The science behind South East Asia’s huge floods - Asia Specific podcast, BBC World Service

Key Concepts

Climate Change and Extreme Weather Events
Flooding and Landslides in Asia Pacific
Sea Level Rise and Coastal Vulnerability
Urbanization and Infrastructure Challenges
Deforestation and its Impact on Water Management
Adaptation Strategies: Hard and Soft Infrastructure
Nature-Based Solutions (Sponge Cities, Mangroves)
Groundwater Extraction and Land Subsidence
Climate Migration and Relocation
Renewable Energy Transition and Policy Impact

Climate Change as a Driver of Recent Floods

Experts, including those from the World Weather Attribution group at Imperial College London, have found evidence linking climate change to the intensification of recent flood events in the Asia Pacific region. While acknowledging that multiple factors contribute, such as urbanization, deforestation, and cyclical weather patterns like La Niña and the Indian Ocean Dipole, the core finding is that climate change has made the rainfall more intense. This aligns with broader projections from the Intergovernmental Panel on Climate Change (IPCC), which indicate that a warmer world leads to more intense tropical cyclones (typhoons, hurricanes) with higher wind speeds and increased rainfall.

Scientific Mechanism of Intensified Rainfall

The intensification of rainfall due to climate change is explained by two primary mechanisms:

Warmer Oceans: A warmer planet traps more heat, a significant portion of which is absorbed by the oceans. This increased ocean heat energy fuels the formation and intensity of tropical cyclones, providing them with more power to form and sustain themselves.
Increased Water Vapor: A warmer atmosphere can hold more water vapor. This increased evaporation from land and oceans leads to a higher concentration of water vapor in the atmosphere, which in turn has a greater potential to fall back as intense rainfall.

Asia Pacific's Unique Vulnerability to Flooding

The Asia Pacific region faces amplified risks from extreme weather events due to its geographical and developmental characteristics:

Coastal and Riverine Urbanization

Many major cities in the Asia Pacific, including Singapore, Manila, Jakarta, and Bangkok, are situated on coastlines or along rivers. This strategic placement is historically linked to their roles as manufacturing hubs, facilitating the export of goods. However, this proximity to water makes them highly susceptible to flooding, especially when combined with extreme weather.

IPCC Findings on Exposure

The IPCC's reports highlight Asia as the most exposed region globally to sea level rise. This is attributed to:

High Population Density in Low-Lying Areas: A significant number of people live in low-lying coastal zones.
Exposure to Storm Surges: These populations are vulnerable to storm surges, where rising sea levels and strong winds push high tides inland.

Land Subsidence: A Double Threat

Compounding the issue of rising sea levels is land subsidence, or the sinking of land, particularly in Southeast Asian cities. This phenomenon exacerbates flooding risks. Contributing factors to subsidence include:

Groundwater Extraction: Rapid economic development has led to extensive groundwater extraction for industrial and domestic use, especially in cities like Bangkok and Jakarta. Sinking wells to access water creates voids, causing the land above to sink.
Weight of Urban Development: The construction of heavy skyscrapers, a common feature in land-scarce Asian cities, further compresses the ground, accelerating subsidence.

Faster Sea Level Rise in Asia

Contrary to a potential misconception, sea levels are rising slightly faster in Asia than the global average. Data from 1993-2018 shows an average rise of 3.5-3.6 mm per year in Asia, compared to the global average of 3.2 mm per year. While this difference may seem small, it accumulates significantly over decades, creating a "double whammy" effect when combined with land subsidence.

Uneven Sea Level Rise Factors

The unevenness of sea level rise globally is influenced by various factors beyond land subsidence:

Wind and Evaporation: These atmospheric conditions affect water distribution.
Temperature: Regional ocean warming patterns vary.
Gravity: Gravitational forces differ across the globe, influencing ocean currents and levels.
Thermal Expansion: The majority of sea level rise is due to the thermal expansion of warming ocean water, and certain pockets in Asia experience higher levels of ocean warming.

The combination of these factors—people living on the coast, sinking land, and rising sea levels—points to a significant future problem, potentially leading to billions of dollars in damage and large-scale migration.

Impact of Deforestation and Illegal Logging

Deforestation and illegal logging significantly worsen the impact of floods and landslides by disrupting natural water management processes:

Disruption of Water Absorption

Natural State: Mountainsides covered in trees and plants allow soil to absorb rainwater, slowing its runoff and allowing it to enter rivers gradually.
Deforested State: When trees are removed, the soil loses its absorbent capacity. Rainwater runs off rapidly, overwhelming rivers and leading to bank breaches and downstream flooding.
Concrete Surfaces: Urbanization, with its extensive concrete surfaces, further reduces water absorption, accelerating floodwaters.

This lack of natural absorption amplifies the damage caused by intense rainfall from typhoons and cyclones.

Mitigation and Adaptation Strategies

Governments and communities in Southeast Asia are exploring various strategies to mitigate future natural disasters:

Hard Infrastructure Solutions

These involve large-scale engineering projects designed to manage water:

Water Pumps: High-capacity pumps to remove water from urban areas quickly.
Giant Canals: Extensive canal systems to channel water away from cities.

Soft Infrastructure / Nature-Based Solutions

These solutions leverage natural processes to manage water:

Sponge Cities: A concept pioneered in China and adopted in cities like Bangkok. This involves creating urban spaces with ponds, wetlands, and large grass-planted areas with underground water tanks. These areas absorb and retain rainwater, releasing it slowly.
Nature Reservations: Protecting and restoring natural landscapes upstream of cities to enhance water absorption.
Mangrove Forests: These coastal ecosystems absorb rainwater and provide crucial protection against storm surges, which are expected to increase in intensity with a warmer climate.

Challenges in Implementation

Cost: Many of these adaptation measures, such as Singapore's Long Island project (estimated at $100 billion USD), are prohibitively expensive for many countries.
Enforcement of Regulations: While regulations against groundwater extraction exist, their enforcement is often lacking, allowing the problem to persist. Governments need resources to monitor and enforce these regulations effectively.

The Role of the Private Sector and Investment

The private sector is increasingly involved in climate adaptation, particularly in economically significant cities:

Advertising Water Resilience: In cities like Bangkok, developers of high-rise buildings advertise features like powerful water pumps and waterproof underground car parks, acknowledging the inevitability of flooding and offering private solutions.
Investment-Driven Projects: Proposals for large-scale projects, such as a string of islands in the Gulf of Thailand to mitigate storm surges, are often designed to attract private investment through tourism and airport development, rather than relying on government or climate funds.
Economic Engines: Major cities like Jakarta, Manila, and Shanghai are considered economic engines, making them attractive for private sector investment in adaptation measures due to their high value and potential returns.

The Reality of Climate Migration and Retreat

In some cases, adaptation may not be sufficient, necessitating relocation:

Pacific Islands: Low-lying island nations like Tuvalu face existential threats from sea level rise and saltwater intrusion, leading to agreements for citizens to relocate to countries like Australia and New Zealand.
Jakarta's Relocation: Recognizing the unsustainable future of the city due to sinking and rising sea levels, Jakarta is undertaking a significant relocation project to a new city in Kalimantan.
Uninhabitable Environments: Extreme weather and environmental degradation can render areas uninhabitable due to saltwater intrusion and lack of fresh water.

While relocation is a difficult reality, it highlights the limits of adaptation when faced with severe climate impacts.

Progress and Hope in Climate Action

Despite the challenges, there are signs of progress in climate action, particularly at local and regional levels:

Progress in Climate Targets

Reduced Warming Projections: While still not meeting international targets, current projections for end-of-century warming have decreased from earlier estimates of 3-5 degrees Celsius to 2.3-2.5 degrees Celsius, indicating some success in reducing the rate of warming.

Local and Regional Advancements

Air Quality in China: Significant improvements in air quality in major Chinese cities like Beijing and Shanghai.
Public Transport: Advancements in public transportation systems in cities like Singapore and Japan.
Electric Vehicles: Increased adoption of electric vehicles in countries like Vietnam and Thailand.
Renewable Energy: China's leadership in renewable energy deployment, including solar and wind power, has driven down global prices for these technologies, making them more accessible to other countries in the Asia Pacific region. While China continues to build coal plants, its rapid investment in renewables and nuclear power signifies a move in the right direction.

These developments, though sometimes slow, demonstrate tangible progress and offer a degree of optimism in addressing the climate crisis.