Review of Regional Haze Situation for April 2021 |

Review of Regional Haze Situation for April 2021

1.1 In April 2021, Northeast Monsoon conditions transitioned to Inter-monsoon conditions as the prevailing winds over most of the ASEAN region became light and variable in direction, except over the Philippines where the prevailing winds blew from the north or northeast.

1.2 During this period, there was an increase in shower activities over most of the northern ASEAN region as the monsoon rainband shifted northwards to be located near the Equator. However, the northern and northwestern parts of the Mekong sub-region experienced drier conditions compared to the other parts of the sub-region. In the southern ASEAN region, wet conditions generally prevailed (Figure 1).

Figure 1: Average Daily Rainfall and Mean Wind for April 2021. (Source: JAXA GsMaP and GFS respectively)

1.3 The hotspot counts over the ASEAN region for April 2021 were either comparable or lower than the previous years in the same review period except for Kalimantan where hotspot counts were higher than previous years (Figures 2 and 3).

Figure 2: Hotspot counts for the northern ASEAN region for the month of April (2017 – 2021). [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2017 – 2018 are based on the Suomi-NPP satellite.]

Figure 3: Hotspot counts for the southern ASEAN region for the month of April (2017 – 2021). [Note: The hotspot counts from 2019 onwards are based on the NOAA-20 satellite, while those from 2017 – 2018 are based on the Suomi-NPP satellite.]

1.4 Hotspot activities were detected in most parts of the northern ASEAN region in April 2021. The hotspot clusters over Myanmar and the northern parts of Lao PDR were more persistent and widespread due to drier conditions over these areas (Figures 4 and 5).

1.5 Moderate to dense smoke haze was observed to emanate from hotspot clusters detected in the northern and southern parts of Lao PDR, and most parts of Myanmar (Figure 6). Smoke haze from the eastern parts of Myanmar and northern parts of Lao PDR was also observed to have been blown into the northern parts of Lao PDR and Viet Nam respectively by the prevailing winds on some days. In view of increased shower activities towards the end of April 2021 helping to improve the hotspot and haze situation over the Mekong sub-region, the Alert Level was downgraded from Alert Level 2 to Alert Level 1 on 30 April 2021.

1.6 In the southern ASEAN region, brief periods of drier conditions led to the development of isolated hotspots mostly in Peninsular Malaysia, Borneo Island, Sumatra and Sulawesi (Figures 4 and 5). No smoke plumes were observed to have emanated from these hotspots (Figure 6).

Figure 4: Distribution of hotspots detected in March 2021 based on NOAA-20 satellite surveillance.

Figure 5: Maximum fire intensity in March 2021 based on NOAA-20 satellite surveillance.

Figure 6: Number of days with moderate to dense smoke haze observed in March 2021 over an area based on satellite imagery, ground observations and air quality reports.