A lot of cool air?

Wednesday 03rd Nov 2010 by theWeather Club

In many areas of the world, rain is a precious and rare resource. In an attempt to encourage rainfall, scientists have for many years been experimenting with 'cloud seeding', which attempts to create rain by dispersing chemicals such as silver iodide and frozen carbon dioxide into the clouds. But newly published research has revealed that this practice may not be nearly as effective as had been hoped.

In a most comprehensive reassessment of the effects of cloud seeding, a team from Tel Aviv University has dispelled the notion that seeding is an effective mechanism for increasing rainfall. The findings were recently reported in Atmospheric Research.

The team studied 50 years' worth of data on cloud seeding efforts from a target area over the Sea of Galilee in the north of Israel. They compared statistics from periods of seeding with data from periods of non-seeding, as well as the amounts of precipitation in nearby non-seeded areas. "By comparing rainfall statistics with periods of seeding, we were able to show that increments of rainfall happened by chance," Professor Alpert explained to reporters. "For the first time, we were able to explain the increases in rainfall through changing weather patterns."

The study revealed that a six year period of increased rainfall – previously thought to be a product of successful cloud seeding – in fact had other causes. The researchers showed that this increase corresponded with a specific type of cyclone consistent with increased rainfall over the mountainous regions. They were able to show a similarly significant rain enhancement over the nearby Judean Mountains, which had not been the subject of seeding.

According to a recent World Meteorological Organization report, there are more than 80 cloud seeding projects around the world despite it being a rather expensive process. The results of the study begs the question, should we spending money on trying to get more rain to fall, or concentrate efforts on how we manage the stuff that has already fallen?