Natural hazards, like much of nature, are part of an interconnected, complex system. While most hazard events seemingly occur independently, they are often correlated and in some cases may greatly influence the probability, frequency, and magnitude of one another. This can be true even when specific hazard occurrences are separated by long distances or periods in time.
The interrelatedness of natural hazards is particularly evident in Colorado’s semi-arid climate. As described in the Colorado Resiliency Framework (2015), three of the most significant hazards of concern in the state are linked together in what has been referred to as the “drought/fire/flood system” (p. 3-7). In this system, the reduced water and moisture availability in a drought increases risks related to wildfire through higher fuel loads (drier conditions, pest infestation, tree mortality, etc.). Severe wildfires can then leave slopes denuded of all vegetation and turn soils into hydrophobic surfaces, preventing rainfall from being absorbed into the ground and in turn rapidly increasing the amount of runoff from heavy rain events. These conditions drastically increase risks related to flash flooding, erosion, and mud/debris flows. As the pattern of these cascading natural hazards suggests, some of Colorado’s most destructive flash flood events can ironically be linked to previous incidents of drought. Many of Colorado’s past disaster events provide clear evidence of these direct relationships between drought, wildfire, and flood, including a recent series of destructive floods in the burn scar areas surrounding Colorado Springs.
While drought, wildfire, and flood hazards are more discernibly related, they are part of the same natural system with direct or indirect relationships to the risk levels for other hazards including extreme heat, severe winds, lightning, soil hazards, landslides, mud/debris flows, and rockfalls. Further, as described in the next section, the projected long-term effects of climate change are expected to influence the risk levels for most natural hazards in Colorado.