Energy Balance of Urban Turfgrass in a Semi-Arid environment

Utah has the second highest per-capita domestic water usage in the United States, with a majority going towards outdoor use. It also has population that is expected to double in the next 50 years, and with most of that growth happening in urban areas, it is increasingly important to understand how much water is being used by the landscape in order to plan for future water use. Previous work has shown that evapotranspiration (ET) of turfgrass surfaces can vary greatly from the prescribed reference ET and crop coefficient values. Added complexity from the surrounding urban area also alters the energy balance for turfgrass, further changing its water use.

This project uses eddy covariance measurements of ET over a golf course with cool-season turfgrass for verifying remotely sensed (RS) ET. Remote sensing is an increasingly popular tool to estimate ET, as it provides a spatial estimate of ET that changes with landscape water needs rather than prescribing a single value to an entire area. These models vary in complexity. A simple ET model is used in this study to see which processes can be captured by the model. A simple RS ET model called the “triangle method” uses normalized difference vegetation index (NDVI) and top of atmosphere (TOA) radiant temperature from Landsat 8 imagery to estimate evaporative fraction based on the distribution of the two variables for the entire image. ET is then calculated after estimating net radiation and ground heat flux. This is tested against eddy covariance ET for select dates during the 2016 and 2017 growing seasons. Preliminary testing has shown that the triangle method estimates ET fairly well under certain conditions for the test site, but needs to be verified for other days throughout the growing season.