1.  CLIMATE MODEL PRECIPITATION TREND ANALYSIS IN THE 20 TH CENTURY Karen Rivas Key Acknowledgements: Xubin Zeng & Koichi Sakaguchi UA/NASA Space Grant Symposium April 21, 2012 1

2. Questions  Based on climate models how will global mean precipitation change?  How reliable are climate models in comparison with observational data in the past ~100 years? 2

3. Approach and Methods  Analyze various climate model precipitation trends  Analyze observational precipitation trends from two distinct set of data  Draw conclusions from comparison of model precipitation trends and observational trends 3

4. Climate Models  “Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice.”  The use of climate models ranges from studying earth weather dynamics, to making predictions about future climate.  Model accounts for incoming and outgoing energy due to electromagnetic radiation 4

5. Data Analyzed  Models:  NCAR-CCSM-4 21 st Century Projections (future)  NASA-GISS-E2-R21 st Century Projections (future)  NCAR-CCSM-4 20 th Century Hindcasts (past)  NASA-GISS-E2-R 20 th Century Hindcasts (past) As used in the coming IPCC Report  Observational Data:  Global Land Precipitation,  Climatic Research Unit (CRU) 5

6. Analysis Techniques Global mean precipitation is used to calculate:  change over ~100 year periods  respective change in 10-year windows 6 Blue: Global mean annual precipitation from GISS E2-R Green: Linear fits for different 10-year periods

7. Results 7 Average annual precipitation rateChange Observational1062.53+35.01 GISS E2R1158.85- 6.78 CCSM41073.44+13.55 Global Average Annual Precipitation (mm/year) and its Change over Historical Period 1900-1998

8. Results 8 ErrorGISS E2RCCSM4 Correlation (R)0.460.10 R2R2 0.210.01 Root Mean Square Error (RMSE) (mm/year/decade) 49.6051.57 Comparison between Models and CRU data for 10 year windows from Historical Period

9. Future Projections 9 Models20 th century21 st century GISS E2R- 6.8+25.6 CCSM3+13.6+34.8 Change of annual precipitation rate (mm/year) over the whole 20 th and 21 st centuries Annual precipitation (black) and 10-year linear fits (colors)

10. Conclusion  Over the entire 20 th century observational global mean precipitation has slightly increased  Over the entire 21 st century both models project an increase in global mean precipitation  For the 10 year timescale, trend is highly variable and the model performance is poor for the 20 th century. 10

11. Future Studies  Look at smaller spatial scales  Look at longer temporal scale  Look at more models 11

12.  Thank You Karen Rivas Department of Chemical and Environmental Engineering University of Arizona April 21, 2012 Tucson, Arizona 12