California’s Water Supply Forecasting
Water Education Foundation: Challenges for Water Operations February 23, 2016
David Rizzardo, PE Chief, Snow Surveys Section Hydrology Branch/Division of Flood Management California Department of Water Resources
1 Background on Water Supply Forecasting Products 2 Southern Cascades and Trinity: Mainly rainfall driven region with peak elevations around 3050 m/ 10000 ft. (other than Mt. Shasta and Mt. Lassen). Highly influenced by volcanic soils and some rain shadowed areas. Flood threats are driven by heavy precipitation events. Northern Sierra: Rainfall driven region. Peak elevations top out at 3050-3350 m /10000- 11000 ft. Heavy rainfall/snowfall events possible. Large area of upper Feather watershed sits in rain shadowed plateau. 1986 and 1997 extreme precipitation Central/Southern storms caused flooding Sierra: Snow melt downstream of this area. driven basins. Large variety in size of Eastern Sierra/Owens watersheds. You are here River: High elevation, Characterized by high snow melt driven elevations (up to 4270 basins. Watersheds m / 14000 ft.), upper are in rain shadow elevations consist of from Sierra Nevada. large areas of exposed Rivers drain to granite batholiths. terminal sinks in Susceptible to snow Nevada desert. Gage melt floods in heavy data is extremely snow pack years. limited. Most Limited data above susceptible to snow 3350 m/11000 ft. which melt flood events. can account for up to 3 15% of watershed. 4 Bulletin 120: Seasonal Runoff Forecasts
April-July Forecast and % of Average Water Year F’Cast Distribution 5 April-July Forecast 80% Prob. Range Water Year Forecast and % of Avg. Water Year F’Cast 80% Prob. Range Water Supply Index (WSI) / Water Year Runoff Forecasts
Sacramento River Runoff (SRR) Sacramento Valley Index (SVI)
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San Joaquin Valley Index is similar
Feather River
4500 4000 3500 How Well Does Fall / 3000 Winter Unimpaired 2500 2000 Runoff 1500 Predict of AJ Volumes? 1000 April-July (taf)Runoff 500 0 0 1000 2000 3000 4000 5000 6000 Kings River 3500 October-March Runoff 3000
2500 2000 1500 1000 July July Runoff (taf) - 500 0 April 0.0 500.0 1000.0 1500.0 Oct-March Runoff 7 Correlation of AJ Runoff to High Elevation Snow Index
Kings River Feather River 4500 3500
4000 3000
3500 2500 3000 2000 2500 2000 1500 July Runoff(taf) July July Runoff (taf) - 1500 - 1000 1000 April 500 April 500 0 0 0 100 200 300 0 50 100 150 200 250 High Snow Index High Snow Index
“Non Snow Driven” Basin (Feather) vs. “Snow Driven” Basin (Kings)
We analyze similar patterns and correlations for precipitation data 8 Graphical Analyses = Reality Check
9 Water Supply Forecast Review April and May Bulletin120 Forecasts 2011
Statewide Precip: 140% avg Statewide Precip: 135% avg
Snow Pack: 170% avg Snow Pack: 185% avg
10 Water Supply Forecast Review April and May Bulletin120 Forecasts 2012
Statewide Precip: 70% avg Statewide Precip: 75% avg
Snow Pack: 50% avg Snow Pack: 40% avg
11 Water Supply Forecast Review April and May Bulletin120 Forecasts 2013
Statewide Precip: 75% avg Statewide Precip: 75% avg
Snow Pack: 40% avg Snow Pack: 15% avg
12 Water Supply Forecast Review April and May Bulletin120 Forecasts 2014
Statewide Precip: 50% avg Statewide Precip: 50% avg
Snow Pack: 25% avg Snow Pack: 15% avg
13 Water Supply Forecast Review April and May Bulletin120 Forecasts 2015
Statewide Precip: 75% avg Statewide Precip: 70% avg
Snow Pack: 5% avg Snow Pack: 2% avg
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February 2016 Water Supply Index Forecasts
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February 2016 Bulletin120 Forecasts
Statewide Precip: 115% avg
Snow Pack: 115% avg Snow Pack: 93% avg
Dry Feb. = Drop in Forecast
16 Questions?
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