OUR WET WORLD

Rainfall—or a lack of it—defines so much about life on this earth. From arid deserts to tropical rainforests, from swampy marshlands to raging rivers, from parched meadows to luscious crops, water is central to the diverse environments of our world.

People have observed rainfall for many thousands of years, learning what to expect and how to take advantage of the different seasons. In time this observation became more sophisticated, with various forms of rain gauges enabling a scientific study of precipitation.  One paper estimates there are now 100,000 “official” rain gauges installed across the world (Kidd et al., 2017); of course this does not include many personal or informal gauges.

Yet, despite their potential accuracy, rain gauges can only tell us about a single location.  Rain radar systems improve the situation significantly, providing a spatial view of the surrounding area. But the addition of satellite-based measurements in more recent years allows us to ‘plug the gaps’ in our understanding, offering data where rain gauge or rain radar measurements are not available. Satellites offer us a truly global perspective on rainfall around our world.

This paper is a visual tour of precipitation patterns across continents and oceans, from several perspectives.

We’ll see the tropical rain belt, a manifestation of the inter-tropical convergence zone (ITCZ) near the equator where warm, moist air from northeast and the southeast trade winds converge. Air is forced upwards, generating heavy precipitation in the process. As it moves up, the air loses its ability to hold moisture, and this falls as precipitation, often heavy. We’ll take a closer look at the tropical rain belt in several parts of the world.

We’ll look at precipitation from cyclones (aka hurricanes or typhoons) as they grow and move across the Pacific and Indian oceans.

We’ll examine how rainfall varies over the course of the day; known as ‘diurnal’ variation. Afternoon rain is common in the tropics. This is driven by convectional process, where precipitation is the result of evaporation in the same area. But the daily warming of the earth causes other effects around the world, such as those due to sea breezes. We’ll look at

examples from the Philippines, Florida and Australasia.

And finally we’ll look at how extreme rainfall varies across the globe, on land and over oceans. Where are the biggest storms—both at short durations and long durations? Are these also the wettest places overall?

Satellite data allows us to ‘plug the gaps’ in our understanding, offering data where rain gauge or rain radar measurements are not available. It has potential to provide seasonal and flood data for a wide variety of endeavours, from agriculture to infrastructure.

References:

Chris Kidd, Andreas Becker, George J. Huffman, Catherine L. Muller, Paul Joe, Gail
Skofronick-Jackson, and Dalia B. Kirschbaum, 2017. So, How Much of the Earth’s Surface Is
Covered by Rain Gauges? Bulletin of the American Meteorological Society, Volume 98: Issue
1, Pages 69–78. DOI: https://doi.org/10.1175/BAMS-D...