Two very dry wet seasons in Brazil, 2013-14 and 2014-15, based on data going back to 1979. Graphic: NOAA

By Leila Carvalho
26 June 2015 (The Conversation) – Exceptional drought, extreme temperatures, unprecedented drops in reservoir levels, and threatening water shortages for millions of people have dominated headlines in California in recent years. Unfortunately, Californians are not the only people being stressed with the “water crisis.” Citizens of one of the most densely populated areas in South America – the São Paulo metropolitan area (SPMA) in southeastern Brazil – are struggling with one of the nastiest water crises in decades. With over 20 million people and the main financial and economic center of Brazil, this region is under the influence of the South American monsoon system and receives the largest fraction of its precipitation during the Austral summer, from October to March. Yet in the last four years, rain gauge stations near the most important reservoirs supplying water to the city have been reporting growing deficits in precipitation. Last year saw the worst since at least 1961, which has been followed by another dry year. To aggravate these conditions, daily records of high temperatures during these summers have increased evapotranspiration, accelerating drought conditions, similar to what has been observed in California. A planet with over seven billion people and limited freshwater resources is already showing environmental exhaustion and signaling humans have crossed the line of sustainability. Our capacity to mitigate the negative effects of environmental changes and how fast we can adapt is limited by multiple factors. But as a megacity – a complex and often disorganized human conglomerate – the population of São Paulo, Brazil is particularly exposed to the effects of extreme weather events. The climatic factors influencing the drought in California and in São Paulo are likely interconnected. Cycles in the Pacific sea surface temperature that occur on decadal timescales are coupled to changes in atmospheric circulation that affect weather patterns worldwide. In some regions, atmospheric conditions are such that they block the passage of cold fronts that cause the storms to bring precipitation, changing the path of these rain events. [more]

Megacity drought: Sao Paulo withers after dry ‘wet season’