Urban Ecology

Waiting on the Rain

by James Hathaway

In the desert, a summer thunderstorm is an event. Monsoon rains are a blessing after months of scorching heat and dryness. The storms explode across the desert and everything changes. Trees get new leaves. Dry grass turns green. Tiny toads sing from temporary lakes on fields and lawns. At Arizona State University, rain storms send a team of scientists into action.

The scientists are part of ASU’s urban ecology research program. They study the building clouds with special urgency. Because monsoon storms only hit a few times each year, the opportunity to study their effect is brief. When it rains in the desert, runoff must be measured, collected, and tested quickly, before it soaks into the ground or runs down the drain.

“Water is a critical player in the processes at work on the landscape,” says ecologist Nancy Grimm. She is co-director of the Central Arizona-Phoenix Long Term Ecological Research Project. “Water moves elements and chemicals that have been deposited on the soil and other surfaces. The sudden influx of water has a significant effect on streams and soils.”

Because of the way the weather works in the desert, a lot happens in a very short time. As a result, the ASU scientists have to work fast when the rain finally falls. While they are not zooming along chasing tornado funnel clouds, these scientists are “storm chasers” of a different kind.

The scientists spring into action any time rainfall is reported in the Phoenix metropolitan area during the day or even in the middle of the night. They try to collect samples. This can be difficult, because monsoon rain often occurs in small areas and does not last long.

In the future, the scientists plan to install automated sensing devices at various collection sites. The devices will send e-mail and other warnings to site monitors whenever rainfall occurs at a particular site.