# Presentation: 446400

## Implications of Climate Change for Water in the United States

## Climate Change and Water: The Big Questions

**The past: ****What has been happening?**** **
**The future: ****Where are we headed? What areas are at risk?**** **
**Mitigation: ****How much change is avoidable?**** **
**Adaptation: ****What will the unavoidable changes look like? **

## Top Three Climate-Water Issues

**Sea-level Rise**
**Snow-pack Loss**
**Redistribution of Water Resources**

## Top Three Climate-Water Issues

**Sea-level Rise**
**Snow-pack Loss**
**Redistribution of Water Resources**

## Model-Estimated Sea-Level Rise

- (Data from IPCC WGI Summary for Policymakers)

## Sea-Level Rise and Water Supplies

**Saltwater contamination of coastal ground-water wells**** **
**Salinity encroachment on municipal water intakes from rivers**

**Coastal States**

## Top Three Climate-Water Issues

**Sea-level Rise**
**Snow-pack Loss**
**Redistribution of Water Resources**

## California Water

**California Water**

**Merced River****at Happy Isles**
**Bridge**

## California Water: Winter

## California Water: Spring

## California Water: Spring-Summer

**Notes:**
Rhythm of the Seasons:
Recreation
Ecosystems; fire
Agriculture (show pie)
Urban Life
Twain, Nicholson

## Snow-Pack Loss and Water

**Snow-Pack Loss and Water**

**Loss of natural flood control system**** **
**Loss of natural winter-summer storage**** **
**Loss of natural fire suppression**

**Snow-Pack States**

## Top Three Climate-Water Issues

**Sea-level Rise**
**Snow-pack Loss**
**Redistribution of Water Resources**

## Are climate-model projections of changing water availability credible?

**Are climate-model projections of changing water availability credible?**

## USGS Streamflow Measurements

- Gaged Streamflow Trends, 1900s

**USGS Streamflow Measurements**

## Gaged Streamflow Trends, 1900s

- Modeled Streamflow Trends, 1900s

## Gaged Streamflow Trends, 1900s

- Modeled Streamflow Trends, 1900s

## Gaged Streamflow Trends, 1900s

- Modeled Streamflow Trends, 1900s

## Gaged Streamflow Trends, 1900s

- Modeled Streamflow Trends, 1900s

## Gaged Streamflow Trends, 1900s

- Modeled Streamflow Trends, 1900s

## Gaged Streamflow Trends, 1900s

- Modeled Streamflow Trends, 1900s

## Model-Projected Changes in Annual Runoff, 2041-2060 Percentage change relative to 1900-1970 baseline. Any color indicates that >66%of models agree on sign of change; diagonal hatching indicates >90% agreement.

**Model-Projected Changes in Annual Runoff, 2041-2060** Percentage change relative to 1900-1970 baseline. Any color indicates that >66%of models agree on sign of change; diagonal hatching indicates >90% agreement.

- (After Milly, P.C.D., K.A. Dunne, A.V. Vecchia, Global pattern of trends in streamflow andwater availability in a changing climate, *Nature*, **438**, 347-350, 2005.)

**Notes:**
The slides and notes in this powerpoint file are a supplement to Milly et al. (2005) and have been prepared by Milly (cmilly@usgs.gov). These notes are the same for all slides in this file. The three slides differ only in the areas used for averaging: countries and subnational units within some larger countries; Water Resources Regions of the USA; and States of the USA.

Mapped areas are colored according to the model-projected percent change in annual runoff for the period 2041-2060, relative to the period 1900-1970. Hatched areas are those where more than 90% of the models agree on the direction (wetting vs. drying) of the change. Non-hatched areas are where 66-90% of models agree. White areas are where fewer than 66% of the models agree.

Actual future changes in runoff can be expected to differ from these projections, primarily because of (1) departures of actual forcing from the SRES A1B scenario, (2) errors in the models' representation of runoff response to climate forcing, and (3) unforced variability ("randomness") of the climate system.

The color of an area is determined only by changes in runoff produced inside the Region. However, where a downstream area receives streamflow from one or more upstream areas, the streamflow through the downstream area will be affected by runoff changes in both the downstream and the upstream area. 

The figure is based on figure 4 of Milly et al. (2005); that reference documents the computations and data sources. Consistent with Milly et al. (2005), these projections are model-estimated changes associated with hypothetical ("SRES A1B" scenario) changes in climate forcing. The computational differences from the published figures are (1) instead of depicting changes in point values of runoff, this figure depicts only changes in areal averages of runoff; (2) instead of compositing experiments, we composited models; and (3) the composite is formed from the more stable median instead of the mean.

Reference:

Milly, P.C.D., K.A. Dunne, and A.V. Vecchia, 2005, Global pattern of trends in streamflow and water availability in a changing climate, Nature, v. 438, p. 347-350.

## Model-Projected Changes in Annual Runoff, 2041-2060 Percentage change relative to 1900-1970 baseline. Any color indicates that >66%of models agree on sign of change; diagonal hatching indicates >90% agreement.

- (After Milly, P.C.D., K.A. Dunne, A.V. Vecchia, Global pattern of trends in streamflow andwater availability in a changing climate, *Nature*, **438**, 347-350, 2005.)

**Model-Projected Changes in Annual Runoff, 2041-2060** Percentage change relative to 1900-1970 baseline. Any color indicates that >66%of models agree on sign of change; diagonal hatching indicates >90% agreement.

**Notes:**
The slides and notes in this powerpoint file are a supplement to Milly et al. (2005) and have been prepared by Milly (cmilly@usgs.gov). These notes are the same for all slides in this file. The three slides differ only in the areas used for averaging: countries and subnational units within some larger countries; Water Resources Regions of the USA; and States of the USA.

Mapped areas are colored according to the model-projected percent change in annual runoff for the period 2041-2060, relative to the period 1900-1970. Hatched areas are those where more than 90% of the models agree on the direction (wetting vs. drying) of the change. Non-hatched areas are where 66-90% of models agree. White areas are where fewer than 66% of the models agree.

Actual future changes in runoff can be expected to differ from these projections, primarily because of (1) departures of actual forcing from the SRES A1B scenario, (2) errors in the models' representation of runoff response to climate forcing, and (3) unforced variability ("randomness") of the climate system.

The color of an area is determined only by changes in runoff produced inside the Region. However, where a downstream area receives streamflow from one or more upstream areas, the streamflow through the downstream area will be affected by runoff changes in both the downstream and the upstream area. 

The figure is based on figure 4 of Milly et al. (2005); that reference documents the computations and data sources. Consistent with Milly et al. (2005), these projections are model-estimated changes associated with hypothetical ("SRES A1B" scenario) changes in climate forcing. The computational differences from the published figures are (1) instead of depicting changes in point values of runoff, this figure depicts only changes in areal averages of runoff; (2) instead of compositing experiments, we composited models; and (3) the composite is formed from the more stable median instead of the mean.

Reference:

Milly, P.C.D., K.A. Dunne, and A.V. Vecchia, 2005, Global pattern of trends in streamflow and water availability in a changing climate, Nature, v. 438, p. 347-350.

## Redistribution of Water Resources

**Changing risk of unmet water demands**
**Changing risk of floods**
**Changing risk of droughts**

**Drying States**

**Wetting States**

## Climate Change and Water: The Big Questions

**Climate Change and Water: ****The Big Questions**

**The past: ****What has been happening?**
**The future: ****Where are we headed? What areas are at risk?**
**Mitigation: ****How much change is avoidable? **
**Adaptation: ****What will the unavoidable changes look like? **

## Impact, Mitigation, and Adaptation (Schematic)

**2000**

**2100**

**Potential Impact**

**2050**

**mitigation**

**adaptation**

## Adaptation: Personal, Business, Government Choices

**Adaptation: Personal, Business, Government Choices**

**Obtain new water supplies**
**Build, retrofit infrastructure**
**Conserve**
**Operational, institutional, legal, economic devices**

## The Strategic Dilemma of Informed Choice

**The Strategic Dilemma ****of Informed Choice**

**Information needed *****now***
**Knowledge base rapidly *****evolving***

## Scientific Information for “Adaptive Adaptation”

**Scientific Information ****for “Adaptive Adaptation”**

**Identification and quantification of *****vulnerabilities***
**Hydrologic and climatic *****monitoring***
**Comprehensive environmental *****modeling***
**Interpretive *****research***
**Enhanced *****communication***** with resource managers**