Assessing climate change vulnerability in water supplies


To develop a Water Supply Vulnerability Assessment Tool (WSVAT) to guide small communities in assessing their vulnerability to being without drinking water because of climate change effects, and to help identify possible adaptations to meet these challenges.


Climate change will likely cause heavier and/or more frequent heavy rainfalls and very likely cause longer and more frequent droughts in New Zealand. Water supplies may be challenged by making it harder to produce enough water and to supply safe drinking-water.


  • helps small communities qualitatively assess the vulnerability of their water supply to climatic or weather events resulting from climate change, and
  • provides information to help users find out what may be contributing to the vulnerability of their water supply, and what actions can be taken to reduce the vulnerability.

The vulnerability of communities increases if they are more likely to be without drinkable water and they are less able to take steps to stop this happening.

Starting from exposure of a water supply to heavy rain or drought as depicted in the Likelihood Assessment Diagram templates (below) and the figure to the right, the tool:

  • identifies the events that may result
  • guides the user in assessing the likelihood of each event as low, moderate or high 
  • shows the user how to estimate the likelihood that members of the community may be without drinkable water (the outcome).

The tool also provides guidance in making a basic assessment of the community’s ability to take remedial actions. Combining the result of this assessment with the likelihood of the “outcome” produces a vulnerability rating.

For each event, the tool identifies:

  • the characteristics of a water supply that could make it prone to the event, and
  • actions that could reduce the likelihood of each event.

The tool’s appendix contains a quick reference guide to the tool’s use [Appendix A], and a worked example [Appendix C] showing how to assess the likelihood of a reticulated water supply failure using a likelihood assessment diagram.


Water Supply Vulnerability Assessment Tool [PDF, 3.6 MB]

Likelihood Assessment Diagrams – heavy rain or drought templates (external link)

Climate Change, Water Supplies and Health Report [PDF, 1.3 MB]

CARE International (2009) Climate Vulnerability and Capacity Analysis Handbook. (external link)

Delpla I., Jung A.-V., Baures E., Clement M., & Thomas O. (2009) Impacts of climate change on surface water quality in relation to drinking water production. Environment International 35: 1225–1233. DOI: (external link)

Groves D.G., Knopman D., Lempert R.J., Berry S.H., & Wainfan L. (2008) Identifying and Reducing Climate-Change Vulnerabilities in Water-Management Plans. RAND Corporation, Santa Monica, USA. (external link)  

Lange M., Nokes C., Baker V. & Gregor J. Climate Change, Water Supplies and Health: Integrating Technical and Social Sciences [PDF, 387 KB]. Water New Zealand Annual Conference & Expo, Christchurch Convention Centre, 22 - 24 September 2010. [386KB PDF]

Watts G., von Christierson B., Hannaford J., & Lonsdale K. (2012) Testing the resilience of water supply systems to long droughts. Journal of Hydrology 414–415: 255–267. DOI: (external link)

(external link) Wilby R.L. & Dessai S. (2010) Robust adaptation to climate change. Weather 65(7): 180-185. DOI: (external link)

Last modified: