Climate variability, climate change, and energy

Knock-on effects: instruments measure temperature and snowfall at Rose Ridge in the Southern Alps and low water at Lake Tekapo, May 2003. Winter snowfall helps recharge the lake following spring melt. (Photos: Bob Newland and Ian Halstead)

Graph of New Zealand mean temperature shows that the temperature has generally been increasing since about 1900. (Click for detail)

Jim Renwick explains how New Zealand’s energy needs and supplies depend on climate.

The security of supply of the New Zealand electricity system has been called into question in recent years, with two climate-related energy 'crises' already this decade. Much of the hydro storage variability that affects the dry-year risk is related to climate variability. To manage the changing risks, we need to quantify links between climate variability and our renewable electricity resources.

Three major factors come into play: the El Niño/Southern Oscillation (ENSO) cycle, the Interdecadal Pacific Oscillation (IPO), and long-term climate change influenced by increasing greenhouse gases (see box below). All three affect the westerly wind circulation in our region; this in turn controls rainfall in the Southern Alps and key hydro catchments, influences the national capacity for wind generation, affects the coastal wave climate, and influences ground-level solar radiation. Moreover, all three factors influence temperature and rainfall patterns in many major population centres, strongly affecting domestic demand for electricity. NIWA research is helping understand the basic mechanisms of these influences, and is helping the energy sector understand the implications for renewable energy supply and demand (see box below, 'Renewables and climate change: current research').

Climate variability

Recent low inflows to New Zealand hydroelectricity generating lakes (for example, mid-2001) are actually rather mild, compared to the dry period of the mid-1960s. NIWA research shows that the period 1977-98 was relatively wet on the South Island west coast and in the headwaters of key southern lakes, compared to the preceding 30 years. Such long-term variability in lake inflows and rainfall is related to alternating phases of the IPO, a recently identified large-scale pattern of climate variation that affects the whole Pacific basin. The IPO may be changing phase again, back to the pattern observed before 1977. If this occurs, low inflow periods for South Island lakes will be more frequent (and possibly more severe) over the next 20-30 years than was the case during 1977-98. This would pose a significant risk for the security of electricity supply.

Climate change

In the longer term, climate change may mean stronger winds over New Zealand, more reliable flows into our hydro lakes, and a larger capacity for wind-generated electricity. However, climate change will also introduce big changes in the seasonality of hydro storage, because it will change the accumulation and melt of snow in the Southern Alps. NIWA is working to quantify this effect, to enable the energy sector to better plan for the coming 50 years.

A warmer climate will also change the seasonality of demand for electricity, increasing demand for cooling in summer, but decreasing the need for heating in winter. Changes in water availability may lead to big changes in energy needs for irrigation. NIWA is developing risk-management tools to help the energy industry plan infrastructure development, in the face of changing and variable climate patterns.

Teachers’ resource for NCEA AS: Science 90313 (2.2); Geography 90337 (2.7). See other curriculum connections at