Southeast Asia and Unusual Flood Seasons: When Natural Disasters Become a Matter of Regional Diplomacy

In late 2025, several Southeast Asian countries were hit successively by exceptionally severe rainfall and flooding. From 26 to 30 October, many locations in central Viet Nam recorded extremely heavy rainfall; some exceeded 1,000 mm, with Khe Tre receiving 1,647 mm [1]. At Cau Lau Station, the Thu Bon River peaked at 5.62 metres, 0.14 metres higher than the historic flood peak recorded in 1964 [2]. In early November, Typhoon Kalmaegi brought heavy rainfall, flash floods and landslides to the Philippines, with Cebu among the areas most severely affected [3]. A few weeks later, Hat Yai in southern Thailand experienced widespread heavy rainfall and flooding, with daily rainfall reported at approximately 335 mm [4]. In late November, Tropical Storm Senyar made landfall in Indonesia and Malaysia, further intensifying heavy rainfall, flooding and landslides in Sumatra and the Strait of Malacca region [5].

In this context, flooding poses a challenge not only to the adaptive capacity of individual countries but also to Southeast Asia’s capacity for cooperation and diplomacy. ASEAN has developed a range of mechanisms for disaster management, among which the ASEAN Agreement on Disaster Management and Emergency Response (AADMER), the ASEAN Coordinating Centre for Humanitarian Assistance on disaster management (AHA Centre), and the “One ASEAN, One Response” initiative constitute important foundations for regional cooperation [6], [7].

The unusual flood seasons of recent years can therefore be viewed not only as manifestations of climate risk, but also as a test of regional diplomacy and Southeast Asia’s capacity to build collective resilience.

A flood occurring within the territory of a country remains, first and foremost, the responsibility of that country. ASEAN also emphasises the principles of respect for sovereignty, territorial integrity and the authority of the affected country to direct disaster assistance operations. Yet this division of sovereign responsibility is precisely what makes interstate coordination an important component of regional disaster governance. This is where regional diplomacy can play a significant role. In the context of disasters, diplomacy does not necessarily take the form of high-level political negotiations. It can operate through highly practical mechanisms: agreeing on procedures for data sharing, establishing communication focal points, mobilising relief resources, coordinating specialist personnel, sharing technology, and developing common standards for warning and response.

    - Legal foundations:

AADMER represents a key legal foundation for ASEAN cooperation in this field. Signed in 2005 and entering into force in 2009, the agreement provides a framework for ASEAN cooperation on disaster management and emergency response. In October 2025, ASEAN launched the AADMER Work Programme 2026–2030, organised around five priority areas: risk assessment, monitoring and early warning; prevention and mitigation; preparedness and response; resilient recovery; and global leadership. Notably, the new Work Programme does not focus solely on response after disasters occur, but places greater emphasis on forecasting, anticipatory action and long-term resilience. ASEAN cooperation on disaster management is gradually shifting from a disaster-response approach towards pre-disaster risk governance [14].

    - Regional cooperation:

One of the clearest expressions of regional cooperation is the One ASEAN One Response mechanism. This initiative was developed to enable ASEAN to respond more rapidly, mobilise greater resources and strengthen coordination when disasters occur. The AHA Centre serves as a key regional coordinating body within this mechanism. From this perspective, disasters can also become an area for confidence-building among countries. Regular cooperation through training, exercises, information sharing and humanitarian assistance helps establish communication networks and practical experience that may also prove useful in addressing larger crises. In 2026, ASEAN continued to emphasise the One ASEAN One Response approach within its vision towards ASEAN 2045, including anticipatory action, innovation, sustainable financing and whole-of-society cooperation [15].

    - Disaster diplomacy and the emergence of a common response space:

Flooding also reveals a broader issue: Southeast Asia’s resilience depends in part on countries’ ability to coordinate in the face of a changing climate. In recent years, ASEAN has strengthened cooperation on climate change adaptation and mitigation, including information sharing, research, capacity-building and policy coordination. ASEAN is also developing the ASEAN Climate Change Strategic Action Plan 2025–2030, adopting an interdisciplinary approach and involving policy institutions, researchers and regional partners [16]. ASEAN climate diplomacy is not confined to intra-regional cooperation. At international forums such as the United Nations Framework Convention on Climate Change (UNFCCC), ASEAN countries have shared interests in coordinating their positions on adaptation, climate finance, technology transfer and support for developing countries. In 2025, ASEAN adopted a Joint Statement on Climate Change towards COP30 while continuing to promote regional cooperation within the global climate negotiation process [17], [18].

    - Disasters and ASEAN’s network of partners:

Southeast Asia’s disaster diplomacy is not limited to relations among ASEAN Member States. Disasters generate demand for cooperation with external partners in areas such as finance, technology, data, training and humanitarian assistance. In disaster management, ASEAN currently maintains cooperation programmes with China, Japan and the Republic of Korea. At meetings held in 2026, ASEAN continued discussions on disaster management cooperation plans with all three partners for the 2026–2030 period. Japan provides a notable example, having supported ASEAN in developing the AADMER Work Programme 2026–2030 through the Japan-ASEAN Integration Fund. Such activities demonstrate how development cooperation and disaster diplomacy can complement each other in reducing environmental impacts and losses [19]. In addition, in July 2026, ASEAN and China continued to advance cooperation on green finance, energy transition and people-centred approaches within the framework of ASEAN–China environmental and climate cooperation for 2026–2030, with the aim of mitigating climate impacts and advancing towards a greener future [20]. Flooding therefore raises not only the question of how ASEAN countries can assist one another, but also a broader question: how can ASEAN use its network of external partnerships to strengthen regional resilience?

The preceding discussion suggests that the relationship between the environment and diplomacy in Southeast Asia is becoming increasingly two-directional. Environmental challenges create greater demand for cooperation among states, while diplomacy, in turn, provides the institutions, resources and networks required to address such challenges at a broader scale.

The effectiveness of environmental diplomacy in the future will therefore be measured not only by the number of cooperation mechanisms established, but also by whether those mechanisms can generate substantive coordination among countries, connect available resources and contribute to the protection of people, ecosystems and the region’s capacity for sustainable development.

Unusual flood seasons demonstrate how environmental cooperation in Southeast Asia can help narrow the gap between political borders and environmental space. Climate systems, river basins, maritime areas and ecosystems do not operate according to national boundaries. In this context, diplomacy does more than generate political consensus; it also enables environmental knowledge and information to be shared across borders.

Cooperation additionally creates the capacity to mobilise and allocate resources at the regional level. Mechanisms such as AADMER, the AHA Centre and One ASEAN One Response allow different resources to be connected within a common framework. When this cooperation is extended to partners such as Japan, China and the Republic of Korea, the network can provide additional technological, financial and capacity-building resources. Diplomacy therefore functions as a mechanism for connecting environmental resources among countries and between ASEAN and its external partners.

Cooperation is also contributing to a shift in emphasis from disaster response towards prevention and long-term adaptation. ASEAN’s focus on risk assessment, early warning, anticipatory action and resilience-building under the AADMER Work Programme 2026–2030 demonstrates the expanding role of regional cooperation. Cooperation between ASEAN and China on climate change, green finance, energy transition and ecosystem restoration further illustrates how environmental diplomacy can address long-term risks rather than simply managing the consequences of individual disasters.

Environmental cooperation also serves as a means of building trust and sustaining regional dialogue. Environmental issues often require continuous coordination among government agencies, specialised institutions, scientists and communities. Activities such as joint exercises, expert exchanges, data sharing, coordinated humanitarian assistance and joint research programmes create regular channels of communication among countries.

Issues such as climate change, climate finance and technology transfer exceed the capacity of any single country, or even of a single region, to resolve independently. When such issues are brought to international forums, ASEAN can translate Southeast Asia’s shared needs and challenges into an agenda at the global level. Regional cooperation therefore not only helps ASEAN respond more effectively to current developments, but also creates opportunities for the region to participate in shaping the rules and resources governing future environmental governance.