Climate, Climate Change, Water, and Ecosystems in Colorado: A Very Brief Introduction

1. Climate, Climate Change, Water, and Ecosystems in Colorado: A Very Brief Introduction SOARS RMNP Field Trip July 9, 2010 – Boulder, CO Jeff Lukas Western Water Assessment CIRES, University of Colorado

2. Outline • Climate dynamics and variability • Hydrology and water resources • Ecosystems • Climate change projections • Potential impacts of climate change on • Water resources • Ecosystems

3. Western Water Assessment (WWA) We provide decision-support information to stakeholders who manage climate-sensitive resources in Colorado, Utah, Wyoming Who we are - Western Water Assessment • Joint CU-NOAA program, sponsored researchers from multiple disciplines assisted by 4 full-time staff • We work directly with stakeholders to frame research questions and develop climate planning strategies • Stakeholders/partners: Bureau of Reclamation, Denver Water, Colorado Water Conservation Board, US Forest Service, Bureau of Land Management, and many others

4. Western Water Assessment (WWA) Three research themes for 2010 and beyond: Who we are - Western Water Assessment Decision support for the Colorado River basin and headwaters Ecological impacts and vulnerabilities Emerging initiatives to inform climate services Outreach and other activities

5. A little geographical orientation… Colorado: The Headwaters State

6. Colorado: Elevation, elevation, elevation RMNP 7500’-14,255’ (2200m - 4300m) • Elevation is main control on spatial variability in climate, and thus distribution of water resources and ecosystems Boulder 5430’ (1640m) 3450’ (1045m)

7. Higher elevation = colder temperatures Average Annual Temperature • Very generally, 3.5oF colder for 1000’ increase in elevation • Exception: cold air drainage in valleys, esp. in winter Source: CO Climate Report, 2008

8. Higher elevation = more precipitation Annual Average Precipitation • Boulder: 18” • Up to >40” in mountains • Rainshadow effect can be very localized (e.g. Lyons) Source: CO Climate Report, 2008

9. Winter (Oct-Mar) moisture - importance and sources • Mid-latitude cyclonic storms carrying Pacific moisture • These storms build the mountain snowpack, and thus streamflow Source: K. Redmond, WRCC

10. Spring (Apr-Jun) moisture - importance and sources • Most important in northeast CO (35-45% of annual) – May is usually wettest month • Moisture comes from Pacific in westerly flow and Gulf of Mexico (SE flow, upslopes) Source: K. Redmond, WRCC

11. Summer (Jul-Aug) moisture - importance and sources • Summer “Monsoon” importance greatest in southeast Colorado • Moisture comes from Pacific and Gulf of Mexico on SE flow Source: K. Redmond, WRCC

12. Average seasonal distribution of precipitation

13. Mesa In any given year, the picture is messier - much of the annual precipitation arrives in several storms Niwot Ridge (9910’) – Water Year 2010 Precip & Snowpack

14. Storm tracks (low pressure centers) over the Pacific and western North America, Nov 2008 – Feb 2009 • About a dozen cyclonic storms impacted Colorado in a 3-month period • Shifts in the position of jet stream and westerly storm tracks can make a huge difference Certain states of the climate system tilt the odds of storm tracks and the monsoon affecting Colorado (hint: Pacific Ocean)

15. ENSO “footprint” on Colorado seasonal precipitation • ENSO (El Nino - La Nina) is the most consistent of these influences – a 3-8 year “sloshing” from warm to cold and back in the tropical Pacific Ocean Colorado Spring (MAM) Winter (DJF) Summer (JJA) Fall (SON) Orange/Red = Seasonal precip. tends higher with El Nino Blue = Seasonal precip. tends higher with La Nina Source: Klaus Wolter, CIRES/NOAA PSD

16. The result: Colorado and Boulder annual precipitation, 1900-2009 Wettest year: 1909 (22.9”) Driest year: 1977 (10.3”) • Huge year-to-year variability • No long-term trend

17. Colorado annual temperature, 1900-2009 2OF • Year-to-year variability relatively small (1-2 degrees), inversely related to precipitation (dry = warm, wet = cool) • Large decadal-scale variability – matches global changes • Statistically significant warming of ~2 degrees F since 1970s; 2000s the warmest decade on record

18. 5 4 Colorado 3 Global 2 1 Temperature anomaly, F 0 -1 -2 -3 -4 -5 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Global vs. Colorado warming • Much greater year-to-year variability in Colorado temps, although trends since 1900 are similar • Can’t judge the global picture by what happens locally in a given year

19. Streamflow as a function of climate • Variation in streamflow is driven mainly by variability in annual precipitation • Temperature, humidity, and winds affect evapo-transpiration and thus flow 100% 80% 20% Averaged across Colorado, about 80% of precip evaporates or transpires, about 20% runs off as streamflow Virtually all runoff comes from the mountains (above 8000’)

20. Snow-dominated annual hydrograph The vast majority of Colorado’s runoff occurs from April-July as snowmelt

22. 30 25 20 Annual flow, MAF 15 10 5 0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Upper Colorado River Basin natural streamflow, 1906-2009 – 70% from western Colorado • 2000-09 – lowest flow 10-year period (12.0 MAF) • No significant long-term trend Data: US Bureau of Reclamation

23. Historic streamflow magnitudes in Colorado • Most streamflow originates on Western slope, most of the population is on the Eastern slope

24. Transbasin diversions in Colorado Grand Ditch Adams Tunnel • 32 ditches and tunnels; 22 convey water to the Front Range

25. Elevational/climatic zonation of ecosystems in Colorado Color represents dominant natural vegetation type (green = forests & mountain grasslands, yellow/tan = prairie, shrublands Source: US EPA

26. Elevational/climatic zonation of ecosystems in Colorado Colder, wetter Warmer, drier Source: Huckaby et al. 2003

27. OK, what about the future climate?

28. Annual Winter Summer Temperature projections for Colorado: more warming Climate models project Colorado will warm by 2.5ºF by 2025 and 4ºF by 2050 relative to the 1950-1999 baseline Multi-model average of 22 climate models; 4 - 12 gridcells cover Colorado, depending on the model. Source: CO Climate Report, 2008

29. Western Colorado Projected annual mean temperature From multi-model ensemble 60°F 50°F 1950 2000 2050 2100 Temperature projections for Colorado: more warming +4ºF Nearly all model runs project between 2ºF and 7ºF of warming by 2050

30. Annual Winter Summer Precipitation projections for Colorado: unclear picture Model projections do not agree whether annual mean precipitation will increase or decrease in Colorado by 2050 wetter drier Colorado is in a zone of small projected precipitation changes, and weak agreement among the models Source: CO Climate Report, 2008

31. Western Colorado Projected annual precipitation From multi-model ensemble 24” 12” 1950 2000 2050 2100 Precipitation projections for Colorado: unclear picture • Some model runs project more precip, some project less • All models project continued high year-to-year variability • Large uncertainty in future behavior of SW monsoon

32. What are the implications of the projected climate change for water resources?

33. Impacts of warming to the water cycle • With higher temperatures…if precip remains the same… • Increased evapotranspiration • More rain, less snow • Reduced snowpacks • Earlier peak runoff • Reduced annual flows • Reduced groundwater recharge • Reduced soil moisture

34. Transforming GCM climate projections into streamflow projections – several methods OR

35. Reconciling projections of future streamflow • The sensitivity of runoff to changes in temperature is difficult to extract from the past record (general range: 3% to 8% decline in flow per 1 degree C of warming) • This sensitivity itself may change under future conditions outside of the envelope of past climate

36. Studies that have projected streamflow for the Upper Colorado River basin under future warming *at Lees Ferry except CRWAS (at state line)

37. These studies of the Upper Colorado consistently project earlier runoff peak & much reduced summer flows with warming Preliminary data from CRWAS

38. What are the implications of the projected climate change for ecosystems in Colorado?

39. We face multiple uncertainties in projecting future impacts of climate on ecosystems • Which future scenario of climate (temperature & precipitation) will actually occur? • Given a certain change in climate, what will be the magnitude of the effects on the water cycle? • e.g., How much will streamflow in in the Colorado River actually be reduced? • How will species, ecosystems, and disturbances like fire and beetles behave under novel conditions of climate and streamflow?

40. Types of expected climate change impacts to species and ecosystems • Direct impacts of warmer air temperatures • changes to timing of life events • shifts in species range (north and upward) • mortality from heat • Direct impacts of increased CO2 : changes in plant behavior, increased water acidity • Indirect impacts as disturbances (e.g., fire) are altered by climate • Impacts expressed through the water cycle

41. When we observe changes to ecosystems, it can be difficult to attribute those changes to climate change • Ecosystems respond to many factors, which interact with each other to buffer or exacerbate change • Other pervasive anthropogenic factors (e.g., habitat loss, invasive species, air and water pollution), have impacts in the same direction as climate change • Since natural climate variability is large, climate impacts to ecosystems will always have a “natural” component

42. Recap: • Colorado's climate has high temporal variability (esp. precip) and spatial variability (elevation) • Significant temperature trends (warming) have been detected in Colorado - reflecting global trends • Climate models consistently project continued warming (~4F by 2050); but precip change is highly uncertain • Future water impacts: earlier peak flows very likely, lower flows likely, but precip is the wild card • Future ecosystem impacts: name your poison

43. Observations: Regional Temperature Trends Regional Temperature Trends Source: CO Climate Report, 2008