Catastrophe modeling firm AIR Worldwide has issued a preliminary report on the floods caused by the heavy rainfall that began lashing the British Isles on Thursday, November 22, prompting hundreds of flood warnings and alerts. “As of Tuesday, November 27 at 3 PM GMT, there were 182 flood warnings, two severe flood warnings, and 225 flood alerts in place, affecting virtually every region in England and Wales,”AIR said.
“The southwest areas of England, particularly the counties of Cornwall and Devon, have thus far borne the brunt of the rainfall, with some places recording over 150 mm [5.85 inches] of precipitation over the past seven days.
“According to the UK Environment Agency, 960 homes have been flooded, the majority of them in the southwest. Aside from the devastation to homes, businesses and the tragic loss of life in the affected regions, there has also been widespread disruption to rail and transport networks, including the partial closure of major motorways.”
AIR noted that while the “weather forecast is improving, groundwater and river levels have not yet peaked, indicating a high possibility of continued flooding, especially in the northeast regions of England and northern Wales.
“The excessive rainfall was the result of consecutive low pressure systems that approached from the southwest, bringing warm, moist air from Africa and the Atlantic. The UK Met Office began issuing flood warnings as early as Monday, November 19, as the first low pressure system was forecast to impact Cornwall and Devon. Heavy rains began in the early hours of the morning of the 21st. At Exeter airport in Devon, 39.2 mm [app. 1 ½ inches] of precipitation was recorded between midnight and 8 a.m. on the 21st. This heavy band of rainfall and gusty winds were the result of a cold front that moved eastward over the southern British Isles before passing to the east through the Netherlands and across France, bringing some respite late Friday and early Saturday.”
However, AIR also explained that at the “southern end of the cold front, which reached down as far as the Iberian Peninsula, another depression was developing. The warm, moist air caused this depression to deepen and, as it moved north-eastward, warnings of heavy rainfall and strong winds were issued, with up to 60 mm [2.34 inches] of precipitation expected first in the southern counties and then continuing along the path of the storm. As this new system arrived on Saturday, the heavy rains fell on already saturated soils, causing the first floods.”
“The system continued to dump heavy rainfall across the Midlands, across the Pennines, and into the northeast before moving into the North Sea on the evening of Sunday, November 25. This passing system resulted in rainfall totals, recorded between midnight and 8 a.m. Saturday morning, of 56.8 mm [2.22 inches] in the town of Plymouth on the south coast and another 48 mm [1.87 inches] at Exeter airport, where the previous high was recorded days earlier. As the system moved northeast through Saturday night, the counties of Yorkshire and Humberside in the northeast began to see totals of 30–36 mm [1.17 to 1.4 inches] between midnight on Saturday and 8 a.m. Sunday morning.
“Yet another low pressure system followed closely behind, again approaching England from the southwest. This system reached the southern counties in the early hours of Monday morning and proceeded along a similar northeast path. The system temporarily stalled over the northeast under the influence of cold winds from the North Sea before finally moving offshore Monday evening.”
The rainfall continued through Tuesday, but was expected to abate later in the day. “However, AIR warned, “river and groundwater levels are expected to peak in the next 48 hours, indicating the possibility of further flooding.”
AIR estimated that since the first flooding began on Saturday, November 24, “some 960 properties have been damaged. Disruption to rail and transport networks was also widespread with closures and delays experienced across much of the country. There have also been widespread road closures, particularly in the southwest and the Midlands, including parts of the M5 motorway in Gloucestershire.
“In the village of Malmesbury near the southern Welsh/English border, floodwaters reached over 1 meter [over three feet] in the center of the town. The Elwy River in North Wales, has overtopped flood defenses with a river height of almost 1 meter higher than the previous record. Approximately 100 homes have been flooded from the Elwy River in the town of St. Aspath, and 400 properties are at risk in the nearby village of Ruthin.
“Voluntary evacuations were in effect in the town of Tewkesbury in Gloucestershire as floodwaters began to rise on the Severn and Avon rivers. To the north, in York, the River Oust burst its banks, resulting in the flooding of riverside buildings.”
Authorities in the UK have estimated that approximately 55,000 homes have been protected from flooding so far by the new flood defenses built since the disastrous flooding in 2007. However, AIR said newly built flood defenses “were overtopped in Kempsey in Worcestershire when one of the pumps designed to redirect the water failed to start. The new defenses cost approximately £1.5 million [$2.385 million] to build and were designed to protect ‘the most flooded village in the country’ from events such as this; Kempsey has been flooded 20 times in the past 30 years by the nearby river Severn.”
According to AIR, the current spate of heavy rains and flooding follows a summer in which the UK experienced multiple flooding events. Most of the summer’s floods were localized in nature, with estimates of insured losses totaling approximately £1 billion [$1.59 billion]. AIR estimates “average annual insured losses of approximately £343 million [$545 million], so 2012 is proving to be an above average year. However, 2012 is still far shy of the approximately £3 billion [$4.77 billion] of loss experienced in the devastating 2007 floods.”
Source: AIR Worldwide
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