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Evaluating likelihood and consequence: understanding the New Lynn storms of 2017

Nancy E. Golubiewski
Auckland Council Research and Evaluation Unit, RIMU
Publication date:  

In March and April 2017, a series of six storm events within six weeks battered Auckland. Heavy rainfall and ground saturation resulted in landslips and flooding throughout the region. The period has been categorised in public discourse as “unprecedented” in terms of both the severity of the storms themselves and their consequences. Indeed, the 2017 New Lynn storms have become a touchpoint for how major storms, and potentially climate change impacts, can affect Auckland. Yet, very little in the way of critical analysis has been conducted to understand the impacts of these storms.

In order to assess the storms’ consequences and the scale at which they occur, a riskbased planning tool was used to frame a post hoc thought experiment1 analysis. The magnitude of the 12 March 2017 storm and its impacts in four overlapping study areas were quantified across four sectors: buildings, lifelines, economy, and health and safety. The severity of impact ratings across sectors ranged from Insignificant to Moderate. In particular, 4.5 per cent of buildings located in floodplains were considered functionally compromised in the New Lynn suburb (and 1.7 per cent of those in the Whau Local Board). The estimated value of damaged buildings was less than 0.5 per cent of the Whau Local Board GDP. All together, combining the likelihood and consequences in a risk framework resulted in a theoretical “acceptable” or “tolerable” risk rating, depending on the storm magnitude estimate used. In order for this postulated level of risk to be considered more definitive, it first needs to be vetted and affirmed via further stakeholder engagement.

Auckland Council discussion paper DP2019/003

February 2019