Wairoa: hundreds of landslides triggered by heavy rainfall in New Zealand

The last few weeks have seen high levels of rainfall in the Wairoa area of New Zealand.  Most notably, in late march a series of major rain events triggered multiple landslides in this important agricultural area within Hawke’s Bay.  RNZ has an excellent report on the situation as per late March, noting that:-

A Wairoa farming leader says the relentless rain still falling in northern Hawke’s Bay is like a recurring nightmare and farmers are beside themselves.  Federated Farmers Wairoa branch chair Allan Newton said conditions were now 10 times worse than after last week’s deluge. Consistent rain meant the soil could not soak up any more water and the ground had turned liquid, he said.

The RNZ report includes a couple of images of examples of the landslides, including this one:-

Landslides in the Wairoa area of New Zealand. Image by Wairoa Helicopters via RNZ.

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These landslides are visible even in the daily imagery collected by Planet.  For example, this is an area affected by these failures (the image is in the area of 38.827, 177.618):-

Satellite imagery showing some of the new landslides in the Wairoa area of New Zealand. Image copyright Planet, used with permission. Image dated 10 April 2022.

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As a comparison, this is the same area on 1 February 2022:-

Satellite imagery showing the area affected by landslides in the Wairoa area of New Zealand. Image copyright Planet, used with permission. Image dated 1 February 2022.

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Below you should be able to see a slider allowing comparison of the before and after imagery:-

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As the original image shows, this is an area that is heavily affected by landslides even before this year, but these rainfall events have triggered multiple shallow slips.  It is notable that these are located primarily in the deforested grassland areas – there is little evidence of new failures in areas of woodland – and there appears to be a strong control by slope aspect (I see fewer slips on the westward facing slopes).

These shallow landslides affect an area that is much larger than I have shown in the images.

The slips will likely cause short and medium term challenges for the farmers, who have lost valuable grazing land, and the sediment into the channels will also have downstream impacts.  The sediment in the river is clear in the photograph at the top of this piece.

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Acknowledgement

Planet Team (2022). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/