The Water Crisis in Sao Paulo City: Drought and its Climate Connections

Abstract:

In 2014, Sao Paulo city had its largest water shortage in history. By the end of the first half of 2014, the Cantareira system of water reservoirs, which is responsible for supplying fresh water for about 9 million people in the city, dried to less than 10% of its active storage, leading to a critical situation and the need to pump water from its dead storage and allocate water from other smaller systems of reservoirs in order to meet the demand of the city and avoid a mandatory water rationing. Understanding and identifying the leading factors for such a water crisis is critical for the security of the city. Here, we investigate historical data of water levels and inflows into the Cantareira system and of the rainfall series over the contributing basin in order to estimate the contribution of climate factors to the variability of the water storage levels at the Cantareira system and shed some light on the main causes of the current water shortage. Preliminary results based on natural inflow data from 1930 to 2014 and water storage levels from 2004 through 2014 reveal that, about 60% of the low frequency (beyond seasonal cycle) variance in the storage level trends is explained by trends in the inflows. A remarkably monotonic decreasing trend of about 1.5% per month in the storage levels is observed since 2010 and is closely associated with a similar decreasing trend in the inflows into the system for the period. In fact, the annual average inflow for 2012 (25.6 m³/s) and 2013 (25.7 m³/s) was 65% of the long term average and still below the 2004-2012 average withdrawal to supply Sao Paulo (26.64 m³/s). By the end of the 2013 rainy season the system had accumulated 63% of its total capacity, but the persistence of low inflows and high temperatures during 2013 did not allowed any increase in the water levels. In 2014 austral summer the system experienced the worst hydrological drought since 1930 based on the available streamflow records. The average inflow for the 2014 rainy season (DJFM) is the lowest value (14.5 m³/s) ever recorded for the season, with an empirical exceedance probability of 98.8%. Analysis of meteorological droughts and climate teleconnections in the region as well as of opportunities and implications of inflow and rainfall forecasts for 2015 from different modeling sources for water management in Sao Paulo are also discussed along this work.