Use of Remotely Sensed Data to Quantify Plant Water Use from Irrigated Lands in Wolf Bay Watershed Area
Type of Degreethesis
Forestry and Wildlife Sciences
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Irrigation is one of the major water uses in the US and the world. An attempt is made to quantify water use from irrigated plants using remotely sensed data. Objectives of the study are to 1) assess the validity of a modified surface energy balance algorithm for land (SEBAL) model in the humid southeastern US; 2) quantify seasonal volumetric ET as an estimate of plant water use in Wolf Bay watershed area during growing season (April to September) of 2005-2008 using remotely sensed data; and 3) derive water demand factors from remotely sensed data to project future irrigation water demand in Wolf Bay watershed area. Daily, monthly, and two-month ET from the modified SEBAL are validated with energy-budget eddy covariance ET measurements from four USGS stations in Florida. SEBAL estimated daily ET with a root mean square error (RMSE) of 0.48 mm/day, % RMSE of 10%, mean bias error (MBE) of 0.05 mm, Nash-Sutcliffe efficiency coefficient (ENS) of 0.82, and coefficient of determination (R2) of 0.83. Monthly ET was estimated with a RMSE of 16 mm, % RMSE of 16%, MBE of -2 mm, ENS of 0.77 and R2 of 0.77. Two-month ET was estimated with a RMSE of 30 mm, % RMSE of 16%, MBE of -5 mm, ENS of 0.71 and R2 of 0.73. The validated SEBAL model is applied in Wolf Bay watershed area to estimate seasonal ET from irrigated areas during the growing season (April-September) in 2005-2008. Area of total irrigated agricultural land in Wolf Bay watershed area is estimated using high quality digital aerial photographs, Landsat 5 TM images, and SEBAL derived parameters: surface albedo, normalized difference vegetation index (NDVI), and evaporative fraction. Results confirm that volumetric ET (Plant water use) from irrigated areas was higher in dry years (2006 and 2007) than in the wet year (2005). Estimated water use from irrigated area in Wolf Bay watershed area in 2005, 2006, 2007, and 2008 was 5.91, 6.26, 6.87, and 6.59 million cubic meters, respectively. Water demand factors derived for different crops and turf farms for years 2005 to 2008 confirmed that plants have higher water demand in dry years than in wet years. Water demand factors and landuse and land cover (LULC) projection maps of Wolf Bay watershed area for years 2010, 2020, 2030, and 2040 were utilized to project irrigation water demand under dry, normal and wet precipitation conditions. Future irrigation water demand is based on the extreme scenario that most crop land in Wolf bay watershed area is converted into golf courses and turf farms with the assumptions that 100% of agricultural land is irrigated in 2040. Results indicate that irrigation water demand for year 2010 will be increased by 59% (6.19 to 9.82 million cubic meters), 65% (6.76 to 11.12 million cubic meters), and 63% (6.45 to 10.52 million cubic meters), under wet, dry, and normal climatic conditions, respectively from 2010 to 2040. Remote sensing method has been found useful in estimating plant water use, deriving water demand factors for different plants, and projecting irrigation water demand. Planners can use the projected irrigation water demand information from remote sensing method to effectively manage water resources in Wolf Bay watershed area. A case study is provided showing how the methods can be used to project future water demand at a watershed scale.