New Zealand's Extreme Rainfall Examined With IMERG

Two extra-tropical cyclones recently dropped very heavy rain over New Zealand. Tropical cyclone Debbie dumped extreme amounts of rain over the northeastern coast of Australia when it hit the Queensland coast on March 28, 2017. After drenching northeastern Australia Extra-tropical Cyclone Debbie transported a river of water over New Zealand last week. Debbie's remnants dropped heavy rainfall that caused widespread flooding near the Bay of Plenty on New Zealand's northeastern coast. Thousands of residents needed to be evacuated with extra-tropical cyclone Debbie.

This week extra-tropical cyclone Cook added to the recent unusually heavy rainfall over New Zealand. Tropical Cyclone Cook earlier killed one person and dropped a reported 300 mm (11.8 inches) when it hit New Caledonia first on April 10, 2017. New Zealand's Bay of Plenty and Hawkes Bay on the northeastern coast of the North Island were again the most effected by this second extra-topical cyclone to hit New Zealand.

New Zealand's Extreme Rainfall Examined With IMERG

NASA's Integrated Multi-satellitE Retrievals for GPM (IMERG) data were used to estimate the total amount of rain that fell in the area from southeastern Australia through New Zealand. IMERG estimates of rainfall accumulation from April 5-14, 2017 were created at NASA's Goddard Space Flight Center in Greenbelt, Maryland using data from several satellites in the GPM constellation of satellites. Rainfall data was produced in near-real time at half hourly intervals from NASA's Integrated Multi-satellitE Retrievals for GPM (IMERG) data. The data were calibrated with measurements from the GPM Core Observatory as well as rain gauge networks around the world. IMERG rainfall totals have been adjusted to reflect observed values in other similar extreme rainfall events.

IMERG data indicates that rainfall totals of over 80 mm (3.1 inches) were common in many areas of New Zealand. IMERG shows that the two extra-tropical cyclones and other low pressure systems dropped heavy rainfall on both the North and South Islands of New Zealand. This IMERG rainfall analysis indicates that an area west of Wellington on the South Island received some of the heaviest rainfall during this period.

New Zealand's Extreme Rainfall Examined With IMERG

Images and caption by Hal Pierce (SSAI/NASA GSFC)