Projected Climate Change Effects on Water Availability of the
Metropolitan Region of São Paulo
Abstract
Climate change affects the global water cycle and has the potential to
alter water availability for food-energy-water production and the
ecosystems services on regional and local scales. In southeastern
Brazil, the Cantareira Water Supply System reached unprecedented low
levels in January 2015 compromising the water supply for the
Metropolitan Region of São Paulo (MRSP). However, there is still few
studies investigating the effects of climate change on water
availability in this region. Here, we assess the influence of climate
change on water availability in the Jaguari Basin, Southeastern Brazil
using a modeling approach. This basin covers and area of about 1200 km2
and it is the main source of the Cantareira Water Supply System,
responsible for providing water for about 7 million people in the MRSP.
To evaluate climate change scenarios, we use the lumped conceptual HYMOD
model on daily time step. This model was calibrated and evaluated using
daily observed data of precipitation, evapotranspiration, and discharge
for the period of 1990 to 2009. To evaluated climate change scenarios,
we used data of an ensemble of 17 General Circulation Models (GCMs),
downscaled by MarkSim GCM working off a 30 arc-second climate surface
spatial resolution forced by two Representative Concentration Pathways
(RCP): RCP 4.5 and RCP 8.5. These data were integrated into the HYMOD to
projected scenarios (up to 2095) of water discharge. We find values of
Nash-Sutcliffe Efficiency Coefficient (NSE) and Coefficient of
Determination (R2) greater than 0.80 for the calibration and evaluation
period. We also noticed an increase in the peak of runoff and a decrease
and baseflow for both scenarios. Such changes reflect in a higher
interannual variability, therefore, increasing the risk of drought and
flood. In terms of Environmental Flow Requirement, the probability of
exceedance Q90, reveal a clear pattern of decreasing, about 23% from
2010 to 2040, and reaching 28% by the end of the century. Our findings
indicate that the water discharge could not be enough for the current
and future water demand. Our results expose the fragility of the studied
basin, presenting a technical and scientific information focusing on
guiding the plans and strategies to deal with situations of water
scarcity.