Scientists continue to debate when and where it rains most frequently on summer afternoons. Previous research has resulted in seemingly contradictory findings.
A new study, however, could help clear the air.
“On average, it rains most on days with high soil moisture,” explained Benoit Guillod, the first author of the study in Nature Communications. “Most precipitation falls, however, over the driest subregion.”
The phenomena can be explained in the following way: over the course of a day, the sun warms the earth’s surface, causing the water in lakes, rivers, oceans, and the ground to evaporate. This water vapor rises throughout the day, where it meets colder layers of air and condenses. It then starts to rain.
The soil’s moisture content plays a decisive role, particularly in areas far from the coast: the more moisture in the soil, the more water can evaporate, which increases the likelihood of precipitation.
But Where Exactly Does it Rain?
Within a humid area, the areas with lower soil moisture produce the warmest air, permitting the water vapor to rise the highest and thus meet the colder air layers the soonest. As a result, it rains most frequently at these locations. Guillod and colleagues base their findings on a wide range of data, including readings from soil sensors at 19 locations across Switzerland as part of the SwissSMEX project. The soil temperature and moisture content are recorded at various depths.
