Percent of Irrigated Cropland in Gravity Irrigation, 1992
This shaded polygon map shows the percent of irrigated cropland in gravity irrigation for each 8-digit hydrologic unit. Areas with 95% or more Federal area are shown as gray. There were 27.5 million acres of gravity irrigated cropland in the U.S. in 1992.
Cautions for this Product:
This map does not show the total amount of gravity irrigated Cropland. Data are not collected on Federal land. Data are not available for Alaska, and the Pacific Basin. Data for Puerto Rico and the U.S. Virgin Islands are shown by 6-digit hydrologic unit.
Source: National Resources Inventory, 1997
NRI sample data are generally reliable at the 95% confidence interval for state and certain broad substate area analyses. Generally, analyses that aggregate data points by smaller geographic areas and/or more specific criteria result in fewer data points for each aggregation and therefore less reliable estimates. NRI maps reflect national patterns rather than site- specific information.
Aggregate Layer: 8 Digit Hydrologic Unit Areas with Federal Land
Other Layers Displayed: States, Rivers
A Land cover/use category that includes areas used for the production of adapted crops for harvest. Two subcategories of cropland are recognized: cultivated and noncultivated. Cultivated cropland comprises land in row crops or close-grown crops and also other cultivated cropland, for example, hayland or pastureland that is in a rotation with row or close-grown crops. Noncultivated cropland includes permanent hayland and horticultural cropland. [NRI-97]
Water is delivered to the farm and/or field by canals or pipelines open to the atmosphere; and, water is distributed by the force of gravity down the field by: [NRI-97] 1. A surface irrigation system (border, basin, furrow, corrugation, wild flooding, etc.) or, 2. Sub- surface irrigation pipelines or ditches.
A hierarchical system developed by the U.S. Geological Survey that divides the United States and the Caribbean into 21 major regions, 222 subregions, 352 accounting units, and further subdivided into 2,150 cataloging units that delineate river basins having drainage areas usually greater than 700 square miles. [USGS]
Land that shows evidence of being irrigated during the year of the inventory or during two or more years out of the last four years. Water is supplied to crops by ditches, pipes, or other conduits. Water spreading is not considered irrigation; it is recorded as a conservation practice. [NRI-97]
Product ID: 6016
Production Date: 5/23/01
Product Type: Map
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