Saturday, September 24, 2011

Patchy rain

In a Weather Eye column last week Paul Simons once again referred to the change in the pattern of rainfall which has become increasingly common worldwide – a trend to shorter but much more intense downbursts. This new phenomenon has been partially responsible for the floods & misery caused by this year's monsoons on the Indian sub-continent.

In this part of northern Europe the downpours also tend to be geographically very concentrated too – it is now common to pass from rain to dry to heavy rain to dry … on the bus ride home, or to stand under a patch of sunlit sky & watch the black clouds burst less than a mile away. And yet we are often told that the total amount of rain which falls each year has not increased in tandem, but remains pretty much as average.

Some may wish to blame this on climate change or natural fluctuation but I have started to wonder if it might be an unexpected consequence of actions taken by humans which have undoubtedly had hugely beneficial effects.

Initiatives such as the Clean Air Act were aimed at getting rid of dark & dirty smog, but we seem also to have greatly reduced the occurrence of fog (& its companion, motorway madness).

Could the huge amounts of particulates (& sulphur) spread into the atmosphere by the burning of wood & coal somehow have spread the moisture around more evenly - in the same way that a sheet of thin tissue paper will spread a blob of water on the kitchen counter without being able to hold on to it if you pick it up? Now that those particulates have gone, , together with the more recent removal of the nastier elements of the exhaust of motor vehicles, the amount of water held by any given cubic meter of air may be much more variable depending on local factors such as topology, updrafts & downdrafts.

But then if we properly understood when, where & how it rains we would have long ago been awash with successful rainmakers.

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