Why forests can mitigate floods of all sizes: Evaluating the scientific basis for forest-based flood mitigation.

Rising flood frequencies and magnitudes are causing the loss of lives, infrastructure damage, and economic disruption, making effective flood management imperative. Nature-based solutions are increasingly promoted, but whether forests mitigate large floods remains a decades-long scientific controversy. Resolving this issue is crucial, as flood management necessitates reliable projections and a sound, scientifically defensible understanding. We show that the conventional deterministic approach uses a non-relevant research question, improper hypothesis, and non-causal experiment, rendering its conclusion that forests have little impact on large floods scientifically indefensible. In contrast, a causal, stochastic approach captures the probabilistic nature of floods and allows for studying anthropogenic effects to hydroclimatic variables through its relevant research questions, falsifiable hypotheses, controlled experiment, and sound physical reasoning. The defensible stochastic approach must replace flawed alternatives, suggesting that forests can mitigate large floods. With rigorous methods, hydrology can support strategies which meaningfully reduce flood risk in an increasingly uncertain future.