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 the surface-groundwater interaction, have not yet been investigated. Here, we assess long-term trends in the streamflow and baseflow of the SFB during 1980–2015 and constrain the most likely drivers of observed decreases through a trend analysis of precipitation (P), evapotranspiration (ET), and terrestrial water storage change (TWS). We found that, on average, over 86% of the observed decrease in streamflow can be attributed to a significant decreasing baseflow trend along the SFR, with a spatial agreement between the decreased baseflow, increased ET, and irrigated agricultural land in the Middle SFB. We also noted a decreasing trend in TWS across the SFB exceeding –20 mm year−1. Overall, our findings indicate that decreasing groundwater contributions (i.e., baseflow) are providing the observed reduction in the total SFR flow. A lack of significant P trends and the strong TWS depletion indicate that a P variability only has likely not caused the observed baseflow reduction, in mainly the Middle and Sub-middle SFB. Therefore, groundwater and surface withdrawals may likely be a driver of baseflow reduction in some regions of 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) Our ECI results were positively correlated with mean slope and mean elevation, corroborating the gaining water condition found in 72% of the catchments located in the Atlantic Forest. Catchments in this biome presented the highest mean elevation and slope (Almagro et al, 2021).…”

Dynamic quantile regression for trend analysis of streamflow time series

“…Overlap of bars with 0 values signifies no change in streamflow Araguaia River in the stretch above the 'Aruanã' gauge. Nonetheless, our results align with recent studies that analysed long streamflow time series, and which also found downward streamflow trends for rivers in the Cerrado biome, including the Tocantins-Araguaia watershed(Lucas et al, 2021;Oliveira et al, 2014). The causal factors responsible for streamflow reduction in the Araguaia watershed will be explored in future research.Nevertheless, investigations already carried out indicate that landuse changes(Latrubesse et al, 2019;Pelicice et al, 2021) and climate change-mainly through increased vapour pressure deficit(Barkhordarian, Saatchi, Behrangi, Loikith, & Mechoso, 2019;Hofmann et al, 2021)-have already impacted the entire Cerrado biome.…”

“…On the other hand, if there is serial correlation, it is necessary to use statistical approaches to control for it, such as pre-whitening filters or variance correction (Hamed, 2009;Santos, Freitas, Gonçalves, & Chang, 2020). Serial correlation is intrinsic to time series streamflow data when daily, weekly or monthly streamflow values are sampled (Lucas et al, 2021;Yue, Pilon, & Phinney, 2003). In most studies that assess trends in streamflow time series, the following approach is used to control for the existing serial correlation: Nonetheless, the approaches described above have shortcomings:…”

Identifying hydrologic signatures associated with streamflow depletion caused by groundwater pumping

“…This suggests that statistically controlling for hydroclimatic variability may be a promising approach for identifying streamflow depletion from hydrographs. Trend analysis on streamflow signatures may reveal hydrograph changes potentially caused by streamflow depletion where trends attributable to climate differ from expected trends due to streamflow depletion (Juracek, 2015; Kustu et al, 2010; Lucas et al, 2021); however, estimates of groundwater pumping would bolster confidence in the occurrence and magnitude of streamflow depletion. The results of this study provide a more robust accounting of expected changes due to streamflow depletion and help prioritize sensitive hydrologic signatures that can form a basis for subsequent efforts on streamflow depletion detection.…”