What Is Normal and Why Is It New? Exploring How, Where, and Why Fire Regimes Are Changing through the Lens of California ^†

Abstract

Catastrophic effects of wildfires on human lives and assets have increased the prominence of wildfire in the media and across the scientific community, and the phrase “the new normal” is now widely used to describe the growing magnitude of these impacts. Although the increase in wildfire impacts on humans is occurring globally, the nature of changes to natural fire regimes and the drivers of altered fire regimes are complex and geographically variable. In California, fire return intervals have been altered in nearly opposite directions in different parts of the state, for different reasons. This complexity contributes to widespread misconceptions about how and why fire regimes are changing, and which management decisions are most appropriate given the context. With its diversity in ecosystems and patterns of human development, California encompasses the global issue of sorting out how and why fires are changing and what their corresponding human and ecological consequences are. For example, fire-climate relationships, impacts of vegetation management, and human land use effects vary across the state. As a result of this variation, climate change and forest stand conditions will likely be top contributors to future large fire activity and severity in the northern part of state. In southern California, however, human ignitions, invasive species, and fire weather are the most important drivers. A better understanding of this geographical variability in both the normal and the new normal of wildfire is critical for matching appropriate solutions to the problems.