Tree Damage During The Burns' Day Storm, 25 January 1990

Following the Bums' Day Storm on 25 Janu- ary 1990, there was unsubstantiated speculation on tree damage which cannot go unchallenged. It really is too simplistic to identify leafiness as the cause of the differences in damage levels between the October 1987 and January 1990 storms. Other valid factors include the spatial distribution of the strongest winds, the character and distribution of the tree cover within the affected area, the type of past woodland management and the occurrence of past damage events, the geology and soils of the areas, etc. Summary estimates of the tree damage in the two storms are:

siderable land area (Fig. 7 in McCallum) whereas in 1990 the affected areas were largely coastal fringes and Comwall and parts of Devon (his Fig. 6). Furthermore, the area of the strongest winds in 1987 had high levels of woodland cover (e.g. East Sussex 15.6 per cent. West Sussex 17.4 per cent, Kent 11.4 per cent and Surrey 18.8 per cent) whereas that in 1990 was not so well wooded (e.g. Comwall 5.1 per cent and Devon 8.0 per cent woodland cover). High levels of damage were therefore experienced in a small number of well wooded counties in 1987. but in 1990 low

Total volume Volume windthrown (mill m3) Forest area Woodland windthrown

broadleaves (per cent) 1.83 13-24 0.14 1-3

windthrown Woodland (mill m3) conifers

16Oct. '87 3.91 1.91 25 Jan. '90 1.26 I .04

Note that the total damage was much less for the Bums' Day Storm regardless of whether the broadleaved or coniferous trees arc considered, and that the percentage of forest area damaged was dramatically less within the main affected counties in lowland England. It is suggested that this is largely due to the lower wind speeds expe- rienced over the inland areas (as opposed to coastal stations). Gusts of 80 knots or more arc frequently associated with catastrophic damage to trees, whereas gusts of 70 knots or so tend to cause more sporadic damage. The area affected by 70-knot gusts was greater in 1990 than in 1987. but thc reverse was true for Wknot gusts; in 1987 wind speeds in excess of So knots affected a con-

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levels of damage occurred over many more counties.

Although the difference in proportion of broadleaved tree damage. rather than total tree damage. may be more confidently ascribed to leafiness there may be an effect of wind speed and woodland type here also. Conifers are generally vulncrable at lower wind speeds than are broad- leaves and this yould tend to increase the propor- tion of conifers damaged in lower magnitude events irrespective of leafiness. Forcstry Commission, C. P. QUINE Roslin. Midlothian

Viewpoint: COMMUNICATING WEATHER INFORMATION

The 'Sideways Look' series and 'View- point', although covering different subjects. commonly suggest that the customer is not get- ting the full value of forccasting improvements which have been accomplished over the years. I t seems to me that the difficulty lies in communication.

The basic rule of communication is that the message must leave the recipient as well in- formed as the originator. I agree with Chaplain, Lynagh, Mansell and others that in public and commercial weather forecasting alike this is not always the case. If this is true it follows that some dedicated forecasts might be considered to be in error by the customer when the originator is verifying them as totally correct. As far as the

Met. Office is concerned. management must take at least some of the blame for this. After all. management selects the communicators for both media and commercial areas but more import- antly it is often those in executive positions (sometimes with little experience in the field of communication) who decide on form and style. Thcrc is littlc to bc gained, for instance. by a Met. Office Director agreeing a road ice warn- ing system with a Local Authority civil engineer unless the forecaster and the road works foreman are on the same wavelength. There is less to be gained by the Director arbitrarily dictating the style or phraseology of a media broadcast, yet in my experience this has sometimes been the practice and in only a few cases would those

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dictating the terms seek or accept advice from below. Communication is a specialised subject and the percentage of good communicators among 1st Class Honours graduates is no higher than it is among staff of lesser academic qualifications so there is no reason why the com- municator, whether in the commercial or media area, should not have a greater say in form and style.

Management is less willing to dictate to other parties. A case in point is the discrepancy in style between the BBC Radio 4 forecasts at 6.55 and 7.55 a.m. and those on the same wave- length at 7.30 and 8.30 a.m. For several years I have fought what has often seemed a lone battle with the BBC, with a little success recently, against the ‘throwaway’ stylc of the latter, which rarely tells the full story. The Met. Office lets this go on, yet insists on verifying a wrirren tran- scription of the 7.55 a.m. London Weather Centre broadcast. This verification demon- strates a lack of understanding of communica- tion, too, for whilst the transcription might possibly be verified as totally correct the listencr could well have missed the whole message through being put off by the clipped tone of the delivery or the sing-song way in which the script was read. Those in authority should lisren to the broadcasts and verify accordingly.

Of TV broadcasts I have only a couple of queries and they again involve management. at least to some extent. 1 question the recent change into showing the negative of satellite imagery se- quences so that deep clouds are dark and vicc versa. This is the opposite of the previous prac- tice. I have no preference one way or the other, there are arguments both ways, but I do question whether the step helps the cause of communica- tion. The problem lies in the fact that the Met. Office appears to have made an arbitrary dcci- sion to change without reference to others who use similar satellite imagery. It is as if one of the School Examination Boards decided in isolation to reverse minus and plus signs! The stupidity of the action is nowhere better demonstrated than on BBC 1, where satellite imagery on breakfast TV forecasts shows the deepest clouds as white whilst in those broadcast during the rest of the day the same clouds are black-except in the case of ‘still’ satellite shots, where they arc white again! How confusing this must be to the lay

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viewer (the customer, remember). Are we to be- lieve that a communicator sanctioned that change? My second query concerns the ‘seven- day’ forecast on BBCl and Radio 4. The sensible instruction until at least 1983 was that no specific day should be mentioned aftex Monday because timing certainty beyond that was accepted to be liable to incremental error. Suitable phrases such as “towards the middle of the week”, ‘after mid- week“, etc. were honestly used and farmers, at whom the forecast was aimed, used to queue at the Royal Agricultural Show to te.11 us how help- ful and accurate it was. Nowadays quite fre- quently every day of the week is mentioned in that forecast and even though forecasting may have improved a little over those few years a simple check reveals frequent timing discrepan- cies. Here is a case where the customer might well believe that accuracy has decreased over the years, when the real fault lies in bad communication.

The simple rules of communication of fore- casts are to ascertain the question of the cus- tomer, answer it in words out of the dictionary rather than a meteorological glossary, be honest about doubts, speak in conversational English (which is different from the written version) and try to give the customer a ‘feel’ of the weather to come. And above all be honest with yourself and self-critical. (This last point applies to non-com- municators, too.) The course is rather longer than that but it has always surprised me how few folk can grasp these main suggestions.

JACK S c m

The fiuurer side of weather Phew! What a Double Howler. Peter-

borough, in the Daily Telegraph, 3 August 1990, gets the Celsifahreniusheit Award for this . . .

“Phew! What a Howler. A Michael Fish award to whoever does the weather for the Northern Echo. Yesterday’s forecast for the North East inshore region: “Occa- sional wintry showers. Wind: West to North West, severe gale force 9.” Yester- day’s weather: sunshine, 84°C and nary a breath of wind.”