Temperature rising

IT'S ALL ON: Young clubbies head into the ocean in a body board race as part of the Gisborne junior surf lifesaving championships at Midway Beach over the weekend. It was another sweltering day but the mercury did not reach the same number as Friday's 37-degree scorcher. Metservice's official high for yesterday was 34.1 degrees at 4pm although in many parts of the city, it was decidedly warmer. January was 0.7 of a degree warmer than the 30-year average (1981 to 2010) — 19.9 compared with 19.2. Picture by Paul Rickard

January's weather has given further solid proof of local climate change, confirming the steady upward trend in Gisborne temperatures.

Strangely the burst of near-record temperatures of the past few days came at the end of a month dominated by cooler southerly winds.

However, analysis of January's weather data shows the month was 0.7 of a degree warmer than the 30-year average (1981 to 2010).

The daily mean temperature was 19.9 degrees, with the 30-year average being 19.2.

While the month's top temperature was a sweltering 37.1 on the 31st, the mercury also plunged to a chilly 7.2 on January 5.

Unusually for January, 19 of the days saw the wind coming from the south or south-east.

Only 11 of the days featured warmer north-west or westerly winds. Otherwise the overall temperatures would have been higher.

The year has started off dry, with rainfall total only 26.6 millimetres — half the January average of 56mm.

On the other hand, the lack of cloud pumped up the sunshine hours for a total of 295 hours compared to the 30-year average of 240.

But like the top temperature, no record was broken, with last year's January setting the sunshine all-time high of 325 hours.

The most important aspect of the month's weather data is only revealed on closer statistical examination.

This shows that January was part of a decisive upward trend in Gisborne's temperatures.

Since accurate and continuous weather recording started at Darton airfield in 1937, MetService has compiled 30-year averages, moving forward every 10 years.

The historical data archived by Niwa (National Institute of Water and Atmospheric Research) show the average January air temperature from 1937 to 1960 was 18.5 degrees.

The first full 30-year average (1941 to 1970) saw that rise to 18.57.

Ten years on, the 1951 to 1980 average had nudged up to 18.8.

The next three sets continued the upwards rise — 19.12 for 1961 to 1990; 19.2 for 1971 to 2000; and also for 1981 to 2010.

January for the 30 years just ended — 1991 to 2020— has hit a mean daily temperature of 19.45.

That means the daily average over the first month of the year has risen by almost a full degree since 1937.

The past ten years have seen some of the warmest Januaries on record, and has pushed the average for that period to the 20-degree mark.

That indicates an acceleration in the rise in temperature, amounting to a degree-and-a-half over 83 years.

For the more immediate future here is the latest outlook from Niwa to the end of April.

For the Gisborne, Hawke's Bay and Wairarapa regions, temperatures are about equally likely to be near average (a 40 percent chance) or above average (a 45 percent chance).

Rainfall totals are most likely to be near normal (a 45 percent chance).

Soil moisture levels and river flows are about equally likely to be near normal (a 40 percent chance) or below normal (a 35 percent chance).