Significant baseflow reduction in the Sao Francisco River Basin

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. However, the drivers of decreased streamflow, particularly the potential role of surface-groundwater interaction, 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 noted 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) is providing the observed reduction in total SFR flow. A lack of significant P trends indicates that only P variability likely has not caused the observed baseflow reduction, mainly in the Middle and Sub-middle SFB. Therefore, groundwater and surface withdrawals may be likely a driver of water scarcity over the SFB.

Are Brazilian catchments gaining or losing water? The effective area of tropical catchments

“…This situation is aggravated by the long‐term conversion of natural vegetation to different agricultural land uses (e.g., sugarcane, soybean, and corn), which have been responsible for more than half of the national grain production (Spera, 2017) mainly in the Cerrado. Furthermore, the increase in irrigated areas for food production in the Cerrado and Caatinga biomes has been recently related to an increase in evapotranspiration and baseflow reduction in these regions (Oliveira et al, 2019; Lucas et al, 2020). The impacts of land use and land cover change (LULCC) on the catchments' water fluxes are still poorly understood.…”

Quantifying Streamflow Depletion from Groundwater Pumping: A Practical Review of Past and Emerging Approaches for Water Management

“…In Brazil, Lucas et al. (2021) suggested streamflow depletion was leading to a decline in baseflow due to a spatial agreement between declining baseflow trends, increasing evapotranspiration trends, and irrigated agricultural land. In contrast to statistical assessments, statistical models applied to streamflow depletion estimation typically attempt to quantify some relationship between groundwater pumping and long‐term changes in streamflow and/or baseflow, often as one of several predictors.…”

“…For example, Kustu et al (2010) observed a spatial match between negative trends in groundwater levels and streamflow across the U.S. High Plains Aquifer and inferred a connection between the two based on the absence of potential explanatory precipitation trends, and Juracek (2015) compared numerous gages in southern Kansas and found significant decreasing streamflow trends in basins with the greatest groundwater level decline and a lack of precipitation trends, which together suggested that streamflow depletion was the cause of observed streamflow trends. In Brazil, Lucas et al (2021) suggested streamflow depletion was leading to a decline in baseflow due to a spatial agreement between declining baseflow trends, increasing evapotranspiration trends, and irrigated agricultural land. In contrast to statistical assessments, statistical models applied to streamflow depletion estimation typically attempt to quantify some relationship between groundwater pumping and long-term changes in streamflow and/or baseflow, often as one of several predictors.…”

Quantifying Streamflow Depletion from Groundwater Pumping: A Practical Review of Past and Emerging Approaches for Water Management

“…High Plains Aquifer and inferred a connection between the two based on the absence of potential explanatory precipitation trends, and Juracek (2015) compared numerous gages in southern Kansas and found significant decreasing streamflow trends in basins with the greatest groundwater level decline and a lack of precipitation trends, which together suggested that streamflow depletion was the cause of observed streamflow trends. In Brazil, Lucas et al (2021) suggested streamflow depletion was leading to a decline in baseflow due to a spatial agreement between declining baseflow trends, increasing evapotranspiration trends, and irrigated agricultural land. In contrast to statistical assessments, statistical models applied to streamflow depletion estimation typically attempt to quantify some relationship between groundwater pumping and long-term changes in streamflow and/or baseflow, often as one of several predictors.…”