Extreme weather

A storm rips off roofs, a cloudburst floods streets, a heatwave makes rivers shrink. Weather extremes like these have always existed, they are part of Earth's weather. Still, it is worth understanding them properly: how they form, why a warmer climate makes some of them more frequent and how to prepare for them well.

How weather extremes form

Behind most extremes is energy in the form of heat and moisture. Storms form when large pressure differences in the atmosphere set air masses moving forcefully. Heavy rain falls when moist, warm air rises quickly, cools down and releases its water all at once, often from towering thunderclouds. Heatwaves build up when a stable high pressure system holds dry, hot air in place for days. And a drought develops when, over weeks or months, far less rain falls than soils, plants and rivers need.

What a warmer climate changes

A warmer climate changes the ingredients for extremes. Warmer air can hold more water vapour, about 7 % more per degree of warming. When it rains, more water often comes down at once. Heatwaves become more frequent and hotter in a warmer climate, and where more water evaporates, soils dry out faster. The difference between weather and climate matters here: a single thunderstorm or one hot day proves nothing on its own, that is weather. Only when measurements over many decades show that certain extremes are becoming more frequent or stronger do we call it a climate trend.

Early warning and preparation

We are not powerless against weather extremes. Weather services watch the atmosphere around the clock and often warn hours to days in advance, via radio, apps and sirens. During a thunderstorm you can even judge the distance yourself: count the seconds between the flash and the thunder, because sound needs about three seconds for one kilometre. Preparation helps on top of that: cities plant trees and create areas where rainwater can soak away, houses are built to withstand storms and heat, and ideally families know where the safest place is when a warning comes. Anyone who takes a warning seriously, puts the bike and the garden furniture away and stays indoors usually gets through without harm.