Meteorological conditions effects in the Brazilian Electricity Sector: A Comparative Analysis between Challenging Dry Years (2020-2021) and Favorable Wet Years (2021-2022)

Brazil is a country of continental dimensions with a great diversity and complementarity of energy resources. Currently, 84% of its electrical matrix is composed of renewable resources which 56% are hydro, 14% are wind, and 5% are solar power. As a result of this share of renewables in the power matrix, the energy sector is heavily dependent on rainfall and weather conditions. Furthermore, the analysis of the complementarity of energy resources is fundamental for the planning and operation of the electricity system by the national operator (ISO) due to the intense expansion of renewable energy generation that has been taking place in recent years, especially wind and solar. This is due to the wind and solar sources compensating for the possible decrease in hydroelectric power production during drought periods. This complementarity reduces dependence on a single source and strengthens the resilience and security of the electricity system in the case of climatic variations and contingencies.

In recent years, Brazil has faced challenging moments in the operation of the system due to drought periods in key regions for the generation and storage of energy in reservoirs, the last being an important factor for the operation security of the National Interconnected System (NIS). These unfavorable conditions were persistent from 2013 until mid-2021, with a pattern change in the last two years, when it had favorable hydrological conditions. Therefore, the focus of this paper is to analyze the meteorological conditions and the impacts on the energy sector at this transition point, when it had consecutive wet periods with opposite behaviors, the 2020/2021 which was unfavorable and the 2021/2022 which was favorable.

During 2020 and early 2021, the rainfall regime presented values too far below climatology in the main river basins relevant to the SIN. This is because the South Atlantic Convergence Zone (SACZ), which is typically associated with rainy periods, moved further north than usual. One of the primary influences of this system is the maintenance of rainfall during the summer season in South America, originated by the combination of large-scale dynamical systems and their effects, identified through significant long-wave radiation and precipitation anomalies.

Since the end of 2020, the unfavorable conditions have led the sector to take extreme extraordinary measures to guarantee the energy supply and the security of the system, such as the activation of more expensive thermoelectric plants that were not initially expected to generate, the creation of an additional charge to the consumer's tariff called the water scarcity tariff flag, the holding of emergency auctions to make new thermoelectric plants viable in record time, the authorization to import electricity from other countries at high prices, the implementation of the demand response program, among other measures.

During the wet period of 2021/2022, still influenced by the La Niña phenomenon and with the SACZ events positioned over the main SIN basins, there was an increase in the frequency of rainfall in the country, which resulted in above-average precipitation accumulations in these regions.

The start of the rains in the second half of October 2021 was fundamental in preventing Brazil from declaring the need for energy rationing. The rainy season from 2021 to 2022 was favorable, which allowed for greater use of run-of-river hydroelectric generation and the recovery of the storage level of the system's large reservoirs. In five months, the energy sector went from one of the biggest crises in recent years to an extremely favorable scenario. In fact, this change in condition has brought us a high cost of regret in relation to the extreme measures adopted at the end of 2021, such as the emergency contracting of thermal power plants at high prices, which came into operation in the system when they were no longer needed and when the cost of energy was already at low levels.

Therefore, in order to obtain the main factors that caused the change in rainfall patterns in Brazil between the two periods of 2020/2021 and 2021/2022, this study will analyze the dynamic factors associated with the formation of the SACZ in the wet period together with the impacts of the effect of the La Niña phenomenon.

Given the importance of meteorological conditions for the Brazilian energy market, it is essential to understand and monitor the climatological elements that directly affect the country's hydrological cycle and its renewable energy resources. More than that, it is extremely important for Brazilian energy planning to anticipate meteorological trends, in order to enable system operations that exploit the energy availability optimally.