The Paraiba do Sul river basin (PSRB) plays a central role in Brazil. Over 180 municipalities in the states of São Paulo, Rio de Janeiro and Minas Gerais depend on its waters, through the operation of multipurpose reservoirs in the main stem and tributaries. The PSRB faced a severe drought in 2014. This event motivated discussions on reservoir operating rules, such as reservoir draft prioritization and reductions of minimum flow requirements that were ultimately established by the national water authority (ANA) in coordination with the national power system operator (ONS). New operative rules enacted by ANA Resolution 1382/2015 prioritize water supply over hydropower. It counteracted the concept that hydropower was responsible for reservoir overdraft, risking water supply of cities such as Rio de Janeiro. However, there is scarce technical justification to validate the new rules, much less to assess their impacts in multiple uses of water. The objective of this paper is to compare alternatives of PSRB operating schemes through a simulation approach. Three scenarios were investigated: (i) Reference Scenario, that considers the operation of the river basin prior to the 2014 water crisis, (ii) New Resolution Scenario, which evaluates the operation after the water crisis and considers the new rules set to prioritize water supply reliability; and finally (iii) an Alternative Scenario, based on guide-curve reservoir operation introduced in this article. A long period of inflow measurements - over 86 years - provides a consistent resource to perform this evaluation. The integrated, basin-wide simulations were made with the Water Evaluation and Planning (WEAP) model of the Stockholm Environment Institute (SEI), a friendly and opened framework for future research.

Keywords: Integrated Water Resource Management, Reservoir operating rules, Paraiba do Sul River Basin, WEAP model.