Downstream Willingness to Pay for Upstream Nature‐Based Solutions to Improve Water Security in a Thirsty Brazilian Megacity

This is the first study to assess public attitudes and willingness to pay (WTP) for water security in one of the global mega‐cities facing Day Zero by taking Nature‐based Solutions (NbS) in the upstream basin feeding the city. Data were collected using in‐person interviews in the São Paulo Metropolitan Region (SPMR) in Brazil. The survey included a state‐of‐the‐art discrete choice experiment (DCE) to estimate WTP for a wide range of possible water security improvement scenarios. Public recollection of past water supply disruptions gradually fades over time as does its impact on choice behavior in the DCE until people remember the extreme restrictions and rationing experienced during the close to Day Zero episode in the SPMR between 2014 and 2015. The latter sparks a significantly higher renewed interest in and WTP for improved water security. Public WTP for a reduction of 10% in frequency and 12 hr in duration of future water shortages is US$8 per month to implement agroforestry in the Jaguari basin. The increase in respondents' water bill corresponds to almost 1% of their disposable household income for the most consequential improvement in water security, indicating that water security is a high priority. The estimated WTP values show that there is sufficient support to provide the critically needed additional financial resources to continue and expand the existing Payments for Ecosystem Services scheme “Conservador das Águas” in the upstream basin feeding the SPMR.