How does climate change affect flooding?

Like other extreme weather disasters, floods involve a number of competing factors that can affect their frequency and intensity.

Floods can occur all year round, in all regions of the world. But discerning the relationship between any given flood and climate change is no easy feat, experts say, made difficult by limited historical records, especially for the most extreme floods, which occur rarely.

It can be tempting to attribute all floods and other extreme events to the forces of global warming. But weather is not climate, although weather can be affected by climate. For example, scientists are convinced that climate change is making exceptionally hot days more common. They are not as sure as climate change makes tornadoes more severe.

Floods fall somewhere on the confidence spectrum between heat waves ("yes , clearly") and tornadoes ("we don't know yet"), said Daniel Swain, a climatologist at the University of California, Los Angeles. "I would say, 'yes, probably, but…'"

Floods, like other disasters, involve a number of competing factors that can affect their frequency and their intensity in opposite ways. Climate change, which worsens extreme rainfall in many storms, is an increasingly important part of the mix.

What causes flooding

ImageNortheast Entrance Road in Yellowstone National Park after historic flooding. Credit...Samuel Wilson-Pool/Getty Images

Several main ingredients contribute to the development of floods: precipitation, snowmelt, topography and soil moisture. floor. Depending on the type of flood, some factors may matter more than others.

For example, a fluvial flood, also called a fluvial flood, occurs when a river, stream or lake overflows with water, often as a result of heavy rain or rapid snowmelt. Coastal flooding occurs when areas of land near the coast are flooded with water, often as a result of a severe storm colliding with high tides.

Flooding can also occur in areas without water bodies. Flash floods, in particular, can develop wherever intense rainfall occurs over a short period.

How floods are measured

Many measurements are used to measure floods, including stage height (the height of water in a river relative to a specific point) and discharge (the amount of water that passes through a specific location over a given time period).

To describe the severity of a flood, however, experts will often use the simpler term "a 100-year flood", to describe a flood that has a 1% chance of occurring. occur in a given year, considered an extreme and rare event. The term is only a description of the probability, however, not a promise. A region can experience two hundred-year floods in a few years.

Have floods increased in recent decades?

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