Linking Riparian Dynamics and Groundwater: An Ecohydrologic Approach to Modeling Groundwater and Riparian Vegetation |
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Authors: | Kathryn J Baird Juliet C Stromberg Thomas Maddock III |
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Institution: | (1) Department of Hydrology and Water Resources, University of Arizona, P.O. Box 210011, Tucson, Arizona, 85721-0011;(2) School of Life Sciences, Arizona State University, P.O. Box 874501, Tempe, Arizona, 85287-4501;(3) Department of Hydrology and Water Resources, University of Arizona, P.O. Box 210011, Tucson, Arizona, 85721-0011 |
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Abstract: | The growing use of global freshwater supplies is increasing the need for improved modeling of the linkage between groundwater
and riparian vegetation. Traditional groundwater models such as MODFLOW have been used to predict changes in regional groundwater
levels, and thus riparian vegetation potential attributable to anthropogenic water use. This article describes an approach
that improves on these modeling techniques through several innovations. First, evapotranspiration from riparian/wetland systems
is modeled in a manner that more realistically reflects plant ecophysiology and vegetation complexity. In the authors’ model
programs (RIP-ET and PRE-RIP-ET), the single, monotonically increasing evapotranspiration flux curve in traditional groundwater
models is replaced with a set of ecophysiologically based curves, one for each plant functional group present. For each group,
the curve simulates transpiration declines that occur both as water levels decline below rooting depths and as waters rise
to levels that produce anoxic soil conditions. Accuracy is further improved by more effective spatial handling of vegetation
distribution, which allows modeling of surface elevation and depth to water for multiple vegetation types within each large
model cell. The use of RIP-ET in groundwater models can improve the accuracy of basin scale estimates of riparian evapotranspiration
rates, riparian vegetation water requirements, and water budgets. Two case studies are used to demonstrate that RIP-ET produces
significantly different evapotranspiration estimates than the traditional method. When combined with vegetation mapping and
a supporting program (RIP-GIS), RIP-ET also enables predictions of riparian vegetation response to water use and development
scenarios. The RIP-GIS program links the head distribution from MODFLOW with surface digital elevation models, producing moderate-
to high-resolution depth-to-groundwater maps. Together with information on plant rooting depths, these can be used to predict
vegetation response to water allocation decisions. The different evapotranspiration outcomes produced by traditional and RIP-ET
approaches affect resulting interpretations of hydro-vegetation dynamics, including the effects of groundwater pumping stress
on existing habitats, and thus affect subsequent policy decisions. |
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Keywords: | Riparian evapotranspiration Ecohydrologic model Groundwater plant functional group MODFLOW |
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