Robustness to Resilience: Transforming Hydrologic Risk

Risk management in water resources has relied on reducing randomness and smoothing variability. Watersheds are engineered to avoid small but frequent flood events or water shortages - this is the hallmark of a robust system. However, the artificial reduction of natural variability in hydrology creates an increasingly fragile watershed. Invisible risk accumulates each year that the system performs within its design capacity, as development expands into hazard areas and community preparedness and consciousness for the hazard is reduced in its absence. While the benefits of these behaviors are immediate and visible, exposure to catastrophic risk grows invisibly under the surface.

We consider risk as the probability of an adverse event and its consequence. Increasing exposure to risk in engineered watersheds is typically driven by increasing the consequences for equally probable events, as the same magnitude flood causes more damage. However, changing climate and land use alters hydrology such that large flooding is more probable. Uncertainty in assessing the probability or consequence of these events is increased by anthropogenic change.

Robust systems with a fixed capacity become less reliable in a changing environment. Communities will require resilient, adaptable measures for reducing current and future potential risk exposure. Resilient measures – such as floodplain management and integrated water resources management - will require some amount of concession to damage from small but frequent detrimental events in order to reduce the risk of catastrophe.