Climate Variability

1. ClimateVariability Eric Salathé Climate Impacts Group&Department of Atmospheric SciencesUniversity of Washington Thanks to Nathan Mantua

2. Northwest Climate: the mean • Factors that influence local/regional climate: • 1. Latitude • day length, intensity of sunlight • 2. Altitude • 3. Mountain Barriers • 4. Proximity to the ocean • ocean currents • 5. location relative to prevailing winds

3. Mean SLP fields • the dominant feature shifts from the subtropical High in summer to the Aleutian Low in winter

5. Oregon Climate Service http://www.ocs.orst.edu

6. Northwest terrain maps the big-picture winds and storms onto a complex landscape • localized cold air outbreaks • the Puget Sound Convergence Zone • rain shadows

7. “Arctic Blasts”

8. The Puget Sound Convergence Zone

9. Annual average rain+snowfall: 1961-1990

10. The predictable part: seasonal rhythms Puget Sound Precip Insolation Insolation Oct Feb Jun Upwelling winds at 48N Oct Feb Jun Jan May Sep Amphitrite Pt SST Oct Feb Jun

11. Year to year variations on the seasonal rhythms Monthly Puget Sound Precip Daily Upwelling winds Monthly Amphitrite Pt SST

12. Northwest Climate Variability

13. Pollen records on the Olympic Peninsula Crocker Lake cedars cool-wet fires: hot-dry alder df cool pines McLachlan, J. S. and L. B. Brubaker. 1995 Local and regional vegetation change on the northeastern Olympic Peninsula during the Holocene. Canadian J. of Botany.

14. The Dust Bowl (1929-1931) was probably not the worst drought sequence in the past 250 years (based on Columbia Basin Tree-ring chronologies) red = observed, blue = reconstructed Source: Gedalof, Z., D.L. Peterson and Nathan J. Mantua. (2004). Columbia River Flow and Drought Since 1750. Journal of the American Water Resources Association.

15. PNW climate variability 1. What does our region’s climate history tell us about “natural variability”? 2. How is climate variability experienced in the Pacific Northwest? * are there patterns within the region? * are there preferred frequencies of change (year to year, decade to decade, etc.) 3. Why does our climate vary?

16. Warm and cool (or “wet” and “dry”) halves of the year: oct-mar versus apr-sep

17. Characteristics of variability? • Lots of year-to-year variability in both halves of the year; longer-term variations • Multi-decadal “cycles” and century long trends • temperatures and precipitation are more variable in cool season than in warm season

18. Washington State Oct-Sept Total Precip 48 36 1907 1927 1947 1967 1987 2007 Washington State Oct-Sept Average Temperature 50 48 46 1907 1927 1947 1967 1987 2007

19. Riffe Lake, west slopes of the CascadesSpring 2001

20. March 15 Snow depth anomalies at Paradise, Mt Rainier Avg=4 meters Avg ~ 4 meters (170 inches) January 5, 2005: 48 inches January 6, 2007: 130 inches

21. Water Year Columbia River streamflow Average annual runoff at The Dalles, Oregon ~ 150 Million Acre-Feet (MAF); Oct 2000-September 2001 ~ 100 MAF

22. NW Climate variability • Why the strong climate changes? • The chaotic nature of the climate system • big volcanic eruptions • natural modes of climate variability internal to the climate system: • in the Pacific sector, changes in ENSO and PDO are important factors

24. Circulation changes are sensitive to the intensity of tropical El Nino events • Contrast the “average” event with the extreme winters of 1982-83 and 1997-98

25. Oct 97-Mar 98: El Niño Oct 98-Mar 99: La Niña

26. El Niño year precip anomalies Oct 1997- Mar 1998 La Niña year precip anomalies Oct 1998- Mar 1999

27. Regional patterns? • Typically, cool-season (oct-mar) climate anomalies are coherent throughout most of the PNW region • warm-season climate anomalies also tend to be regionally coherent, but to a lesser degree

28. Regional patterns? Observations Regional Simulation Dry wet Leung et al 2003

29. Accumulated daily rainfall: Oct 1 1998-Sept 20 1999 A very wet year everywhere but Yakima! http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/current_impacts/global_precip_accum.html

31. “composite avg” PNW temperature and precipitation during El Niño and La Niña (based on averages of past century’s events) EN-LN

32. The Pacific Decadal Oscillation • an El Niño-like pattern of climate variability • 20 to 30 year periods of persistence in North American and Pacific Basin climate • warm extremes prevailed from 1925-46, and again from 1977-98; a prologed cold era spanned 1947-76 1925 1947 1977 1998? Mantua et al. 1997, BAMS

33. October-March PDO Regression fields Maps show typical warm PDO climate anomalies Surface Air Temperature Precipitation dry Strong Aleutian Low Strong Aleutian Low dry wet Warm dry dry Figures produced by Todd Mitchell, UW/JISAO

34. A history of the PDO A history of ENSO warm warm cool 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

35. Real time “nowcasts” of the PDO? Because we don’t know how the PDO works (key mechanisms for decadal patterns remain mysterious), we can’t be sure that the SST pattern (and PDO index) is a good indicator for where we are with this pattern. Recent years have a variable PDO index…but perhaps no moreso than the late 1980s… Monthly PDO index: 1900-Jan 2008 http://jisao.washington.edu/pdo

36. PDO and PNW monthly temperatures and precipitation

37. PDO and Cascades snowpack

38. Water year stream flow composites for Columbia River “natural” flows at The Dalles, Oregon

39. PDO/ENSO and NW hydrology • Because extremes in ENSO and PDO tend to favor either “warm and wet” or “cool and dry” conditions, these combinations lead to amplified responses in snowpack and streamflow • Ex: cold wet weather, lower snowline, more precipitation, more snow, less evaporation and more runoff

40. Cool/Warm PDO and Paradise snowdepth histograms

41. From the National Climate Data Center: www.ncdc.noaa.gov

42. A regionally averaged view of PNW cool season Temps and precip October-March OR-ID-WA Temperature and Precipitation 2001 1994 1944 * 1977 Major drought years

43. Winter winds and pressure over the North Pacific Summer winds and pressure over the North Pacific L L H H “Subtropical High” “Aleutian Low”