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Dan Cayan, Scripps Institute for Oceanogrphy & USGS
California's water supply is highly variable due to its narrow rainy season and dependence on a few large storms each year. The current multi-year drought is characteristic of the state's climate, but climate change is projected to exacerbate water stresses by reducing snowpack and increasing temperatures. While droughts will remain a natural part of California's climate, human-caused warming from greenhouse gas emissions will likely increase the intensity, duration, and frequency of droughts in the future.
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Dan Cayan, Scripps Institute for Oceanogrphy & USGS
- 1. key points •Drought andFlood are a common occurrence in California, 2012-2015 Drought is intense and warm as well as dry •The absence of very large storms drives California dry (and wet) spells • Climate change will likely exacerbate stresses on water resources Climate Change Will Stress California’s Already Volatile Water Supply Dan Cayan with Mike Dettinger, Mary Tyree, Sam Iacobellis Scripps Institution of Oceanography and USGS Climate Change Will Stress California’s Already Volatile Water Supply Dan Cayan with Mike Dettinger, Mary Tyree, Sam Iacobellis Scripps Institution of Oceanography and USGS UC Davis Oct 2015
- 2. Sierra discharge highlyvariable stddev/mean = 0.44 lowest 1977 highest 1983 Sierra discharge highly variable stddev/mean = 0.44 lowest 1977 highest 1983 But ,Columbia discharge is quite steady, stddev/mean = 0.19 But ,Columbia discharge is quite steady, stddev/mean = 0.19 Annual discharge varies considerably in the Sierra Nevada Annual discharge varies considerably in the Sierra Nevada and Colorado discharge is intermediately variable, stddev/mean = 0.33 Cayan et al 2003 and Colorado discharge is intermediately variable, stddev/mean = 0.33 Cayan et al 2003
- 3. California and muchof western region has been more-or-less dry since 1999 observed precipitation departure (% of average), 1998-99 thru 2013-14 California and much of western region has been more-or-less dry since 1999 observed precipitation departure (% of average), 1998-99 thru 2013-14 % departure from 1981-2010 average
- 4. U.S. Drought Monitor/NationalWeather Service Hanford
- 5. Dettinger and CayanDrought and the Delta—A Matter of Extremes accepted, San Francisco Estuary and Watershed Science, April 2014 a few large storms (or their absence) account for a disproportionate amount of California’s precipitation variability a few large storms (or their absence) account for a disproportionate amount of California’s precipitation variability 5yr smoother LARGE STORM CONTRIBUTION LARGE STORM CONTRIBUTION 95%ile
- 6. Recent dry yearshave mostly been warmer than normal. 2013-14 was exceptionally warm. Recent dry years have mostly been warmer than normal. 2013-14 was exceptionally warm. Precipitation Departure during dry years Temperature Departure during dry years 2013-14
- 7. Anomalous warmth duringwinter 2014-15Anomalous warmth during winter 2014-15
- 8. virtually all climatesimulations project warming, but with a wide envelope of temperature change virtually all climate simulations project warming, but with a wide envelope of temperature change +3°C CMIP5 GCMs project +3°C summer warming by 2060, under mid and high RCPs 14 GCMs X 3 RCP Emissions Scenarios IPCC 5th Assessment (CMIP5) models July Temperature change Sacramento Need to kmow Which emissions pathway will we take? How much summer amplification of warming? How will temperature change in Near term? Need to kmow Which emissions pathway will we take? How much summer amplification of warming? How will temperature change in Near term?
- 9. Sierra Snowpack hasbeen extremely low 2015 and 2014 spring snowpack disproportionately light Sierra Snowpack has been extremely low 2015 and 2014 spring snowpack disproportionately light
- 10. Dettinger and AndersonSFEWS 2015
- 11. Loss of CaliforniaSpring Snowpack from 21st Century warming Loss of California Spring Snowpack from 21st Century warming •Under this scenario, California loses half of its spring (April 1) snow pack due to climate warming. Less snow, more rain, particularly at lower elevations. The result is earlier run-off, more floods, Less stored water. This simulation by Noah Knowles is guided by temperature changes from PCM’s Business-as-usual coupled climate simulation. (this is a low-middle of the road emissions and warming scenario) •Under this scenario, California loses half of its spring (April 1) snow pack due to climate warming. Less snow, more rain, particularly at lower elevations. The result is earlier run-off, more floods, Less stored water. This simulation by Noah Knowles is guided by temperature changes from PCM’s Business-as-usual coupled climate simulation. (this is a low-middle of the road emissions and warming scenario) Knowles, N., and D.R. Cayan, 2002: Potential effects of global warming on the Sacramento/San Joaquin watershed and the San Francisco estuary. Geophysical Research Letters, 29(18), 1891.
- 12. Declining odds ofmedian or higher snowpack Source: Cayan et al. (2011)
- 13. Drier Summer Landscapes increasedwarming and diminished snow causes successively greater soil drying throughout 21st Century (this picture could change somewhat under more recent CMIP5 simulations) Drier Summer Landscapes increased warming and diminished snow causes successively greater soil drying throughout 21st Century (this picture could change somewhat under more recent CMIP5 simulations) early 21st middle 21st late 21st Cayan et al. Ch 6 Southwest Climate Assessment
- 14. Projected patterns ofprecipitation changes 2090-2099 versus 1980-1999 Globally, dry regions become drier?
- 15. Although the numberof wet days is projected to decrease with climate change, Although the number of wet days is projected to decrease with climate change, the intensity of the largest wet days is projected to increase ! the intensity of the largest wet days is projected to increase ! Suraj Polade Polade, S.D., Pierce, D.W., Cayan, D.R., Gershunov, A., and Dettinger, M.D., 2014, The key role of dry days in changing regional climate and precipitation regimes: Nature Scientific Reports, 4:4364, 8 p., doi:10.1038/srep04364. 28 CMIP5 RCP 8.5 GCMs (2060–2089) vs. (1960-1989)
- 16. • California’s climateis prone to year-to-year and longer term variation in precipitation—drought is an expected part of our climate.. • California’s current dry spell has built up over multiple years, a more/less dry pattern has been in place since 1999. • The absence of a few very large storms is often a key driver of dry years. And large storms are frequently involved in “busting” drought. . • Continued, substantial climate warming is highly likely but changes in annual precipitation is not well understood in California. However, climate change may shift precipitation characteristics—fewer overall wet days but more intense heavy events. • In addition to the present ongoing dry spell, recurrent wet and dry events and episodes, in the midst of warm temperatures will provide future learning opportunities. SummarySummary
- 19. Whole CONUS PDSI CA/NVPDSI California/Nevada drought only moderately correlated w whole U.S. PDSI from NCDC divisional dataset California/Nevada drought only moderately correlated w whole U.S. PDSI from NCDC divisional dataset
- 20. ground water withdrawl increases greatlyin dry years ground water withdrawl increases greatly in dry years Dry Year Typical Year Faunt et al 2009 USGS pumping
- 21. How are droughtsmade? >80% Mike Dettinger
- 22. California’s large yearlyvariation in precipitation is dictated by the presence or absence of storms during a narrow seasonal window California’s large yearly variation in precipitation is dictated by the presence or absence of storms during a narrow seasonal window California has only about 120 days to accumulate two thirds of its annual precipitation. When Pacific winter storms Are diverted from California (as last winter) dry conditions result. California year-to-year variation in precipitation is has the most volatile! of the entire U.S. Cayan et al.2003
- 23. Multi-year dry spellsare quite common in California Sacramento Drainage Divi standardized precip index 1900-2014 showing Intensity and Duration Multi-year dry spells are quite common in California Sacramento Drainage Divi standardized precip index 1900-2014 showing Intensity and Duration Anne Steinemann et al. 2015 J. HydroMet. in press
- 24. Calif dought footprintis quite broad in western U.S. Sierra flows often in same phase (wet or dry) as the Columbia or the Colorado Calif dought footprint is quite broad in western U.S. Sierra flows often in same phase (wet or dry) as the Columbia or the Colorado Low Sierra flows associated with large regional pattern Cayan et al.2003
- 25. Sierra Nevada Annual Precipitation Coefof Variation ~31.5% mean 39.1 inches std dev 12.3 inches Sierra Nevada Annual Precipitation Coef of Variation ~31.5% mean 39.1 inches std dev 12.3 inches 2012-2014 dry spell is characteristic of California’s volatile precipitation climate 2012-2014 dry spell is characteristic of California’s volatile precipitation climate WY 2014 precip estimated at 65% of LT mean From California Climate Tracker Western Regional Climate Center California has a narrow seasonal window to generate its annual water supply. If atmospheric conditions are unfavorable during that period, a dry year results
- 26. prevalence of anomalouslywarm daytime temperatures during cool season months of drought years Sacramento Drainage Division Dark bars are from 20% driest years Pale bars are all years 1895-2014 prevalence of anomalously warm daytime temperatures during cool season months of drought years Sacramento Drainage Division Dark bars are from 20% driest years Pale bars are all years 1895-2014
- 29. CA1 ACCESS 1.0 CMCC CM CMCCCMS Climate Models indicate occasional drought for California In 21st Century Climate Models indicate occasional drought for California In 21st Century
- 30. Recent Water Lossover Western U.S. Surface displacements from GPS network show progressive uplift due to water mass loss in drought Recent Water Loss over Western U.S. Surface displacements from GPS network show progressive uplift due to water mass loss in drought GPS estimate by Borsa et al showing deficit of ~240km**3 water in March 2014 relative to 2003-2014 baseline over western U.S., west of 109°W. This is in general agreement with GRACE satellite observations, S. Castle et al 2014 GRL found ~65km**3 water water loss in Colorado Basin during 2004- 2013. GPS estimate by Borsa et al showing deficit of ~240km**3 water in March 2014 relative to 2003-2014 baseline over western U.S., west of 109°W. This is in general agreement with GRACE satellite observations, S. Castle et al 2014 GRL found ~65km**3 water water loss in Colorado Basin during 2004- 2013. Borsa et al. 2014
- 31. Meko, D.M., Woodhouse,C.A., and Touchan, R., 2014, Klamath/San Joaquin/Sacramento hydroclimatic reconstructions from tree rings: Report to California DWR 4600008850, 117 p. 1100 years of Sacramento River Discharge little overall change but considerable variability and multi-year spells reconstructed from tree ring records bu Dave Meko and colleagues, Univ Arizona 1100 years of Sacramento River Discharge little overall change but considerable variability and multi-year spells reconstructed from tree ring records bu Dave Meko and colleagues, Univ Arizona
- 32. prevalence of anomalouslywarm daytime temperatures during cool season months of drought years Sacramento Drainage Division Dark bars are from 20% driest years Pale bars are all years 1895-2014 prevalence of anomalously warm daytime temperatures during cool season months of drought years Sacramento Drainage Division Dark bars are from 20% driest years Pale bars are all years 1895-2014
- 33. Co- occurrences ofhigh (h) and low (l) annual Columbia, Sierra, Colorado discharge anomaly magnitudes > 0.7 1906-1999; anomalies +0.7 standard deviations above long-term means are counted as high, more than –0.7 standard deviations below normal are counted as low. Co- occurrences of high (h) and low (l) annual Columbia, Sierra, Colorado discharge anomaly magnitudes > 0.7 1906-1999; anomalies +0.7 standard deviations above long-term means are counted as high, more than –0.7 standard deviations below normal are counted as low. Sierra h l Columbia h 8 3 l 2 13 How often do extreme annual flows co-occur in Sierra, Columbia, Colorado? Sierra h l Colorado h 13 4 l 2 16 Sierra and Columbia High and especially low flows co-occur. Relatively few Years when they have Opposing anomalies Sierra and Columbia High and especially low flows co-occur. Relatively few Years when they have Opposing anomalies Sierra and Colorado High and especially low flows co-occur. Relatively few Years when they have Opposing anomalies Sierra and Colorado High and especially low flows co-occur. Relatively few Years when they have Opposing anomalies Cayan et al.2003
- 34. 34 Atmospheric Rivers West Coastflood generators Atmospheric Rivers West Coast flood generators
- 35. Summary Drought Characteristics •California’s climateis prone to year-to-year and longer term variation in precipitation—drought is expected.. •California’s current dry spell has built up over multiple years, a more/less dry pattern has been in place since 1999. •Temperature during cool seasons of drought years—in recent decades, has more often been warmer than cooler than average. As with precipitation,, anomalous temperature strongly controlled by atmospheric circulation Drought prediction is a challenge: •The absence of a few very large storms is often a key driver of dry years. And large storms are frequently involved in “busting” drought. •there is not a unique atmospheric drought-circulation pattern. . •Anomalous Pacific SST patterns, tropical and extratropical appear in advance, during and after strong drought circulation months, but signals are somewhat weak.
- 36. 500mb height anomaliesaveraged, all months during Dry years500mb height anomalies averaged, all months during Dry years
- 37. ENSO vs. CaliforniaPrecipitation Southern California K. Redmond et al Western Regional Climate Center
- 38. K. Redmond etal Western Regional Climate Center
- 39. Nino 3.4 hatchedregionNino 3.4 SST Number dry yrs Drought years occur during All phases of ENSO Drought years occur during All phases of ENSO
- 40. PDO SST AnomalyPattern K. Redmond et al Western Regional Climate Center Number dry yrs PDO Index Drought years occur during both phases of PDO Drought years occur during both phases of PDO
- 41. over 21st Century occursa marked decline of chances of reaching or exceeding historical median Snow Water Equivalent Sierra Nevada+ 10% ….and, chances of historical 10th percentile or less SWE increases greatly 40% Median Apr 1 SWE 11.9cm 10th % Apr 1 SWE 3.6cm
Editor's Notes
- #13 The question of “not enough water” in California means we need to look at the snowpack because that is the ultimate reservoir of water for us during the dry summer months. Already we have evidence that the snowline is rising higher up on the mountains because of the increase in temperatures. That means, again, that less of the precipitation falls as snow, and more as rain So, as soon as mid-century, the water stored in snow could drop to ~ 2/3 of the historical average. And by the end of the century, only ~ 1/3 of historical median amount could be left. That in and of itself does not mean there is less water overall > it just means there is more water that has to be stored in reservoirs, but that makes the management of floods more difficult.