High resolution climate simulations and future change over Vietnam Kim Nguyen, Jack Katzfey and John McGregor 9-14th December 2012 Melbourne

OUTLINES Conformal Cubic Atmospheric Model (CCAM) simulation forced by ERA-Interim at 20 km over Vietnam (preliminary study) Rainfall for the wet and dry half years compared against GPCP (2.5 degree), CRU (0.5 degree) and APHRODITE (0.25 degree) Inter-annual variability of rainfall and El Nino Southern Oscillation (ENSO) 2. Changes in rainfall by 2030 using results from the previous project (PCCSP, CMIP3 high emission scenario A2) 60 km CCAM global simulation

CCAM SURFACE ELEVATION Elevation (meter)

MSLP AND 1000 hPa WIND April to September (summer half year) Southwesterly from Bay of Bengal Cross-equatorial flow from the Southern Hemisphere April to September (summer half year) October to March (winter half year) Northeasterly originated from Mongolia and northern China merges with easterly flow from the Pacific MSLP AND 1000 hPa WIND plot_climatic_wind.jnl

SUMMER MONSOON MEAN RAINFALL April to September High rainfall on the windward side and less rain on the lee ward side (rain shadow)

WINTER MONSOON MEAN RAINFALL NE WINTER MONSOON MEAN RAINFALL October to March High rainfall along windward side of the Truong Son range

RAINFALL BIAS April to September October to March Rainfall bias in mm day-1, with red overestimation and blue underestimation and only bias at 95th significant level shown RAINFALL BIAS April to September October to March

MONTHLY RAINFALL AMOUNT AND BIAS AVERAGED OVER VIETNAM mm

APR-SEP OCT-MAR -14.75 North Vietnam North VN

APR-SEP OCT-MAR Central Vietnam Central VN

APR-SEP OCT-MAR South Vietnam South VN

ENSO

Interannual variability of rainfall and ENSO ENSO is defined using Nino 3.4 index. El Nino/La Nina when all Nino 3.4 indices of the season are at least 0.5oC above/below normal. Neutral season when all Nino 3.4 indices of the season are between -0.5oC and +0.5oC, exclusively Wet season (summer monsoon) from April to September Dry season (winter monsoon) from October to December of the current year and January to March of the following year

RAINFALL ANOMALY APRIL TO SEPTEMBER In general, rainfall over Vietnam influence of ENSO is moderate and patchy slightly above normal in neutral years slightly below normal under both ENSO phases, except for the southern tip of South Vietnam, where rainfall above normal under La Nina years RAINFALL ANOMALY APRIL TO SEPTEMBER above normal everywhere slightly above normal below normal In the wet season, ENSO moderately and patchy influences rainfall over VN maybe due to wind is south-westerly Explain what is El Nino, La Nina and neutral

RAINFALL ANOMALY OCTOBER TO MARCH 1. ENSO has strong influence on rainfall along the east coast of Vietnam. 2. El Nino (La Nina) years, rainfall along the east coast is below (above) normal. below normal above normal In El Nino years, rainfall is below normal may be TC genesis is shifted east to central and eastern Pacific. Whereas in La Nina years, TC genesis is closer to VN, rainfall is above normal. Also, wind has two components: northeasterly and easterly from the Pacific. This easterly is weaken in El Nino and strengthen in La Nina years

PREDICTION OF FUTURE RAINFALL CHANGE OVER VIETNAM BY 2030 USING PREVIOUS PROJECT (PCCSP, CMIP3, A2) CCAM 60 KM GLOBAL SIMULATIONS

SURFACE ELEVATION

RAINFALL CHANGE BY 2030 IN GFDL2.1 OCT-MAR APR-SEP CCAM OBS rainfall trend (%/year ) Increase rainfall decrease rainfall

RAINFALL CHANGE BY 2030 IN ECHAM5 OCT-MAR APR-SEP CCAM OBS rainfall trend (%/year )

RAINFALL CHANGE BY 2030 IN UKMO HadCM3 APR-SEP OCT-MAR UKMO UKMO Rainfall changes in mm day-1, with red increase and blue decrease and stippling shows changes at 95th significant level The host GCM UKMO HadCM3 shows changes not significant in both seasons, except for the southern tip VN, where rainfall is predicted to decrease with significant in wet season VN CCAM CCAM shows increase in both seasons along the east coast with significant only in the wet season

CONCLUSIONS Climatic rainfall for the wet and dry seasons over Vietnam and surrounding regions was validated against observed GPCP, CRU and APHRODITE. CCAM captures well the mean rainfall patterns for both seasons and closely resembles APHRODITE rainfall patterns Influence of ENSO on rainfall over Vietnam in the wet season: patchy and moderate, above normal rainfall in neutral years in the dry season: strongly along the east coast, El Nino (La Nina) years rainfall is below (above) normal. Future changes: CCAM forced by host GFDL2.1 SST captures well observed rainfall trend. CCAM projects rainfall increase along the east coast and decrease in the north Vietnam.

THANK YOU CCAM Downscaling for Viet Nam | Kim Nguyen

CCAM Downscaling for Viet Nam | Peter Hoffmann

Keith Linda CCAM OBS Tropical depression < 34 knots Low resolution and not well defined pressure center

RAINFALL CHANGE BY 2030 IN ECHAM5 Rainfall changes in mm day-1, with red increase and blue decrease and stippling shows changes at 95th significant level The host GCM ECHAM5 shows decrease/increase in wet/dry season but not significant CCAM shows increase in both seasons from south of central to north Vietnam, but significant only over central Vietnam The differences between CCAM and host GCM rainfall change in the wet season is mainly over orography RAINFALL CHANGE BY 2030 IN ECHAM5 ECHAM5 OCT-MAR APR-SEP CCAM

RAINFALL CHANGE BY 2030 IN GFDL2.1 Rainfall changes in mm day-1, with red increase and blue decrease and stippling shows changes at 95th significant level The host GCM GFDL2.1 shows changes not significant in dry season. In wet season, rainfall is predicted to decrease with significant over Cambodia, south and north VN RAINFALL CHANGE BY 2030 IN GFDL2.1 GFDL2.1 OCT-MAR APR-SEP CCAM CCAM shows increase in wet season along the east coast

CCAM SURFACE ELEVATION Central Vietnam South China Sea Bay of Bengal Tibetan Plateau Thailand Cambodia Laos North South Vietnam CCAM SURFACE ELEVATION Elevation (meter) 20km resolution region