Anthony Morse

Evapotranspiration on the Watershed Scale Using the SEBAL Model and Landsat Images

SEBAL (Surface Energy Balance Algorithm for Land) is an image-processing model comprised of twenty-five submodels that calculates evapotranspiration (ET) and other energy exchanges at the earth’s surface. SEBAL uses image data from Landsat or other satellites measuring thermal infrared radiation, visible and near-infrared. SEBAL was developed in the Netherlands by Bastiaanssen and was modified during this study for mountainous terrain and clear, cold lakes. ET is computed on a pixel-by-pixel basis from an energy balance. The Bear River Basin covers 20,000 km 2 of Idaho, Utah, and Wyoming and contains about 190,000 ha of crop land. ET maps were generated on a monthly basis. The maps show a progression of ET during the year as well as distribution in space. Predicted ET was compared with lysimeter measurements of ET with good results, with monthly differences averaging +/- 16%, but with seasonal differences of only 4% due to reduction in random error.

Use of the METRIC evapotranspiration model to compute water use by irrigated agriculture in Idaho

In 1995, the U.S. Geological Survey estimated consumptive water used by irrigated agriculture accounted for more than 99% of total water use in Idaho. The most recent water-use estimate was done for the year 2000. Unlike previous years, USGS did not report water use by irrigated agriculture. The value of Idahos irrigated agriculture was S2.58 billion in 1997. The Idaho Department of Water Resources wanted water use statistics for 2000, but knew the process would be expensive and time-consuming. A remote-sensing based method, METRIC, offered an alternative solution. METRIC was developed jointly by the University of Idaho and the Idaho Department of Water Resources under a NASA/Synergy grant. METRIC is an evapotranspiration model that uses the visible, near infrared, and thermal infrared bands of any appropriate satellite to compute a complete energy balance for each image pixel. Landsats 7 and 5 were used for this application, with multiple dates processed for nine nominal scenes for the year 2000 in 28 counties of southern Idaho, the region of the state where irrigated agriculture is concentrated. Land in irrigated agricultural was delineated using National Land Cover Data, other data, and thresholding of evapotranspiration values. METRIC computed 9,313,503 acre feet of evapotranspiration from 3,552,174 irrigated acres, or 2.6 acre feet per acre. The irrigated acreage is biased high due to the generalizing affect of the land use/land cover data set. Nevertheless, the results suggest that past water use data may have under estimated consumptive use. The next phase of the study is to compare METRIC-derived evapotranspiration processed from year 2000 MODIS data with the Landsat results

Mapping historical change in the irrigated agriculture of the lower Boise River Valley, Idaho.

Abstract Changes in irrigated agricultural land use were mapped using 1938–1939 and 1994 aerial photographs for 2,600 square kilometers of the lower Boise River Valley of Idaho. The project was a joint effort between the U.S. Bureau of Reclamation and the Idaho Department of Water Resources to develop land use change data that will be used for comprehensive water management and administration. The method involved scanning aerial photographs to produce image files that were rectified and mosaicked using geographic information system (GIS) software. The images were interpreted on-screen into 24 land use and land cover classes for the 1994 data and into two classes for the 1938–1939 data. Commercial GIS software and custom-developed programs facilitated the image interpretation and helped create land use change data, maps, and tables.