THE CALIFORNIA DROUGHT

Transcription

1 THE CALIFORNIA DROUGHT Helen Dahlke Assistant Professor in Integrated Hydrologic Sciences, LAWR, UC Davis DECEMBER 13,

2 Signs of a 4-year drought NOAA drought index THE DILEMMA OF WATER MANAGEMENT Aug 2013 Nov 2013 Jan 2014 May 2014 Aug 2014 Dec 2014 Annual average temperature: rd warmest year Total Annual Precipitation: 2013 Driest year to date

3 Signs of a 4-year drought August 18, 2015 THE DILEMMA OF WATER MANAGEMENT August 11, 2015 August 18, 2015 Source: c onditions/

4 Famiglietti et al., 2014 THE DILEMMA OF WATER MANAGEMENT California Groundwater

5 THE DILEMMA OF WATER MANAGEMENT How did we get here? The California Water Budget Evapotranspiration ~ 125 MAF Precipitation ~ 200 MAF 3 Storages in California SNOW Water available as runoff ~ 75 MAF? RESERVOIRS GROUNDWATER Source: Hanak et al Managing California s Water From Conflict to Reconciliation

6 California s Water Conveyance THE DILEMMA and OF Storage WATER MANAGEMENT System Source: Hanak et al Managing California s Water From Conflict to Reconciliation

7 THE DILEMMA OF WATER MANAGEMENT California s Water Conveyance and Storage System Source: comparison/index.html

8 THE DILEMMA OF WATER MANAGEMENT Implications of Climate Change: snowpack loss Early rain Reservoir Rule Curve Flood Control Pool Conservation Pool Source:

9 Source: DWR, 2015: California Climate Science and Data for water resources management THE DILEMMA OF WATER MANAGEMENT Implications of Climate Change for water management Current Conditions Runoff is stored in snowpack and reservoirs Storage meets most of the summer demand Shortages are minimal Projected Conditions Earlier runoff Increased summertime water demand Shortages more common

10 THE DILEMMA OF WATER MANAGEMENT Changes in cropping patterns in the Sacramento Valley Average values (in acres) for five northern Sacramento Valley counties. Crop Change Need reliable water supply! Deciduous Nuts & Fruits 219, ,113 38,931 Olive & Citrus 28,997 37,002 8,005 Vineyard 4,000 3, Rice 348, ,316 1,927 Pasture 112, ,528 14,905 Grain & Hay 71,774 61,434-10,340 Field Crops 58,440 37,874-20,566 Truck Crops 33,788 33, Idle Land 32,204 26,609-5,595 Total 909, ,146 26,749 Source: Northern Region, Land Use Section, 2012

11 THE DILEMMA OF WATER MANAGEMENT Changes in irrigation methods in the Sacramento Valley Average values (in acres) for five northern Sacramento Valley counties. Irrigation Method Change Basin Flood 353, , Surface Drip 60,232 83,393 23,161 Micro Sprinkler 46,725 88,390 41,665 Border Strip 117,521 76,581-40,940 Furrow 87,912 59,392-28,520 Hand Move Sprinkler 24,704 19,609-5,095 Buried Drip 600 2,515 1,915 Solid Set Sprinkler 1,624 1, Source: Northern Region, Land Use Section, 2012

12 THE DILEMMA OF WATER MANAGEMENT Farm level decisions impact on groundwater resources Statewide adoption of drip and microsprinkler irrigation systems: Advantages: Reduced crop stress, more efficient crop fertilization Increased yields, improved crop quality More food grown per unit of water and land Consequences: Less groundwater recharge Irrigation inefficiency is a major source of groundwater recharge! More reliance on groundwater than surface water for drip/microirrigation (timing, sediment)

13 THE DILEMMA OF WATER MANAGEMENT 2015 impact of the drought Reduction in surface water supply: 8.7 MAF 6 MAF increase in groundwater pumping Net water supply shortage: 2.7 MAF Accepted price for water: $650 on average Direct agricultural costs of drought is about $1.84 billion and 10,100 direct seasonal jobs. Source: Howitt et al. 2015: Economic Analysis of the 2015 Drought For California Agriculture

14 Glenn County - Groundwater THE elevation DILEMMA OF change WATER MANAGEMENT from Spring 2004 through Spring 2014 Source: DWR, Thomas Harter

15 THE DILEMMA OF WATER MANAGEMENT Sustainable Groundwater Management Act Responsibilities: 1 Develop regulations to revise groundwater basin boundaries 2 Adopting regulations for evaluating and implementing Groundwater Sustainability Plans (by 2020) and coordination agreements 3 Identifying basins subject to critical conditions of overdraft 4 Identifying water available for groundwater replenishment 5 Publishing best management practices for sustainable management of water

16 THE DILEMMA OF WATER MANAGEMENT Water Availability Analysis Estimate the current and forecast the future availability of winter (Nov Apr) excess streamflow for on-farm recharge Excess streamflow: Flood flows or flows above 90 th percentile of the hydrograph 90 th percentile threshold is determined from full historical record Water availability metrics: magnitude, frequency, timing, and duration of winter flood flows above the 90 th percentile Long (>50 years) historic daily streamflow records for 93 stream gauges on streams within the Central Valley Estimates are summarized for different analysis periods (e.g. monthly, seasonal, 6-months, annual) and water year types (e.g. dry, below normal, wet years)

17 THE DILEMMA OF WATER MANAGEMENT (Dec - Feb)

18 THE DILEMMA OF WATER MANAGEMENT

19 THE DILEMMA OF WATER MANAGEMENT Groundwater banking: An agricultural systems approach for water security in California What is groundwater banking? is the active and intentional recharge of groundwater aquifers during years when rainfall is abundant to increase water supply reliability during drought years Research objectives: Estimate whether it is feasible to recharge groundwater during winter using agricultural fields and flood flows. What locations are most suitable? What cropping systems can tolerate this practice? What costs and benefits does agrecharge have? How does recharge impact groundwater quality? Scott Valley, Siskiyou County

20 THE DILEMMA OF WATER MANAGEMENT What form of banking is an agricultural systems approach? Direct percolation but possibly not in the form we might first envision.

21 How much water can be recharged THE DILEMMA in a OF conventional WATER MANAGEMENT alfalfa field? 6 week recharge period Total recharge: 140 AF 6 ft rise in groundwater table 6- year old stand, flood irrigated

22 Thank you! Questions?