We hope that these materials have been helpful in highlighting the limitations and uncertainties of the science of hydrology, as well as exciting new advances in our application and understanding of the field.

Here are some key takeaways:

• Hydrologic science plays an important role in multiple overlapping environmental statutes (CWA, SDWA, CAA, EPCRA, RCRA, and CERCLA, among others) as well as several aspects of natural resources and takings law.
• Water resources around the country are becoming strained by droughts, floods, and water quality issues­—sometimes in the same location. Many of these challenges are exacerbated by human impacts such as rapid urban development, infrastructure operations and maintenance, and sea level rise.
• The field of hydrologic science is evolving, with new types of data availability and modeling processes increasing the potential complexity of analysis and forecasting. The most appropriate model should be selected for a given project, balancing complexity, data availability, scope, and computational expense.
• Dealing with these issues is complex and involves a combination of engineered, nature-based, and nonstructural (behavioral) approaches. Any selected approach should consider tradeoffs between costs, co-benefits, environmental and social sustainability, and resilience.