Western Water Assessmenthttp://sciencepolicy.colorado/wwa

An Overview of Climate and its Relationship to Water in Colorado

29th Colorado Water WorkshopJuly 28-30, 2004Gunnison, Colorado

Brad UdallManaging Director CU-NOAA Western Water AssessmentBradley.Udall@colorado.edu

What is the Western Water Assessment?

The mission of the Western Water Assessment is to identify and characterize regional vulnerabilities to climate variability and change,

and,

to develop information, products and processes to assist water-resource decision-makers throughout the Intermountain West.

Why Western Water Assessment?

Help NOAA Consider and Implement Future “Climate Services”, an analog to the National Weather Service but Different…

Who?

University of Colorado Scientists

Legal and Policy

Snow and Geography

Water Quality

Economics

Climate Diagnostics Center Scientists

Policy

Climatologists

Snow Scientists

Paleoclimatologists

Colorado State University Scientists

Some Current Projects…

1. South Platte Regional Assessment Tool

2. Streamflow Reconstructions using Tree Rings

3. Climate Services Clearinghouse

4. Improved “Week 2” Streamflow Forecasts

5. Seasonal Forecasts for Drought Task Force

Long Term Climate Trends

Enormous Climate Variability

Source: NOAA

The reconstruction of streamflow at Lees Ferry is the reconstruction most well-known to western U.S. water managers.

.

Climate Variability and Colorado Compact

Issues??

Source: Woodhouse, 2003

Predicting Climate Variability in Colorado – ENSO – Based Seasonal Forecasts

Source: Wolter Website, 2004

http://www.cdc.noaa.gov/people/klaus.wolter/SWcasts/index.html

1. “Perfect Ocean for Drought” -Science Magazine, 2003

2. Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation - Proceedings of the National Academy of Sciences, 2004

3. 2000 Years of Drought Variability in the Central United States, American Meteorological Society, 1998

4. Declining Mountain Snowpack – Various 2003,2004

New Research on Climate Variability

Perfect Ocean for Drought – La Nina and Warm Indian Ocean

Source: Hoerling, 2003

Perfect Ocean for Drought --

Models vs. Actual 1998-

2002

Source: Hoerling, 2003

2000 Years of Drought Variability in Central United States

Source: Woodhouse, Overpeck 1998

•20th Century Droughts not Representative of the full range of droughts over the last 2000 years

•Multidecadal Droughts of the late 13th and 16th Centuries were of much greater duration and magnitude than 20th Century Droughts

Evidence suggests that droughts before the 13th Century were decades in duration

•Droughts since the 13th Century have tended to be a decade or less in duration, with exception of 16th Century drought

•Droughts of the 20th Century have been moderate severity and short duration relative to entire record

Here, drought is defined as one or more consecutive years below long-term average.

Source: Woodhouse, 2004

Brown = 1437-2002

Yellow = 1900-1999

Reconstructed Upper Colorado Streamflow

Drought Frequency

Blue River

Reconstructed Upper Colorado River Streamflow, 1437-2002 smoothed with a 5-weight filter

The early 20th century wet period does not appear matched in prior centuries. However, drought similar to the 1950s drought have occurred.

Source: Woodhouse, 2003

Blue River

Source: Hoerling, 2003

Source: Woodhouse, 2003

Blue RiverPresentation Slide w/o bottom

General Public – CU and NOAA

Source: Woodhouse, 2003

Declining Mountain Snowpack in Western North America

• Much of the Mountain West has lost April 1 Snowpack in the period 1950 to 1997

• Largest Decreases where temperature is mild, Northern CA and Cascades

Source: Mote, et al, 2004

Less April 1 SWE Since 1950

Source: Mote, et al, 2004

1916 to 1997 Change in Timing of Peak Snowpack

Source: Mote, et al, 2004

March 2004 Climate Variability? Or

Something Else?

Source: Mote, et al, 2004

AMO and

PDO

•There is a natural greenhouse effect. It keeps the Earth warmer than it would be otherwise. Confidence index = 10.

•Greenhouse gases are increasing in the atmosphere because of human activities, and they are increasingly trapping more heat. Confidence index = 9.

•There is a collective picture of a warming world, and human activities have likely contributed. Confidence index = 7.5.

•A continued growth in greenhouse gases is projected to lead to very significant increases in global temperatures and sea level. Confidence index = 6.

•It is a complex planet and we have imperfect knowledge; so, prediction of further details suffers. A more vigorous hydrological cycle is likely, however other regional changes cannot be predicted reliably. Confidence index = 4.

Climate Change – Albritton Congressional Testimony

•The climate change issue is a real one.

•The first signs of human-caused climate change have likely occurred.

•Some degree of further changes appears inevitable due to the CO2 already in the atmosphere.

•Exactly which regions, how quickly, and the magnitude of climate change are all hard to predict.

•Human-caused climate change would be slow to reverse.

Albritton Summary…

How can we have both more droughts and more floods?

–Increased temperatures means both more evaporation and more precipitation

•Modeling suggests 1% to 2% increase in Evaporation per 2F increase

–Increased temperatures increase the ability of the atmosphere to hold moisture

•Physics suggests that moisture holding ability increases by 7% per 2F increase

–Rainfall intensity will increase at the 7% rate

•Rainfall is the ‘inverse’ of moisture holding ability – when atmosphere cools it rains and loses moisture at this higher rate

–But because our new evap rate is much less than this new rainfall rate, there will be decreases in number of rainfall events.

–And the increased evaporation means increased drying

More Vigorous Hydrologic Cycle – A Brief Technical Discussion

Normal Climate Variability is Huge! Will likely swamp climate change ‘signal’ for some time.

Current Ability to Predict Seasonally based on El Nino conditions, with some skill.

Tree Rings provide good look back to 1400 or so.

Tree Rings indicate that we are likely to have more variability in the future, not less.

By studying oceans we may have predictive break-throughs in next few years.

Summary Climate Variability

Science is Real, No Matter what you read.

Huge Uncertainties! Especially amount and timing of warming.

At this time, not “actionable” for water managers.

Read IPCC, National Assessment, Skeptics; don’t rely on the popular press ( with apologies to members of the 4th Estate) – www.ipcc.ch

IPCC 4th Assessment Due 2006/07.

High Certainty of:

Warmer TemperaturesMore Droughts and FloodsEarlier RunoffCould be either wetter or drier

Summary Climate Change

Graphic: Scientific American, 2004

Get Used to Uncertainty!

Future may be very different from the past.

Be careful what you hope for: climate predictions may lead to better operations, but at a price of increased vulnerability.

Population pressures are more significant than Variability or Change.

Order of concerns on a 10-year horizon: population pressures, climate variability, climate change.

Order of concerns on a 100-year horizon: population pressures,climate change, climate variability.

Overall Summary

Get Used to Uncertainty!

Past may not be guide to the future

Be careful what you hope for: predictions lead to more efficiency, but at a price of increased vulnerability.

Population pressures are more significant than Variability or Change.

Order of concerns on a 10-year horizon: population pressures, climate variability, climate change.

Order of concerns on a 100-year horizon: population pressures,climate change, climate variability.

Overall SummaryThe End…..

To Be Completed..

Bibliography

Additional Material

Antarctic Ice Core Data Back 400,000 Years

Source: Petit, et al, 1999

Source: IPCC, 2001

1000 Year Temperature Data

Presentation Slide w/o bottom

General Public – CU and NOAA

IPCC Extreme Weather and Climate Events

Source: IPCC, 2001

CO2, CH4, N20 Changes Since 1000

AD

Source: IPCC, 2001

• Climate is not static and assumptions made about the future based on the climate of the recent past may be inaccurate. Water managers should factor in the potential for climate change when designing major new infrastructure.

• Assumptions about the probability, frequency, and magnitude of extreme events should be carefully reevaluated.• There is substantial stress on the water sector even in the absence of climate change. There are numerous

watersheds that are already over-appropriated,and new stresses are coming from population dynamics,land use changes,and changes in international economies. In some areas,the new demands associated with instream flow needs for habitat protection and Indian water rights settlements may cause major shifts in water supply and water rights. Climate change may pose additional stresses and could result in thresholds being reached earlier than currently anticipated.

• Waiting for relative certainty about the nature of climate change before taking steps to reduce risks in water supply management may prove far more costly than taking proactive steps now. (The suggested risk-reducing or “no regrets”steps are those that would have other beneficial effects and so are appropriate regardless of climate change.)

• The types of changes encountered in the future may not be gradual in nature. Non-linearities and surprises should be expected, even if they cannot be predicted.

• The problems that are likely to result from climate change are intergenerational. Decisions made today will commit future generations to certain outcomes. It is important to e valuate benefits of projects over long time frames,and develop an educated citizenry.

Source: National Assessment, 1999

Key Messages for Water Managers from National Assessment