Drought in a megacity: Sao Paulo is withering after a dry "wet season"

Really low: reservoir levels for dams and reservoirs that provide water in Sao Paulo state are at historic lows. Image: Nacho Doce/Reuters.

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 Sao Paulo metropolitan area (SPMA) in southeastern Brazil – are struggling with one of the nastiest water crises in decades.

With over 20m 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; this has been followed by another dry year.

 Other citizens are drilling through their basement floors to extract the precious water

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 7bn people and limited freshwater resources is already showing environmental exhaustion, and signaling that 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 Sao Paulo, Brazil is particularly exposed to the effects of extreme weather events.

Blocked storm patterns

The climatic factors influencing the drought in California and in Sao 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 the cold fronts that cause the storms to bring precipitation, changing the path of these rain events.

As long as these blocking conditions persist, there will be regions undergoing dry conditions, whereas others will be extremely wet. The North Pacific has been entering a phase that will likely increase the probability of these blocking mechanisms that favor dry conditions in California and other regions of the planet, including Sao Paulo.

Of course, similar oceanic and atmospheric conditions have occurred in the past and will continue to occur in the future. The problem that we should confront without hesitation is: how can global warming aggravate these extreme conditions, particularly in locations with high rates of urban growth such as Sao Paulo? How fast should governments act and how much should be invested to mitigate these unprecedented conditions?

Filling at a public tap: water rationing has turned off regular water services at some homes. Image: Roosevelt Cassio/Reuters.


In the Sao Paulo metropolitan region, the main water supply system, which provides water for about 8.8m inhabitants, reached critical levels in early 2015. It had only 5 per cent storage of its 1.3bn m3 capacity on January 2015, and 15 per cent at the end of the rainy season in March 2015. An impending ration mandate could leave residents without access to water for a few days a week.

The main water utility has already reduced pressure in the pipes to force conservation, a strategy that has cut off running water to millions of customers for hours and even days, depending on where one lives. Unlike California, isolated rain showers have occurred in Sao Paulo, and the desperate population, particularly in poor districts, has stored the rainwater in open containers and buckets to save it for the days of water shortage. Other citizens are drilling through their basement floors to extract the precious water leaving open wells.

As a consequence, the entire state of Sao Paulo, with a population of 40m inhabitants, is undergoing a deadly dengue fever outbreak. In the SPMA, where the situation is really dramatic because of the limited access to water, the government created many improvised ambulatories throughout the city to attend the population with symptoms of the disease. Officials go door-to-door searching for infectious mosquito larvae and educating the population about the disease. However, all these measures have proven to be inefficient to control the dengue larvae proliferation.

Two very dry wet seasons based on data going back to 1979. Image: NOAA.

What the future will bring for the growing population of the SPMA remains unknown. In the short term, it is possible the blocking conditions that have prevented storms from coming through will become less persistent in the next summer and increase the probability of extreme precipitation in the region. However, the temporary relief will not solve the imminent water crisis in Sao Paulo, nor in California, in the years to come.

Populations and governments in the world need to raise awareness about limited freshwater resources so the present sets the right stage for a sustainable future. No matter where we live, or the rate of economic growth of a given nation, populations are, and will always be, vulnerable to water scarcity.

Resilience depends on numerous factors. But how populations will cope with disasters of various magnitudes is largely dictated by political actions, socioeconomic development and education.

The ConversationLeila Carvalho is associate professor of meteorology & climatology at University of California, Santa Barbara.

This article was originally published on The Conversation. Read the original article.


Green roofs improve cities – so why don’t all buildings have them?

The green roof at the Kennedy Centre, Washington DC. Image: Getty.

Rooftops covered with grass, vegetable gardens and lush foliage are now a common sight in many cities around the world. More and more private companies and city authorities are investing in green roofs, drawn to their wide-ranging benefits which include savings on energy costs, mitigating the risk from floods, creating habitats for urban wildlife, tackling air pollution and urban heat and even producing food.

A recent report in the UK suggested that the green roof market there is expanding at a rate of 17 per cent each year. The world’s largest rooftop farm will open in Paris in 2020, superseding similar schemes in New York City and Chicago. Stuttgart, in Germany, is thought of as “the green roof capital of Europe”, while Singapore is even installing green roofs on buses.

These increasingly radical urban designs can help cities adapt to the monumental challenges they face, such as access to resources and a lack of green space due to development. But buy-in from city authorities, businesses and other institutions is crucial to ensuring their success – as is research investigating different options to suit the variety of rooftop spaces found in cities.

A growing trend

The UK is relatively new to developing green roofs, and governments and institutions are playing a major role in spreading the practice. London is home to much of the UK’s green roof market, mainly due to forward-thinking policies such as the 2008 London Plan, which paved the way to more than double the area of green roofs in the capital.

Although London has led the way, there are now “living labs” at the Universities of Sheffield and Salford which are helping to establish the precedent elsewhere. The IGNITION project – led by the Greater Manchester Combined Authority – involves the development of a living lab at the University of Salford, with the aim of uncovering ways to convince developers and investors to adopt green roofs.

Ongoing research is showcasing how green roofs can integrate with living walls and sustainable drainage systems on the ground, such as street trees, to better manage water and make the built environment more sustainable.

Research is also demonstrating the social value of green roofs. Doctors are increasingly prescribing time spent gardening outdoors for patients dealiong with anxiety and depression. And research has found that access to even the most basic green spaces can provide a better quality of life for dementia sufferers and help prevent obesity.

An edible roof at Fenway Park, stadium of the Boston Red Sox. Image: Michael Hardman/author provided.

In North America, green roofs have become mainstream, with a wide array of expansive, accessible and food-producing roofs installed in buildings. Again, city leaders and authorities have helped push the movement forward – only recently, San Francisco created a policy requiring new buildings to have green roofs. Toronto has policies dating from the 1990s, encouraging the development of urban farms on rooftops.

These countries also benefit from having newer buildings, which make it easier to install green roofs. Being able to store and distribute water right across the rooftop is crucial to maintaining the plants on any green roof – especially on “edible roofs” which farm fruit and vegetables. And it’s much easier to create this capacity in newer buildings, which can typically hold greater weight, than retro-fit old ones. Having a stronger roof also makes it easier to grow a greater variety of plants, since the soil can be deeper.

The new normal?

For green roofs to become the norm for new developments, there needs to be buy-in from public authorities and private actors. Those responsible for maintaining buildings may have to acquire new skills, such as landscaping, and in some cases volunteers may be needed to help out. Other considerations include installing drainage paths, meeting health and safety requirements and perhaps allowing access for the public, as well as planning restrictions and disruption from regular ativities in and around the buildings during installation.

To convince investors and developers that installing green roofs is worthwhile, economic arguments are still the most important. The term “natural capital” has been developed to explain the economic value of nature; for example, measuring the money saved by installing natural solutions to protect against flood damage, adapt to climate change or help people lead healthier and happier lives.

As the expertise about green roofs grows, official standards have been developed to ensure that they are designed, built and maintained properly, and function well. Improvements in the science and technology underpinning green roof development have also led to new variations on the concept.

For example, “blue roofs” increase the capacity of buildings to hold water over longer periods of time, rather than drain away quickly – crucial in times of heavier rainfall. There are also combinations of green roofs with solar panels, and “brown roofs” which are wilder in nature and maximise biodiversity.

If the trend continues, it could create new jobs and a more vibrant and sustainable local food economy – alongside many other benefits. There are still barriers to overcome, but the evidence so far indicates that green roofs have the potential to transform cities and help them function sustainably long into the future. The success stories need to be studied and replicated elsewhere, to make green, blue, brown and food-producing roofs the norm in cities around the world.

Michael Hardman, Senior Lecturer in Urban Geography, University of Salford and Nick Davies, Research Fellow, University of Salford.

This article is republished from The Conversation under a Creative Commons license. Read the original article.