UK Battered by Relentless Winter Storms, Floods: AIR Analysis

February 12, 2014

A report from catastrophe modeling firm AIR Worldwide notes that “since October 2013, the United Kingdom has been experiencing a seemingly endless succession of severe winter storms that have produced multiple floods, even in areas off of floodplains.

“Over 370 mm [app. 14 ½ inches] have fallen across Scotland, Wales, and western and southern England during December and January, making it the wettest for those months since detailed data was first published, in 1910. The January rainfall total is the highest since 1766, according to the Met Office. The most recent January rainfall totals comparable to this year was in 1948.”

There’s been no letup in the succession of storms, as the rain continues to fall. As of the evening of Monday, February 10, heavy rainfall dumped up to 20 mm [app. ¾ inch] in areas of southern England and Wales, according to MeteoGroup, and another 30 mm [1.17 inches] are expected to fall Tuesday, February 11, in parts of southwestern England.

“Several of England’s major rivers are either currently at flood stage or are expected to reach flood stage in the coming days,” said Dr. Hemant Chowdhary, senior scientist at AIR Worldwide. “These include the River Thames, and the Severn and Stour rivers. The Environment Agency currently has 16 severe flood warnings in effect, with 14 in Berkshire and Surrey, and 2 in Somerset.”

Over 120 additional flood warnings and over 200 flood alerts have also been issued for regions across the United Kingdom.

The UK’s Met Office explained that the “North Atlantic jet stream is very strong and is tracking south of its usual position, which is north of Scotland. The result is a steady series of winter storms that have affected southern and western areas of England over the past two months producing downpours and storm surges. Snowfall has also impacted several areas, including parts of Wales.”

AIR’s report notes that on December 5, 2013, “a winter storm affected Scotland and northern England with heavy winds, rain, and storm surges. After a week’s respite, another severe storm on December 18-19 affected western Scotland and Northern Ireland.

“From December 23-24, over 60 mm [2.34 inches] fell in several areas including Dorset and East Sussex. Major storms occurred again on December 26-27, bringing another 10-20 mm [app. ¼ to ¾ inches] of rainfall to many areas, and another 20-30 mm fell in western and southern England from December 29-31. An additional severe storm affected the region on January 3 and additional storms continued to affect large areas of England and Wales throughout January.”

Dr. Chowdhary observed: “Storms are still affecting the country. They are initially characterized by heavy winds, affecting the northern areas first and then moving southward. Accumulated rainfall has produced severe flooding along many river catchments, including the River Thames and other large rivers such as the Severn River. High spring tides and river flows in January have increased water levels, particularly along coastal areas in southern and western England, while the strong winds have caused large waves that increase the damage to coastal properties.”

According to AIR’s analysis the “floods have damaged over 5,000 homes in the Thames valley and in Somerset, and threatened many others. Coastal communities have been affected by high waves as well, due to the strong winds. At Aberystwyth, the historic promenade has been severely damaged by waves.

“Across southwest England, the Royal Marines and local police and fire departments have evacuated homes after several flood defenses failed. A flood barrier in Somerset failed, prompting the evacuation of 60 homes.

“About 1,000 homes along the River Thames, in Chertsey, Wraysbury, and Datchet, have been evacuated. In Worcestershire, over 100 homes are flooded. However flood defenses have successfully protected over 200,000 properties over the past 10 weeks, according to government officials. Flooded rivers have claimed several lives including a kayaker in Wales, and two people in Aberdeenshire and Devon.”

As previously reported, “rail travel is severely impacted, particularly in areas west of London, around Maidenhead, Berkshire and in southwestern areas where rail tracks are damaged. Floods, falling trees, and landslides are also making roads impassable. Power cuts are widespread; about 64,000 properties in Wales are without power.”

AIR described most of the residential buildings in this region as “detached, semi-detached, or terraced (row) houses and are primarily of masonry construction. Commercial building stock uses a wider variety of materials including masonry, reinforced concrete, or steel. Light metal is often used for low-rise storage buildings. Mid-rise residential buildings generally have exterior non-load bearing walls made of masonry although they may have light-gauge steel stud walls or concrete panels. The vulnerability of caravans (mobile homes) is much greater than that of other residential construction types.

“Commercial buildings are usually built to stricter standards under the supervision of an engineer and therefore usually have sophisticated flood defenses in place, particularly in zones with a lower return period for flood. However, post-disaster surveys indicate that low-rise commercial wood frame and masonry buildings are generally non-engineered and have vulnerabilities similar to those of their residential counterparts. Large apartment and condominium buildings frequently receive a degree of engineering attention similar to that given to engineered commercial construction, reducing their vulnerability.

Dr. Chowdhary concluded: “Meteorologists expect the heavy rain to continue in southern England this week. Government officials expect that the River Thames, the Severn River, and the Wye River, which are at high risk, will flood later this week. The groundwater levels are extremely high and several areas can expect continued flooding for weeks to come; in some areas, flooding may persist for several months.”

Source: AIR Worldwide

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