Landmark new research shows how global warming is messing with our rainfall

By Steven Sherwood, Anna Ukkola, UNSW Sydney

The past century of human-induced warming has increased rainfall variability over 75% of the Earth’s land area – particularly over Australia, Europe and eastern North America, new research shows.

The findings, by Chinese researchers and the UK Met Office, were published overnight in the journal Science. They provide the first systematic observational evidence that climate change is making global rainfall patterns more volatile.

Climate models had predicted this variability would worsen under climate change. But these new findings show rainfall variability has already worsened over the past 100 years – especially in Australia.

Past studies of the observational record either focused on long-term average rain, which is not systematically changing globally, or rainfall extremes where changes are hard to measure accurately. This study looks solely at variability, which refers to uneven timing and amount of rainfall.

The results are consistent with previous research, including ours. This means dry periods are drier than in the past, and rainy periods are wetter.

Alarmingly, the problem will worsen as global warming continues. This raises the risk of droughts and floods – a pertinent issue for Australia.

What the study found

The research shows a systematic increase in rainfall variability since the 1900s. Day-to-day rainfall variability increased by 1.2% per decade, globally. The trend was more pronounced in the latter half of the century, after 1950.

The increase in variability means rain is more unevenly distributed over time. It might mean a year’s worth of rain at a given location now falls in fewer days. It can also mean long, dry periods are interspersed by torrential downpours, or drought and flooding in quick succession.

The researchers examined observational data and found since the 1900s, rainfall variability has increased over 75% of the land areas studied. Europe, Australia and eastern North America were particularly affected. These are areas for which detailed and long-running observations are available.

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