The Delaware Geological Survey released a new Report of Investigations titled “Estimating Evapotranspiration for 2016 Growing Season Using Landsat 8 Data and Metric Model in Sussex County, Delaware”, which was prepared by Changming He and A. Scott Andres of the Survey, and Kevin Brinson and Tracy DeLiberty of the University’s Department of Geography and Spatial Sciences. DGS RI No. 84 documents the methods and results of using satellite data combined with local climatic data to estimate monthly distribution of evapotranspiration (ET) in Sussex County, Delaware.

ET is a major part of the water cycle. Reliable measurements or estimates of ET can greatly improve quantitative forecasts and hindcasts of water demand by crops, horticulture, and natural vegetation, and can also be used to help manage and conserve water resources. Compared to direct measurement of ET in the field, which is limited to small areas, remote sensing methods have proved cost-effective in providing accurate regional and global coverage. This study used an energy-balance based ET mapping tool called METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration) that utilizes satellite images and weather data to estimate ET.
This method is validated by comparing simulated results with field measurements using an eddy covariance instrument. The study results shows that the total estimated ET during Sussex County’s growing season (May-September) in 2016 accounts for 77 to 87 percent of historical-averaged annual ET in this region. The model-simulated seasonal ET for agricultural land is about 33 percent higher than urban/suburban areas and about 22 percent lower than forested areas. This study also shows that when forestlands are converted to urban/suburban uses, significant amounts of water are diverted from ET and are then available to run off and/or infiltrate. Given that urban/suburban land has impervious surfaces in the forms of rooftops, roads, driveways, parking lots, sidewalks, etc., much of the water not lost to the atmosphere through ET presumably becomes part of the surface runoff portion of the water budget, thus underscoring the need for adequate storm-water management systems for urban/suburban lands. The results also imply that the practice of ET-based irrigation scheduling could be valuable in Sussex County and throughout the 20 percent of Delaware farmland that is irrigated.
The report fulfills part of the DGS’s mission to understand hydrologic systems and to advise, inform, and educate Delawareans about the results of such investigations so they can serve as a resource for scientists, engineers, planners, emergency managers, and the public.

Research of Investigations No. 84 is available in pdf format from the DGS web site at http://www.dgs.udel.edu/publications. For additional information, contact the Survey at (302) 831-2833 or via email at delgeosurvey@udel.edu.