1. Climate Means and Climate Variability Scenarios for Mainland Southeast Asia for Impact and Vulnerability Assessments Anond Snidvongs 1 John L. McGregor 2 Nguyen Kim Chi 2 Wirote Laongmanee 1 Weerasak Weerakant 1 Jantira Ratanarat 1 1 Southeast Asia START Regional Center, Bangkok, Thailand 2 CSIRO Atmospheric Research, Aspendale, Australia

2. Outline Why do we need climate mean and climate variability CCAM for SE domain and its ‘raw’ outputs Empirical adjustment of CCAM rainfall outputs Climate change scenario for each sub-domain Our scenarios in comparison with others Projected climate means and variability for each sub domain and at our 3 IV&A Assessment sites

3. CCAM for Southeast Asia Some Important Features 18 vertical levels Final output domain: 5 o -35 o N and 92 o -110 o E Output resolution was interpolated to 0.1 o (about 10 km) Some Selected Daily Outputs Tmax, min and avg T ( o C) Rainfall (mm/d) Wind speed (m/s) and direction Radiation (W/m 2 ) Specific humidity (kg/kg) Heat flux (W/m 2 ) Pressure (hPa) Cloud cover (%)

4. Putting Time Slice into the Scenario CCAM was run for 10 years each at 360 ppm CO 2 baseline, 540 ppm (1.5xCO 2 ) and 720 ppm (2xCO 2 ) 540 ppm 720 ppm Based on SRES A1FI these CO 2 levels correspond to: 360 ppm  1980-89 540 ppm  2040-49 720 ppm  2066-75

5. CCAM Output and Verification: Temperature

6. CCAM Output and Verification: Precipitation

7. Problems with CCAM rainfall outputs 1.Slightly overestimate the annual rainfall 2.Rainfall season onset delayed by 8-10 weeks 3.Daily variation not large enough 4.Overestimate number of rain days

8. CCAM Precipitation Output Adjustment Key Principle: Preserve original CCAM spatial and temporal resolutions Made statistical adjustment based on cumulative rainfall using a non-linear function to exponentially increase the daily variability An arbitrary rainfall threshold of 3 mm/day was applied to reduce number of rain days

10. CCAM ‘Rescaled’ Output: Precipitation

11. Compare ours with other global scenarios

21. Ubon Rachathani, Thailand 2. More distinct mid-season dry spell at 540 ppm 3. More continuous rainy season at 720 ppm and total rain increased by about 10% 4. More cloud overcastting could compensate for temperature rise 1. Rainfall season onset will be earlier by about 20 days at 540 and 720 ppm

22. Seasonal and Annual Variability Ubon Rachathani, Thailand

23. Savannakhet, Lao PDR 3. More cloud overcastting could compensate for less temperature rise 1. At 540 ppm, rainfall season onset will be earlier by about 10 days and offset be delayed slightly but no substantial change in total rainfall 2. At 720 ppm, only slight shift in rainfall season but total rainfall will be increased by about 20%

24. Seasonal and Annual Variability Savannakhet, Lao PDR

25. Long An, Vietnam 1. At 540 and 720 ppm, both rainfall season onset and offset will be earlier by about 10 days 3. At 720 ppm the total rainfall will be increased by about 10% but rainfall in Qtr 4 will be less 2. At 540 ppm mid-season dry spell could be more prominent but not so at 720 ppm

26. Seasonal and Annual Variability Long An, Vietnam

27. Site360 ppm540 ppm720 ppm Ubon Rachathani767493 Savannakhet8883105 Long An606379 Average # of days with T > 33 o C Average # of days with T < 15 o C Site360 ppm540 ppm720 ppm Ubon Rachathani13179 Savannakhet263419 Long An000

28. Some Conclusions and Implications 1.Under elevated CO 2 environment the mean climate of the region will be slightly more wet (10-20%) and more warm (1-2 o C) which may only has a slight effect on water resource (or even be positive impact) 2.Even though the mean climates (T and Precip) will generally not be much affected by CO 2 increase but the change in climate variability and seasonality will be more important and the rain-fed agricultural sector is naturally more susceptible to this 3.Inland part of the Mekong Basin (i,.e., Lao PDR and Thailand) has a more abrupt rainy season onset than the delta part (I.e., Vietnam). Ability to do seasonal forecast for rainfall onset will certainly increase capacity of rice farmer to cope with future change in climate variability