Science Centres: Climate

The Northland floods of July 2007. (Photo: Northland CDEM Group)

Number of rain-days per month near Kawakawa, Northland.

Data series for May only.

Rain-days in Kawakawa

It is often useful to ‘visualise’ the variability of meteorological data by using a diagram format invented by Danish meteorologist Ernest Hovmöller (who incidentally passed away this year). The larger figure (right), usually called a ‘Hovmöller diagram’, shows the number of rain-days per month near Kawakawa, Northland. The data series run from 1960 to 2008 (vertical axis), and are shown by month (bottom axis).

The pattern shows typically higher numbers of wet days in winter, often with 12 to 16 days, and drier conditions in summer, with usually 10 or fewer wet days. Up to 23 wet daysin a calendar month have been estimated by this analysis, in July 1963 and again in July 1991.

The additional figure bottom shows the data series for May only. The number of rain-days has varied from 22 in 2001 down to 2 in 2007, and, subjectively, appears to be more variable in recent years.