Let me introduce you to my home city, but maybe you know about it after the disastrous World Cup… ah well!
With the purpose of explaining the title, Sao Paulo is as close as you can get from the Tropic of Capricorn. It grew very fast over the last 60 years and what used to be pristine atlantic forest, now is a massive pile of concrete with very little trees.
Its climate is classified as humid subtropical. Humid, you say? Yes, during the summer (southern hemisphere summer, that is), due to a lot of nerdy physics stuff, the wind blows mainly from the sea, which can bring a lot of rain. During very particular meteorological conditions, a streak of cloud which extends from the Amazon all the way to Sao Paulo also brings a lot of constant, heavy rain. This fills up reservoirs and keeps the city afloat during the dry season. During the wet season, any rain is enough to flood huge parts of the city… but that’s beside the point.
This year, these monsoon rains didn’t happen. The average summer rain was way below average. Anyway, it happens! But now, what happened as a consequence? Just another quirk of subtropical climates are the dry winter months. Since the summer rains didn’t come, the reservoirs that supply the city with water are down to below 15%, with no rain in sight.
With dry weather, lack of water in a metropolis that lack trees, only has concrete in sight, and with millions of cars stuck in traffic jams all day, the air quality goes way down and dryness go very high up! How high? Yesterday, 6th of August, 2014, some parts of the city register relative humidity down to 18%, according to INMET, the Brazilian Met service. There in no rain forecasted in the days to come with high pressure dominating the weather, it can (and will) get drier.
How dry is this??? Well, yesterday, the city of Bechar, Algeria, which is in the middle of the Sahara Desert registered 14% and the Atacama Desert registered a 12% relative humidity (the driest place on Earth).
Well, in a metropolitan area with nearly 20 million people, this can be a bit of a problem…