Land use change scenarios and their effects on hydropower energy in the Amazon

Highlights

• Four land use and land cover changes scenarios are assessed.

• The SWAT model was calibrated for a large basin between the Amazon and the Brazilian Savanna.

• SWAT flow rate from LULCC was used to estimate hydropower production.

• The LULCC cause great impacts on the water balance of the basin.

• The Tucuruí hydropower response to land use change scenarios is energy inefficiency.

Abstract

Accelerated changes in land use in the regions of the Brazilian Amazon and Cerrado in the last four decades have raised questions about the possible consequences for the regional hydrology. Our study area is the Tocantins-Araguaia River Basin (TAW), focusing on the Tucuruí Hydropower Plant (THP), downstream of the TAW. In this study, we evaluated four scenarios of change in land use and cover for the TAW in which forest areas were replaced by pasture, then by agriculture, then by reforestation vegetation and, finally, by regenerated forest to investigate the impacts on the hydrological components of the basin and the hydropower potential of the THP according to these scenarios. For this evaluation, the SWAT model was used to simulate the streamflow of each scenario, so it was possible to predict the hydropower potential in the TAW under different environmental perspectives. Nonparametric statistics were used to identify the efficiency of turbines in converting the streamflow into energy at the 5% significance level. A reduction was observed in the annual evapotranspiration rate and increments were observed in the surface runoff and streamflow, but despite the increase in flow, there was no increase in the energy produced at the THP due to the inability of the turbines to convert excess water into energy, with losses in the energy production of up to 30% per month and 65% in the annual balance. Our results emphasize the importance of the sustainable management of hydrological basins located in tropical regions and aid in planning and decision-making to create public policies that better meet the demand for the exploitation of natural resources.

Introduction

Management of water resources, according to the availability of water and the production of electric energy, is a main concern for the future of countries that are extremely dependent on hydropower, such as Brazil. Therefore, changes in the hydrological regime, due to climate variability and the dynamics of land use and cover, make these countries highly vulnerable. Brazil relies on its water resources to generate electric energy, as almost 71% of all electric energy is produced by hydropower plants (EPE, 2018; Oliveira et al., 2017).

Hydropower plants are the most widely used renewable energy sources in the world and represent approximately 16% of the world's energy matrix and >65% of the current global energy production capacity (Balkhair and Rahman, 2017). Compared to other renewable energy sources, hydropower is reliable, economical, and highly efficient, with low maintenance costs and large storage capacity (Yuksel, 2010). In this sense, future perspectives on new hydroelectric energy explorations should be considered over the next 20 to 30 years in Brazil using the hydrological potential of the Amazon and the Cerrado (EPE, 2018).

Regarding this, the Tocantins-Araguaia Watershed (TAW) is a large-scale tropical basin and is found in the transition between two Brazilian biomes (Bressiani et al., 2015a), the Amazon and the Cerrado, having its entire territory within Brazil. This basin contains the Tucuruí Hydropower Plant (THP), a large multiple-use plant with a gravity dam, which regulates power generation through Francis-type turbines (EPE, 2018).

Land use and land cover change (LULCC) has resulted in significant interest in environmental studies, especially regarding the world's largest rainforest (Malhi et al., 2008; Lewis et al., 2015; Trumbore et al., 2015). In the last four decades, the Amazon has undergone great fragmentation of its flora, which has had environmental and socioeconomic impacts (Soares-Filho et al., 2006; Soares-Filho et al., 2014; Nepstad et al., 2014; Martini et al., 2015). Other tropical and extratropical forests are also threatened by LULCC (Trumbore et al., 2015). In the forests of the southwest coast of Bangladesh, agribusiness advanced between 1980 and 2016 (Akber et al., 2018). Great agricultural advances have been observed in Ethiopia, in which forest coverage decreased by 83% between 1973 and 2014 (Tolessa et al., 2017). The agricultural expansion in West Java, Indonesia is another example (Bahri, 2020).

The hydrological cycle and hydropower energy production are closely linked to LULCC, so accelerated changes in land cover have been considered one of the factors that most affect freshwater availability (Silva et al., 2018a, Silva et al., 2018b). It is clear to the world scientific community that changes in land use can alter the water balance, causing positive and negative impacts on society. These impacts have already been observed in Europe (De Roo et al., 2001; Guse et al., 2015), eastern Amazonia (Sampaio et al., 2017), Slovakia (Cebecauer and Hofierka, 2008), the southern Amazon (Castello et al., 2013; Dos Santos et al., 2018), Africa (Op de Hipt et al., 2019), Indonesia (Bahri, 2020), China (Wang et al., 2020), and in tropical forests (Bruijnzeel, 1990; Dosskey et al., 2010; Avitabile et al., 2012).

In this current conjecture, hydrological models become powerful instruments in monitoring and prognosis and have evolved a lot over the years (Crawford and Linsley, 1966; Metcalf, 1971; Beven and Kirkby, 1979; Arnold et al., 1998; Migliaccio and Srivastava, 2007; Pandey et al., 2016). For example, the SWAT (Soil and Water Assessment Tool) model has already been widely used for the management of water resources in different basins in the world (Gassman et al., 2014; Abbaspour et al., 2015; Bressiani et al., 2015b; Krysanova and White, 2015; Bressiani et al., 2015a; Tan et al., 2019; Pereira et al., 2016; Silva et al., 2018a, Silva et al., 2018b; Wang et al., 2019). SWAT has been used for modeling the energy potential of watersheds, as described by Kusre et al. (2010), Pandey et al. (2015), Kumar and Sharma (2016), Balkhair and Rahman (2017) and Abera et al. (2018).

Therefore, the objectives of this study follow two lines: (1) to perform an effective diagnosis of the TAW streamflow for power generation at the THP and (2) to evaluate the impacts of different plausible scenarios of land use and cover on the production of hydropower generated in the TAW.