Why are cities vulnerable to climate change?

With more than half of the global population living in urban areas, and up to 79% of all people in developed economies living in cities, the rate and scale of growth of cities and their populations present unique development challenges. Cities are complex systems which host a heavy concentration of people, services and infrastructure, and they often face challenges relating to transportation, adequate and reliable access to resources such as water and energy, and conflicts over space.

Climate variability and change bring critical additional risks to these already challenging urban settings. Many cities are situated in high-risk locations, such as along coastlines and on floodplains. As cities expand outwards into surrounding areas and experience influxes of populations from rural regions and climate refugees, their exposure to climate and disaster risk is increasing further.

City populations – both businesses and households – can face often devastating direct and indirect climate impacts. Climate change is increasing disease risk in many cities globally, particularly from vector-borne and water-borne diseases such as malaria and dengue fever. Severe climatic events, such as heatwaves, flooding, wildfires, storms and coastal inundation, meanwhile, can lead to major disruption to businesses, transport and food networks, and health and education facilities. Drought during the 2015–16 El Niño, for example, led to the ‘Day Zero’ countdown in South Africa and caused widespread disruption for businesses across the region. Unstable water and hydro-electric power supplies left urban businesses unable to maintain activities, provide services or fulfil their commercial obligations.

In addition, climate hazards can interact with and compound risks from other urban challenges, such as poverty, poor housing quality and service backlogs. For example, a heatwave may compound existing pressures on health systems, as occurred in many places during the COVID-19 pandemic.

Coastal cities, and cities that are home to the poorest people, are often disproportionately at risk from climate change. Many climate risks will affect the most vulnerable within these urban populations the most severely – such as those living in densely populated, informal settlements, who are unlikely to have the resources to adapt without assistance.

What are cities doing to adapt to the effects of climate change?

Most climate change adaptation decisions are made by ‘private actors’, including households, businesses and individuals, who try to manage their exposure to risks and to maximise opportunities when they arise. But they cannot adapt effectively to climate change alone: they require supportive enabling conditions and policies that equip them with the necessary incentives, resources, knowledge and skills.

Many cities have developed or are designing planned adaptation strategies to help people and businesses to adapt to climate change. For example, in Mexico City, where a complexity of pressures threatens the supply and management of its water resources, a newly designed Local Climate Action Strategy (ELAC) 2020-2040 and the Climate Action Programme of Mexico City (PACCM) 2020–2026 are aimed, in part, at strengthening the adaptive capacity and resilience of ecosystems, infrastructure, production systems, people and their wellbeing against the negative impacts of climate change. To help improve the quantity and quality of the water supply, the city has a goal of installing 10,000 household rainwater harvesting systems annually, for example. This is in direct response to opinion poll results showing that while 80% of the city’s population were willing to install such systems in their homes, only one in three claimed to have the resources to do so.

Cities have also sought to adapt public infrastructure and investments to present and future climate risks. For example, in Melbourne, Australia, a major risk-focused adaptation strategy published in 2009 saw 100 climate change adaptation actions implemented. These include increased stormwater harvesting to irrigate parks and street trees and investment in green space, canopy cover and enhancing biodiversity, to increase nature’s ability to absorb emissions, reduce the impacts of heatwaves and reduce the risk of flash flooding. The city’s Climate Change Adaptation Strategy Refresh 2017 includes further measures, such as increasing permeable surfaces to reduce the impact of flooding.

Various cities have also been implementing smaller public adaptation projects, with wide-ranging impacts. In Dar es Salaam, Tanzania, a concrete seawall not only prevents beach erosion from waves and allows the beach to recover from storms, but has also helped develop the area into a recreational zone, encouraging residents outdoors. This has enabled small businesses to flourish, and newly-planted trees add to the green environment. The encouragement of green spaces and infrastructure has also been evident in projects such as vehicle parking management in Jaipur, India, utilisation of unused and vacant spaces for green space and tree planting in Bangkok, Thailand, and micro-gardening in Dakar, Senegal.

In general, a city climate change adaptation strategy can be a standalone (but linked) plan, or a component of a climate action plan and/or a comprehensive city plan. Linkages between other city-focused policies are helpful as cities need to integrate climate risk into sectoral and urban planning. Since adaptation can produce trade-offs, cities that do not consider their climate risks in a wider, integrated planning process can increase their vulnerability to climate change by transferring risks from one sector or activity onto another. Of course, there is no universal approach that will work in all cities as local conditions shape the different risks they face, as well as the feasibility and desirability of different adaptation interventions.

A list of short case studies on various successful actions taken in cities towards effectively reducing climate risks and creating healthier and more sustainable cities for residents can be found here. A list of journal articles on adapting cities to climate change can be found here.

International action

There are international dialogues and commitments focusing on how cities respond to climate change, too. For example, the United Nations New Urban Agenda (October 2016) focuses on housing and sustainable urban development, and commits its signatories to building resilient and responsive cities that foster climate change mitigation and adaptation. Additionally, Sustainable Development Goal 11, ‘Make cities and human settlements inclusive, safe, resilient and sustainable’, includes Target 11.5: ‘By 2030, significantly reduce the number of deaths and the number of people affected and substantially decrease the direct economic losses relative to global gross domestic product caused by disasters, including water-related disasters, with a focus on protecting the poor and people in vulnerable situations.’ These agendas offer advice and guidelines to cities in their climate-related strategies.

The cost of adapting – and of not adapting – to climate change in cities

Many climate adaptation plans have not yet been implemented, and much more adaptation is needed in cities. This will require targeted financing. A 2021 joint report by the World Bank Group and the Global Facility for Disaster Reduction and Recovery indicates that the global cost of climate adaptation could reach US$300 billion per year by 2030, while the State of Cities Climate Finance report (2021) estimates an annual investment on adaptation of US$11–20 billion by 2050 to protect urban infrastructure from climate risks.

There are currently large gaps between current public adaptation finance flows and the funds required for adaptation, especially in developing countries. Early action and investment makes economic sense as well as supporting social justice goals. Adapting now will cost much less than if adaptation is delayed, as cities will have to face the higher economic and social costs of disaster relief and recovery.

While the emphasis of climate finance has traditionally been on activities to mitigate climate change (to cut emissions), largely due to the ease of measuring success and possible political perceptions, there is a strong economic case for investing in climate adaptation: benefit-cost ratios range from 2:1 to 10:1.

Moreover, many adaptation investments serve multiple purposes and can deliver wide-ranging health, social, environmental and economic ‘co-benefits’ for urban populations – for example, reducing traffic congestion and local air pollution – as well as minimising risks to lives and livelihoods from climate risk. These are often called ‘no or low regrets’ adaptation options.

As outlined in the examples offered above, there is potential for nature-based flood risk solutions, such as strengthened river embankments and urban wetland restoration, to generate a wide range of additional benefits for city residents including generating new parks, pedestrian walkways, cycle lanes and green spaces. As well as reducing flood and drought risk, these can provide shade and cool spaces to protect buildings and citizens from extreme heat, absorb greenhouse gas emissions, improve air quality, enhance citizen wellbeing, and make cities more desirable to tourists.

Adaptation action to reduce the risk of climate-related disasters occurring can also improve political security and contribute to a stable environment for more equitable social and economic development. Additionally, with the growing interest in environmental, social and governance (ESG) factors, city-driven adaptation action can encourage localised private sector investment and likely improve a city’s credit rating in the process.

This Explainer was written by Denyse Dookie and Kate Gannon.

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