METRIC is a computer model (Mapping EvapoTranspiration at high Resolution with Internalized Calibration) that uses Landsat satellite data to compute and map evapotranspiration (ET) developed by Richard Allen et.al. at the University of Idaho. [1]
Climate Change is a world wide problem that affects every country on earth. Understanding the processes and factors that control or affect ecosystem response to climate change is essential to mitigate impacts. Studying the regional to global radiation balance, hydrologic energy, water and carbon dioxide fluxes is important to understand effects of climate change on ecosystem health and evolution, including impacts of invasive species such as cheatgrass (bromus tectorum) in the western US. The exchanges of water and carbon at the plant-atmosphere interface are coupled through the active control of leaf and needle stomata on the exchange of gas into or out of leaves with the atmosphere and by effects of direct evaporation from soil. Given the importance of carbon uptake and vapor outputs, the ability to quantify the uptake is important, particularly in large areas with significant capability to assimilate carbon.
In the upper Snake River system of Idaho, the most common ecosystems, besides farms, are alpine forest, sage brush, invasive cheatgrass and bunch grass. A primary goal of this research is to contribute toward a better understanding and methods of quantifying the magnitude, timing, distribution and coupling of carbon, energy and water fluxes in these three dominant natural ecosystems, including effects of burning, and improve the accuracy of modeling sensible heat flux (H) and evapotranspiration (ET) via land surface process and remote sensing models.
Surface energy flux(s) is important for understanding hydrological exchanges and energy exchange dynamics around the world. This study looks at how these hydrologic exchanges and dynamics are effected by climate change and differences in how vegetation “meters” out scarce water. It is especially important to determine the latent heat flux from evapotranspiration (ET) to examine exchanges of energy and mass between the land, hydrosphere, atmosphere, and biosphere. METRIC helps us estimate surface energy flux(s) on a large scale when ground data isn't available.
Experimentally, the calculation of evapotranspiration can be made with potentially good accuracy using weighing lysimeters, eddy covariance techniques and the Bowen Ratio. These methods are limited because they provide point values of ET for a specific location that why METRIC is so valuable because it can produce ET maps that have values across the entire landscape. This limitation has motivated the use of remotly sensed data from satellites to evaluate ET over large areas. The major advantage of remote sensing is that ET can be computed without quantifying other complex hydrological processes through the use of energy balance.
ET is calculated as a "residual": ET=Rn−G−H
Rn= net radiation G= soil heat flux H= sensible heat flux