Modelling climate change impacts on inflows, lake storage and spill in snow-fed hydroelectric power catchments, Southern Alps, New Zealand.

Climate change impacts on water resources and increasing demand for renewable electricity will have significant impacts on the management of hydroelectric power catchments globally. In New Zealand, where 55% of electricity currently comes from hydroelectricity generation, rainfall over the major South Island hydroelectric power catchments is expected to increase in coming decades, and the seasonality and volatility of that rainfall is expected to change. This paper uses a change factor methodology linked to a model cascade to estimate changes to hydroelectric power catchment inflows in 12 regions of New Zealand. These future river flows are then put through an all of New Zealand electricity system model to examine impacts on flows downstream of the hydroelectric power stations, lake storage, and spill in the large South Island hydroelectric power catchments. An overall 2% increase in annual hydroelectric power catchment inflows over the whole of New Zealand is projected between 2020 and 2050. Seasonal impacts are projected to be larger, with total New Zealand inflows projected to be 10% higher in winter and 6% lower in summer by 2050. Projected changes to inflows are equivalent to between -3% of current total summer New Zealand electricity generation and +5% of winter generation. The four main snow-fed hydroelectric power catchments in the Southern Alps (Pukaki, Tekapo, Clutha, and Manapouri) are predicted to get higher inflows than currently in winter, and lower inflows in summer, with a small increase in annual flows. Modelled changes to inflows and catchment management results in, on average, higher modelled lake storage levels in the snow-fed hydroelectric power catchments in the South Island, which are predicted to spend more time at full lake levels and less time at low lake levels in 2050 than in 2020. The changing inflows, combined with higher storage levels and changes in the electricity system, results in a potential doubling of modelled spill from the large South Island hydroelectric power scheme lakes by 2050. These significant seasonal changes to inflows will better match electricity demand, but the increase to annual spill levels is projected to more than offset any increases in annual inflows over the study period. [ABSTRACT FROM AUTHOR]