Weatherwatch: rainclouds are travelling farther in warmer world

Have you ever wondered how far a raindrop has travelled before it lands on you? It may have journeyed thousands of kilometres from the ocean, sea or lake it evaporated from – and now research shows raindrops are travelling even farther than they used to.

Warmer air can hold more water vapour, and that is changing not only how much rain we receive but also where it falls. Travis Aerenson, of the University of Wyoming, and his colleagues modelled atmospheric moisture movements in the US over more than three decades. Their research showed that in the southwestern and southern plains, moisture in the atmosphere travels 30 to 50 miles (50 to 80km) farther than it did 35 years ago, staying aloft for an extra two to four hours before falling as rain.

Their findings, published in Geophysical Research Letters, also show that more evaporation is occurring from ocean surfaces and less from land surfaces. The change in atmospheric moisture pathways affects where and when precipitation occurs, with implications for land use. The researchers also note that the trend for moisture to travel farther will result in the water security of more countries and states falling increasingly outside their borders, requiring greater collaboration between neighbours.