Abstract:
Understanding variation in extreme precipitation values is vital to climate researchers as this will enable scientists to produce feasible short-term to long-term forecasts for regional rainfall climates. In order to enhance our understanding, we need to investigate the nature of precipitation (namely rainfall) over local and regional scales in relation to elevation, wind direction frequency and large-scale atmospheric circulation modes such as the Southern Annular Mode and the El Nino Southern Oscillation, as these factors are important drivers of weather regimes across New Zealand. The analysis presented here of these drivers is conducted for the East Cape region of New Zealand across all four seasons with a focus on the summer and winter periods. By using Principal Component Analysis and Cluster Analysis, four primary topographic rainfall regions are identified across the study area. This rainfall regionalisation provides a spatial framework for exploration of extreme rainfall-SAM and SOI relations. Subsequent analysis of the rainfall regions suggests seasonal differences are present in association with elevation, wind direction and SAM and SOI activity. For example, the Gisborne district shows a significant positive relationship with the SOI during November indicating La Nina event activity. There is also a positive significant relationship between the frequency of easterly winds and rainfall extremes at Gisborne, hikuwai 4 and Matawai. In contrast, the Te Araroa rainfall station indicates a negative association with easterly winds. Many of these findings are consistent with numerous other climate studies conducted in New Zealand. This research has also provided a basis for future climate studies in the East Cape Region as it appears to contain a unique rainfall climate compared to the rest of New Zealand.
