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

New Scenario: "Current Policy" or "Continued Changes in Practice". ESHMC Meeting 13 November 2007 B. Contor. Purpose of Scenario. Rationale Changes in practice could occur even w/o change in policy Hydrologic changes might also occur The Question:

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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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