Significant baseflow reduction in the Sao Francisco River Basin. Is it
time to call for attention on groundwater withdrawals?
Abstract
Water scarcity is a key challenge to global development. In Brazil, the
Sao Francisco River Basin (SFB) has experienced water scarcity problems
because of decreasing streamflow and increasing demands from multiple
sectors (e.g., food and energy production and urban supply). However,
the drivers of decreased streamflow, particularly the potential role of
groundwater withdrawals, have not been yet investigated. Here, we assess
long-term trends in baseflow, quickflow, and streamflow of the SFB
during 1980–2015 and constrain the most likely drivers of observed
decreases through trend analysis of precipitation (P),
evapotranspiration (ET), and terrestrial water storage change
(TWS). We found that over 82% of the observed decrease in
streamflow can be attributed to a significant decreasing baseflow trend
(< -20 m3 s-1
y-1) along the SFR with spatial agreement between
decreased baseflow, increased ET, and irrigated agricultural
land. We also found a decrease in TWS across the SFB with trends
exceeding -20 mm y-1. Overall, our findings indicate
that decreasing groundwater contributions (i.e., baseflow) are the
primary cause of the observed reduction in total SFR flow. A lack of
significant climate trends indicates that climate variability likely has
not caused the observed baseflow reduction, mainly in the Middle and
Sub-middle SFB, and therefore groundwater and surface withdrawals may be
the most likely driver of water scarcity over the SFB. We call for
increased attention on groundwater’s key role for the SFB and integrated
regional management of surface and groundwater.