Mud in reservoir: Levels in the Cantareira reservoir system remain dangerously low. Fires to clear land for agriculture in Sao Felix Do Xingu municipality, Para, Brazil - June 20, 2009. In Brazil's biggest city, a record dry season and ever-increasing demand for water has led to a punishing drought. It has actually been raining quite heavily over the last few days in and around Sao Paulo but it has barely made a drop of difference. The main reservoir system that feeds this immense city is still dangerously low, and it would take months of intense, heavy rainfall for water levels to return to anything like normal. So how does a country that produces an estimated 12% of the world's fresh water end up with a chronic shortage of this most essential resource - in its biggest and most economically important city? It's interesting to note that both the local state government and the federal government have been slow to acknowledge there is a crisis, despite overwhelming evidence to the contrary. That might have been a politically expedient position to take during the recent election campaign, when the shortage of water in Sao Paulo was a thorny political issue, but the apparent lack of urgency in the city and wider state now is worrying many. At the main Cantareira reservoir system, which feeds much of this city's insatiable demand for water, things have almost reached rock bottom. Huge pipes suck out what water remains as the reservoir dips below 10% of its usual capacity.

Just 227 tree species dominate Amazon

Researchers were surprised to find that such a small proportion of species dominated the Amazon . Despite being home to about 16,000 tree species, just 227 "hyperdominant" species account for half of Amazonia's total trees, a study suggests. An international team of researchers found that the region was, in total, home to an estimated 390 billion trees. Writing in Science, they added that the rarest 11,000 species made up only 0.12% of tree cover. However, they added that the new data could help unlock ecological secrets held by the biodiversity hotspot.

The results were based on a survey of 1,170 plots and half-a-million trees across the six-million-square-kilometre area, often described as the lungs of the world. The authors said that the underlying cause of the hyper dominance of the 227 species, which accounted for 1.4% of the estimated number of species in the region, remained unknown. "We knew that, normally, a few species dominate ecosystems, but if you have a system that has 16,000 tree species but just 227 make up half of the trees, that was pretty surprising even for us," said lead author Dr Hans ter Steege from the Naturalis Biodiversity Center in the Netherlands. He told the Science podcast: "We don't really know why these species are so incredibly dominant because they do not have any particular ecological feature that stands out."

The Brazilian Chamber of Deputies has