Review of Regional Haze Situation for April 2023
1.1 The Northeast Monsoon conditions gradually gave way to the inter-monsoon as the monsoon rainband shifted northwards towards the Equator in April 2023. The prevailing winds over the Mekong sub-region blew mostly from the southeast or southwest. For the rest of ASEAN region, the prevailing winds were light and variable in direction except over the Philippines where the prevailing winds blew from the northeast or east (Figure 1).
1.2 The prevailing dry conditions over the Mekong sub-region persisted for most of April 2023, although some showers returned over parts of the sub-region towards the end of the month. While wet weather was generally observed over the rest of the ASEAN region, it was dry over the Philippines. Parts of Peninsular Malaysia and Borneo also experienced brief period of drier conditions during the period (Figure 1).
Figure 1: Average Daily Rainfall and Mean Winds for April 2023. (Source: JAXA GsMaP and GFS, respectively)
1.3 Under the influence of the prolonged dry conditions, the hotspots counts in the Mekong sub-region during the review period were mostly higher compared to the previous years. In particular, the hotspot counts for Lao PDR and Myanmar in April 2023 were the highest in 5 years (Figure 2). In the southern ASEAN region, the hotspot counts were generally lower than or comparable to the previous years except for Kalimantan where hotspot counts were slightly higher than the previous years (Figure 3).
Figure 2: Hotspot counts for the northern ASEAN region for the month of April (2019 – 2023) based on NOAA-20 satellite surveillance.
Figure 3: Hotspot counts for the southern ASEAN region for the month of April (2019 – 2023) based on NOAA-20 satellite surveillance.
1.4 The elevated hotspot and smoke haze activity persisted over the Mekong sub-region for most of April 2023. Scattered to widespread hotspots were detected over may parts of the sub-region. In particular, clusters of hotspots were persistent and more intense (Figure 5) over parts of Myanmar as well as the northern parts of Thailand and the northern and central parts of Lao PDR. The return of the showers helped to alleviate the hotspot situation towards the end of the month. Elsewhere in the ASEAN region, isolated hotpots were detected in the Philippines, Peninsular Malaysia, Sumatra and Borneo but most of them were short-lived (Figure 4).
Figure 4: Distribution of hotspots detected in March 2023 based on NOAA-20 satellite surveillance.
Figure 5: Maximum fire intensity in March 2023 based on NOAA-20 satellite surveillance.
1.5 Widespread moderate to dense transboundary smoke haze was observed to blanket the eastern parts of Myanmar as well as the northern parts of Thailand, Lao PDR and Viet Nam on many days of the month. Moderate to dense smoke haze was also observed on many days over the northern, western and central parts of Myanmar (Figure 6 & 7). Moderate smoke haze was observed over the central parts of Thailand on some days of the month (Figure 6 & 8). In view of the improving hotspot and smoke haze situation with the return of shower activities towards the end of the month, the Alert Level for the Mekong sub-region was downgraded from Alert Level 3 to Alert Level 2 on 24 April 2023. For the southern ASEAN region, localized smoke plumes were observed to emit from isolated hotspots along the east coast of Peninsular Malaysia and Sumatra on some days during brief drier periods.
Figure 6: Number of days with moderate to dense smoke haze observed in March 2023 based on satellite imagery, ground observations, and air quality reports.
Figure 7: Dense smoke haze observed over Myanmar as well as the northern parts of Thailand, Lao PDR and Viet Nam on 14 April 2023, based on NOAA-20 satellite surveillance.
Figure 8: Moderate smoke haze observed over the central parts of Thailand on 17 April 2023, based on NOAA-20 satellite surveillance.
