Tropical Cyclone Senyar Disaster: Warning of Weak Mitigation and the Effects of Environmental Degradation

Indonesia is fundamentally not a country that is vulnerable to the threat of tropical cyclones. However, the situation has changed in line with the increasing trend of tropical cyclone formation. The disasters that struck Aceh, North Sumatra, and West Sumatra serve as a warning to enhance mitigation efforts against the threat of tropical cyclones in the future.

Tropical cyclone Senyar, which struck waters as far as Sumatera, causing a major hydrometeorological disaster, is indeed unusual. Geographically, the likelihood of a tropical cyclone forming in the waters surrounding Indonesia is relatively small. Indonesia, located along the equator, has a very small potential Coriolis force effect.

According to Emilya Nurjani, a climate and environmental expert from Gadjah Mada University in her presentation, Coriolis force is a requirement for the formation of tropical cyclones. This Coriolis force causes the wind to bend and also forms a vortex of water that is lifted following the movement of the wind. The formation of the Coriolis force in latitude areas less than five degrees from the equator is very unlikely, making it difficult for tropical cyclones to form.

According to a study titled "Tropical Cyclones: Trends, Forecasting, and Mitigation," at least 80 cyclones occur in tropical waters around the world each year. Some of the most common occur in the northwestern Pacific Ocean and parts of the northern Indian Ocean. Several countries vulnerable to the threat of tropical cyclones in the northern Indian Ocean rim include Bangladesh, Myanmar, Sri Lanka, and India. Despite directly bordering the eastern Indian Ocean, western Indonesia is relatively unaffected by the threat of tropical cyclones.

However, this does not mean that Indonesia is free from disasters caused by tropical cyclones. In fact, Cyclone Senyar has arrived, bringing heavy rainfall that has resulted in floods and landslides in parts of Sumatra. This occurrence is indeed an anomaly, but it remains a sign that tropical cyclone phenomena are becoming more frequent in Indonesia. This event follows a number of tropical cyclones that had previously been monitored as they threatened parts of Indonesia.

For example, Cyclone Seroja, which formed in the waters off Rote Island, caused heavy rain, flooding, and landslides in East Nusa Tenggara in 2021. The cyclone resulted in 181 fatalities and affected more than 40,000 people.

This cyclone is just one of dozens of tropical cyclones that form in Indonesia and its surrounding areas. According to the study "The influence of El Niño-Southern Oscillation (ENSO) on the characteristics of tropical cyclones in Indonesian waters," there were 2,885 tropical cyclones in the 50-year period from 1973 to 2022. On average, there are around 57 cyclones annually in Indonesia and its surrounding areas.

The distribution of tropical cyclones is divided into four regions in Indonesia. The first region is located in the waters near Aceh and North Sumatra. The second region is the area with the most frequent occurrence of tropical cyclones, which is situated around the waters of the South China Sea to the west of the Pacific Ocean. The third region extends from the western coast of Sumatra to the western part of Java, while the final area encompasses most of Java-Bali to Eastern Indonesia.

The numerous tropical cyclone phenomena that emerge in Indonesian waters do not always result in major disasters as often seen in Bangladesh, Myanmar, Sri Lanka, or India. However, considering Cyclone Seroja (2021) that struck NTT and Senyar (2025) which caused hydrometeorological disasters in Sumatra, it must be a serious concern to take mitigation steps as soon as possible. The readiness for disaster mitigation in facing tropical cyclones needs to be enhanced because the public's knowledge regarding the threats posed by these cyclones is relatively limited.

So far, the Meteorology, Climatology, and Geophysics Agency (BMKG) has indeed been active in providing early warnings about the presence of tropical cyclones in Indonesian waters, including the potential impacts generated by the cyclones. However, the early warning information provided has not been effectively communicated. The community appears to still be unfamiliar with the emergence of tropical cyclones in Indonesia. Typically, only residents in coastal areas are aware of the cyclone threats, prompting fishermen to temporarily cease their activities at sea to avoid high waves and storms.

Learning from countries vulnerable to tropical cyclones, it turns out that disseminating early warning information is crucial on a massive scale and more frequently. The study, "A Great Escape from the Bay of Bengal 'Super Sapphire–Phailin' Tropical Cyclone: A Case of Improved Weather Forecast and Societal Response for Disaster Mitigation," reveals the success of tropical cyclone prediction models and information dissemination in India.

In addition to improving the quality of tropical cyclone prediction models, the dissemination of information about cyclones is carried out more intensively. The information provided includes the levels of potential damage impacts that may occur in various regions. This helps communities in the affected areas to estimate the magnitude of the threat posed by the tropical cyclone. Warnings are also issued every three hours, or even hourly, as the cyclone approaches land. This information is disseminated through various media, including television, social media, and even SMS.

The dissemination of this information is also carried out through multiple platforms such as high-frequency radio and a satellite-based cyclone warning dissemination system (CWDS) to ensure that information is conveyed even if terrestrial networks are damaged. Press conferences by institutions monitoring cyclone movements are held regularly every day during the period of cyclone activity around the Indian mainland.

Furthermore, the Indian government has also increased disaster management capacity down to the district level and built hundreds of special shelters to deal with cyclone disasters. These efforts were successful in evacuating nearly one million people in Odisha and Andhra Pradesh from tropical cyclone Phailin in 2013. The death toll was significantly lower than that of supercyclone Orisha in 1999, when both cyclones had similar hazard levels.

In addition to strengthening disaster mitigation, preparedness for tropical cyclones must also be carried out by minimizing other disaster risk factors, such as maintaining green spaces and reducing deforestation. Moreover, the environmental carrying capacity in the regions of Aceh, North Sumatra, and West Sumatra is already in a critical condition due to deforestation, illegal logging, and massive land conversion.

The phenomenon of declining environmental support has impacted the occurrence of flash floods and landslides in several affected areas. For instance, in March 2024, floods and landslides struck 12 regions in West Sumatra due to heavy rainfall and environmental degradation.

The decline in environmental carrying capacity further increases disaster risk factors in northern Sumatra, which is among the most vulnerable zones for hydrometeorological disasters. According to the 2024 Disaster Risk Index, northern Sumatra, including several areas in Aceh, North Sumatra, and West Sumatra, is among the top 10 most vulnerable to flooding, landslides, and extreme waves.

The combination of vulnerabilities further exacerbates the impacts that can arise from tropical cyclone disasters. This is similar to what is currently happening, where the high rainfall caused by Cyclone Senyar has led to significant flooding and landslides in the three affected areas. In the flow of the floods and landslides, many large pieces of wood were swept away, indicating the extensive deforestation occurring in the region.

In light of the increasingly frequent trends of tropical cyclones causing hydrometeorological disasters in Indonesia, efforts to mitigate the impact of these storms need to be strengthened. This preventive action aligns with the growing threat of cyclones that is becoming more apparent in Indonesia.