When storms cause `endemic creep'

 

Two years have passed since the infamous and tragic Christmas storms. There were two, you may remember, that followed identical paths - one, the more severe, on Christmas Eve 1997, and a second on Christmas Day.

Both moved from Galway Bay towards Belfast, and then across Scotland and on towards Scandinavia. They brought winds that gusted to more than 100 m.p.h, many violent thunderstorms to help the wind cause havoc with the electricity, and personal tragedy in the form of injuries and even death.

There were other costs as well. The insurance companies claimed to have incurred liabilities of some £38 million on foot of damage caused by the 1997 Christmas storms.

And Coillte, the Irish Forestry Board, calculated that some 360,000 cubic metres of timber, or something like half a million trees, were either snapped or blown over.

Depressions as intense as these are not unusual. Many appear in the North Atlantic every year, but they become noteworthy as far as Ireland is concerned only if they pass close enough to cause destruction.

During the summer months, they tend for the most part to follow a track that takes them well to the north of us, but the preferred path of wintertime depressions lies very close to Ireland - so winter storms of this ferocity are not a rarity.

Based, naturally enough, on its experience with trees, Coillte estimates damaging storms seem to happen every 10 to 15 years, with very severe ones every 30 or 40 years or so.

The worst this century, as far as tree damage was concerned, was on February 26th-27th, 1903. There were other comparable events in 1936 and 1955, and in 1957 some 280,000 trees were destroyed in January and February storms.

By 1974 Coillte had progressed to measuring trees in cubic metres, and in a major storm that year 374,000 of these cubic metres were destroyed - more than 1 1/2 times the usual annual timber harvest.

There have been one or two nasty blows since, notably in 1976, when 134,000 cubic metres were blown down, and again in 1990. The loss in an average year, apparently - that which foresters rather nicely call "endemic creep" - is usually fewer than 100,000 cubic metres, or some 9 per cent of annual harvest.

And then, as we have seen, there was 1997. The Christmas storms were not as bad as those of 1974, but the winds were particularly vicious in the vicinity of Cork where 250,000 cubic metres of timber, about 70 per cent of the total loss, were destroyed.