WSI (12/08/14 1316)

Department of Water Resources California Cooperative Snow Surveys WATER SUPPLY INDEX (WSI) FORECASTS 2015 Water Year Hydrologic Classification Indices 2015 Water Year Forecast as of December 1, 2014 SACRAMENTO RIVER UNIMPAIRED RUNOFF - SACRAMENTO RIVER INDEX (SRR) Probability of Exceedance Forecast Date 99% 90% 75% 50% 25% 10% -------------------------------------------------------------------------------- Dec 1, 2014 4.9 (27%) 7.2 (39%) 9.7 (53%) 13.7 (75%) 18.5(101%) 23.7(130%) Sacramento River Runoff is the sum of unimpaired flow in million acre-feet at: Sacramento River above Bend Bridge Feather River at Oroville (aka inflow to Lake Oroville) Yuba River near Smartville American River below Folsom Lake Also known as the "Sacramento River Index", this index was previously used to determine year type classifications under SWRCB Decision 1485. Also previously referred to as the "4 River Index" or "4 Basin Index". Water Year Runoff through end of last month: 2015 (current year) = 0.8 MAF 56% of average 2014 (last year) = 0.7 MAF 49% of average Previous Water Year Total Runoff: 2014 = 7.5 MAF 41% of average 1977 (Min) = 5.1 MAF 28% of average 1983 (Max) =37.7 MAF 206% of average 1961-2010 average =18.3 MAF SACRAMENTO VALLEY WATER YEAR TYPE INDEX 40-30-30 (SVI) Probability of Exceedance Forecast Date 99% 90% 75% 50% 25% 10% -------------------------------------------------------------------------------- Dec 1, 2014 2.7 3.5 4.3 5.6 7.2 8.8 Index = 0.4 * Current Apr-Jul Runoff (1) + 0.3 * Current Oct-Mar Runoff (1) + 0.3 * Previous Year's Index (2) Notes: (1) Runoff is the sum of unimpaired flow in million acre-feet at: Sacramento River above Bend Bridge Feather River at Oroville (aka inflow to Lake Oroville) Yuba River near Smartville American River below Folsom Lake (2) Maximum 10.0 for previous year index term Previous Water Year Indices: 2014 = 4.1 50% of average 1977 (Min) = 3.1 38% of average 1983 (Max) = 15.3 186% of average 1961-2010 average = 8.2 Year Type Classification: Index based on flow in million acre-feet: Wet Equal to or greater than 9.2 Above Normal Greater than 7.8, and less than 9.2 Below Normal Greater than 6.5, and equal to or less than 7.8 Dry Greater than 5.4, and equal to or less than 6.5 Critical Equal to or less than 5.4 This index, originally specified in the 1995 SWRCB Water Quality Control Plan, is used to determine the Sacramento Valley water year type as implemented in SWRCB D-1641. Year types are set by first of month forecasts beginning in February. Final determination is based on the May 1 50% exceedence forecast. SAN JOAQUIN VALLEY WATER YEAR TYPE INDEX 60-20-20 (SJI) Probability of Exceedence Forecast Date 99% 90% 75% 50% 25% 10% -------------------------------------------------------------------------------- Dec 1, 2014 0.7 1.0 1.4 2.0 2.8 3.8 Water Year Index based on flow in million acre feet Index = 0.6 * Current Apr-Jul Runoff (1) + 0.2 * Current Oct-Mar Runoff (1) + 0.2 * Previous Year's Index (2) Notes: (1) Runoff is the sum of unimpaired flow in million acre-feet at: Stanislaus River below Goodwin Reservoir (aka inflow to New Melones Res.) Tuolumne River below La Grange (aka inflow to New Don Pedro Reservoir) Merced River below Merced Falls (aka inflow to Lake McClure) San Joaquin River inflow to Millerton Lake (2) Maximum 4.5 for previous year index term Previous Water Year Indices: 2014 = 1.2 35% of average 1977 (Min) = 0.8 26% of average 1983 (Max) = 7.2 219% of average 1961-2010 average = 3.3 Year Type Classification: Index based on flow in million acre-feet: Wet Equal to or greater than 3.8 Above Normal Greater than 3.1, and less than 3.8 Below Normal Greater than 2.5, and equal to or less than 3.1 Dry Greater than 2.1, and equal to or less than 2.5 Critical Equal to or less than 2.1 This index, originally specified in the 1995 SWRCB Water Quality Control Plan, is used to determine the San Joaquin Valley water year type as implemented in SWRCB D-1641. Year types are set by first of month forecasts beginning in February. Final determination for San Joaquin River flow objectives is based on the May 1 75% exceedence forecast. SACRAMENTO VALLEY & SAN JOAQUIN 8 RIVER INDEX Previous month: Nov 460 TAF This index is the sum of the previous month's unimpaired runoff for the 8 rivers that are included in the above SACRAMENTO RIVER UNIMPAIRED RUNOFF and the SAN JOAQUIN VALLEY WATER YEAR TYPE INDEX A listing of reconstructed indices based on historical observed runoff is posted at http://cdec.water.ca.gov/water_supply.html The official year types are based on May 1 forecasts, not the observed runoff. If you have any questions contact the Snow Survey Staff Dave Rizzardo (916) 574-2983 david.rizzardo@water.ca.gov John King (916) 574-2637 john.j.king@water.ca.gov Steve Nemeth (916) 574-2634 stephen.nemeth@water.ca.gov Andy Reising (916) 574-2181 andrew.reising@water.ca.gov Sean de Guzman (916) 574-2208 sean.deguzman@water.ca.gov If you would like to receive an email that includes a discussion of the forecast and a notification that this report has been posted, send an email to: LISTSERV@listserv.state.ca.gov Put only the following information in the message body: SUBSCRIBE [space] DWR_WSI [space] Full Name