 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,

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

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

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

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

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

Results 7 Average annual precipitation rateChange Observational GISS E2R CCSM Global Average Annual Precipitation (mm/year) and its Change over Historical Period

Results 8 ErrorGISS E2RCCSM4 Correlation (R) R2R Root Mean Square Error (RMSE) (mm/year/decade) Comparison between Models and CRU data for 10 year windows from Historical Period

Future Projections 9 Models20 th century21 st century GISS E2R CCSM 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)

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

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

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