Different Hazards, Different Tools
Natural disasters are not one problem. A flood, an earthquake, a hurricane and a heat wave behave differently, arrive with different amounts of warning, and harm buildings and people in different ways. A city that prepares well usually matches its tools to the hazards it actually faces, which vary a great deal by location. Some cities face several at once.
This article walks through four common hazards and the four broad levers cities use for all of them: where building is allowed, how buildings are built, how people are warned, and how recovery is organized.
Floods
Floods are among the most common and costly hazards worldwide. They come from rivers overflowing, heavy rain overwhelming drains, or sea water pushed inland by storms.
- Land use. Keeping the most flood-prone land open, or limiting what can be built there, reduces exposure. Flood maps are the usual starting point, though they reflect past conditions and may understate future ones.
- Building standards. In flood-prone areas, codes may require raising the lowest floor, using water-resistant materials at lower levels, and keeping utilities above expected water levels.
- Drainage and storage. Pipes, channels, ponds and parks that can hold water temporarily all help, and green infrastructure can ease pressure on older drains in moderate storms. Some cities use designs that let certain areas flood on purpose so that others do not.
- Warning. River gauges and weather forecasts can give hours or days of notice for some floods, but flash floods can allow very little.
Earthquakes
Earthquakes cannot currently be predicted in the short term, so preparation focuses on buildings and readiness.
- Building standards. Modern seismic codes aim to keep structures from collapsing, which protects lives even if repairs are needed. Older buildings, especially unreinforced masonry and certain older concrete structures, are often the greatest concern.
- Retrofits. Strengthening older buildings is expensive, so cities often phase requirements, starting with schools, hospitals and the most vulnerable structure types.
- Land use. Soft or water-saturated ground can shake harder, and some soils can lose strength during shaking. Slopes may slide. Siting and soil investigation matter.
- Lifelines. Water mains, gas lines, electric grids and roads all need to be considered, along with emergency access for fire crews, since fires and outages after a quake can cause as much trouble as the shaking.
Some regions also have early warning systems that can give seconds of notice, which is enough to stop trains or open fire station doors but not to move people far.
Storms
Storms include hurricanes, typhoons, cyclones, severe thunderstorms and tornadoes, with wind, rain, hail and, on coasts, storm surge.
- Building standards. Wind-resistant roofs, connections that hold a structure together, and protection for windows and doors reduce damage. Storm surge calls for elevation or siting away from the shore.
- Evacuation. Coastal cities often depend on evacuation, which requires clear routes, transport for people without cars, and shelters. Evacuation can be a challenge for people with disabilities, older adults and those with low incomes.
- Trees and power lines. Falling trees and downed lines cause many outages, so vegetation management and, in some places, burying lines or hardening them are options. These can be costly.
- Warning. Storm tracking generally provides days of notice, though intensity and exact path remain uncertain.
Extreme Heat
Heat is less visible than a flood but can be deadly, particularly for older adults, people with health conditions, outdoor workers and people without cooling at home.
- Cooling places. Public buildings and shaded outdoor spaces that stay open during heat waves.
- Building design. Shading, reflective roofs and ventilation can reduce indoor temperatures.
- Warning and outreach. Heat alerts work better when paired with contact programs for isolated residents.
- Urban form. Dense pavement and buildings hold heat, so trees and green space can help, within limits discussed in other guides on urban heat islands.
The Four Levers Together
Land use reduces how much is exposed. Its effect is long-lasting but slow, since it mostly shapes new development.
Building standards reduce how vulnerable structures are. Codes mostly affect new construction, so the older building stock lags behind.
Warning and response reduce harm to people but cannot protect property much. They only work if people receive, understand and can act on the message.
Recovery arrangements determine how quickly a community returns to normal. Planning for temporary housing, debris removal and funding in advance makes later decisions faster and fairer. Disaster recovery planning is a topic of its own.
Limits and Trade-Offs
No combination of measures eliminates risk. Money is limited, and every dollar spent on one hazard is unavailable for another. Measures that protect against one hazard can worsen another: for example, a sealed, heavily insulated building can be good for storms and cold but poor in a heat wave without cooling, and raising a building for flood protection can affect accessibility.
Benefits and burdens are also uneven. Questions of environmental justice arise because households with fewer resources may live in older buildings or hazard-prone areas, and have less ability to evacuate or recover. A strategy that looks good on average can leave some residents behind, so planners often check who is covered and who is not.
Finally, climate change is altering the frequency and severity of some hazards, such as floods and heat, in many regions. Plans based only on historical records may need revisiting regularly.
Where to Begin
For a city with limited resources, a sensible starting point is a candid list of the hazards that have actually affected the area and could again, an inventory of what is exposed, and a few steps that reduce harm at reasonable cost: open the worst hazard land to fewer new buildings, shore up critical facilities, make sure warnings reach everyone, and write down who will do what after an event. Starting small and updating regularly is usually more realistic than aiming for a perfect plan.