up increases; that long-term precipitation trends can be captured with a smaller number of rain gauges (roughly six) then the 85 gauges deploy in the WGEW; and, that an observed decrease in runoff from 1966 to 1998 from the 150 square kilometer (58 square miles) watershed is not significantly affected by factors other than precipitation such as land cover change.
 
**Investigating uncertainty in distributed flash-flood forecasting for semi-arid regions
 
Yatheendradas, S.                    University of Arizona
Wagener, T.                             PennStateUniversity
Gupta, H.                                 University of Arizona
Unkrich, C.L.                           SouthwestWatershedResearchCenter
Goodrich, D.C.                        SouthwestWatershedResearchCenter
Schaffner, M.                           National Weather Service

Stewart, A.                               University of Arizona
 
One-third of the earth's surface can currently be classified as arid or semi-arid. This fraction may increase in the future for example due to global warming effects. Many arid and semi-arid regions are particularly affected by flash floods, caused mainly by convective storm systems, and often resulting in significant damages to life and property. The short duration and the small geographic extent of these events make predicting the subsequent floods extremely difficult. To improve our predictive flood capability, we have developed a semi-arid specific model based on the well-established USDA-ARS event-based rainfall-runoff model KINEROS2.  The model is driven by high-resolution, near real-time radar rainfall inputs.  The ability of this modeling system to predict floods was investigated as well as how uncertainty in the rainfall data and the model affects these predictions.  The model was found to make good predictions when calibrated but it was found that the predictive uncertainty of the model is dominated by the radar-rainfall depth estimates. This points out the need to use radar rainfall data and ground-based rain gauge data to improve predictions.

 
**DotAGWA:  A case study in web-based architecture for connecting surface water models to spatially enabled web applications
 
Cate, A.                                   University of Arizona
Semmens, D.                            US EPA
Guertin, D.P.                            University of Arizona
Goodrich, D.C.                        SouthwestWatershedResearchCenter
 
DotAGWA is an Internet based application that combines geospatial data and surface water models.  End-users delineate a watershed and define a management plan for the watershed by drawing points, lines and/or polygons on a map.  The input data are gathered from various databases built into the application or accessible through the Internet.  The input data sets are extracted by using the delineated watershed and once created are passed to the hydrologic models.  Users run the model(s) and are allowed to download the output data for further analysis and/or review.  All of the features built into the web application are hosted on a server that making the application available to anyone with a computer and an Internet connection.  This paper discuses findings and experiences that have emerged during the development process of the DotAGWA web application.  This paper also discusses possible solutions used to address any technical problems that emerged during application development.

 
**A Dual-Monte-Carlo Approach to Estimate Model Uncertainty: Application to the Rangeland Hydrology and Erosion Model
 
Wei, H.                        University of Arizona
Nearing, M.A.              SouthwestWatershedResearchCenter
Stone, J.J.                    SouthwestWatershedResearchCenter
Breshears, D.P.            University of Arizona
 
Natural resources models are useful tools often used to aid in decision making regarding resources management. Due to multiple reasons such as the uncertainty associated with the model input parameter values, all model predictions involve certain level of uncertainty, which is called model predictive uncertainty and can be expressed as the confidence interval around a model prediction value. Model predictive uncertainty describes the confidence of a model prediction, provides important supplementary information for aiding decision making on natural resources management. As an example for an erosion model, predictive uncertainty provides more useful information for assessing the erosion risk and evaluating different conservation practices effects, comparing with a single model predicted soil loss value. This paper describes a new method called "Dual-Monte-Carlo" (DMC) to calculate model predictive uncertainty based on input parameter uncertainty. The framework of DMC was explained and then DMC was applied to the Rangeland Hydrology and Erosion Model (RHEM) as a case study. Results from DMC for model RHEM were compared with the natural variations associated with measured erosion plot data.  Both datasets showed a similar relationship between the variation of soil loss and the magnitude soil loss. We also found that the model uncertainty intervals for RHEM were highly related to the predicted soil loss value and some of the input parameters, thus regression relationships (R2>0.97) were developed to estimate the uncertainty interval for any input parameter set without the need to run the Monte-Carlo simulations each time the model is used. The results was also applied to different storms and different site conditions to illustrate how DMC can be served as useful tool for assisting decision making on natural resources management.

 
**Quantifying Riparian Evapotranspiration
 
Scott, R.L.                   SouthwestWatershedResearchCenter
Huxman, T.E.               University of Arizona
Williams, D.G.              University of Wyoming
Hultine, K.R.                University of Utah
Goodrich, D.C.            SouthwestWatershedResearchCenter
 
A multi-disciplinary group of government scientists and university researchers has been working to better understand the hydrological functioning of riparian systems in the Southwest.  Perhaps the most socially-relevant facet of this research has been the quantification of riparian evapotranspiration (ET).  It has long been known from groundwater modeling studies that water use by riparian vegetation is an important component of the water balance in the basin.  Yet because the quantification of ET was based on indirect techniques like stream flow data or by untested empirical approaches, its magnitude was highly uncertain.  This article reviews our work conducted over the last 10 years on making direct measurements of ET on the SanPedroRiver of southern Arizona using micrometeorological and plant physiological techniques.  We review our approaches and some of the important results that this effort has generated.
 
**Separation and Measurement of Soil Carbon Dioxide Organic and Inorganic Fluxes
 
Emmerich, W.E.           SouthwestWatershedResearchCenter
Martens, D.A.              SouthwestWatershedResearchCenter (deceased)
 

The second largest pool of carbon in the world is in soil organic carbon and the third largest is inorganic carbon in the soil.  To understand more about the worlds' carbon budget, scientist need to know how much carbon is coming out of the soil to the atmosphere from soils that contain both organic and inorganic sources in the soil.  This research developed a procedure to separate the carbon coming out of the soil into fractions that are from organic and inorganic sources in the soil.  With additional data on the total carbon coming out of the soil, estimates of yearly movement of carbon to the atmosphere from the two sources were determined.  This work will help scientist understand the worlds' carbon budget and the process of climate change.  

 
**Tree growth response to zero-flow events:  Can tree rings be used to reconstruct streamflow intermittency?
 
Morino, K.A.               University of Arizona
Scott, R.L.                   SouthwestWatershedResearchCenter
Glenn, E.P.                   University of Arizona
Meko, D.M.                 University of Arizona
 
Characterizing streamflow regimes is integral component to developing restoration and

conservation plans for threatened and endangered river systems throughout the United

States. Our ability, however, to accurately represent streamflow variability over time and space is largely restricted by data availability. In addition to the limited length of many streamflow records, a further constraint to flow characterization is that it is based on point data-streamflow gages-that are often sparsely distributed within a river basin.  This work shows that Fremont cottonwood trees growing along an intermittent flow reach of the SanPedroRiver in Arizona experience significant stress and stop growing during the growing season due to water table declines and stoppage of streamflow. This stress appeared to cause an identifiable "false" tree ring to form within the sequence of annual growth rings.    Thus, tree ring chronologies from cottonwood trees may prove to be a useful tool to better characterize historical streamflow regimes along rivers.
 
**Fifty Years of research and data collection, USDA-ARS Walnut Gulch Experimental Watershed
 
Moran,  M.S.               SouthwestWatershedResearchCenter
Emmerich, W.E.           SouthwestWatershedResearchCenter
Goodrich, D.C.            SouthwestWatershedResearchCenter
Heilman, P.                   SouthwestWatershedResearchCenter
Holifield Collins, C.       SouthwestWatershedResearchCenter
Keefer, T.O.                SouthwestWatershedResearchCenter
Nearing, M.A.              SouthwestWatershedResearchCenter
Nichols, M.H.              SouthwestWatershedResearchCenter
Renard, K.G.               Retired ARS

Scott, R.L.                   SouthwestWatershedResearchCenter
Smith, J.R.,                   SouthwestWatershedResearchCenter
Stone, J.J.                    SouthwestWatershedResearchCenter
Unkrich, C.L.               SouthwestWatershedResearchCenter
Wong, J.K.                  SouthwestWatershedResearchCenter
 
To understand the complex water balance of semiarid regions, it is necessary to have long-term information on soils, vegetation, hydrology, and climate at a given location.  Such data have been collected for decades as part of interdisciplinary experiments at the U.S. Department of Agriculture (USDA) Walnut Gulch Experimental Watershed (WGEW) operated by the USDA Agricultural Research Service (ARS) Southwest Watershed Research Center (SWRC) in southeast Arizona USA.  In association with the 50th anniversary of the establishment of WGEW, SWRC scientists provided web-based access to continuous measurements of precipitation, runoff, sediment, meteorological, soil moisture, vegetation, CO2 and water flux, and geographic information system (GIS) data (http://www.tucson.ars.ag.gov/dap/) and published the most recent research results in one journal issue.  In this issue, there are over 20 manuscripts providing WGEW history, metadata, data access and recent results of WGEW data analysis.  The goal of these publications and the associated web site is to encourage cooperative studies of semiarid ecohydrology on WGEW.

 
**Partitioning evapotranspiration in semiarid grassland and shrubland ecosystems using time series of soil surface temperature
 
Moran,  M.S.               SouthwestWatershedResearchCenter
Scott, R.L.                   SouthwestWatershedResearchCenter
Keefer, T.O.                SouthwestWatershedResearchCenter
Emmerich, W.E.           SouthwestWatershedResearchCenter
Hernandez, M.             University of Arizona
Nearing, G.S.               University of Arizona
Paige, G.B.                   University of Wyoming
Cosh, M.H.                  USDA-ARS Hydrology Lab

O'Neill, P.E.                NASA

 
Encroachment of woody plants in grasslands has become a common phenomenon across the Western U.S. over the past 150 years.  Shrublands have a different water demand from grasslands, manifesting in different water availability for plant transpiration (T).  In turn, these shifts in evaporation (E) versus T related to vegetation change can impact management strategies in dryland ecosystems associated with land use and climate change.   To study this phenomenon, a network of towers is in place to measure evapotranspiration (ET) in grass- and shrub-dominated ecosystems throughout the Western U.S.  A method is described and tested here to partition the daily measurements of ET into E and T based on simple measurements of surface temperature.   The method was tested at Walnut Gulch Experimental Watershed in southeast Arizona over three years, 2003-2005.  Results showed that reasonable estimates of daily T were obtained for a multi-year period with ease of operation and minimal cost.  With known season-long daily T, E and ET, it is possible to determine the soil water availability associated with grass- and shrub-dominated sites and better understand the hydrologic impact of regional woody plant encroachment.
 
**Evaluating Hydrological Response To Forecasted Land-Use Change
 
Kepner, W.G.              US EPA
Semmens, D.                US EPA
Hernandez, M.             University of Arizona
Goodrich, D.C.            SouthwestWatershedResearchCenter
 
It is currently possible to measure changes on the earth's surface over large areas and determine trends in these changes of land cover and land use using satellite-based images.  A primary, and global, source of these images, are the digital images from the Landsat series of satellites that have been in operation since 1972.  With this set of images the earth's land cover can be monitored and analyzed for change detection.   Interpretations from these images can also be used to estimate important information needed for watershed simulation models (for both water quantity and quality).   Future land use and land cover can also be projected based on, stakeholder preferences, zoning, and patterns of growth.  This article presents two studies in which future land-use scenarios were examined relative to their impact on surface-water conditions using watershed simulation models associated with the Automated Geospatial Watershed Assessment (AGWA) tool. A third study utilized historical land-cover data to validate the approach and explore the uncertainty associated with scenario analysis.  These studies provide examples of integrating modeling with satellite observing technology to produce information on trends and make plausible forecasts for the future from which to understand the impact of landscape change on watershed and ecological conditions.

 
**Carbon exchange variability associated with meteorology, physiology, phenology, and water availability in semiarid riparian ecosystems
 
Jenerette, G.D.             University of Arizona
Scott, R.L.                   SouthwestWatershedResearchCenter
Barron-Gafford, G.A.   University of Arizona
Huxman, T.E.               University of Arizona
 
Identifying the dynamics of carbon dioxide cycling in ecosystems in semiarid regions will lead to an improved understanding of ecosystem functioning and the potential to better assess the ecological responses to future changes in climate. To facilitate this understanding, there is a need for scientists to construct models that adequately represent and characterize how carbon dioxide exchange is influenced by factors such as meteorology, plant physiology and activity, and water availability. In this paper, the authors develop a relatively simple ecosystem model that is based on established theory and then apply this model at two sites in southern Arizona where measurements of carbon dioxide exchanges have been made. The authors demonstrate that this model adequately reproduces the measurements. The model is then used to better understand how the ecosystems are influenced by different factors.  Results are consistent with previous findings that the biological responses to environmental variation are equally or even more important than the magnitudes of the environmental variation.
 
**Post wildfire runoff and erosion from oak woodlands in southeastern Arizona, USA
 
Stone, J.J.                    SouthwestWatershedResearchCenter
Paige, G.                      University of Wyoming
Guertin, D.P.                University of Arizona
Gottfried, G.                 USFS

 
The areal extent and severity of wildfires have been increasing in the western U.S. for reasons including prior fire management, changes in winter precipitation, increases in population, and extension of the wildland urban interface. In 2003 and 2005 wildfires burned two oak savanna sites in the SanRaphaelValley in southeastern Arizona.  On these sites, the microtopography and vegetation composition are interrelated.   The interspace areas are occupied by warm season grasses while small mounds form under oak and shrubs.  Rainfall simulator experiments were conducted at the burned sites and their unburned equivalents to determine the effect of the fire on the amounts and rates of runoff and erosion.  The results show that the fires have little effect on runoff but can increase the amount of erosion by a factor of 8.  The increase in erosion was in part because of a loss of cover but more importantly because of an increase the runoff's capacity to transport sediment.  The increase was more evident in proximity to mounds which form under manzanita shrubs.  The mounds concentrate the runoff which allows for more sediment to be transported.  A good relationship between the sediment yield and amount of bare soil was found.  In addition, the data show that the threshold amount of bare soil for accelerated erosion decreases as the rainfall/runoff rates increases.  The results suggest that immediate post-fire erosion rates increase more for sites with high densities of manzanita than for sites with lower densities.   
 
**Simposio Internacional Sobre Sistemas de Apoyo para la Toma de Decisiones en el Manejo de los Recursos Naturales
 
Heilman, P.                   SouthwestWatershedResearchCenter
Yanxin, D.                    Tetratech

Sanchez-Cohen, I.        INIFAP
Stone, J.J.                    SouthwestWatershedResearchCenter
 
Arid environments are under increasing pressure because of growing populations and the inherent fragility of arid ecosystems. Improved Decision Support Systems (DSS) will be an important tool in the management toolbox for water management. This paper makes two contributions. First, it describes a number of English language resources, primarily available on the internet, to help create decision support systems for water management in arid environments. Second, a prototype DSS for rangeland watershed management is presented. Specifically, the prototype DSS can be used to study the economics of reducing sediment yield on rangelands. DSS will be a key mechanism to improve natural resource management, but given the complexity of rangeland ecosystems and the fragmented institutional framework for rangeland management, building operational decision support systems for rangeland management will require ongoing effort and coordination.

 
**Remote Sensing of Rangeland Health in Southeastern Arizona
 
Buono, J.                      University of Arizona
Heilman, P.                   SouthwestWatershedResearchCenter
Archer, S.                    University of Arizona
Nash, M.                      US EPA
 
Rangeland health is a widely accepted method to assess key ecological processes, but is labor intensive and therefore expensive. Remote sensing holds the promise of making regional or national scale rangeland health assessments, but the method was designed to be performed on-site by a trained professional. This study is a proof-of-concept demonstration that, with additional effort, remote sensing could be used to assess departure from reference conditions. Some of the additional effort required includes generating landscape scale maps of ecological sites and developing methods to use a computer to assign departure categories and evaluate the preponderance of evidence for rangeland health attributes. The study demonstrated the potential to use remote sensing to conduct rangeland health assessments with reasonable accuracy though a significant research effort would be needed to make remote sensing an operational tool for rangeland health assessment at the landscape scale.  

 
**Localizing the Rangeland Health Method for Loamy Upland in Southeastern Arizona
 
Buono, J.                      University of Arizona
Heilman, P.                   SouthwestWatershedResearchCenter
Carrillo, E.                    NRCS

Robinett, D.                  NRCS

Nash, M.                      US EPA
 
This paper is a condensed version of an NRCS Technical Note that addresses Rangeland Health assessment by localizing the national approach to an ecological site found in southeastern Arizona. A national interagency manual, "Interpreting Indicators of Rangeland Health", Version 4 (Technical Reference 1734-6), exists, but application to a particular location requires extensive experience. The method might not be applied consistently until supporting documentation for each ecological site is developed. This paper describes the development of such documentation: a reference sheet that describes the condition of areas with little or no departure from reference conditions (the historic climax plant community) as well as an evaluation matrix that describes five departure categories for each of the 17 indicators. Expanding this effort to document reference sheets and evaluation matrices systematically to all ecological sites would require a significant effort, but would facilitate more consistent interagency application of the rangeland health method.
 
**Creating Decision Support Systems for Arid Environments
 
Heilman, P.                   SouthwestWatershedResearchCenter
Yanxin, D.                    Tetratech

Sanchez-Cohen, I.        INIFAP
Stone, J.J.                    SouthwestWatershedResearchCenter
 
Arid environments are under increasing pressure because of growing populations and the inherent fragility of arid ecosystems. Improved Decision Support Systems (DSS) will be an important tool in the management toolbox for water management. This paper makes two contributions. First, it describes a number of English language resources, primarily available on the internet, to help create decision support systems for water management in arid environments. Second, a prototype DSS for rangeland watershed management is presented. Specifically, the prototype DSS can be used to study the economics of reducing sediment yield on rangelands. DSS will be a key mechanism to improve natural resource management, but given the complexity of rangeland ecosystems and the fragmented institutional framework for rangeland management, building operational decision support systems for rangeland management will require ongoing effort and coordination.

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