Groundwater, Vegetation, and Atmosphere: Comparative Riparian Evapotranspiration, Restoration, and Water Salvage

Abstract

As water shortages persist throughout the Western U.S., a great deal of money and effort is directed toward decreasing riparian water loss, thereby enabling continued water use by irrigators, industry, and municipalities. This study focuses upon long-term measurement of evapotranspiration (ET) by native and non-native riparian species along the Middle Rio Grande (MRG) in New Mexico where riparian ET has been estimated to be 20 to 50 percent of water budget depletions. Leaf area index (LAI) was most strongly related to average ET rates, irrespective of species composition. Decreased LAI caused by crown dieback in native cottonwood was found at sites where the drought has also resulted in groundwater decline. Saltcedar ET, on the other hand, increased from 6 to 9 mm/day during groundwater declines of up to 7.5 cm/day. Atmospheric conditions that influence ET rates include vapor pressure deficit, net radiation, precipitation, friction coefficient, and the relative contribution of winds that are tangential and transverse to the riparian corridor. Some of these conditions interact to affect ET rates. For example, precipitation events are associated with lower net radiation, vapor pressure deficit, and ET. Potential water salvage following removal of non-native vegetation was predicted by comparing ET and LAI rates in various vegetation types. Lowest LAI and ET are found in a saltcedar/saltgrass non-overlapping mixed stand. In contrast, a dense monospecific saltcedar stand frequently consumes up to 11.5 mm/day, especially when flooded. ET from other vegetation types along the Middle Rio Grande seldom spikes so high. Conversion from dense monospecific saltcedar to sparse saltcedar/saltgrass woodland is predicted to save 0.2 m per year, based upon both ET and LAI changes in such a conversion. Previous studies of water salvage place this value between positive or negative, for unsuccessful removal of saltcedar may result in increased ET.

Parent Publication

• Monitoring Science and Technology Symposium: Unifying Knowledge for Sustainability in the Western Hemisphere

Citation

Cleverly, J. R.; Dahm, C. N.; Thibault, J. R.; McDonnell, D.; Coonrod, J. E. Allred. 2006. Groundwater, Vegetation, and Atmosphere: Comparative Riparian Evapotranspiration, Restoration, and Water Salvage. In: Aguirre-Bravo, C.; Pellicane, Patrick J.; Burns, Denver P.; and Draggan, Sidney, Eds. 2006. Monitoring Science and Technology Symposium: Unifying Knowledge for Sustainability in the Western Hemisphere Proceedings RMRS-P-42CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 75-80