High Intensity Rainfall Design System

HIRDS is a simple online tool that can estimate rainfall frequency at any point in New Zealand. 

High Intensity Rainfall Design System (HIRDS)

Despite the best efforts of many city and district councils, intense downpours can quickly overload stormwater drainage systems, causing sewage to flow into nearby waterways and beaches. NIWA's High Intensity Rainfall Design System (HIRDS) offers planners and engineers more certainty about the frequency of high-intensity rainfalls, enabling them to better design stormwater drainage systems and other structures.

HIRDS is a simple online tool that can estimate rainfall frequency at any point in New Zealand. It can be used to estimate rainfall depths for hydrological design purposes, and to assess the rarity of observed storm events.

Go to the HIRDS tool

Users can enter a street address, or click a location on a map, and HIRDS provides storm rainfall depths for durations from 10 minutes to 72 hours, for once-a-year storms, or one-in-100-years, and every contingency in between. A table appears on the screen with a series of depth, duration, and frequency statistics for rainfalls in minutes and hours. 

New features included in Version 3 of HIRDS are:

  • an updated database from New Zealand sites for durations of 10minutes to 72 hours
  • enhancements to the method of regional frequency analysis of high intensity rainfalls
  • extreme rainfall assessments for given climate change temperature scenarios
  • option to generate HIRDS tables either as rainfall depths or as rainfall intensities.

Contact

Graeme Horrell
Engineering Hydrologist
graeme.horrell@niwa.co.nz 

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Commuters struggle with heavy rain in central Wellington. [Dave Allen]

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This map of the 100-year return period 24-hour rainfall total is based on HIRDS.