Precipitation delivery trajectories associated with extreme river flow for the Waitaki River, New Zealand

Abstract. Analysis of large-scale climate conditions associated with extreme river flow is an important first step in the development of predictive relationships for such events. The potential of this approach is demonstrated here for the Waitaki River (a river of national importance in terms of electricity generation), in the Southern Alps of New Zealand. Here, atmospheric circulation anomalies and air parcel trajectories associated with such events are investigated for the period 1960–2010, using the NCEP/NCAR reanalysis and HYSPLIT trajectory model. Results show that atmospheric circulation variation and air parcel trajectories associated with extreme high Waitaki river flow events typically follow two distinct patterns. These patterns are associated with differences in both New Zealand- and hemispheric-scale atmospheric circulation, but all occur under a similar pattern of monthly average pressure anomalies. As such, the results indicate that different precipitation generation mechanisms are captured by a single monthly climate anomaly pattern – providing substantial new understanding of the cascade of processes linking atmospheric to surface hydrological variation in the Southern Alps, and pointing the direction for future process-informed research on sources of predictability for Waitaki river flow.