Irrigated Acreage Delineated from Landsat-Derived Maximum Normalized Difference Vegetation Index (NDVI) 1975-2010, Walker River Basin Nevada and California

These data represent the extent and spatial distribution of irrigated acreage delineated from maximum Normalized Difference Vegetation Index (NDVI) derived from Landsat scenes in the Walker River Basin, California and Nevada, at five-year intervals from 1975-2010. The field boundaries in this data set are digitized from one-year composite maximum NDVI data derived from atmospherically corrected Landsat 2 Multispectral Scanner (MSS), Landsat 5 MSS, and Landsat 5 Thematic Mapper (TM) scenes. NDVI was calculated from the corrected reflectance data for each selected scene during the growing season (May through early October) and a single, composite image of maximum NDVI values was derived for each five-year interval. Selecting the maximum NDVI value removed low values associated with plant phenology, harvest cycles, and irrigation operations. Initial field boundaries were digitized from the 2010 National Agriculture Imagery Program (NAIP) data and boundary geometries were divided and shaped based on temporal changes in irrigation practices, crop rotations, and other changes identified in the Landsat-derived maximum NDVI data. Each polygon is attributed with an estimated irrigation status of irrigated or non-irrigated. Mapped fields were classified as irrigated during a growing season if more than 45-percent of a field had a maximum NDVI value greater than or equal to 0.4.