San Francisco Estuary and Watershed Science

California’s variable hydroclimate is projected to become increasingly volatile in the 21st century. Yet, there is widespread recognition that extreme events, such as record-breaking heatwaves and catastrophic wildfires, are already becoming the new normal. The 2025 edition of the State of Bay–Delta Science (SBDS) presents the current state of the science on climate change and extreme events affecting the Delta and its watershed, and in doing so, generates new insights on knowledge gaps and promising directions for future research. In this essay we present five perspectives to advance science-informed decision-making in the era of climate change and extreme events. To meet these challenges, Delta scientists and decision-makers can leverage the many effective practices that are already in place, such as long-term monitoring programs, collaborative synthesis venues, science-informed decision-making processes, and Tribal and community partnerships. New and sophisticated tools that harness big data are helping to streamline information flows to scientists. Open science practices are facilitating greater collaboration and improving access to more integrated datasets and to models that link different parts of the system. These assets have strengthened innovation and learning across the Delta. Nevertheless, serious challenges remain. Climate change signals can be difficult to detect as a result of the variable hydroclimate. Greater levels of uncertainty as a result of evolving climate models can present challenges for decision-making. Looking forward, the Delta scientific system can help maintain its relevance to natural resource management by strengthening its capacity for collaborative, open, and actionable science. Such an emphasis is required for anticipating and responding to the new climate and weather realities of the 21st century.