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

Abstract

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.

Floods in the Southern Alps of New Zealand: the importance of atmospheric rivers

“…Indeed, northwesterly airflow under this situation is associated often with high precipitation over the Southern Alps (e.g. Pearson and Henderson, 2004;Salinger and Mullan, 1999) and furthermore to high upper Waitaki lake inflow at both the monthly and event scale (Kingston et al, 2016;Kingston and McMecking, 2015).…”

Atmospheric Rivers and Weather Types in Aotearoa New Zealand: A Two‐Way Story

“…Our results also suggest that the available moisture in the subtropical regions east of Australia could be a key variable to include in future studies, especially for the northern parts of ANZ. The question of the moisture sources for ARs could be addressed for example, by using back trajectories or Lagrangian approaches-as already indicated by Kingston and McMecking (2015) for flooding events in the Southern Alps. Latent heat fluxes at the interface between atmosphere and oceans (e.g., over Tasman and Coral seas) or continent (Australia) are intuitive candidates that could favor increased moisture in the lower troposphere, more likely to lead to AR formations.…”

Understanding and predicting large-scale hydrological variability in a changing environment

“…The back-wards trajectory thus reveals how parcels of air reach the hydrologically significant event and interact with larger-scale weather types and/or circulation patterns (e.g. Kingston and McMecking, 2015;Sahin et al, 2015). Alternatively to tracking the physical trajectory of air parcels, the geochemical characteristics of precipitation delivered to the land surface can also provide information on air-mass characteristics, precipitation source and moisture recycling from the surface to the atmosphere (e.g.…”

“…Seasonal lag-lead relationships typically focus on the role of slowly-varying components of the climate system, particularly SSTs (e.g. Kingston et al, 2013;Ionita et al, 2017), whereas on daily to weekly scales it has recently been shown that by focussing on water vapour transport instead of directly on precipitation has the potential to increase the forecast horizon by up to three days (Lavers et al, 2014).…”