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

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

Jeff Lukas

Western Water AssessmentCIRES, University of Colorado

SOARS RMNP Field TripJuly 9, 2010 – Boulder, CO

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

– Water resources– Ecosystems

Who we are - Western Water AssessmentWestern 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

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

A little geographical orientation…

Colorado: The Headwaters State

Colorado: Elevation, elevation, elevation

• Elevation is main control on spatial variability in climate, and thus distribution of water resources and ecosystems

3450’ (1045m)

Boulder5430’ (1640m)

RMNP7500’-14,255’(2200m - 4300m)

Average Annual Temperature

Source: CO Climate Report, 2008

Higher elevation = colder temperatures

• Very generally, 3.5oF colder for 1000’ increase in elevation

• Exception: cold air drainage in valleys, esp. in winter

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)

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

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

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

Average seasonal distribution of precipitation

MesaNiwot Ridge (9910’) – Water Year 2010 Precip & Snowpack

In any given year, the picture is messier - much of the annual precipitation arrives in several storms

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)

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

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

• 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

2OF

-5-4-3-2-1012345

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Tem

pera

ture

ano

mal

y, F Colorado

Global

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

• 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%

Snow-dominated annual hydrograph

The vast majority of Colorado’s runoff occurs from April-July as snowmelt

Upper Colorado River Basin natural streamflow, 1906-2009 – 70% from western Colorado

0

5

10

15

20

25

30

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Annu

al fl

ow, M

AF

• 2000-09 – lowest flow 10-year period (12.0 MAF)

• No significant long-term trend

Data: US Bureau of Reclamation

• Most streamflow originates on Western slope, most of the population is on the Eastern slope

Historic streamflow magnitudes in Colorado

• 32 ditches and tunnels; 22 convey water to the Front Range

Transbasin diversions in Colorado

Adams TunnelGrand Ditch

Elevational/climatic zonation of ecosystems in Colorado

Source: US EPA

Color represents dominant natural vegetation type (green = forests & mountain grasslands, yellow/tan = prairie, shrublands

Elevational/climatic zonation of ecosystems in Colorado

Source: Huckaby et al. 2003

Colder, wetter

Warmer, drier

OK, what about the future climate?

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

Climate models project Colorado will warm by 2.5ºF by 2025 and 4ºF by 2050 relative to the 1950-1999 baseline

Annual Winter Summer

Multi-model average of 22 climate models; 4 - 12 gridcells cover Colorado, depending on the model.

Temperature projections for Colorado: more warming

Projected annual mean temperatureFrom multi-model ensemble

Western Colorado

1950 2000 2050 2100

50°F

60°F

Temperature projections for Colorado: more warming

+4ºF

Nearly all model runs project between 2ºF and 7ºF of warming by 2050

Colorado is in a zone of small projected precipitation changes, and weak agreement among the models

Annual Winter Summer

Source: CO Climate Report, 2008

Model projections do not agree whether annual mean precipitation will increase or decrease in Colorado by 2050Model projections do not agree whether annual mean precipitation will increase or decrease in Colorado by 2050

wetter

drier

Precipitation projections for Colorado: unclear picture

1950 2000 2050 2100

24”

12”

Projected annual precipitationFrom 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

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

With higher temperatures…if precip remains the same…• Increased evapotranspiration• More rain, less snow

Reduced snowpacksEarlier peak runoff Reduced annual flowsReduced groundwater

rechargeReduced soil moisture

Impacts of warming to the water cycle

Transforming GCM climate projections into streamflow projections – several methods

OR

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

Studies that have projected streamflow for the Upper Colorado River basin under future warming

Study Temp Runoff*

Christensen et al. (2004) +3.1oF -18%

Milly et al. 2005 varies -10 to -20% (multiple models)

Christensen and Lettenmaier (2006)

+4.5oF -6%

McCabe and Wolock (2007) +3.6oF -17%

Colorado River Water Availability Study Phase 1 (2010)

varies 4 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)

These studies of the Upper Colorado consistently project earlier runoff peak & much reduced summer flows with warming

Preliminary data from CRWAS

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

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?

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

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

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

Regional Temperature Trends

Source: CO Climate Report, 2008

Observations: Regional Temperature Trends