Late rain boosts March rainfall totals

News release

3 April 2008

Late rain boosts March rainfall totals

Significant rainfall events at the start and end of March saved most of the region from what was otherwise a very dry month, but figures show rainfall in the eastern Wairarapa is still well below average.

Greater Wellington’s monthly hydrological summary for March shows that overall rainfall totals for the month in the west of the region were 150% to double the long-term averages.

However, the eastern Wairarapa remains in the grip of a drought, with rainfall totals between 50-75% of the monthly average. North-eastern Wairarapa is particularly dry, with Greater Wellington’s Tanawa Hut station receiving only 113mm of rain since the beginning of January, 47% of its long term average.

Despite high overall rainfall totals in western areas, there was little or no rain between the 6th and 29th of March due to a series of anticyclones to the east of New Zealand creating a stable, east-northeasterly flow over the Wellington region.

River flows in most of the region’s rivers were also well below long-term March averages, particularly the Waikanae (57% of average) and Ruamahanga rivers (44%). During March, flows in the Waikanae, Hutt, Wainuiomata, and Ruamahanga rivers fell to levels expected only once every 8 - 10 years.

Aquifer levels across the region have also generally been below long term average levels, with some recording all time low levels since monitoring began, due to both reduced rainfall and river recharge to groundwater systems, and increased irrigation over the dry summer.

Groundwater levels from the deep confined Parkvale aquifer continue to track below long term minimum levels. There have also been reports of some shallow boreholes in the Wairarapa drying up over the summer.

During March, rainfall on the Wairarapa plains resulted in a noticeable increase in soil moisture. In the eastern Wairarapa hills though, soil moisture has not changed significantly since January and the rainfall during the month had only a small impact. Across the whole region, a significant amount of rainfall is still required to return soil moisture to pre-summer levels.

More information is available in Greater Wellington’s monthly hydrological summary or by visiting www.gw.govt.nz/monitoring.

ENDS

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