Science Centres: Energy

NIWA predicts only a one-in-five chance of above normal inflows

New Zealand daily storage (last updated Monday 10 April 06)

New Zealand’s total hydroelectric lake storage is still in a lower than normal position for this time of year, based on M-co updates (www.comitfree.co.nz) and NIWA monitoring. This is a cause for concern as winter approaches. At the end of March the storage was in a similar position to that of 1992, at less than 70% of the normal storage for this time of year.

For April–June, NIWA’s National Climate Centre (www.niwascience.co.nz/ncc) is predicting normal or below normal river flows in the South Island hydro catchments, indicating that situation is unlikely to improve. The Centre’s predictions show only a 20% chance of above normal April–June flows into the main Southern Alps hydro lakes.

Typically in winter the river flows in the main hydro catchments are relatively low. The South Island hydro lakes are usually replenished by rainfall in spring and snowmelt in summer. Hokitika (which is a representative for West Coast, South Island rainfall) received average rainfall last spring, so why are the lake levels low this year? The low inflows were due to lack of snow available to melt and to West Coast rainfall not ‘spilling over’ into hydro lake catchments.

NIWA is proposing improved ice and snow monitoring systems to upgrade information on these critical sources of flow. An improved understanding of the timing and volume of enhanced flows from snow and ice melt will be critical to good decision-making on hydroelectricity, irrigation, and water supplies.