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Flood events triggered by extreme rainfall are expected to increase globally with a warming climate. We want to find out more to help improve projections of such events in the future.
To effectively plan for the future in terms of infrastructure and systems design, MBIE and the New Zealand government need an accurate understanding of the expected magnitude and frequency of hydroclimate extremes. While current models allow for some confidence in the direction of regional change (wetter/drier), and even its “average magnitude”, there’s still considerable uncertainty about these extreme events. Changes in atmospheric circulation can lessen or worsen this effect regionally.
This project will advance the work of three other projects:
GCT and LOCH have given GNS Science a large repository of paleoclimate data, including a seasonally-resolved record of flood deposits from Lake Ohau. We will also work on integrating the LOCH and RICE records of change.
The novelty of this project is the introduction of high-resolution climate modelling, integrated with pre-instrumental records of environmental change, using data science techniques like machine learning. This will better accommodate New Zealand’s steep topography.
Modern instrumental records are too short to confidently assess the frequency of extreme weather events. In their place, we turn to what are called “Paleoclimate proxy reconstructions”. These include flood deposits in lake sediments, such as those we recovered from Lake Ohau in the South Island.
That sediment record has laminated mud sequences, with seasonal compositional changes associated with summer rainstorm events. Preliminary analysis indicates a high correlation between flood frequency and the Interdecadal Pacific Oscillation (IPO), a 40-60-year variability in Pacific sea surface temperatures (SSTs) that influences large-scale atmospheric circulation and global rainfall patterns.
We believe this sediment record will help address a key debate: do climate models underestimate decadal-scale SST variability in the Pacific, or is there systematic bias in Pacific SST proxy reconstructions?
There is scientific debate about whether current climate models are producing the right sort of data on this atmospheric circulation in the Pacific.
We have what’s called the Interdecadal Pacific Oscillation (IPO). This is a 40-60-year variability in Pacific sea surface temperatures (SSTs) that influences large-scale atmospheric circulation and global rainfall patterns.
We need better information that might help us answer two major questions:
Our main interest is the time of transition through the Medieval Warm Period to the Little Ice Age. Two things happened during this time. Flood frequency decoupled from global temperature, in contrast to what is expected from most climate models. The first humans arrived in the South Island, raising two intriguing questions:
Dan is an ice sheet and climate modeller working to understand the impacts of climate changes on the Antarctic ice sheet in the past, present and future. His research interests include past deglaciations, parameter uncertainty in ice sheet models, ice sheet-solid Earth feedbacks, ice shelf-ocean interactions and ice sheet surface mass balance. He was a Contributing Author to the Intergovernmental Panel on Climate Change report.
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