Abstract
AbstractThe 2013–2015 drought in the Metropolitan Region of São Paulo exposed the lack of resilience of the regional water supply system, highly dependent on the Cantareira reservoirs. In this paper, inflows to each of the four main Cantareira reservoirs are tested for systematic change. Persistent trends in streamflow, rainfall, temperature and evapotranspiration are first evaluated. Streamflow was also tested for step change. Double-mass curves were employed to assess modification in the precipitation–runoff relationship. Subsequently, we used the climate elasticity method and the ABCD model to quantify the relative contribution of climate and human activities into the detected trends. Only Cachoeira and Atibainha sub-basins showed a significant downward trend in streamflow. The results for step change were also significant, and the year of occurrence coincided with breakpoints in precipitation–runoff relationship. For both Cachoeira and Atibainha, human activities had a more significant impact on streamflow reduction than climate variability. Land use and cover maps suggest that the reduction of pasture/abandoned land parallel to an increase in reforestation/silviculture is behind streamflow reduction. The results highlight the importance of coordinating land-use patterns and water management, as an important contributor beyond any considerations of a changing climate. Implications for better managing regional water resources are discussed.
Highlights
Ensuring the reliability of water supply services in the Metropolitan Region of São Paulo (MRSP) is increasingly a challenge due to social, climate and environmental dynamics
The aims of this study are (1) to investigate whether a systematic change in streamflow is occurring in Cantareira watershed; and, in the affirmative case, (2) to characterize the nature of the changes in reservoir inflows, using climate elasticity and the ABCD hydrological model to separate the relative influence of climate variability and human interference
Since 1998, the interannual variation for both Annual Precipitation (AP) and Annual Streamflow (AS) in all Cantareira sub-basins was reduced. This coincides with the onset of a shorter negative phase of Pacific Decadal Oscillation (PDO), which lasted for about 4 years (1999–2002) (Peterson et al )
Summary
Ensuring the reliability of water supply services in the Metropolitan Region of São Paulo (MRSP) is increasingly a challenge due to social, climate and environmental dynamics. Brazil accounts for nearly 20% of the world’s water reserves (Ceratti ), most of them (74%) are in the Amazon, rather distant from the main consumption centers. Annual water availability in the Alto Tietê River Basin, where the MRSP is located and which supplies water for part of its population, is merely 201 m3 per capita (World Bank ). The MRSP becomes highly dependent on water diversion from nearby river basins. The main source is the Cantareira system, a network of reservoirs which transfers water from the Piracicaba River Basin, being responsible for serving nearly half of the MRSP population
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