Submitted to: Society for Range Management Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/14/1994
Publication Date: N/A
Technical Abstract: Various equations have been used to estimate reference evapotranspiration (ET) for agronomic crops. They are also commonly used in the ET components of rangeland hydrologic models. Comparisons of ET, equations for cropland applications have shown that the equations not only calculate different amounts of ET, but that there is also a distinct interaction between the equations and local climatic regimes. To evaluate ET, equations for rangeland applications, we used weather records from three sagebrush- grass range sites on the USDA Agricultural Research Service, Reynolds Creek Experimental Watershed. The three sites represent an elevation gradient of over 3000 feet. Preliminary results indicate that during the early growing season, calculated ET values differed by over 100%. By midsummer, these differences were less than 50%. This paper compares several ET equations in terms of amounts of ET, calculated and site-equation interactions. ET measured by lysimeters and the Bowen ratio-energy balance method will be used to help evaluate the utility of the various equations for use with rangeland models. ET equations compared include: Penman, Penman-Monteith, Jensen-Haise, modified Jensen-Haise, and a modified Penman that is used in the SPUR model.