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Science Results (Spring 2006)
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A new dynamic, rangeland soil erosion model based on WEPP and KINEROS2


Bulygina, N.S.                          University of Arizona

Nearing, M.A.                           SouthwestWatershedResearchCenter

Stone, J.J.                               SouthwestWatershedResearchCenter

Nichols, M.H.                           SouthwestWatershedResearchCenter


Regulatory policy and land management approaches include the use of soil erosion assessment tools to provide the information on natural hazards and human impacts to support soil conservation planning, both through agricultural legislation that defines maximum tolerable soil loss rates, and through federal and local legislation that requires soil erosion controls on many construction sites. To be useful for decision makers, soil erosion models must have simple data requirements and must be applicable to a variety of regions with minimum calibration.  We have two models, KINEROS2 and WEPP, which each have their distinct advantages and disadvantages.  The intention of this research was to create a model that is easy to use, can be parameterized given basic field data, can well represent the effects of management practices on erosion, and is based on best available process representations.  Thus we decided to unite the advantageous features of both models: to have KINEROS2 as a base and to insert a WEPP-like dynamic erosion module instead of its former steady-state version.  The impact of this research will be more accurate representations and understanding of the effects of land management on soil erosion and sediment yields when making predictions with USDA hydrologic assessment tools such as AGWA.


A four year record of tracking sediment sources in small agricultural watershed


Kimoto, A.                               University of Arizona

Nearing, M.A.                          SouthwestWatershedResearchCenter

Shipitalo, M.J.                          North Appalachian Experimental Watershed

Polyakov, V.O.                        University of Hawaii


Data has been collected from soil erosion from plots and watersheds for nearly 100 years, but there has always been a fundamental issue that has never been answered: how can one track the redistribution of sediment within watersheds?  We can physically measure what leaves a plot.  We can measure net loss and gain at points through radioactive fallout of a Cesium isotope.  But never have we been able to track how sediment generated from one part of the landscape moves with time through the watershed.  As such, there are basic aspects of sediment and contaminant movement that we don't understand (diffusive vs. longitudinal transport), and models that we cannot verify.  Now, with this study, we have developed a multiple tracer technique that for the first time gives us a complete sediment balance as a function of landscape position.  This data is unique in the world and an important advance for the science of soil erosion and conservation.  The impact of the work will be better spatial information on soil erosion and contaminant transport which will reduce costs and improve effectiveness of conservation plans and programs.



Chapter 3:  Assessment of climate change impacts on water resources, adaptation and vulnerabilities


Kundzewicz, Z.W.                    Potsdam Institute-Germany

Mata, L.J.                                University of Bonn, Germany

Nearing, M.A.                          SouthwestWatershedResearchCenter


The consensus of atmospheric scientists is that the hydrologic cycle is becoming more vigorous, with increasing precipitation means and even more so the most intense precipitation. Rainfall amounts and intensities are the most direct and important factors controlling erosional changes under climate change.  All of the studies to date on soil erosion suggest that increased rainfall amounts and intensities will lead to greater rates of erosion, and there appears to be little doubt that both average rainfall amounts and intensities are on the rise world-wide.  Thus, erosion will also be on the increase, unless amelioration measures are taken.  While soil erosion rates are expected to change in response to changes in climate for a variety of reasons, the most direct is the change in the erosive power of rainfall.   In terms of implications of climate change for soil conservation efforts, a significant realization from recent scientific efforts is that conservation measures more than ever before must be targeted to the extreme events.  Large, high intensity rainfall events contribute a disproportionate amount of erosion relative to total rainfall contribution, and this effect will only be exacerbated in the future as the frequencies of large and intense storms are on the rise around the world.


Estimation of rainfall erosivity using 5 to 60 minute fixed-interval rainfall data from China


Yin, S.                                      BeijingNormalUniversity

Xie, Y.                                     BeijingNormalUniversity

Nearing, M.A.                          SouthwestWatershedResearchCenter

Wang, C.                                 BeijingNormalUniversity


Rainfall erosivity is one of the six factors in the Universal Soil Loss Equation (USLE) and the Revised Universal Soil Loss Equation (RUSLE) erosion prediction models.  It quantifies the ability of rainfall to cause soil loss from hillslopes.  Soil loss may be estimated using either the USLE or RUSLE by multiplying the rainfall erosivity factor, R, together with the other five factors: soil erodibility (K), slope length (L), slope steepness (S), crop type and management (C), and supporting conservation practices (P).  Calculation of erosivity requires detailed rainfall intensity data that is not available in all parts of the world, including China.  The objective of this study was to develop methods for determining rainfall erosivity using the quality of rainfall data that is more commonly available in China.  The results will be used to improve the estimation of rainfall erosivity indices, prediction of soil erosion, and hence the conservation of soil in China and other parts of the world.


Seasonal and Interannual Variation of Evapotranspiration for a Semiarid

Watershed Estimated by MoistureFluxTowers and MODIS Vegetation Indices


Nagler, P.L.                              University of Arizona

Glenn, E.                                  University of Arizona

Kim, H.                                    University of Arizona

Emmerich, W.E.                       SouthwestWatershedResearchCenter

Scott,  R.L.                              SouthwestWatershedResearchCenter

Huxman, T.                              University of Arizona

Huete, T.                                  University of Arizona


Evapotranspiration (ET), the evaporation from the soil surface and plants is a major component of the land surface water budget in arid and semi-arid watersheds. There is a great need to develop methodologies to predict ET over entire watersheds; however measurements at this scale are not available. This study applies a method that uses information readily available from satellites to estimate ET over a semiarid watershed in southern Arizona.  The method is shown to accurately reproduce estimates made from ground instruments and it is used to estimate ET across the watershed.  The results of this study suggest that this relatively simple approach might provide accurate and cost effective ET estimates in basins with similar climate and vegetation.


Statistical protocols for quality control of ecosystem CO2 fluxes over an abandoned field in Kazakhstan.


Perez-Quezada, J.F.                 University of Chile

Saliendra, N.Z.                         USDAForest Service

Emmerich, W.E.                       SouthwestWatershedResearchCenter

Laca. E.A.                                University of California, Davis


Micrometeorological and CO2 flux data are subject to interpretation by individual scientist and is a very labor intensive.  Because of the individual interpretation there are differences in the final results produced.  This work evaluated the differences between scientists and models to do the interpretation.  The models were able to produce results similar to a group of scientist with less variability.  Incorporating model into processing this type of scientific data will result in less labor and produce more consistent quality control of the data.


Decision support for nitrogen management in tile-drained agriculture


Heilman, P.                               SouthwestWatershedResearchCenter

Malone, R.W.                            National Soil Tilth Laboratory

Ma, L.                                      Great Plains System Research Unit

Hatfield, J.L.                             National Soil Tilth Laboratory

Ahuja, L.R.                               Great Plains System Research Unit

Ayen, J.                                   USDA-NRCS

Boyle, K.                                  USDA-NRCS

Kanwar, R.                               IowaStateUniversity


This paper outlines an eleven step process to define, populate, and apply a database of management effects to support conservation planning by the NRCS. A case study for reducing nitrogen loading from tile-drained corn and soybean production in Iowa presents the approach. Basic information from the case study is presented, although only the first five steps, through calibration and validation of a simulation model against observed data, have been completed. The strength of the approach is the ability to integrate the best available data to quantify management effects over a large area. The main weakness of the approach is the need for a substantial initial investment to create the database. Once populated, customized views of the database would be available for farmers, NRCS conservationists, and researchers.



Optimization of grazing management for watershed sediment control


Duan, Y.                                   University of Arizona

Heilman, OP.                            SouthwestWatershedResearchCenter

Guertin, D.P.                            University of Arizona


This paper presents the derivation of constrained optimization model to calculate the cost to a rancher of reducing, by various amounts, sediment produced from the ranch. The model maximizes the profit of a representative ranch that can utilize all grazing lands in a watershed with constraints on forage resources, sustainable utilization, and production technology and sediment yield control objectives. The model simulates reduced grazing that leaves more vegetative cover to reduce erosion. The reduction in grazing results in less erosion but also less income. The model calculates the tradeoff between ranch income and sediment. The model could be used to understand the severity of hardship required by ranchers to reduce sediment problems on rangelands. A case study for the Walnut Gulch Watershed in Arizona showed a shift of the spatial distribution of optimal stocking rates with increasing sediment control objectives, so that less grazing occurred near the watershed outlet.



A web-based tool for economic analysis of sediment control on rangeland watersheds


Duan, Y.                                   University of Arizona

Heilman, P.                               SouthwestWatershedResearchCenter

Guertin, D.P.                             University of Arizona


This paper presents the architecture of a web-based decision support system for assessing Best Management Practices (BMPs) for development of Total Maximum Daily Load (TMDL) plans. As the BMPs can be defined specified spatially, the whole system is called a Spatial Decision Support System, or SDSS. The benefits of the approach are that the user does not have to manage all of the spatial data, which can be centrally managed. The disadvantage is that the division of labor has to be coordinated, so that SDSS developers have clearly defined requirements and support for future development and users have the specialized tools they need. Screenshots of the prototype SDSS showing its ability to calculate budgets, present maps showing results, and plot sediment abatement cost curves for the Walnut Gulch Experimental Watershed are provided.


Runoff and erosion modeling by WEPP in an experimental Mediterranean watershed


Licciardello, F.                          University of Catania-Italy

Amore, E.                                University of Catania-Italy

Nearing, M.A.                           SouthwestWatershedResearchCenter

Zimbone, S.M.                         Mediterranean University of Reggio Calabria-Italy


Regulatory policy and land management approaches include the use of soil erosion models to provide the information on natural hazards and human impacts to support soil conservation planning, both through agricultural legislation that defines maximum tolerable soil loss rates, and through federal and local legislation that requires soil erosion controls on many construction sites. To be useful for decision makers, soil erosion models must have simple data requirements and must be applicable to a variety of regions with minimum calibration.  In this syudy the results of applications of the Water Erosion Prediction Project (WEPP) model to monitored watersheds were analysed in order to draw conclusions on model implementation and performance in semi-arid regions of Sicily.  The results of the study showed that the modfel could be calibrated in such a way as to be effecitve for this region.  This has important implications in that it shows that erosion models may be effecitvely applied in semi-arid environments for the purposes of helping to make land management and engineering decisions. 


Partitioning evapotranspiration using diurnal surface temperature variation


Moran, M.S.                             SouthwestWatershedResearchCenter

Keefer, T.O.                             SouthwestWatershedResearchCenter

Paige, G.B.                               University of Wyoming

Scott, R.L.                               SouthwestWatershedResearchCenter

Emmerich, W.E.                       SouthwestWatershedResearchCenter

Cosh, M.H.                              USDA-ARS Hydrology and Remote Sensing Lab

O'Neill, P.E.                              NASA


Encroachment of woody plants in grasslands is becoming a common phenomenon across the Western U.S.  This transformation alters the balance of water loss through transpiration (T) from plants and evaporation (E) from the soil.  In semi-arid, water-limited environments, this can result in a reduction in total vegetation growth and a disruption in natural carbon cycling.  At a recent conference on Ecohydrology, scientists identified the partitioning of E and T as one of the most important ecohydrological challenges.  In this study, daily evapotranspiration (ET) was partitioned into E and T using measurements of diurnal soil surface temperature.  The difference between the mid-afternoon and pre-dawn soil surface temperature, termed Apparent Thermal Inertia (IA), was used to identify days when E was negligible.  For dates when E?0 and ET was known, T was determined as the residual.  This approach was validated at two sites dominated by woody and herbaceous vegetation using conventional instrumentation that was maintained in place continuously for two years.  These preliminary results show promise for addressing important hypotheses posed for semiarid sites, such as 1) woody plant encroachment should increase potential soil evaporation (E) and 2) the T/ET ratio is sensitive to changes in woody plant cover.



Temporal Persistence and Stability of Surface Soil Moisture in a Semi-Arid watershed


Cosh, M.                                  USDA-ARS Hydrology and Remote Sensing Lab

Jackson, T.J.                            USDA-ARS Hydrology and Remote Sensing Lab
Moran, M.S.                             

Bindlish,  R.                              SSAI


Satellite remote sensing of the land surface requires some ground-based validation to insure the satellite is accurate.  The diversity of the land surface requires robust and flexible algorithms as well as good quality ground information to produce a valuable satellite program.  The Advanced Microwave Scanning Radiometer (AMSR-E) is one such satellite instrument, which produces a soil moisture product for the earth's land surface.  Land validation data for soil moisture can be collected several ways, but the most cost efficient is in situ networks at large scales.  This study investigates the quality of one such network in southeastern Arizona, known as the Walnut Gulch Experimental Watershed.  This network is found to have a very good agreement with the average watershed soil moisture as determined by high density sampling that was conducted as part of a large scale experiment.  Also, the network is shown to be temporal stable, indicating it is consistent and reliable over time.  Finally, a comparison of a satellite measure (emissivity) to the watershed average indicates that future calibration and validation efforts using this watershed should be fruitful.