Climate summary on below-normal precipitation in Southeast Asia
since spring 2015 and related atmospheric circulation
Please note that the discussion in this summary should not be deemed as
constituting seasonal prediction or outlook for any individual country.
1. Climate characteristics
Anomalously low precipitation and related impacts were reported in Southeast Asia
since spring 2015. The Indochina peninsula had below-normal precipitation especiallyin the beginning of the 2015 rainy season, while precipitation amounts over the easternpart of the Kalimantan Island and the southern part of the Philippines from December
2015 to March 2016, when in normal years large amount of precipitation would be
expected in these regions, were exceptionally low at 40% of normal.
As seen in Figure 1, twelve-month precipitation totals from April 2015 to March
2016 are less than 60% of the normal in parts of the Kalimantan Island, while over partsof the Indochina Peninsula, precipitation totals range from 60 to 70 % of the normal.
Cumulative precipitation starting from April 2015 averaged over the Indochina
Peninsula and the southern part of the Philippines evolves at the slowest pace since2000 (Figure 2).

Figure 1 Twelve-month precipitation amount in Southeast Asia
Spatial distribution of twelve-month precipitation ratios (%) from April 2015 to March
2016 compared to the normal (30-year average from 1981to 2010).

Figure 2 Areal average of cumulative precipitation evolution for the Indochina
Peninsula (left) and the southern part of the Philippines (right)
The red and yellow lines indicate cumulative precipitation from April 1 to March 31 of
2015/2016 and 2014/2015, respectively. The blue lines indicate that for the wettest year
since 2000/2001 and grey lines for other years.
2. Atmospheric circulation related to below-normal precipitation
The El Niño conditions, which had emerged in summer 2014 but remained
relatively weak during the following months, started to renew its strength in spring 2015.
In association, convective activity was enhanced over the equatorial central to eastern
Pacific and suppressed over the equatorial Southeast Asia.
During the summer monsoon season in 2015, anticyclonic circulation anomalies in
the lower troposphere remained pronounced over the northern part of Southeast Asia,and the monsoonal wet southwesterly flow was weaker than normal. In relation,
convective activity was suppressed and precipitation amount averaged over the region
was below normal. On the ground that the atmospheric circulation anomalies describedabove resemble those observed in the past El Niño events, it can be deduced that
below-normal precipitation over the northern part of Southeast Asia in the 2015 summer
monsoon season was also related to the El Niño conditions.
3. Remarks on the latest results from JMA’s ensemble prediction system
The El Niño conditions, which have lasted since the boreal summer 2014, will likely
dissipate by the beginning of this summer. Meanwhile, the sea surface temperatures(SSTs) in the tropical Indian Ocean are predicted to remain above normal all through thesummer (see the latest El Niño Outlook updated on April 11).

According to the latest results from the JMA seasonal ensemble prediction system
driven by the expected SST anomalies including those mentioned above, during the firsthalf of the summer monsoon season anticyclonic circulation anomalies in the lower
troposphere are predicted to be dominant over the northern part of Southeast Asia,
indicating weaker-than-normal southwest monsoon circulation (see the Tokyo ClimateCenter Monthly Discussion on Seasonal Climate Outlooks No. 26 updated on April 25).