Change in Irrigated Land, 1992-1997
This dot density map shows change in irrigated land between 1992 and 1997. Dots are aggregated by and placed randomly within 8-digit hydrologic units. Each red dot indicates a 2,500 acre decrease in the amount of irrigated land between 1992 and 1997, while each blue dot indicates a 2,500 acre increase in irrigated land. This shows where there has been increased and decreased demand on water supplies for agricultural purposes. Areas with 95% or more Federal area are shaded gray. There was a total increase of 2,852,000 acres, a total decrease of 3,171,400 acres. The net decrease for the U.S. was 319,400 acres.
Cautions for this Product:
This map may not be used to determine site- specific information. Within an 8-digit hydrologic unit, dot counts represent acreage totals correctly plus or minus one dot to account for remainders. Data are not collected on Federal land. Data are not available for Alaska or the Pacific Basin. Data for Puerto Rico and the U.S. Virgin Islands are aggregated by 6-digit hydrologic unit. Irrigation data are only collected from cropland and pastureland.
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: Cross of State with 8 Digit Hydrologic Units and 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]
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]
Pastureland and Native Pasture:
A Land Cover/Use category of land managed primarily for the production of introduced or native forage plants for livestock grazing. Pastureland may consist of a single species in a pure stand, a grass mixture or a grass-legume mixture. Management usually consists of cultural treatments-fertilization, weed control, reseeding, or renovation and control of grazing. (For the NRI, includes land that has a vegetative cover of grasses, legumes, and/or forbs, regardless of whether or not it is being grazed by livestock.) [NRI-97]
Product ID: 5349
Production Date: 12/13/00
Product Type: Map
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