Summary

Bodeker Scientific led a major project for the New Zealand Dam Safety Hydrology Group (DSHG) to modernise the estimation of Possible Maximum Precipitation (PMP) for dam safety applications across New Zealand. The work was undertaken with specialist contributions from Headwaters Hydrology, NIWA and Riley Consultants.

PMP represents the greatest precipitation that could plausibly occur over a catchment within the physical constraints of the weather and climate system. It is an important input to the design and safety assessment of dams, particularly where the consequences of failure are high.

The project built on the established New Zealand “Blue Book” methodology that has underpinned PMP assessments for several decades. The project team automated and standardised this methodology, while also investigating how modern datasets and analytical techniques could improve the underlying estimates. These included high-resolution digital elevation data, contemporary precipitation observations and reanalyses, extreme-value statistics, and large ensembles of regional climate-model simulations.

A major innovation was the explicit treatment of climate change. The project developed approaches for estimating how extreme precipitation, and therefore PMP, may change as the atmosphere warms, providing multiple lines of evidence from physical scaling relationships, observations and climate-model simulations.

The resulting system was designed as a web-based PMP assessment tool. Users can define a catchment and obtain PMP estimates across precipitation durations ranging from one hour to five days, greatly improving the consistency, transparency and reproducibility of PMP assessments.

The project provides a foundation for progressively incorporating improved datasets, methods and climate-change science into New Zealand dam-safety hydrology.

Related Publications

Bodeker, G.E.; Barrett-Garnier, O.; Kittridge, M.; Carey-Smith, T.; Rosier, S.; Improved Possible Maximum Precipitation (PMP) Estimates for New Zealand, 2024. available here.