This webpage provides a brief summary of climate and hydrological conditions in the region. This service is only updated during periods in which closer monitoring is required (regardless of time of the year), in recognition that we are in a dry spell of weather. It does not define an official council position on drought or drought declaration.
Most of the North Island and half of the South Island had been extremely dry during the beginning of the year. The large spatial extension of the drought event has been highly unusual. As a result, the Agriculture Minister declared a large scale adverse event for the entire North Island, and parts of the South Island, in March. The last large-scale adverse event classification for drought in New Zealand was in 2013.
Substantial rains throughout May and June have allowed for a good replenishment of soil moisture levels for most of the North Island. The drought index from NIWA shows, as of late June, that the meteorological drought is over.
However, the large accumulated deficit over the last hydrological year in some areas means that more sustained rain, and in particular above average rain, are still needed in order to replenish the surface and groundwater storage levels.
The Wairarapa finished the hydrological year (1 June 2019 to 31 May 2020) with a deficit ranging between 100 and 200 mm from Masterton to the eastern coast, while the high elevation areas of the Tararuas finished the year with a deficit of around 1,000 mm.
This indicates that longer-term, sustained rainfall is still needed for the maintenance of ongoing hydrological balance (see below for the long-term effects of climate change).
The main climate drivers such as El Niño – Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Southern Annular Mode (SAM) have been mostly neutral, with little bearing on the evolution of the winter season so far. However, the expectation of a developing La Niña towards spring may contribute towards more easterly flows further down the track.
La Niña is normally associated with abundant winter rain for most of the region, evolving to predominant easterly flows and warmer than normal temperatures during spring. Overall, this is a good set up for the hydrological replenishment during winter.
International climate models suggest that for the remainder of winter the region will continue to receive above average rainfall towards the west coast, and average to below average on the eastern coast. There is a high chance of at least one additional extreme rainfall event developing before the end of the season, which could considerably increase the total seasonal accumulation in some areas.
Temperatures should continue to be above average for the seasonal average. In light of the warm Sea Surface Temperatures around New Zealand, it is unlikely that extreme cold waves and frost periods would be very long-lasting.
With climate change, droughts are expected to become more severe, and to occur more frequently in the Wellington region, particularly in the Wairarapa. Even if international climate policy efforts successfully contain global warming under 1.5-2 degrees (the Paris Agreement’s ambition), it is important that we build water resilience and be prepared for a “new normal” climate pattern, significantly drier than in the past.
We note that the warming temperatures also mean that the evapotranspiration of soil and plants is greatly increased, and so our soils are already getting drier in the long-term, and ground water storage is decreasing, even during years when the rainfall is close to average.
How different has recent rainfall/soil moisture been compared with the same time in previous years?
Click on the links below to see the relevant anomaly map
|Kapiti Coast (lowland)||Otaki at Depot|
|Kapiti Coast (high altitude)||Penn Creek at McIntosh|
|Porirua||Horokiri Stream at Battle Hill
|Wellington City||Kaiwharawhara Stream at Karori Reservoir|
|Hutt Valley (upper catchment)||Hutt River at Kaitoke Headworks|
|Upper Hutt||Upper Hutt at Savage Park||Upper Hutt at Savage Park AQ|
|Wainuiomata||Wanuiomata River at Wainui Reservoir|
|Wairarapa (high altitude)||Waingawa River at Angle Knob|
|Wairarapa Valley (north)||Kopuaranga River at Mauriceville|
|Wairarapa Valley (Masterton)||Ruamahanga River at Wairarapa College||Wairarapa College AQ|
|Wairarapa Valley (south)||Tauherenikau River at Racecourse||Tauherenikau River at Racecourse|
|Wairarapa (north-eastern hills)||Whareama River at Tanawa Hut||Whareama River at Tanawa Hut|
|Wairarapa (south-eastern hills)||Waikoukou at Longbush||Waikoukou at Longbush|