Wednesday, June 17, 2015

Tokyo's micro-climate - here comes the rain again

It's raining. I mean seriously raining. A short time ago it was a clear, warm day but the light was already changing. When it starts to turn a distinct muddy yellow colour you know the heavens are about to open. The lightening strikes are sudden and close in the centre of the city and the sky will blackout completely if the storm continues to strengthen. The interesting thing though is that a few miles away it may well be picnic weather, not a cloud in the sky. Tokyo is a climate control centre unto itself.

The city is, in effect, one massive concrete coating on the landscape. The heat island effect it creates means that when it's storm weather in Shibuya, it may be clear a few miles away. The inverse is also true. When it's snowing in the suburbs, it can be cool and dry in downtown. A few kilometres can make all the difference, especially when it comes to flood warning. The old river courses having long since been cement lined, deepened and narrowed, can soon swell to the street level. Announcements are sometimes made over the local Tannoy system, telling people to stay clear.

Rain storms can bring several centimetres of rain in a matter of hours. If the weather looks like becoming extreme I'll put a rain gauge outside and it's not uncommon to see four or five inches in a day. On this scale though rain can cause flooding when the run off is now so limited compared to the past. And the question often arises, when an evacuation warning is issued, where do you go in a city that is under a deluge, surely everywhere is wet? The answer is simple. Evacuate up. 

The vast labyrinth of Tokyo's underground flood defences 

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