Climate in the Wellington Region

Wellington generally enjoys a temperate marine climate, with the warmest months ranging from December to February where temperatures average from 20-30C. The coldest months are from June to August where the temperature can reach a maximum average of 10-15C but generally sit around 12-13C during the day. The coastal location helps to moderate the weather in Wellington so we do not generally experience weather extremes such as snow and very high temperatures. However Wellington is well known for its windy climate. These strong winds come about because of the Cook Strait and surrounding mountainous landscape that creates a sort of wind funnel affect. Because of this Wellington is one of the windiest main centres in New Zealand with a mean annual wind speed of 22km/hr. October is our windiest month of the year with an average of 27 days of wind speeds over 15 knots. North-westerly winds, the warmer winds, dominate in the spring and summer months whereas the cold southerlies become common place in winter. It is estimated that Wellington experiences gale force winds of 75km/hr about 175 days every year.

Wellington experiences an average of 2,000 hrs of sunshine year (around 169 days) .This sunlight presents itself as a hazard in the summer months due to the suns strength in this part of the world. This is due in part to a thinner ozone layer as well as the earth’s proximity to the sun in the southern hemispheres summer (we are closer to the sun than our northern counterparts in summer). However Wellington’s topography can affect solar access because we are a rather mountainous region. North facing slopes generally receive more solar access than their southern facing neighbours. In clearer terms Wellington experiences sunshine about 49.5% of daylight hours with the remaining 54.1% being cloudy or shaded with haze or low sun intensity. During summer and spring Wellington experiences an average of 5-8 hrs of sunshine a day and in winter to autumn this drops to about 3hrs.

Rainfall is another important topic of conversation. In Wellington the annual average rainfall is from about 1250mm per year compared to a national average of about 1400mm. Due to climate change this figure is expected to rise over the next decade. Again Wellington’s mountainous topography creates challenges when dealing with rainfall. During the wettest months June-July the region experiences heightened rates of erosion. The quality of soil also creates problems as Wellingtons soil consists of mainly thin rocky and clay based soils which do not drain very well creating some flooding issues.

During winter as well as experiencing heightened rainfall, colder temperatures and strong winds the Wellington region also experiences frosts in the hillier suburbs.

From this general analysis of Wellington weather important things to consider when building a sustainable structure include

- Building to protect against wind conditions - Considering the topography of the site and building to allow the most sun access - Considering the temperature drops in winter and building accordingly - Corrosion from seawater if applicable to your particular suburb - Considering flooding risks and soil erosion on hillier sites (also due to poor soil material) - Also considering earthquake proofing because of Wellingtons placement atop a fault line

Temperature Ranges

Summer (Dec – Feb): Daytime 19°C – 21°C Autumn (Mar – May): Daytime 14°C – 19°C Winter (Jun – Aug): Daytime 12°C – 13°C Spring (Sep – Nov): Daytime 14°C– 17°C

SUNLIGHT HOURS

The number of hours during which the Sun is visible (black line), with various degrees of daylight, twilight, and night, indicated by the color bands. From bottom (most yellow) to top (most gray): full daylight, solar twilight (Sun is visible but less than 6° from the horizon), civil twilight (Sun is not visible but is less than 6° below the horizon), nautical twilight (Sun is between 6° and 12° below the horizon), astronomical twilight (Sun is between 12° and 18° below the horizon), and full night.

AVERAGE SUNLIGHT HOURS YEARLY

YEARLY CLOUD COVER

The median cloud cover ranges from 56% (partly cloudy) to 71% (partly cloudy). The sky is cloudiest on November 26 and clearest on March 18. The clearer part of the year begins around January 25. The cloudier part of the year begins around May 13.

The median daily cloud cover (black line) with percentile bands (inner band from 40th to 60th percentile, outer band from 25th to 75th percentile).

PRECIPITATION DATA WELLINGTON

YEARLY RAINFALL/PRECIPITATION

HUMIDITY DATA

WIND DATA

The graph below shows the mean number of days per month wind speeds at the Wellington airport that exceed 15 knots and 20 knots for at least one hour per day. A mean of 15 knots was selected as the minimum amount of wind required for most sailors to have a reasonable light wind sail; the 20 knot threshold was selected to identify higher wind conditions.

Extras

Extra data

Hydrological Summary Wellington region (summer 2014-15)

http://www.gw.govt.nz/assets/Our-Environment/Environmental-monitoring/Environmental- Reporting/Summer-2014-15-Hydrological-Summary.pdf

Interactive map shows the yearly average number of hours of direct sunlight received in a day and a breakdown for mornings and afternoons in Wellington City.

http://app.dumpark.com/sunlight/