1. Global pattern of trends in streamflow and water availability in a changing climate
By Milly, PCD, DA Dunne, and AV Vecchia
In: Nature vol. 438 (17), pp (2005)

2. General Question
How will climate change impact the water cycle on regional and global scales?
-streamflow
-precipitation
-temperature

3. Climate and Hydrology Temperature, SVP Precipitation shifts, regional
Streamflow=P-ET
when averaged over many years
for large river basins

4. Methods, briefly Streamflow volume Climate models Approach:
165 large rivers, globally distributed
28-99 years of streamflow data collection
Climate models
To predict streamflow from precipitation and temperature changes
14 models aggregated
Approach:
Compare modeled streamflow to known streamflow
Predict future streamflow with most accurate models

5. Regions of Predicted Streamflow Increase
by 10-40%, during
La Plata Basin
Eastern equatorial Africa
high latitude North America and Eurasia

6. Regions of Predicted Streamflow Decrease
by 10-30%, during
upload.wikimedia.org
Southern Europe
Southwest North America
Middle East
Southern Africa

7. The Skeptics Say…
Runoff equates with “sustainable water availability”???
Pollution
Groundwater
Irrigation
Questionable model accuracy
Large variability in each model’s predicted streamflow
Does aggregating the 14 most-accurate models solve the problem?
28 vs. 99 years of data
Low correlation between observations and model output: .34
Streamflow prediction assumptions:
Future greenhouse gas emissions
Volcanic activity
Solar activity
Temporal lag in streamflow, due to storage

8. What’s Missing? Further data collection?
Resource management implications?
Are the results valid, useful?