Category Archives: Haze Review for Year 2021

Review of Regional Haze Situation for December 2021

1.1 By December 2021, Northeast Monsoon conditions had become fully established over the ASEAN region. The prevailing low-level winds over regions north of the equator blew mostly from the north or northeast while the winds over regions south of the equator blew mainly from the west or northwest. Alert Level 1 for the Mekong sub-region was issued on 7 December 2021, indicating the start of the dry season. Persistent dry conditions were observed over the sub-region in December 2021. Higher rainfall was observed over the rest of the ASEAN region, particularly over Peninsular Malaysia and the southern Philippines, which were affected by heavy rainfall in December 2021 (Figure 1). In particular, Super Typhoon Rai made landfall over the southern Philippines on December 16, 2021 and caused severe damage, flooding and loss of lives. Floods also affected several Malaysian states including Pahang, Melaka, Negri Sembilan and Johor in the second half of December, resulting in significant damage and casualties.

1.2 For the December 2021 review period, overall hotspot activities started to increase in the Mekong sub-region following the onset of dry conditions, while wet conditions continued to subdue hotspot activities in the southern ASEAN region. The hotspot counts for the Mekong sub-region in December 2021 were mostly lower compared to previous years, while the hotspot counts over the southern ASEAN region were generally comparable to those in previous years (Figures 2 and 3).

1.3 During the review period, isolated to scattered hotspots were detected throughout the Mekong sub-region and isolated smoke plumes were sometimes observed to emanate from the detected hotspots. Although isolated hotspots were detected in Sumatra, parts of Peninsular Malaysia and Kalimantan, the hotspot activities were generally subdued over the southern ASEAN region (Figures 4 and 5).

Review of Regional Haze Situation for November 2021

1.1 In November 2021, the inter-monsoon conditions gradually made way for the Northeast Monsoon over the ASEAN region. The prevailing low-level winds over the northern ASEAN region blew mostly from the northeast or east while the winds over most parts of the southern ASEAN region were light and variable in direction. Wet weather conditions were observed over most parts of the ASEAN region, except for the northern parts of the Philippines as well as the northern, western and central parts of the Mekong sub-region where conditions were persistently drier. Overall, the observed rainfall amount was higher over the coastal areas of central Viet Nam, the southern parts of Thailand and the coastal areas of northern Peninsular Malaysia (Figure 1). Due to the heavy rainfall, floods affected several southern Thailand and central Viet Nam provinces in November 2021.

1.2 For the November review period, overall hotspot activities were mostly subdued due to the wet conditions over the ASEAN region. The hotspot counts over the region for 2021 were mostly lower or comparable to those in previous years (Figures 2 and 3).

1.3 During the review period, isolated to scattered hotspots were detected mainly in the Mekong sub-region and central Sumatra. While these hotspots were mostly short-lived, hotspots were relatively more persistent in the southern parts of Myanmar, northern Viet Nam and central Thailand. On most days, no smoke plumes were discernable.

Review of Regional Haze Situation for October 2021

1.1 Southwest Monsoon conditions transitioned to the inter-monsoon in mid-October 2021 as the winds over most parts of the ASEAN region turned light and variable (Figure 1). In the first half of October 2021, Tropical Storm Lionrock and Typhoon Kompasu contributed to increased rainfall over the northern parts of the Philippines and central parts of Viet Nam. In particular, Typhoon Kompasu caused significant damage and casualties in the Philippines due to landslides and flash floods. The southern ASEAN region experienced continued shower activities during the review period and Alert Level 0 was issued for the region on 18 October 2021, signaling the end of its traditional dry season. Average daily rainfall was relatively higher in western Kalimantan and northern Sumatra, while persistent dry conditions were observed over eastern Java and the Lesser Sunda Islands.

1.2 In October 2021, overall hotspot activity in the ASEAN region was subdued, contributed by wet weather conditions. While most of the hotspots in the southern ASEAN region were detected in Kalimantan, the number of hotspots for the southern ASEAN region were lower or comparable to previous years’ counts (Figure 2), except for Sabah and Sarawak where it was slightly higher. For the northern ASEAN region, most of the hotspots were detected in Viet Nam. The number of hotspots detected in the northern ASEAN region were also lower or comparable to previous years (Figure 3).

1.3 For the October 2021 review period, isolated to scattered hotspots were detected mainly in central Viet Nam, Borneo, and Sumatra (Figure 4 and 5). On a few days, short-lived localized smoke haze was observed to emanate from clusters of hotspots in central Kalimantan. There was no transboundary smoke haze observed over the ASEAN region during the review period.

Review of Regional Haze Situation for September 2021

1.1 In September 2021, Southwest Monsoon conditions persisted over the ASEAN region as the prevailing winds blew mainly from the southeast or southwest (Figure 1). In particular, there were three tropical cyclones that affected the northern ASEAN region during the review period. In the first half of September 2021, Typhoon Chanthu and Tropical Storm Conson contributed to the increased rainfall over northern parts of the Philippines. In the last week of the review period, Tropical Storm Dianmu made landfall over Viet Nam, and widespread showers with gusty winds caused floods and landslides in Viet Nam, Lao PDR and Thailand. For the southern ASEAN region, rainy weather was observed over many areas despite this period of the year being its traditional dry season. Average daily rainfall was highest in Sabah, western Kalimantan, and central Sumatra, while relatively drier conditions were observed over the Java Sea region.

1.2 For the September 2021 review period, hotspot activity in the ASEAN region was generally subdued due to wet weather. Most hotspots in the southern ASEAN region were detected in Kalimantan. Overall, the number of hotspots for the southern ASEAN region were lower or comparable to previous years’ counts (Figure 2). For the northern ASEAN region, a majority of the hotspots were detected in Viet Nam. The hotspot counts in Viet Nam, Lao PDR and Myanmar were slightly elevated compared to the same review period in previous years, while the hotspot counts elsewhere in the northern ASEAN region were lower compared to the same review period in previous years (Figure 3).

1.3 In September 2021, isolated to scattered hotspots were detected mainly in Viet Nam, Borneo, and southern Sumatra (Figure 4 and 5). On a few days in the month, localized smoke haze was observed to emanate from persistent hotspot clusters in western Kalimantan. Slight smoke plumes were occasionally detected from some of the isolated hotspots in eastern Kalimantan and southern Sumatra. Otherwise, no significant transboundary smoke haze was observed over the ASEAN region during the review period.

Review of Regional Haze Situation for August 2021

1.1 With the low-level winds blowing from the southeast or southwest on most days, Southwest Monsoon conditions continued to prevail over the ASEAN region in August 2021 (Figure 1). The first week of August was relatively dry for most parts of the southern ASEAN region, with the monsoon rain band located north of the Equator. In subsequent weeks, the movement of the monsoon rain band closer to the Equator brought wet weather to much of the ASEAN region except its southernmost regions (Java, the Lesser Sunda Islands and southern Sumatra).

1.2 For the August 2021 review period, the hotspot counts over the southern ASEAN region were much lower than those detected in previous years (Figure 2). The hotspot counts over the northern ASEAN region were similar to those detected in previous years, with the exception of Thailand and Viet Nam which recorded higher hotspot counts (Figure 3).

1.3 Isolated to scattered hotspots continued to be detected in most parts of the southern ASEAN region in August 2021 (Figures 4 and 5). There was increased hotspot activity in areas where drier conditions were experienced, such as over the southern ASEAN region in the first week of August, and throughout the month in Java and the Lesser Sunda Islands. At times this month, localised smoke plumes were observed emanating from clusters of hotspots in Sumatra and Kalimantan. This was particularly so for West Kalimantan, where a persistent cluster of hotspots was observed on most days this month (Figure 5).

1.4 Isolated hotspots were detected mainly in the southeastern parts of the northern ASEAN region in August 2021. Towards the middle of the month, localised smoke plumes were observed in parts of central Viet Nam; no smoke plumes were observed elsewhere in the northern ASEAN region (Figures 4 and 5).

Review of Regional Haze Situation for July 2021

1.1 In July 2021, Southwest Monsoon conditions prevailed over the ASEAN region with the low-level winds blowing from the southeast or southwest on most days (Figure 1). During the first fortnight of the month, wet weather was observed over most parts of the ASEAN region as the monsoon rain band remained near the equatorial southern ASEAN region. Towards the second fortnight of the month, the monsoon rain band shifted further north of the Equator. This led to dry conditions over parts of the southern ASEAN region and indicated the start of the region’s traditional dry season.

1.2 As it is the traditional wet season for the northern ASEAN region, showers were observed over the region on most days during the month. The average daily rainfall was highest over the northern parts of the Philippines during the month (Figure 1) due to the influence of Typhoon Cempaka that formed in the South China Sea, west of the Philippines in the second fortnight of the month.

1.3 For the July review period, the hotspot counts over the ASEAN region for 2021 were mostly lower or comparable to those in previous years (Figures 2 and 3), except for Sabah and Sarawak as well as the Philippines where slightly higher hotspot counts were detected.

1.4 Isolated to scattered hotspots were detected in most parts of the southern ASEAN region (Figure 4) in July 2021. Under drier conditions in the second fortnight of the month, the hotspot situation over central and southern parts of Sumatra as well as the northern and western parts of the Borneo Island worsened. Hotspot clusters with intense fires were detected in Riau, Jambi, South Sumatra, Lampung, Bangka-Belitung and Sarawak as well as in West and North Kalimantan (Figure 4 and Figure 5). Localised smoke plumes were observed to emanate from clusters of hotspots detected in Sumatra and Borneo Island on some days.

1.5 In the northern ASEAN region, isolated hotspots were detected mostly in Viet Nam and Cambodia during periods of drier conditions, but no smoke plumes were observed (Figure 4).

Review of Regional Haze Situation for June 2021

1.1 The ASEAN region transitioned to Southwest Monsoon conditions in June 2021, with prevailing winds over regions south of the equator blowing from the southeast while prevailing winds over regions north of the equator blew mainly from the southwest.

1.2 During this period, the monsoon rain band stayed in close proximity to the equator and shower activities were observed over most of the ASEAN region. However, drier conditions persisted in the Lesser Sunda Islands and eastern Java (Figure 1).

1.3 The hotspot counts over most of the ASEAN region for June 2021 were comparable to those in previous years. More hotspots were detected in Cambodia and the Philippines compared to previous years while lesser hotspots were detected in Sumatra and Peninsular Malaysia compared to previous years. (Figures 2 and 3)

1.4 In June 2021, isolated hotspots were detected in most parts of the southern ASEAN region, contributed by brief periods of drier weather. Isolated to scattered hotspots were also detected in the eastern and central parts of the Mekong sub-region but were alleviated by an increase in shower activities. On the whole, hotspot activities remained relatively subdued in the ASEAN region with no significant smoke haze observed from satellite imagery (Figures 4 and 5).

Review of Regional Haze Situation for May 2021

1.1 Inter-monsoon conditions prevailed over most of the ASEAN region in May 2021. While most of the region experienced light and variable winds, the prevailing winds over Java, the Lesser Sunda Islands, the Philippines, and Sulawesi blew from the east or southeast.

1.2 During this period, shower activities were observed over most of the ASEAN region. However, drier conditions persisted in the Lesser Sunda Islands and eastern Java (Figure 1).

1.3 For the May review period, the hotspot counts over the ASEAN region for 2021 were slightly lower or comparable to those in previous years (Figures 2 and 3).

1.4 Although hotspot activities were detected in most parts of the ASEAN region, no significant smoke haze was observed in May 2021. Isolated hotspots were detected in most of the southern ASEAN region, contributed by the development of drier conditions there. In the northern ASEAN region, although some hotspot clusters were detected, an increase in shower activities throughout the month led to a gradual improvement of the hotspot situation. ASMC declared the end of the northern ASEAN dry season on 21 May 2021 with the downgrading of Alert Level 1 to Alert Level 0 (Figures 4 and 5).

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).

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).

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).

Review of Regional Haze Situation for March 2021

1.1 In March 2021, Northeast Monsoon conditions gradually weakened over the ASEAN region and the prevailing winds started to turn light and variable on several days. In the northern ASEAN region, the prevailing winds blew mainly from the northeast or southeast, although light and variable winds prevailed over the western parts of the Mekong sub-region. Extended dry conditions persisted over the sub-region in this month as its traditional dry season became established.

1.2 For the southern ASEAN region, the prevailing winds blew mainly from the northeast or east. Northern and central Sumatra as well as parts of Peninsular Malaysia experienced drier conditions in early March 2021 under the influence of the dry phase of the Northeast Monsoon. Elsewhere over the ASEAN region, isolated to scattered showers were observed.

1.3 For March 2021, slightly higher hotspot counts were detected in Cambodia compared to previous years for the same period. In other parts of the ASEAN region, the hotspot counts for March this year were lower or comparable to previous years (Figures 2 and 3).

1.4 Widespread to scattered hotspot activities were detected in most parts of the Mekong sub-region in March 2021, especially in Myanmar, northern Thailand, northern Cambodia and Lao PDR where persistent clusters of hotspots were detected on many days (Figures 4 and 5), contributed by continued dry conditions throughout the month.

1.5 Moderate to dense haze was observed emanating from clusters of hotspots on most days in the Mekong sub-region, particularly over Myanmar and northern parts of Thailand, Lao PDR and Cambodia (Figure 6).

1.6 In the southern ASEAN region, there were brief periods of drier weather in the first half of March 2021 over northern and central Sumatra, Peninsular Malaysia and West Kalimantan. This led to the development of isolated hotspots with localised smoke plumes on several days in the drier areas. As shower activities returned in late March 2021, the hotspot activities and smoke haze situation became more subdued.