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Evapotranspiration rates and the ground water component of evapotranspiration at a site in Colorado's San Luis Valley that is dominated by shrubby phreatophytes (greasewood and rabbitbrush) were compared before and after a water table drawdown. Evapotranspiration (ET) rates at the site were first measured in 1985–1987 (pre-drawdown) when the mean water table depth was 0.92 m. Regional ground water pumping has since lowered the water table by 1.58 m, to a mean of 2.50 m. We measured ET at the same site in 1999–2003 (post-drawdown), and assessed physical and biological factors affecting the response of ET to water table drawdown. Vegetation changed markedly from the pre-drawdown to the post-drawdown period as phreatophytic...
Evapotranspiration determined using the energy-budget method at a semi-permanent prairie-pothole wetland in east-central North Dakota, USA was compared with 12 other commonly used methods. The Priestley-Taylor and deBruin-Keijman methods compared best with the energy-budget values; mean differences were less than 0.1 mm d−1, and standard deviations were less than 0.3 mm d−1. Both methods require measurement of air temperature, net radiation, and heat storage in the wetland water. The Penman, Jensen-Haise, and Brutsaert-Stricker methods provided the next-best values for evapotranspiration relative to the energy-budget method. The mass-transfer, deBruin, and Stephens-Stewart methods provided the worst comparisons;...
Non-native shrub species in the genus Tamarix (saltcedar, tamarisk) have colonized hundreds of thousands of hectares of floodplains, reservoir margins, and other wetlands in western North America. Many resource managers seek to reduce saltcedar abundance and control its spread to increase the flow of water in streams that might otherwise be lost to evapotranspiration, to restore native riparian (streamside) vegetation, and to improve wildlife habitat. However, increased water yield might not always occur and has been substantially lower than expected in water salvage experiments, the potential for successful revegetation is variable, and not all wildlife taxa clearly prefer native plant habitats over saltcedar....
In dryland ecosystems, the timing and magnitude of precipitation pulses drive many key ecological processes, notably soil water availability for plants and soil microbiota. Plant available water has frequently been viewed simply as incoming precipitation, yet processes at larger scales drive precipitation pulses, and the subsequent transformation of precipitation pulses to plant available water are complex. We provide an overview of the factors that influence the spatial and temporal availability of water to plants and soil biota using examples from western USA drylands. Large spatial- and temporal-scale drivers of regional precipitation patterns include the position of the jet streams and frontal boundaries, the...
Summary Human activities have historically affected hydrology in the upper Midwestern United States, specifically through the conversion of forests and prairie grasslands to agricultural uses. The hydrologic impacts of land-use change due to settlement on the water balance of three Great Lakes states: Minnesota, Wisconsin, and Michigan were analyzed using the Variable Infiltration Capacity (VIC) large-scale hydrology model, and changes in the spatial distribution of vegetation types were studied. Point model simulations demonstrated that the VIC model simulated changes in average annual and monthly evapotranspiration (ET) and total runoff response were in the same direction and had similar magnitudes to values from...
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Synopsis: This study analyzed the effects of vegetation change on hydrological fluctuations in the Columbia River basin over the last century using two land cover scenarios. The first scenario was a reconstruction of historical land cover vegetation, c. 1900. The second scenario was more recent land cover as estimated from remote sensing data for 1990. The results show that, hydrologically, the most important vegetation-related change has been a general tendency towards decreased vegetation maturity in the forested areas of the basin. This general trend represents a balance between the effects of logging and fire suppression. In those areas where forest maturity has been reduced as a result of logging, wintertime...


map background search result map search result map Effects of land cover change on streamflow in the interior Columbia River Basin (USA and Canada). Effects of land cover change on streamflow in the interior Columbia River Basin (USA and Canada).