Atmospheric circulation drivers of lake inflow for the Waitaki River, New Zealand

摘要

Hydro-electricity is a critical resource in New Zealand, and as such improved understanding of the drivers of water resource availability is a key research goal. Large-scale atmospheric circulation is the principal driver of surface climate and water resource variability over New Zealand. Focusing on the Waitaki River (located in the South Island; one of the most important rivers for hydro-electricity in New Zealand), a comprehensive analysis is presented of the large-scale atmospheric circulation drivers of monthly inflow to the three main headwater lakes, Ohau, Pukaki and Tekapo. Analyses are undertaken using composite, correlation, partial least-squares (PLS) regression and cross-wavelet analyses. Environment-to-climate composite analysis indicates that variation in lake inflow is driven primarily by the strength of the NE-SW pressure gradient over the three lakes (i.e. parallel to the axis of the Southern Alps, from which the lakes are fed). Relatively strong winds from a north-westerly direction are associated with high lake inflow; weaker winds from a more south-westerly direction occur during times of low inflow. Climate-to-environment composites of lake inflow, together with correlation, PLS and wavelet analysis, indicate that inflow is described well by the MZ1 and MZ2 New Zealand-based circulation indices, but not larger-scale modes of atmospheric circulation. The MZ1 and MZ2 indices have rarely been considered previously as explanatory variables for water resources in the South Island of New Zealand, but here it is suggested that these indices represent a promising new direction for future studies, particularly relating to season-ahead prediction of water resource availability.