Flash flood on the Craigie Burn, Perth, Scotland

[knocker]

The summer of 2002 in eastern Scotland was, in general, much wetter than average. Rainfall totals across the region, from the start of June to the end of July, were commonly around 150% above the long-term average (LTA). River flows were up to 400% above LTA on some catchments. A high proportion of this two-month rainfall was in the form of intense convective thunderstorms.

 

Such synoptic conditions seemed more frequent than usual throughout these months in this part of Scotland. A notable cluster of thunderstorms (associated with warm air from the south) had a severe impact on river levels in both large and small catchments in eastern and central Scotland between 30 and 31 July. Less than one week later another cluster of intense thunder cells (again associated with a continental airmass) became slow-moving over parts of Perthshire. The weather over Perth and its wider hinterland had generally been good on 6 August 2002, with blue skies and warm sunshine persisting for most of the day. As the afternoon progressed, however, the synoptic conditions around the area of Pitlochry (40 km north of Perth) and over much of the Grampian Highlands became dominated by strong convective thunder cells producing very intense, localised rainfall over steep mountain catchments. The geomorphological impacts and resultant damage from this rainfall and rapid runoff were spectacular within the middle River Tay and lower River Tummel valleys. The spatial extent of these intense thunder cells was to increase later in the day, and the fair city of Perth (Fig. 1) was not to escape ferocious downpours.

 

http://onlinelibrary.wiley.com/doi/10.1256/wea.50.03/epdf