Conversion of irrigated agricultural land in the Intermountain West to non-agricultural uses: consequences for water management and hydrology

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For over a century, irrigated agriculture has dominated water use in the Intermountain West. Agricultural land is now being replaced by suburban and exurban development, changing the way water is managed and used. We used stakeholder interviews and hydrologic analysis to assess the effects of such land conversion on water use, water management, and hydrology in the Henry's Fork watershed, Idaho and Wyoming. We found that traditional irrigated agriculture consumptively uses 25% of the water withdrawn; most of the remainder recharges local and regional aquifers. This irrigation-dependent recharge, due primarily to canal seepage, maintains late-season stream flow, groundwater supply for domestic and agricultural use, and ecosystem services associated with groundwater emergence. Watershed-wide, 5% of irrigated land has been replaced by development, but large areas of irrigated land have become fragmented into patchworks of smaller irrigated parcels surrounded by non-agricultural uses. Physical fragmentation, lack of communication among rapidly diversifying stakeholders, and disjoint planning processes for land and water use challenge the ability of small irrigation companies to maintain and operate canal-based irrigation. Although we found no difference in consumptive use of water per unit area between subdivisions and agricultural land, subdivisions tend to use more groundwater and less surface water. Thus, land conversion has the net effect of decreasing groundwater supplies. Although resulting hydrologic regimes are generally closer to the natural surface-dominated regimes that existed prior to European settlement, institutional and ecological systems have evolved over the past century around the groundwater-dominated system created by irrigated agriculture. Changes to that system will potentially benefit resources dependent on surface-dominated hydrologic regimes (e.g., native fish) but negatively affect resources and water users dependent on groundwater. To minimize unintended hydrologic consequences associated with land-use changes, we recommend increased integration of water and land-use planning and are actively communicating this message to stakeholders and decision-makers.

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ELECTRONIC FILE - Ecology [presentation and abstract]

SWAP (2/19/2016) citation:
Van Kirk R, Apple B, Baker JM, Everett Y, Finney B, Liegel L, Orosz V, Peterson K, Ragotzkie K, Swensen D, et al. 2012. Conversion of irrigated agricultural land in the Intermountain West to non-agricultural uses: consequences for water management and hydrology. In: Proceedings of the 2012 USDA–NIFA National Water Conference: Land and Sea Grant Initiatives for a Changing World; 2012 May 20–24; Portland, OR.