Water Appropriation on the Agricultural Frontier in Western Bahia and Its Contribution to Streamflow Reduction: Revisiting the Debate in the Brazilian Cerrado

Abstract

Over the last three decades, almost half of the Brazilian tropical savanna (Cerrado biome) has been converted into cropland and planted pastures. This study aims to understand the implications of the expansion of the agricultural frontier for water resources in western Bahia state. We use an interdisciplinary approach that combines quantitative and qualitative data (spatial and hydrological analysis, interviews) to tie together land use changes in the Corrente basin, the streamflow and precipitation time series in the Pratudão River sub-basin (part of the Corrente basin), and the perceptions of soybean farmers and smallholder communities about the transformations of the hydrological cycle over the last few years. We observed an almost 10-fold increase in agricultural surface area in the Corrente River basin over the last three decades (1986–2018), going on from 57,090 ha to 565,084 ha, while center-pivot irrigated areas increased from 240 ha to 43,631 ha. Over this period, the streamflow has reduced by 38% in the Pratudão River. Our hydrological analyses, based on the Mann-Kendall test, of seven fluviometric stations and 14 pluviometry stations showed a statistically significant streamflow trend in the Pratudão River sub-basin for both minimum and mean streamflow series (p ≤0.05). Surface runoff coefficient, which relates streamflow and precipitation annual data coefficient, decreased from around 0.4 in the late 1990s to less than 0.2 in 2015. In addition, most precipitation time series analysis (number of annual rainy days) showed no statistically significant trend (p > 0.05). Our results indicate that agricultural changes rather than climate change may be the main driver of downward streamflow trends in the Pratudão River sub-basin that is part of Corrente River basin.

Water balance components and climate extremes over Brazil under 1.5 °C and 2.0 °C of global warming scenarios

“…Such projections can have a direct impact on the two largest Brazilian biomes (Amazon and Cerrado – Brazilian tropical savannah) and one of the country’s most important agricultural frontiers, called MATOPIBA (an acronym formed from the names of the states of Maranhão, Tocantins, Piauí, and Bahia). The MATOPIBA region is strategic for the Brazilian economy, mainly due to the quantities of agricultural commodities produced there (Silva et al 2021 ), such as soybeans (Marengo et al 2022 ; Rattis et al 2021 ; Bragança, 2018 ). In recent decades, soybean cultivation in the region has expanded, in part, due to irrigation (Lopes et al 2021 ; Silva et al 2021 ).…”

“…The MATOPIBA region is strategic for the Brazilian economy, mainly due to the quantities of agricultural commodities produced there (Silva et al 2021 ), such as soybeans (Marengo et al 2022 ; Rattis et al 2021 ; Bragança, 2018 ). In recent decades, soybean cultivation in the region has expanded, in part, due to irrigation (Lopes et al 2021 ; Silva et al 2021 ). Irrigation is the highest water-using activity in the country, accounting for around 70% of total use relative to other uses (ANA 2019a ).…”

Integrating Human Rights and the Environment in Supply Chain Regulations

“…However, in the long term, type 1 impacts might turn into type 2 impacts. For instance, the decrease in water sources can lead to water insecurity and negatively affect the right to water and food [42]. Another important example from Brazil's soy sector is the intensive use of pesticides, which has not only polluted local environments, but also contributed to negative health impacts, such as the poisoning of thousands of Brazilian citizens [8].…”

“…Type 2 impacts: Many of the negative externalities of Brazil's soy and beef supply chains have been associated with inter-linked environmental and human rights impacts. Deforestation and land use change in Brazil have mainly been caused by a combination of land grabbing and land speculation, the (largely illegal) logging of timber and the expansion of cattle ranching, indirectly driven by the expanding cultivation of crops such as soybeans [40][41][42][43][44][45]. The deforestation and degradation of the Amazon has attracted much scholarly and socio-political attention, as this rainforest is one of the key elements in the Earth's climate system whose dieback may trigger catastrophic climate change [45].…”

New improved Brazilian daily weather gridded data (1961–2020)

“…(2020); Silva et al . (2021) did not used BR‐DWGD because the number of years covered was insufficient for the long trend analysis they were performing.…”