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New Scenario: "Current Policy" or "Continued Changes in Practice"

The ESHMC meeting held on November 13, 2007, focused on the potential impacts of hydrologic changes and agricultural practices, even in the absence of policy changes. Key topics included irrigation efficiency, urbanization effects, and managed recharge strategies. The proposed approach utilized a steady-state model to assess how various hypothetical changes could influence agricultural water use, crop management, and overall water budgets. Factors like climate variability, agricultural practices, and infrastructure improvements were evaluated, with a focus on their speculative nature and potential for significant qualitative insights.

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New Scenario: "Current Policy" or "Continued Changes in Practice"

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  1. New Scenario:"Current Policy" or "Continued Changes in Practice" ESHMC Meeting 13 November 2007 B. Contor

  2. Purpose of Scenario • Rationale • Changes in practice could occur even w/o change in policy • Hydrologic changes might also occur • The Question: • Where might we be headed if any of these things were to actually happen?

  3. Proposed Approach • Steady-state • we don't know how fast changes might occur • Superposition • so we can tease out the effects of individual hypothetical components • Not fine tuned • this is all highly speculative anyway; no utility in extreme refinement of numbers

  4. Proposed Approach • Assessment of probability: • No assessment? • Limited qualitative assessment? • Reporting format: • Single report summarizing all analyses

  5. Potential changes to evaluate • Irrigated agriculture ET • Continued conversion to sprinklers • Canal lining • Urbanization • Managed recharge

  6. Irrigated agriculture ET • Increase: • Possibly caused by • climate change (hotter, drier) • crop mix (more alfalfa & corn) • changes in crop varieties • more intense management • Model 10% of 2006 ET as discharge, on GW & Mixed-source lands, plus SW lands where net recharge > 0.5 feet/year

  7. Irrigated agriculture ET • Decrease: • Possibly caused by • climate change (wetter; also, more C02 = stomatal control) • crop mix (more beans, grain & potatoes) • Model 10% of 2006 ET as recharge on all ag lands

  8. Conversion to sprinklers • Assume all remaining lands will be converted • Two mechanisms on all lands • increased net acreage (bumps, field roads, high spots) • increased vigor due to better timing of irrigation

  9. Conversion to sprinklers • Additional mechanism on water-short lands: • Improved CU reduces percolation loss • recovered water is available for ET on former dry spots

  10. Conversion to sprinklers • Modeled stress based on current sprinkler percent & ET adjustment factors • (1.05 - 1.00) * (1 - current Spr. %) * (2006 ET), modeled as discharge • If net SW recharge < 0.5 ft/year, model additional 0.25 ft/year discharge

  11. Canal Lining • Assumptions: • Only changes in diversions, returns, and CU will affect the water budget • All other impacts of lining are only changes in spatial distribution • Lining will occur only if financial incentive exists

  12. Canal Lining • Limited financial incentives exist • No incentive for reduced diversions • natural flow: goes to next junior • storage: rental pool price is too low to justify cost of lining • No incentive to increase returns or spills • goes downstream to next user

  13. Canal Lining • There are only two meaningful financial incentives • Reduce GW pumping on mixed-source lands (no change in water budget) • Increase CU (better crops) on SW-only lands (changes water budget) • Increased CU on SW-only lands will occur only where crops are currently water stressed

  14. DANGER, WIL ROBISON! Canal Lining • There are only two meaningful financial incentives • Reduce GW pumping on mixed-source lands (no change in water budget) • Increase CU (better crops) on SW-only lands (changes water budget) • Increased CU on SW-only lands will occur only where crops are currently water stressed

  15. Canal Lining • Proposal • If net SW recharge > 0.5 ft/year, no change due to canal lining • If net SW recharge < 0.5 ft/year, change = 15% of SW diversion volume, represented as extraction from aquifer • Spatially apply to main canals • Calibration data • Hyd2mil shapefile

  16. Urbanization • Use 2004 & 2006 NAIP aerial images to assess annual rate of change in size & shape of urban areas • Rexburg • Rigby • Idaho Falls • Pocatello • Jerome

  17. Urbanization • Use rates of change to construct year-2011 polygons (2006 + 5) • Intersect w/current irrigated-lands polgyons • GW & Mixed: No change • Not irrigated: No change • SW-irrigated: 30% of current net SW recharge, applied as negative stress (discharge) to the model

  18. Urbanization Rationale • GW & Mixed-source irrigated lands, non-irrigated lands: • all in-home & landscape irrigation will be supplied by transfer of GW rights or other fully-mitigated GW pumping • SW-irrigated lands • in-home use supplied by transfer or other fully-mitigated GW pumping • landscape irrigation supplied by existing SW rights but at reduced diversion & recharge rates

  19. Managed Recharge • Key assumptions • managed recharge is "current policy" • the future may bring some limited success in achieving this policy

  20. Managed Recharge • Conceptual approach • absolute lower limit = zero • absolute upper limit = old recharge scenario • lower limit for this scenario = old recharge scenario * "X" • upper limit for this scenario = old recharge scenario * "Y" (0 <= X <= Y <= 1.0)

  21. We can set "X" and "Y" by combining preferences of ESHMC members

  22. (End)

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