What observations already show
The IPCC Sixth Assessment Report, Working Group I (2021), assessed that the frequency and intensity of heavy precipitation events have increased since the 1950s over most land areas with sufficient data (high confidence), and that human-induced climate change is likely the main driver.
This is not simply “more rain”. Even where annual totals change little, the shape of rainfall is shifting toward more intense bursts concentrated in short periods.
Why warming makes rain heavier
Water vapour in the air
As temperature rises, the atmosphere can hold more water vapour (the Clausius–Clapeyron relationship), so there is more material for rain.
About 7% per 1 °C
AR6 projects that extreme daily precipitation events will intensify by about 7% for each 1 °C of global warming.
Rare events, more often
Extreme rainfall that used to be rare is projected to become more frequent and more intense at higher levels of warming.
What it means for cities
Urban drainage was built to design standards set from past rainfall records. When the “past rain” those standards were based on no longer represents future rain, the same infrastructure hits its limits more often.
Local downpours that fall on a small area in a short time can vary sharply between stations. As the risk grows, the eyes that catch it early need to become denser too.
What cities can prepare
- Revisit design standards and risk maps regularly with recent rainfall data
- Observe rainfall directly near places where water collects, such as underpasses, semi-basement homes and low-lying roads
- Build early warning that turns observations straight into staff decisions and resident evacuation
Sources
- Climate Change 2021: The Physical Science Basis — Summary for Policymakers — IPCC Working Group I (AR6), 2021
- State of the Global Climate (연례 보고서) — WMO
