By Paul Homewood
h/t Dave Ward
From the NY Times
KASUKABE, Japan — The cavernous underground cisterns here north of Tokyo could hold the Statue of Liberty, a scale that underscores the site’s immense task: protecting the world’s most populous metropolis from flooding.
Linked by tunnels that divert water away from the region’s most vulnerable floodplains, the $2 billion underground anti-flood system, completed in 2006, is an extraordinary example of the defenses that global cities are readying as they face an era of extreme weather brought on by climate change.
In the United States, towns and cities battered by a string of devastating hurricanes are just starting to come to terms with what it could take to bolster their storm protections. Houston city officials have pleaded for state and federal funds to help build a new $400 million reservoir that could keep storm water from inundating downstream neighborhoods.
“We’re preparing for flooding beyond anything we’ve seen,” said Kuniharu Abe, who heads up the underground site. “Until now, at least, we’ve been successful.”
Kuniharu Abe, head of the underground system designed to protect Tokyo from flooding, in Kasukabe. Credit Kentaro Takahashi for The New York Times
But even in Tokyo, the onset of more frequent and intense storms has forced officials to question whether the region’s protections are strong enough, a concern that has become more urgent as the city prepares to host the 2020 Olympic Games.
Across Japan, rainfall measuring more than two inches an hour has increased by 30 percent over the past three decades, the Japan Meteorological Agency estimates. The frequency of rainfall of over three inches an hour has jumped 70 percent. The agency attributes the increase of these intense rains to global warming, heralding a new era in a country that is already among the world’s wettest, with a language that has dozens of words for rain.
Rising oceans also make the Tokyo metropolitan region, home to 38 million people, vulnerable to storm surges, even as major redevelopment projects open up the previously industrial waterfront to new residences and businesses. And years of pumping groundwater has led some parts of the city to sink by almost 15 feet over the past century. Wide areas of Tokyo now sit below sea level, protected by aging dikes.
I become immediately suspicious when I see such claims about extreme weather, based on such a short period of data, in this case since 1976. Particularly so when ocean cycles can have such major effects.
This is the analysis linked to:
And we can see the pattern is clearly similar to the PDO.
Between 1976 and 1995, the heavy rainfall was less common, coinciding with the warm phase of the PDO.
During this warm phase, ocean temperatures around Japan are cooler than usual. This obviously reverses during the cool phase, when we see more extreme rainfall.
In other words, heavier rain appears to occur when sea temperatures are higher.
If we look at monthly rainfall trends for Tokyo, there does not appear to be much going on:
Rainfall was lower in that 1976 to 1995 period, but rainfall levels since don’t seem to be much different to the previous warm PDO phase from the 1940s to 70s.
The same applies to the extreme monthly rainfalls.
In short, there is no evidence that trends in Japanese rainfall have anything at all with global warming, but plenty that they are nothing more than natural variations.
There is one interesting statement however which stands out in the NY Times report:
Years of pumping groundwater has led some parts of the city to sink by almost 15 feet over the past century. Wide areas of Tokyo now sit below sea level, protected by aging dikes.
This is surely extraordinarily worrying.
While everybody obsesses about 7 inches of sea level rise in the last century, nobody seems to notice the real problem.
It is to the credit of the Japanese that they are taking such bold actions to mitigate floods, but, in case anyone is dubious, the history of Japan is littered with severe deadly floods, as this study revealed:
The heavy rainfall and the shorter and small river basin in Japan are the main factors effected on flood disaster compared with the case in China (Nakagawa et al., 1996). Konkoku floods, the oldest recorded flood events in Japan, occurred around the middle of the 7th century. Disastrous flood events happened essentially annually during the rainy period from 623 and 741 A.D. Floods threatened Kyoto and destroyed the Barada bank in 750 A.D. Economically catastropic floods also occurred in Kinugawa and Aratamakawa in 758 AD and 761 AD. The 772 AD Yodo river flood caused the Barada bank to break again. During 796 to 1530 A.D., more than 48 floods occurred in the Kyoto area, including 19 in Kinki following a long period of rain. Enormous mortality and destruction resulted from floods in years 858, 1231, 1486, and 1530 A.D. Japanese floods frequency increased after 1530 with the 1542 Kamanashikawa flood, 1604 Kantou flood, 1610 Toukaidou flood, 1624 Tonekawa, Arakawa, Chikumakawa flood, 1650 Kyushu Kinki Toukaidou flood, 1681 Takamatsu flood and the 1694 Fujikawa Chikumakawa flood. More than 100 Kunkoku floods occurred between 1530, the largest of which killed more than 10,000 people. The 1742 Inunomansui flood disaster (see Table 1) killed 2800 people. The Muroto Typhoon of 1934 and the Vera Typhoon of 1959 led to major floods and killed more than 3000. The Tokai Flood in 2000 caused 10 fatalities and 115 injuries. The Niigata-Fukushima Flood on 13 July 2004 resulted in 16 dead or missing victims (Zhai and Ikeda, 2008). More recent floods have two emerging characteristics; they occur during large typhoons with intense rainfall falling over a large area and; damage per flooded area has increased (Luo et al., 2010). Flood management efforts have reduced urban flood inundation but development density due to rapid economic growth has led to increased damage density.
There are three factors that lead to frequent flood disasters in Japan.
- (1) Steep elevation. Japan’s topography is characterized by relatively narrow islands with steep mountain ridges running down the center making the rivers short and steep in elevation.
- (2) High precipitation intensity. The mean rainfall in Japan is approximately 1700 mm – well above the world average of 970 mm ( Inoue, 2007).
- (3) Large, swift floods. Because river basin areas are small, the rivers are short and steep, and precipitation is high, floods in Japan start and end comparatively quickly ( Inoue, 2007). Flood intensity in Japan is much higher than the world average flood discharge per unit area.
via NOT A LOT OF PEOPLE KNOW THAT
October 12, 2017 at 04:30PM
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