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Floods not unusual

THURSDAY OCTOBER 01, 2009

 

Apparently now it's official: the heavier rainfall that has caused floods over the past week in Britain has been due to global warming. "A new scientific report will link global warming with storms like the recent drenching of London and surrounding areas of England ," wrote one reporter. "One-in-10 homes are now at risk of flooding", proclaimed another, continuing with "On Saturday some parts of Oxfordshire and Gloucestershire had one inch of rain. That is nearly a month's rain in one afternoon. With the increasingly violent weather patterns that we are experiencing, many more parts of the UK are potentially vulnerable " Well, Kaeo in Northland received one month of rain in an hour, but NZ scientists did not cite global warming. Possibly they know from past media battles with skeptics, especially those in the strident climate-science coalition, that they might come off second-best. One UK reporter added - "..Scientists Say To Expect More." Hmm..when..?  It is bound to rain again sometime, and heavily. If a doctor says expect more headaches, throbbing, or relapses, you are paying for his opinion for the next few hours or days to come. The time frame is important or what he says is meaningless. A climatologist usually means 50 and 100 years time. That is why they keep saying ‘ a once in 100 years flood’, or in the case of Gloucestershire, once in 200 years. And when another happens in a matter of months, as happened in Kaeo, the likes of Helen Clark say well, it was one in a 100, now it is more often, so this is proof that the climate has changed.  But it could also be proof the scientists keep getting it wrong.

 

Unless global warming is the suspect, a severe weather event seems hardly worth reporting. Global warming is the cause of everything, from the lack of hurricanes to the increase in them, polar blasts or lack of snow, sun or cloud, and if you don’t see a polar bear. There has been a scaling downwards so that now 73mph winds are called tornadoes rather than waiting for an 83mph one which was the old criterion. Statisticians can now say more tornados are coming than before and insurance companies can justify higher premiums. The public have not been told the goalposts have been shifted. With the ending of wars like Vietnam, the Cold War, Aghanistan, Gulf War, Bosnia, and Angola, and now that Iraq and the Middle East have become boring, in the minds of many Nature has stepped in as the new invader, and reporters in the field are behaving like war correspondents, seeking out the most carnage and human suffering. Science has joined the excitement. Extreme weather makes TV ratings go through the roof. From a commercial point of view one can understand why global warming could be the official line. Not as many newspapers would be sold if they headlined with the non-comforting "NOT AS BAD AS PAST FLOODS" just when everyone is suddenly homeless. Much better to gain some little joy out of the fact that it is the worst ever, because to the poor uninsured people who lost everything it probably is the worst ever.

There have, of course in Britain been lots of previous floods. Britain is mainly flat and many towns are dotted around marshes and river mouths because it is the most fertile farmland. On 16 August 2004 severe flooding devastated the small North Cornwall village of Boscastle. In 2002 the longest river in Great Britain, the River Severn that in 354kms drains the Cambrian Mountains, flooded and the town of Shropshire in Shrewsbury got submerged. The town has a long history of flooding problems, with notable events occurring in 1795, 1941, 1946, 1947, 1960, 1964, 1965, 1968, 1998 and 2000.  In October and November 2000 peak flows from five major rivers - Thames, Trent, Severn, Wharfe, and the Dee, resulted in floods lasting 90 days. At first they said these river levels were the highest for sixty years - then they decided the September/November rainfall was the highest since records began in 1766 which was 230 years – but then they revised that to ‘not seen in 270 years’, going back to 1630.

 

In 1947 there was a major flood event when 3,000 properties were flooded in Oxford alone, and some 1,000 km2 (386 mi2) of farmland was under water for up to three months. Most of Britain was also covered in flood waters in 1894, 1875 and 1852. In October/November in 1894, up to 75 mm (3 inches) of rain fell every day in southern Britain, flooding all of central and southern England.

Flooding is not only about rain. Often it is about management of rivers and stopbank maintenance by regional councils, and people building dwellings on flood-prone reclaimed land. That many choose to live on flood plains is hardly the fault of nature or global warming. People do have to take some responsibility for building in the wrong place. Whangarei and Gisborne have undertaken river diversion projects for flood prevention and now seldom suffer calamities. Kaeo of course has not. In the UK, despite the many floods in the last two centuries, two million homes have been built in the natural floodplain of rivers or the coast and are now vulnerable to flooding; and now property, land and assets to the value of £214 billion is at risk in England and Wales. After their big flood on 31 January 1953 London eventually built the mighty mechanical Thames Barrier, the biggest such system in the world, which by raising huge floodgates keeps extra tidal water out of the part of the river that winds through the city. The 185 miles of flood wall is designed to last until 2030. As a result London mostly escaped this recent flooding. Ashburton might take note.

 

The global warming logic is flawed. If climate was changing unpredictably then forward predictions are impossible. If climate is known to be changing, then how it is changing would be known. If such was the case then the recent floods could have been foretold months and years ago. Yet forecasters in Britain failed to warn of the worst floods in 60 years for Gloucestershire, rendering 10,000 homeless and 45,000 without power.  If driving SUVs and flying in aeroplanes is to blame for this flood then what was to blame in 1894? Were the horses walking too fast? What about 1630 - no factories, no cars, no emissions. And, if nature caused floods then, why can't nature be the cause now? The current floods came with the higher tides of the July new moon and rainwater was unable to get away. Between 11-15 August the new moon returns, and in my longrange crystal ball I see another dollop of heavy rain crossing Ireland and traveling east with considerable force across Wales and England. It is hardly rocket science to assume that in low-lying marshes some flooding will repeat.

 

There are lessons for NZ and especially South Canterbury, for we often built our pioneer towns along and beside the rivers before we had roads. Floods are part of our historical past. Blaming floods on climate change, global warming, pollution, or Al Queda will continue to be unhelpful and completely fiscally wasteful. Councils reclaim land to put up housing developments because they gain revenue from more ratepayers. This enables expansion and contributes to regional prosperity. The bigger short term take is more important than the future flood worry. This must now be seen to be dangerous and shortsighted. Returning flatlands to marshes of mangroves is what is needed in some areas to absorb extra flows of water. And Nature will eventually do it even if man doesn’t.

The Waimakariri, Rakaia, Ashburton, and Rangitata still have minor glaciers at or near their sources, these being puny remnants of the great tongues of ice that must have filled their valleys only a few thousand years ago. These are the main rivers that built the Canterbury Plain of shingle brought from the high country. In the plain itself they flow in wide terraced channels along courses subject to capricious change. Of interest to Christchurch is the lower Waimakariri. There are smaller rivers in mid and South Canterbury such as the Waipara, Ashley, Selwyn, Orari, Opihi, Pareora, and Waihao, fed to flood mainly by rains from an easterly quarter in contrast to the nor-westerly storms that flood those of the back country.

A drought or a flood will occur roughly every 9 years in the same place, being half the lunar cycle of 18-19 years. All local rivers including Rakaia, Opihi, and Hinds have flooded regularly. The first recorded major flood in Ashburton from the Ashburton River was in 1864. Over the following century in Ashburton the flood years were 1878, 1887, 1888, 1913, 1920, 1924, 1925, 1930, 1936, 1945 and 1951, making that 11 in 100 years which is a 9-yr average. 20 years after the March 1986 flood would have been 2006 so perhaps the 40cm snow that covered the town from the wintry blast of June 12, 2006 was the potential flood event returning. The next high rainfall event looks likely in late October and then this December just after Xmas. Next year in May, August and November we may also see high flood potential rainfall events in the district. Whether or not a flood will occur will be up to the strength of the stopbanks on the North Branch of the Ashburton River around the area adjacent to Digby's Bridge.  In some places due to a continuing build up of shingle the river bed is higher than the adjacent farm land as in the reach in the North Branch of the Ashburton River between Shearers Crossing and Thompsons Track Bridge. Until fixed, this will pose a high flood risk to properties downstream.

Floods should not be regarded as unusual or extreme weather events in a location like Ashburton. District planners should treat flooding as en expectancy. It is up to council to ignore fantasies and hand-wringing about climate change and what will happen in 50 years time. They should not worry over who is lighting open fires and whether or not that is putting carbon dioxide into the air because when a log is burned it merely puts back CO2 that was absorbed from the atmosphere during the growing process. It is the same with coal, oil and gas. Forget Kyoto, forget greenhouse, forget Al Gore. All the resources of councils should be directed towards flood management, because the economic disaster of not being able to get to work is greater than any inconvenience of having to undo a top shirt button because the climate is a tad warmer. Councils can and should act now.

 

 

 

Refs: http://www.thedailygreen.com/2007/07/23/global-warming-blamed-for-british-floods/4192/

http://www.savethechildren.org.nz/?gclid=CO3jhfHzwY0CFRWZYAodqyCSIA

http://www.ashburtondc.govt.nz/services/civildefence/local+hazards.htm

http://www.teara.govt.nz/1966/L/Landscape/RiverSystems/en

       


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