13 September 2012

Hydrological Research Team Find That Parched and Dry Soil Trigger Afternoon Rain Storms

According to a team of scientists from countries such as UK, Holland, Austria and France, parched and dry soil are more likely to trigger afternoon storms. The team examined the movement, distribution, and quality of water processes across six continents. Their hydrological study is published in the scientific journal, Nature.

The work of the team may give more insight into the workings of the environment in terms of rain and droughts. These may then be used to construct better and more precise climate models to track the Earth's existing climate cycle.

Climate is the weather condition of an area averaged over a period of time (usually in years). The difference between weather and climate is that weather is the condition of the area in that specified time. Aside from measuring devices such as barometers, weather satellites provide images and data on a global scale on how the present condition of the Earth's climate.

Using satellite imagery, the research team noticed that rain clouds developed more in places where the ground is dry. They scientists examined the images which track the development of storm clouds across the globe and matched up where new storms appeared alongside images of how wet the ground was.

Video: Water Vapor, the Hydrological Cycle, and Climate Change

Dr. Chris Taylor from the NERC Centre for Ecology & Hydrology in the UK led the research team conducting the study. According to him, "We had been looking at storms in Africa and knew that rain clouds there tended to brew up in places where it hadn't rained in the previous few days. We were surprised to see a similar pattern occurring in other regions of the world such as the US and continental Europe. In those less extreme climates, with more vegetation cover, we expected the soil wetness effect would be too weak to identify."

The researchers compared their observations with six global weather and climate models used to simulate climate change. They found that the existing models do the wrong thing, triggering rain over wetter soils.

The implication is that existing climate models are more likely to go into a vicious circle whereby dry soils decrease rainfall, leading to even drier soil conditions. The paper concludes that fixing this problem is a priority for scientists developing the climate models.

Dr Taylor added, "Both heat and moisture are critical ingredients for rain clouds to build up during the afternoon. On sunny days the land heats the air, creating thermals which reach several kilometres up into the atmosphere. If the soil is dry, the thermals are stronger, and our new research shows that this makes rain more likely."

Co-author Dr Fran├žoise Guichard from CNRM-GAME (CNRS and Meteo-France) said, "We need to improve climate models so that we get a better idea of what global climate change will mean on smaller regional scales over land."


Centre for Ecology & Hydrology
Natural Environment Research Council
CNRM-GAME (CNRS and Meteo-France)
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