The goal of this research was to develop a watershed-scale model for predicting changes in plant species distribution and abundance (phytogeography) that might occur as a result of changes in climatic factors with global warming. The model was designed: 1) to be spatially explicit and applicable across the entire watershed; 2) to apply to a number of particular species rather than general vegetation types; 3) to predict abundance as well as presence/absence; and 4) to work with simple environmental data, but reflect a biological rationale. Correlations were sought between current phytogeography in the watershed and the synoptic climate variables mean annual temperature, total annual precipitation and cool-/warm-season precipitation ratio. The contribution of edaphic and topographic variables to correlative models was examined and found to be negligible. The correlations established for current conditions were extended to hypothetical future conditions of changed climate in which the values of the variables were manipulated and the model run to produce predictions of altered future phytogeographies. Twenty-seven different hypothetical climate scenarios were modeled, incorporating a 1°C or 2°C rise in temperature with as much as a 10% increase or decrease in seasonal precipitation. Spatial articulation of the model was achieved through raster analysis of gridcell based data layers in a geographic information system. Primary input layers were a series of high-resolution (360x360m) interpolated climate-variable surfaces and a geographically referenced database of plant species presence and abundance derived from an aerial videography sample of the watershed. Logistic regression analysis was used to calculate, for a given set of conditions, the most probable state (present/absent) and abundance class for ten plant species at each grid-cell location in the watershed. Fragmentation of species' distributions before and after change was examined. Results for all studied species showed marked changes in distribution and abundance with temperature rise. Desert species will likely increase in abundance and occupiable area as forest and woodland species decrease, but much depends on the interaction of precipitation with temperature. Model predictions are conservative compared with paleoecological evidence of past changes.

Two piñon (Pinus edulus) tree-ring chronologies developed on each of three substrates (sandstone, shale, and alluvial fan deposits) in southern Utah for the period 1702 to 1997 demonstrate that geologic substrate affects dendrochronologic streamflow reconstructions. Chronologies from alluvial fan deposits explain the most variance of cool-season (October 1 to May 31) flow with an adjusted coefficient of determination (Rₐ²) equal to 0.59. Chronologies from sandstone deposits account for 52 percent of the variance, while those on shale deposits account for 45 percent. Correlation coefficients among the three substrates are significantly different at the 95% confidence level. The highest single-site annual discharge reconstruction (October 1 to September 30), Rₐ² = 0.25, is provided by chronologies from shale deposits. The highest substrate-pair annual discharge reconstruction, Rₐ² = 0.27, is provided by chronologies from alluvial fan deposits. The highest summer discharge reconstruction(July 4 to September 3), Rₐ² = 0.14, is provided by chronologies from sandstone. Over 90 percent of the summer reconstructions are below Rₐ² = 0.10.

OWRT Project No. A-069-ARIZ / Agreement No. 14-34-0001-6003 / Project Dates: July 1975-September 1977 / Acknowledgement: The work upon which this report is based was supported by funds provided by the United States Department of the Interior, Office of Water Research and Technology, as authorized under the Water Resources Research Act of 1978. / In dealing with water management methods for a watershed possibly subject to intensive development in the future, such as the Sonoita Creek Basin in Arizona, a model of the hydrologic system is the only possible link between the hydrologist and the systems engineer. The water balance picture that was taken by the hydrologist has to be advanced up to a point in which the response of the aquifer considered, to different water policies, will be known. At this point the integration between the environment and its management can be properly addressed. From a standpoint of the hydrologist, a model is therefore the overall goal of his study. Such a model will enable him to simulate the relationships between recharge, discharge and ground-water elevation. Consequently, a water balance model was calibrated, and a working routine with the model was developed that was used by the systems engineers.

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A methodology is presented for evaluating timber clearing as a means for beneficially increasing water yields from forested watersheds. Stochastic models of temperature and precipitation are developed and used to generate long term synthetic records of rain, snow, snowmelt, and potential evaporation. A deterministic hydrologic watershed model transforms the synthetic climatic data into long term streamflow records reflecting the hydrologic effects of clearing selected percentages of watershed area, either on a permanent or rotational basis. The simulated streamflow regimes are then analyzed in relation to the impacted reservoir and water supply system. Evaluation categories discussed include timber and forage production, agricultural water supply, flooding, hydroelectric power production, and reservoir-based recreation. A 38.8 square mile watershed on the East Fork White River in east-central Arizona is used to illustrate the procedures developed in this study. Vegetation management alternatives modeled are permanent conversion of 0, 20, 33, 50, 67, and 100 percent of the watershed area, as well as periodic harvesting, with subsequent timber regrowth, of 20, 33, and 50 percent of the watershed area. A hypothetical reservoir system serves as the basis for evaluating a 250 year simulated streamflow record induced by each management option. All conversion activities result in increased streamflow, better ability to meet water demands, greater recreational activity, and more power production. However, potential for flood damage and wasted reservoir releases also increase. Depending on specific management objectives, the ultimate choice lies within the 20 to 50 percent range of permanent conversion activities.

In 1985 the USDA - Agricultural Research Service initiated a national project called Water Erosion Prediction Project (WEPP) to develop a new generation water erosion prediction technology which will replace the USLE by 1992, the most widely used technology for estimating soil erosion by water. For simplicity, the WEPP model was developed assuming quasi-steady state conditions. An evaluation of the effects of formulating the unsteady state sediment continuity equation by assuming quasi-steady state conditions is presented. A methodology was developed to study soil erosion process in rainfall simulator plots treated as a microwatersheds. This was achieved by explicitly separating interrill and rill areas in the rainfall simulator plots using areal photographs and microtopographic data. A detailed analysis was conducted using response surface plots on the model structure of both formulations of the sediment continuity equation. The shape of the response surface plots indicated for each formulation whether the soil erosion parameter estimates were successfully identified. As an additional information, the sediment concentration graphs and the total sediment yield were used to determine major differences between the two formulations of the sediment continuity equation. Rainfall simulator plot data collected in five locations of the US were used for the calibration and validation of the model WESP. The unsteady state approach yielded lower values of the objective function than the quasi-steady state formulation. Using the unsteady state approach, physical interpretation may be associated with the soil erosion parameter values Kᵣ, T(cr), and Vₑ. The quasi-steady state soil erosion estimates showed a weak and unclear physical association. The shape of the sediment concentration graphs were similar for both formulations of the sediment continuity equation. The benefit obtained by using the more complicated unsteady state approach was a more accurate estimation of the peak, or maximum, sediment concentration. Total sediment yield estimates from both formulations were similar. Thus, insignificant benefit was obtained from using the unsteady state approach. In this study hydrographs reached equilibrium due to the long duration of simulated rainfall. The two model formulations might perform far differently under experimental conditions where steady state runoff is not reached.

Changes in redox potential (Eh), major sulfur species and the solubility of selenium and boron in reduced flue gas desulfurization (FGD) sludge, when exposed to atmosphere were studied in laboratory experiments. Also the effect of organic carbon and temperature on reduction of FGD sludge and changes in concentration of major S species was studied. Stable isotopic ratios of sulfur and carbon compounds were used to investigate the possible pathways of S transformation in FGD sludge disposal site. Oxidation of reduced sludge appears to be a two step process, a fast step of chemical oxidation followed by a slow step of biological oxidation and is significantly affected by moisture content and mixing of the sludge. With the addition of organic carbon Eh of the FGD sludge dropped exponentially and reduction of sulfate initiated at Eh of about -75 mV and was maximum in the range of -265 to -320 mV. Temperatur8e of the profile and organic carbon appear to be the key factors affecting the rate and extent of reduction in flooded FGD sludge. Selenium solubility decreased four times as Eh dropped from 215 mV to -350 mV while boron solubility was unchanged in this range of Eh. Stable isotopic ratio of sulfate and sulfide are typical of bacterial reduction and suggest that only aqueous sulfate was being reduced. The low δ³⁴S values of CaSO₄ from the upper layers of profile indicate the production and upward movement of hydrogen sulfide gas in the FGD sludge.

In situ radiometric field data and data simulated with a radiative transfer model were used to evaluate the performance and biophysical interpretation of spectral indices Concurrently with remotely sensed measurements, temporal biophysical measurements for different vegetation types for two semi-arid regions in Niger were made, including leaf area index (LAI), fraction of absorbed photosynthetically active radiation (fAPAR), percent vegetation cover, and biomass. The spectral dynamics of vegetation and soil were characterized at the leaf and canopy scale by optical measurements under many adverse conditions, including variability in vegetation optical and structural properties, soil reflectance properties, sun and view geometry and atmospheric perturbations. The spectral indices evaluated in this research comprised spectral vegetation indices and spectral mixture model indices, computed from spectral reflectances. The performance of different vegetation indices and their sensitivity to green and non-green vegetation and soils were compared and quantified by utilizing estimates of percent relative error in spectral vegetation indices, and estimates of vegetation equivalent noise expressed in terms of biophysical parameters (LAI, fAPAR). The soil adjusted vegetation index (SAVI) and modified normalized vegetation index (MIND VI) were improvements over the normalized difference vegetation index (NDVI), but were still sensitive to many perturbing variables such as soil and vegetation distribution, soil optical properties, litter and green vegetation optical properties and leaf angle distribution. The spectral mixture model indices were designed to be sensitive to vegetation, soil and non-green vegetation components and were shown to provide useful surface information that can aid in minimizing the noise in spectral vegetation indices, and also in improving their biophysical interpretation. Vegetation and soil brightness imagery were created from remotely sensed reflectance data, by calibrating the spectral mixture model with the data generated with a radiative transfer model. The effect of standing litter on spectral indices was shown to possibly cause both an increase and a decrease in the vegetation index, depending on the coupled spectral and structural properties of litter, green vegetation and soil. In situ measurements confirmed the results obtained from the analysis of data sets generated with a radiative transfer model. The implications of the effect of perturbing variables on spectral indices were also discussed.

Watershed models have two significant shortcomings that limit their application to management problems in arid and semi-arid regions. The first is that the performance of event-based hydrologic models for ephemeral stream networks declines significantly as watershed size increases. The second is that no single model is capable of simulating runoff, erosion, and geomorphic response in the channel network for multiple consecutive events. A diffusion-wave routing subroutine was developed for the Kinematic Runoff and Erosion Model (K_INEROS2) using a four-point iterative solution to the modified variable-parameter Muskingum-Cunge (MVPMC4) technique. It was tested against kinematic-wave routing at scales ranging from 0.05 to 150 km² on the Walnut Gulch Experimental Watershed in southeastern Arizona. Analyses demonstrated that MVPMC4 routing significantly improves simulated outflow hydrographs for small to moderate events on watersheds that are 95 km2 and larger. A geomorphic model was developed by modifying KINEROS2 to compute width, depth and slope adjustments from computed changes in sediment storage at each time step. Width and depth adjustments are determined by minimizing total stream power for each reach. A GIS-based interface was developed for model parameterization, coordinating multiple-event batch simulations, tracking cumulative geomorphic change, computing the sediment mass balance, visualizing results, and comparing results from different simulations.

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