Ensemble Climate Scenarios for Vietnam

1. Ensemble Climate Scenarios for Vietnam Dr Carol McSweeney, Met Office Hadley Centre Scenario Dissemination Workshop, IMHEN, Hanoi Monday 20th February 2012

2. Ensemble Climate Scenarios for Vietnam Table of Contents • Generating scenarios that account for model uncertainty • What do the projections indicate?

3. Addressing Policy Needs in the Provision of Climate Scenarios Needs: • Need to account for projections from more than one model • Need projections to be High-Resolution (downscaled) for policy-relevant impacts assessments Constraints: • Downscaling is resource intensive • Restriction on ability to use an RCM to downscale GCMs from different modelling centres Solution: • Downscale models from HadCM3Q family • Sampling of an ensemble to give a sub-set of 4-6 models that represent the range of outcomes from a larger ensemble for downscaling • Reference: McSweeney et al (Submitted to Journal of Climate) ‘Selecting ensemble members to provide regional climate change information’.

4. Sampling from a GCM Ensemble • Sample uncertainty caused by range of magnitudes of climate change in the different GCMs (changes by 2080s under SRES A1B) • Sample based on multiple climate variables, and sub-regions • Q0-16 are members of the Hadley centre’s own ensemble Reference: McSweeney et al (Submitted to Journal of Climate) ‘Selecting ensemble members to provide regional climate change information’.

5. Regional Model Domain • 25km resolution • Extends considerably further North of Vietnam to include Red River basin • Outputs available at daily resolution • Model run 1950-2050 • Driven at the boundaries by 5 different Global Models

6. How do the new scenarios Improve on earlier scenarios?

7. Why model uncertainty but not emissions uncertainty? • There are large differences in spatial patterns of rainfall change in different models which can cause large uncertainty for some regions.

8. Why model uncertainty but not emissions uncertainty? • On timescales of interest for planning (i.e up to 2050), there is little difference between the emission scenarios • The range of uncertainty across different models, are much larger than the uncertainties cause by emissions scenarios.

9. How do HadCM3 scenarios improve on ECHAM4? Problems with the old scenarios inherited from the Driving GCM ECHAM4

10. ECHAM4 based scenarios

11. Future Climate for Vietnam Initial Results

12. Daily maximum temperature change 2020-2050 compared with 1970-2000(JJA) • Range of responses across different ensemble members • Also a range of spatial patterns in those changes.

13. Summary of Projected Changes in Temperature for Vietnam

14. Rainfall change 2020-2050 compared with 1970-2000(JJA) • Range of responses across different ensemble members • Also a range of spatial patterns in those changes.

15. Summary of Projected Changes in Rainfall for Vietnam For most regions the projections include both increases and decreases in total rainfall

16. Derived Outputs: Extremes Indices • Change in the number of days with ‘heavy rainfall’ (higher than 95%ile) • Increases in heavy rainfall in more regions than average rainfall

17. Derived Outputs: Storm tracks • Initial results on the number of storm tracks passing through each model grid-box • Still work to on the verification of the storm tracks and the projected changes. • Range of responses across the 5 models indicates importance of multi-model approach.

18. Questions and answers

19. Eliminate model that are particularly unrealistic In this region, no need to eliminate any models

20. Climate Model Uncertainties Structural Uncertainty (IPCC CMIP3 multi-model ensemble) Parameter Uncertainty (QUMP perturbed physics ensemble)