Water-Energy Nexus with Fast-Changing Operation Constraints in the Metropolitan Region of São Paulo, Brazil

The Metropolitan Region of São Paulo (MRSP) water supply system in Brazil is one of the largest in the world. It supplies water to 21.5 million inhabitants and is upstream of the Metropolitan Region of Campinas. The region has 3.1 million inhabitants in the Piracicaba, Capivari, and Jundiaí River basins (PCJ). The water supply system consists of seven main reservoir subsystems and is currently recovering from the worst drought in history. Cantareira subsystem is the largest in both water supply and storage capacity. It transfers water from the PCJ to the MRSP. There are two newly built water transfer systems: one from the Jaguari Reservoir, directly linked to the Cantareira subsystem, and another from the São Lourenço Reservoir, which is connected to a new water treatment plant. Both water transfer systems operate at very high energy costs. Additionally, there exist conflicts among all water users. The primary role of the two new water transfer systems was to increase water security. Since 2017, the newly imposed minimum required flows at PCJ increased the releases from Cantareira subsystem by 5 m³/s. But this increase necessitates both São Lourenço and Jaguari to operate at almost full capacity as well as at much higher energy cost, while the less expensive Cantareira subsystem stands operating with idle capacity to sustain higher required downstream releases. Currently, Brazil is facing a new record-breaking drought, now in the southeast region, with simultaneous water and energy crisis. In this paper we use SISAGUA, a previously developed nonlinear optimization model, to evaluate the impacts of the modified constraints on the management of the MRSP water supply system, considering energy consumption, operational costs, and water security.