The week from Monday 25th of June 2007 will be forever remembered by the People of the Sheffield and Rotherham. Two People sadly died and many had the stress of getting home, worrying about loved ones that were stranded or just late in returning home. RAF air crews were scrambled to winch stranded workers of Factory roofs as the River Don burst it’s banks and reclaiming it’s flood Plain. Meadowhall became flooded, Railways flooded and public transport suspended. In Brightside, a rescue boat was used to rescue stranded workers. Steering past abandoned cars that were being washed away during it’s journey. Up Market Apartments on Nursery Street and Corporation street became down market in a matter of hours as flood water swept through them. The journey home for some took hours if it could be completed at all. If not, emergency accommodation was set up in places like Hallam University. Hillsborough flooded and a substation blew plunging the area into darkness. Over night the Ulley Reservoir wall was damaged. The flood waters leading to fears of collapse and people having to be rushed to safety. The nearby Motorway the M1 had to closed while the nearby Power cables meant Sheffield and the local area could plunge into darkness. As the flood waters moved downstream other rivers burst their banks possibly claiming another life in Doncaster. Fears of more rain over the coming weekend could lead to more flooding will unnerve People clearing up. So how did this happen? Heavy Thunderstorms and Rain associated with a Low Pressure that moved NE across the country provided the starting ground for the floods. Indeed there were floods associated with this Low and the rainfall of 120 mm was followed by smaller amounts. but enough to keep the catchment areas saturated. The area was ready for more major flooding all it needed was the trigger. As the first Low moved NE another Low began to form of the SW of England. Combined with moist warm air moving up from France and colder drier air moving down from the North this created the formation of band of slow moving heavy rain. This formed over Northern regions with Sheffield just being on the southern most edge. Rainfall started overnight Sunday and continued until late Monday evening. The heaviest bursts lasting about an hour from 16:00 as the rain area finally started moving away SE.. The catchment areas unable to cope allowed most of the rain to run into the major rivers including the Don, Sheaf and later the Rother. Smaller floods caused by bad drainage maintenance by the Council also added to the problems no doubt hampering the rescue services as they tried to attend areas flooded by the Don. Heeley Bridge being one of these. Webcam pictures can be viewed here. A collection kindly out together by a fellow member from the NetWeather fourms. The media is now blurring the picture with claims that it was the heaviest day of rain in Sheffield ever. It wasn’t. In fact the 24 hour rainfall total wasn’t remarkable and happens at least once in every two years. Taking the 48 hour total pushes the event up the list a little but again it isn’t remarkable being the 6th wettest period since 1989. Now what is strange is having two very wet spells close together and the huge amount that fell between 13th to the 15th of the Month 123.5 mm. This is the main reason why the floods were so bad. Linking the floods into Global warming could well be alarmist but when the planet warms the chances of extremes go up. Will we see a days rainfall like this again. Certainly, probably in the next two years or so or even this weekend. The chances of getting two spells of such severity again. It’ll happen but the return period will probably be over 25 years. I’ve created a pdf file which shows the heaviest rainfall since 1989. To qualify the daily rainfall for one day in the period must be over 40 mm. The file can be found here.