Coastal Hazards and Climate Change. A guidance manual for Local Government in New Zealand

Climate change will not introduce any new types of coastal hazards, but it will affect existing hazards. Coastal hazards in many areas are expected to increase as a result of the effects of climate change. As development of coastal areas and property values increase, the potential impacts of coastal hazards increase. There is increasing confidence in the predictions of the effects of climate change. Sea level has risen in New Zealand by about 0.25 m since the mid-1800s (historical sea-level rise has been approximately 0.16 m per century), and this rise is expected to accelerate. Under the most likely mid-range projections, sea level is projected to rise a further 0.14 - 0.18 m by 2050, and 0.31 - 0.49 m by 2100. In developing scenarios, it is recommended that at least the most likely mid-range scenario for sea-level rise is used: it is recommended that council staff use a figure of 0.2 m by 2050 and 0.5 m by 2100 when considering sea-level rise in projects or plans. Sea-level rise and other climate change effects, such as increased intensity of storms and changes in sediment supply to coastlines, are expected to modify coastal hazards in many areas around New Zealand. Because climate change effects are very gradual, land-use planning decisions must have long-term horizons to accommodate the lifetimes of structures. It is vital that planning occurs now for climate change effects, particularly where decisions are being made on issues and developments that have planning horizons and life expectancies of 50 years or more. This Guidance Manual is intended to help local authorities manage coastal hazards by: providing information on the effects of climate change on coastal hazards; presenting a decision-making framework to assess the associated risks; providing guidance on appropriate response options. Three main types of coastal hazard are addressed: coastal erosion caused by storms and/or long-term processes; coastal inundation caused by storms or gradual inundation from sea-level rise; coastal inundation caused by tsunami. This document recommends Risk Management standard AS/NZS 4360 as the undergirding standard for all risk assessment procedures and processes relating to coastal hazards in a changing climate.