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Climate, Climate Change, Water, and Ecosystems in Colorado: A Very Brief Introduction Jeff Lukas Western Water Assessment CIRES, University of Colorado.

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Presentation on theme: "Climate, Climate Change, Water, and Ecosystems in Colorado: A Very Brief Introduction Jeff Lukas Western Water Assessment CIRES, University of Colorado."— Presentation transcript:

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

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

3 Who we are - Western Water Assessment Western Water Assessment (WWA) We provide decision-support information to stakeholders who manage climate-sensitive resources in Colorado, Utah, Wyoming 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 Who we are - Western Water Assessment Western Water Assessment (WWA) Decision support for the Colorado River basin and headwaters Emerging initiatives to inform climate services Ecological impacts and vulnerabilities Three research themes for 2010 and beyond: Outreach and other activities

5 A little geographical orientation… Colorado: The Headwaters State

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

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

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

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

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

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 Source: Klaus Wolter, CIRES/NOAA PSD Winter (DJF) Spring (MAM) Summer (JJA) Fall (SON) Orange/Red = Seasonal precip. tends higher with El Nino Blue = Seasonal precip. tends higher with La Nina Colorado 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

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

17 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 Colorado annual temperature, 1900-2009 2OF2OF

18 -5 -4 -3 -2 0 1 2 3 4 5 190019101920193019401950196019701980199020002010 Temperature anomaly, F Colorado Global Global vs. Colorado warming Much greater year-to-year variability in Colorado temps, although trends since 1900 are similar Cant judge the global picture by what happens locally in a given year

19 Variation in streamflow is driven mainly by variability in annual precipitation Temperature, humidity, and winds affect evapo- transpiration and thus flow Streamflow as a function of climate 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) 100% 80% 20%

20 Snow-dominated annual hydrograph The vast majority of Colorados runoff occurs from April-July as snowmelt

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22 Upper Colorado River Basin natural streamflow, 1906- 2009 – 70% from western Colorado 0 5 10 15 20 25 30 19001910192019301940195019601970198019902000 Annual flow, MAF 2000-09 – lowest flow 10-year period (12.0 MAF) No significant long-term trend Data: US Bureau of Reclamation

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

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

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

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

27 OK, what about the future climate?

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

29 Projected annual mean temperature From multi-model ensemble Western Colorado 1950200020502100 50 ° F 60 ° F Temperature projections for Colorado: more warming +4ºF Nearly all model runs project between 2ºF and 7ºF of warming by 2050

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

31 1950200020502100 24 12 Projected annual precipitation From multi-model ensemble Western Colorado 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 Precipitation projections for Colorado: unclear picture

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

33 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 Impacts of warming to the water cycle

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 StudyTempRunoff* Christensen et al. (2004)+3.1 o F -18% Milly et al. 2005varies-10 to -20% (multiple models) Christensen and Lettenmaier (2006) +4.5 o F-6% McCabe and Wolock (2007)+3.6 o F-17% Colorado River Water Availability Study Phase 1 (2010) varies4 of 5 scenarios show declines Joint Front Range Climate Change Vulnerability Study (2010) +1.8F/+7.2F-6% / -26% *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 CO 2 : 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 Regional Temperature Trends Source: CO Climate Report, 2008 Observations: Regional Temperature Trends


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