Submitted to: Encyclopedia of Water Science
Publication Type: Book / Chapter
Publication Acceptance Date: 5/1/2003
Publication Date: 10/1/2003
Citation: Wilcox, B.P., Seyfried, M.S., Breshears, D. 2003. Water balance on rangelands. Encyclopedia of Water Science.
Interpretive Summary: In general, rangelands are regions in which precipitation is low and the natural vegetation is therefore dominated by shrubs and grasses. These regions are commonly used for livestock production throughout the world. Due to the scarcity of water in these regions, it is especially important the we learn where water can be found and where the flow of water is greatest. In this chapter we describe, in general terms, what happens to water that enters rangelands either as rain or snow. Throughout these regions, most incoming water is either evaporated directly back to the atmosphere, or passes through plants to the atmosphere. That portion which passes through plants is variable, but also very important because it is directly related to plant growth and carbon sequestration. A much smaller portion, usually among 5%, runs off to streams. This portion, though small, is often critical because it results in damaging floods, erosion and, in some cases recharges the groundwater. Groundwater recharge is also a very small portion. It can, however, be
Technical Abstract: On rangelands, the water balance is driven and defined to a great extent by the fact that potential evapotranspiration is much greater than precipitation, which in turn contributes to a large soil water deficit. As a rule, therefore, evapotranspiration is the largest component of the water balance equation; the other components are generally quite small (nevertheless, they may be exceedingly important). In addition, both the magnitude and the definition of the different water balance components, particularly runoff, are very much scale-dependent. Newer technologies allow us to estimate more precisely than ever before the water balance components. It is now possible to directly measure plant-community-level evapotranspiration, soil water evaporation as a percentage of transpiration, interception loss during an actual rainstorm, groundwater recharge, and runoff¿all at multiple scales. Application of these technologies promises to help us gain the vital information required to develop workable strategies for solving the growing problems of rangeland degradation.