1. California’s climate

3. Sierra Nevada snow depth, April 13, 2005 April 1 snowpack was 3 rd largest in last 10 years 500 100 10 0 50 250 cm snow Source: NWS-NOHRSC

4. Sierra Nevada snow water equivalent April 13, 2005 200 100 50 10 1 0 5 25 cm water 0.1 Source: NWS-NOHRSC

5. Sierra Nevada snow water equivalent April 1, 2007 200 100 50 10 1 0 5 25 cm water 0.1 Source: NWS-NOHRSC

6. >2.0 1.8 1.3 0.9 0.6 0.4 <0.3 >1.8 1.5 1.0 0.4 0 snowpack depth, m precipitation, m precipitation increases snowpack increases N 2000 km Sierra Nevada precipitation

7. Snow cover in the Western U.S. –exhibits considerable interannual variability –occurs on only a small fraction of the landscape –yet it sustains the streamflow & groundwater recharge of much of the west

8. Serreze et al., 1999 Most runoff & recharge comes from snowmelt Sierra Nevada:67% Colorado:63% Utah:60% Arizona/New Mexico:39% 20 40 60 80 100 120 140 OctNovDecJanFebMarAprMayJunJulAugSep Month Average Monthly Flow (1000AF) 0 1 2 3 4 5 6 Average Monthly SWE(in) SWE Flow Snow contributions to annual precipitation

9. Drought, snow cover & climate change Having 6 years of drought focused attention on western water. It made scientists & decision-makers alike push for new measurements & understanding of mountain hydrology to close critical knowledge gaps. This understanding is needed for longer-term sustainable water management.

10. Drought, snow cover & climate change Conditions have improved in California & the Southwest, but the West still has a drought.

11. Drought, snow cover & climate change Conditions have improved in California & the Southwest, but the West still in a drought.

12. Drought, snow cover & climate change Still a drought in 2007

13. 172 108 62.7% CA 48 46 95.8% NV 68 67 98.5% AZ 75 73 97.3% NM Southwest water balance Source: USGS Water Use Report 1990 Precipitation Evapotranspiration Water balance component Data in billion gallon/day

14. Climate outlooks –Is the drought over? –A warm winter to follow a warm summer? –Will it be wet or dry?

15. Jan-Feb-Mar temperature outlook

16. Jan-Feb-Mar precipitation outlook

17. Nov 2004 Developing El Niño

18. April 2005 Lack of anomaly

19. Drought, snow cover & climate change Having 6 years of drought focused attention on western water. It made scientists & decision-makers alike push for new measurements & understanding of mountain hydrology to close critical knowledge gaps. This understanding is needed for longer-term sustainable water management.

20. Snow cover & climate change –Western snowpacks hold less water than 50 years ago –They are also melting earlier –Result is earlier runoff & drier summer soil –These trends should continue as climate warms further

21. 20 th century temperature trends –+ 3 o C 2 o C 1 o C Positive trends of 2-3 o C (3-5 o F) per century over much of the West Kart et al., 1996

22. Estimating influence of possible +6ºC on SNOW vs RAIN Derived from UW’s VIC model daily inputs, 1950-1999 "Great things are done when men & mountains meet.”-- William Blake Dettinger, unpublished

23. Estimating influence of possible +6ºC on SNOW-SEASON LENGTH Derived from UW’s VIC model daily inputs, 1950-1999 Dettinger, unpublished

24. Estimating influence of possible +6ºC on RAIN-FLOOD STORMS Derived from UW’s VIC model daily inputs, 1950-1999 Dettinger, unpublished

25. April 1 snow water equivalent (SWE) in Pacific NW has declined up to 60% since 1950 + – Mote et al., GRL 2003 Snowpack decline in Cascades

26. A