9: Plan for extremes

Knowing that the daily average temperature is 71○F has little meaning if the daily temperature ranges from 115○F during the day and 27○F at night. We all know the perils of walking across a river with an "average depth of four feet." Planning for extreme ecosystem events (like floods and storms), and not just the average, is prudent.

Extreme natural events like hurricanes, floods and earthquakes are part of the natural system. Planning for them prevents future problems like having to move your house because it wasn’t set back enough from the beach to start with. Photo: J. Gaydos

High variation and diversity are key characteristics of living systems, and averages can mislead people seeking to understand and manage nature. For instance fisheries management based on “average abundance” will fail to account for poor years, and is likely to drive the species extinct. Yet resource users often will prefer to manage for the average.

A major discovery of environmental science in the 20th Century was the ecological significance of ‘natural extreme events.’ Many people still view these kinds of events only as disasters that wreak havoc on society and cause humanitarian tragedies. The emergence of disturbance ecology illustrated the critical roles that rare extreme events like wildfires, hurricanes, droughts, floods, and El Niño Southern Oscillation events have played in sustaining biodiversity and ecological integrity in oceans. As citizens, scientists and decision makers begin to envision a restored Salish Sea that vision must include policies, laws, and management actions that account for extreme but natural events.