How Extreme was the Drought?

Abstract

In 1993/94 a severe drought on the North Island of New Zealand caused water shortage in the Auckland metropolis. How extreme was the drought? This paper presents comparisons of frequencies of the 1993/94 drought in four North Island regions using different indicators of drought and including both streamflow and rainfall data. With regard to streamflow deficit volume and duration the exceedance probabilities ranged from 1 to 25%; however, the 7-day annual minimum flows in 1993/94 were less extreme with non-exceedance probabilities from 10 to 34%. With regard to rainfall the drought in the Auckland region was most extreme (on average 2% exceedance probability) when annual rainfall totals were analysed compared to seasonal totals (on average 6% exceedance probability for half-annual totals and 13-38% for three-month totals). Thus, the conclusion was that the 1993/94 drought was extreme because of its duration rather than its magnitude.