Council has received the latest update to the High Intensity Rainfall Design System (HIRDS), providing the region with its most accurate and up-to-date information on extreme rainfall events. Earth Sciences New Zealand (ESNZ) prepared the new rainfall dataset, which incorporates rainfall records up to 2024 and includes significant improvements to rainfall modelling methodology.
HIRDS is a nationally recognised tool used to estimate the frequency and intensity of heavy rain events at locations across New Zealand. The updated data is essential for flood modelling, infrastructure design, stormwater management, and climate change assessments across Marlborough.
Council’s Hydrology Scientist, Charlotte Tomlinson, says the update is an important step for the region’s resilience planning. “The improved rainfall data gives us a clearer picture of extreme weather patterns across Marlborough, especially in our most vulnerable areas. This ensures our flood protection, infrastructure planning, and climate adaptation work is based on the best available science.”
The new HIRDS dataset shows notable changes across the region compared to the previous version. Rainfall estimates have generally decreased in the southern inland mountain ranges but increased across the Richmond and Bryant Ranges, Marlborough Sounds, and south-eastern coastal areas. In the Wairau River catchment, where most Council flood protection assets are located, rainfall estimates have decreased in southern tributaries and increased in northern ones.
“These updates reflect not just new data, but a much-improved methodology that matches what we’re seeing on the ground,” Ms Tomlison said. “This will help Council make sound decisions for managing flood risks and adapting to climate change.”
The updated HIRDS dataset will now be used in Council’s floodplain management, climate change, and risk reduction work programmes. It will remain the region’s primary rainfall dataset until the release of the next national HIRDS update, expected in October 2026.
To learn more about Council’s hydrology monitoring, visit our website.
