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3.2.    Vulnerability, Resilience and adaptive capacity – managing for variability

The preceding section has introduced the concept that anthropogenic disturbance of natural ecosystems can significantly affect the ability and vulnerability of such systems to sustain their functioning and to recover following disturbance. This section seeks to ‘un-package’ what these terms imply for the management of freshwater ecosystems, particularly considering the high level of natural hydrological variability that can occur. Freshwater ecosystems and the services they provide society are constantly affected by natural changes in the environment such as seasonal changes in flow or extreme hydrological events such as floods and droughts. This variability in quantity, timing and quality is a central part of what drives the unique ecosystems that can exist (N. Poff 2009), renewing and sustaining higher ecological functioning. These systems are also increasingly under threat from anthropogenic disturbance of such natural variability, particularly where more static environmental conditions are created in order to maintain more dependable water supplies (e.g. abstraction for agriculture, reservoirs) or provide flow regulation (e.g. dams, weirs). While such intervention might serve to reduce the vulnerability of human populations to extreme hydrological events, the vulnerability of the natural environment to such shocks can be increased - with repercussive impacts upon parts of society that depend on the services these affected ecosystems provide. The aim of this section is to outline the fundamental concepts relating to ecological and social vulnerability and how these relate to the growing awareness that managing for hydrological variability is a central part of sustainable water management.