Extreme precipitation of the Waikato region, New Zealand

This study investigates the relationship between regional precipitation and large-scale climate variations. The Waikato is an economically important region of New Zealand that is dependant on a reliable source of precipitation for agriculture and hydroelectric power generation, but is also prone to flooding. Previous long-term precipitation studies have represented this region by a single rain gauge. This study has incorporated more data from more rain gauges and extended the analysis period to 107 years, 1900-2007. The meteorological causes of extreme precipitation events within the region were examined. This identified that heavy precipitation is associated with periods of increased baroclinicity that produces a rapid sequence of mid-latitude cyclones or the presence of a blocking high to the east of New Zealand. A regionally representative time series was used to compare known climate variations to the occurrence and magnitude of extreme precipitation events. Since 1900 there have been no significant variations in the total annual precipitation nor in the occurrence or magnitude of extreme precipitation events, indicating that the precipitation resource in this region is dependable. Events were also uncorrelated to the large-scale Interdecadal Pacific Oscillation, El Nino-Southern Oscillation and Southern Annular Mode indicating that the seasonal probability of extreme precipitation is independent of these circulations. Copyright (C) 2010 Royal Meteorological Society