Regional Climate Change over Southeast Asia Region
Mohan Kumar Sammathuria, Ling Leong Kwok & Wan Azli Wan Hassan
Malaysian Meteorological Department
Ministry of Science, Technology & Innovation, Malaysia
Email: wanazli@met.gov.my
ABSTRACT
The United Kingdom Meteorological Office Hadley Centre’s Regional
Climate Modelling system, PRECIS (Providing REgional Climates for Impact
Studies) was used to run climate change model simulations for the South East Asia
(SEA) region. The 50km resolution PRECIS simulation was driven by the 150km
resolution HadAM3P GCM data. The boundary data from HadAM3P was supplied by
the Hadley Centre, which is the results of their simulation using sea surface
temperature as boundary conditions at the sea points from their coupled oceanatmosphere GCM, namely HadCM3. PRECIS was then used to downscale to 50km
regional simulations for the baseline and future climate simulations using the IPCC’s
SRES lower emission (B2) and higher emission (A2) scenarios with sulphur cycle
included. The baseline simulation period is 1961-1990 and the simulation experiments
period is 2071-2100.
The precipitation and temperature observation data (CRU20) from the Climate
Research Unit, University of East Anglia, United Kingdom is used to validate the
model performance in simulating the current climate. The PRECIS captures important
regional information on seasonal rainfall, which is missing in its parent GCM
simulation. The basic parameters analysed to study the future climate change
occurring during 2071-2100 are the mean surface (1.5 meters) temperature and
precipitation. The analysis is comprised of both annual mean and seasonal mean for
December-January-February (DJF), March-April-May (MAM), June-July-August
(JJA) and September-October-November (SON). To detect the possible atmospheric
circulation change during the monsoon periods (DJF and JJA) in the future climate we
analyzed the mean 850hPa wind for the lower emission scenario (B2).
Overall, both the lower emission (B2) and the higher emission (A2) scenarios
produce an increase in the annual mean temperature over SEA during 2071-2100.
However, the A2 scenario shows the larger increase in temperature. The land area
show higher annual mean warming compared to maritime regions. The SEA land
surface annual mean warming is in the range of 1.5-3.0 °C for B2 and 3.0-4.5 °C for
A2. Meanwhile the SEA maritime surface annual mean warming is 0.5-1.5 °C for B2
and 2.0-3.5 °C for A2. Both the B2 and A2 scenarios show the highest increase in
mean annual temperature to occur over western Sumatra, southern Borneo and central
Thailand. The A2 simulation projects a spatial difference by about 0.5°C between the
maritime SEA and western Pacific region. However, this spatial difference in
warming is not observed with the B2 simulation. At a more localized scale, over
Malaysia, the annual mean surface temperature increase is lowest for northern
Peninsular and highest for central Peninsular and Sabah. Seasonally the rate of
warming varies with the greatest change occurring during the summer months (JJA)
for both B2 and A2, with the most significant warming to occur over western Sumatra
and southern Borneo.
The precipitation change has greater spatial variation compared to the
temperature change. Overall, both scenarios show a positive anomaly of mean annual
precipitation over continental SEA while a negative anomaly over maritime SEA
region. Seasonally, continental SEA will experience the highest positive anomaly
during the inter-monsoon months of SON, but maritime SEA will experience the
highest negative anomaly during the other inter-monsoon months of MAM. SEA, at
large will experience a deficit in mean annual precipitation for both A2 and B2
scenarios, with B2 giving the larger deficit. Locally, northern Peninsular Malaysia
will experience positive mean annual precipitation anomaly while southern Peninsular
Malaysia will experiences negative mean annual precipitation anomaly by both
scenarios. Sabah and Sarawak, overall, will experience a deficit in annual mean
precipitation. In terms of mean seasonal precipitation, SEA in general will experience
a negative anomaly during all the seasons with B2 bringing more deficit in
precipitation. The same pattern of the above precipitation deficit is true during the
winter months (DJF) for the whole area of Malaysia. Northern Peninsular Malaysia
will experience a positive mean seasonal precipitation anomaly during the summer
months (JJA) and inter-monsoon months (SON) but a negative anomaly during the
winter months (DJF) and inter-monsoon months (MAM). Southern Peninsular
Malaysia will experience a negative mean seasonal precipitation anomaly during
winter (DJF), inter-monsoon (MAM) and summer (JJA) but a positive anomaly
during the other inter-monsoon (SON). Sabah will experience the largest deficit in
seasonal mean precipitation during the winter months (DJF) and inter-monsoon
months (MAM), while Sarawak will experience the largest deficit in precipitation
only during winter (DJF).
The analysis of 850hPa level wind anomaly during the winter months (DJF)
for the period 2071–2100 compared to the baseline period of 1961–1990 for B2 show
a significant weakening of the easterly over the western Pacific region by 2.0 to 3.5
m/s. This may indicate a weakening of the northeast monsoon experienced in the SEA
region. In the summer (JJA), over the Indian Ocean, west of Sumatra, the anomalous
easterly component winds with a magnitude of 1.5 to 2.5 m/s will tend to enhance the
positive Indian Ocean Dipole (IOD) phenomenon.