Accurate estimation of evapotranspiration (ET) is essential for assessments of water balance and hydrologic responses to forest restoration treatments in uplands adjacent to the Desert LCC. As part of the Four Forests Restoration Initiative, a new paired watershed study is being planned to assess the hydrologic effects of mechanically thinning and restoring a more frequent fire regime to the ponderosa pine forests of Arizona. Water and energy balances will be measured and modeled in these paired watersheds to help inform and better plan for the hydrologic responses of future forest restoration actions. Researchers at Northern Arizona University have collected six years of eddy covariance measurements of ET in the ponderosa pine forest of Northern
Arizona. One site consists of a thinned pine stand and the other one is an undisturbed-control pine stand. These studies show a short-lived and transient decrease in ET at the thinned site similar to the hydrological results of separate paired watershed studies in Arizona’s ponderosa pine forests from the 1950s to 1980s using only precipitation, stream discharge and basal area change data. We propose to 1) continue to directly measure ET via eddy covariance measurement at the thinned site, and 2) examine the capability of existing models and algorithms to predict ET of upland forests of the Desert LCC based on comparisons with ET measured by eddy covariance. Models evaluated will include BIOME-BGC, SoilWat, and Preistley-Taylor.
The results of this study will provide a validated technique for measuring landscape-scale ET in upland semi-arid forests that supply water to the Desert LCC. Because ET is the largest component of the hydrological cycle that returns water to the atmosphere, it has the largest influence on the hydrologic response of recharge and runoff processes which provide surface water and groundwater to rare aquatic resources in the Desert LCC. The proposed 2-year project will begin October l, 2012 and be completed by September 30, 2014.