How do you reduce disaster risk in river deltas?

by Zita Sebesvari and Michael Hagenlocher | United Nations University, Institute for Environment and Human Security
Wednesday, 20 June 2018 13:10 GMT

Michael Roberts, who came from northeast Louisiana, looks for residents to rescue in flood waters from Tropical Storm Harvey in Orange, Texas, U.S., August 30, 2017. REUTERS/Jonathan Bachman

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Delta communities are often poorly prepared for floods, leaving the most vulnerable at risk.

Costal river deltas are important hotspots of global change and, being highly populated, are ecologically and economically important hubs. Understanding the challenges faced by these unique landscapes and its inhabitants will help us to address the sustainability changes of today and tomorrow.

Today, almost 360 million people live on river deltas. The dynamic mix of land, fresh water, brackish and salt water create a unique, biologically diverse ecosystem with plenty of natural resources, allowing for intensive agricultural production.

At the same time the many waterways of deltas provide opportunities for transportation, serving as a gate towards inland locations. It is this fertility and connectivity, which made river deltas an attractive place to settle thousands of years back.

While entire economies depend on these fertile landscapes, delta communities face a high risk of environmental hazards and climate change impacts.

The dynamic nature of coastal deltas means that river flooding and erosion commonly occur alongside coastal hazards, such as tidal flooding, storm surges, cyclones, and sea water intrusion into freshwater agricultural areas – all of which are expected to intensify with climate change.

At the same time, human action, or inaction, are important drivers of risk for fragile ecosystems and people’s livelihoods in coastal river deltas.

Flooding and its adverse effects, for example, are not only influenced by changing patterns in rainfall and sea level, but also by deforestation, upstream hydropower operations (e.g. the installation of new dams for energy production), rapid urbanization and surface sealing.

While the above actions are leading to changes in river flows and flood patterns, the ability of deltaic communities to prepare for, cope with, and adapt to flooding is often limited or unequally distributed, leaving the most vulnerable most at risk.

As much as risk in deltas is driven by the complex interplay of human and natural processes, the solutions for risk reduction and adaptation are also manifold, including solutions to protect ecosystems and populations; or to enable better response to hazards if they cannot be avoided.

Examples include, but are not limited to, protecting land from inundation by dykes, flood walls and embankments, protecting shorelines from erosion by using ecosystem-based solutions, such as mangroves which reduce the force of waves and storm surges, advancing shorelines through beach regeneration or sand dune protection to protect coastal structures and communities, or living with flood waters by elevating houses and critical infrastructure such as roads.

This means that in most cases a combination of different solutions is needed to reduce disaster risk and support adaptation, calling for comprehensive approaches to identify exposure and vulnerability, as well as for solutions that consider both communities and ecosystems.

However, to date, vulnerability and risk in deltas is mostly characterised with respect to single hazards, either at the delta scale or based on individual case studies at the local level. To overcome these gaps and support the planning of targeted risk reduction and adaptation strategies, including ecosystem-based solutions, we have developed an innovative assessment concept and methodology, the Global Delta Risk Index (GDRI). The GDRI was developed in a consultative, participatory process, and piloted in the Mekong, Ganges-Brahmaputra-Meghna, and Amazon deltas.

Since the future of coastal river deltas and their resilience will greatly enhance or undermine progress towards achieving the Sustainable Development Goals (SDGs), methodologies to characterise and analyze risks in deltas, such as the GDRI, offer an enormous potential to help make deltas a safe and prosperous place for all.