The Vulnerability Sourcebook sourcebook provides a standardised approach to vulnerability assessments covering a broad range of sectors and topics (e.g. water sector, agriculture, fisheries, different ecosystems) as well as different spatial levels (community, sub-national, national) and time horizons (e.g. current vulnerability or vulnerability in the medium- to long-term). It refers to vulnerability as ‘the degree to which a system is susceptible to, and unable to cope with, adverse effects of climate change, including climate variability and extremes. Vulnerability is a function of the character, magnitude, and rate of climate change and variation to which a system is exposed, its sensitivity, and its adaptive capacity.’ Based on this definition, the Vulnerability Sourcebook distinguishes between and assesses four key components that determine whether, and to what extent, a system is susceptible to climate change: exposure, sensitivity, potential impact and adaptive capacity.