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 there is potential for dry spells, or irregular hydrological recharging. It does not define an official council position on drought or drought declaration.
The difficult ‘Coronavirus year’ of 2020 was characterised by an extremely variable rainfall pattern in our region.
The year started with overall drought conditions and evolved into a few prominent extreme rainfall events from March onwards, with a mixed bag of westerlies and easterlies. Overall, rainfall was largely insufficient from summer through to winter in both the Wairarapa and the high elevations of the Tararua ranges, failing to achieve full hydrological maintenance and recovery.
This was followed by the wettest spring on record in Wellington, and the third wettest spring on record in Masterton. As a result, the new hydrological year starting 1 June 2020 has been brought to well above average for some sites.
This could be brought again to below average by February, in the absence of replenishment. The climate situation has been therefore of constant ups and downs, as a mature La Niña developed. The ‘normal’ longer-term water balance is becoming increasingly hard to maintain due to climate change and increased high frequency climate variability, with more unreliable weather patterns.
Warm oceanic conditions consistent with La Niña have largely developed north of New Zealand. The projections based on the evolution of the climate drivers for the season (see below) support the continuation of an irregular rainfall pattern, alternating between dry spells and further easterly events (potentially heavy), as La Niña matures.
La Niña is expected to continue to mature, and start to weaken through autumn. A neutral Indian Ocean Dipole (IOD) and a predominantly positive Southern Annular Mode (SAM) are also expected, which are more or less typical of La Niñas.
In summer, La Niñas tend to evolve to relatively dry conditions, with a predominant north-easterly flow bringing thunderstorms in the Wairarapa. There are higher than normal chances of a hot and humid warm season ahead, with possible marine heatwaves.
The rainfall pattern is expected to continue to be highly irregular both on a month-to-month basis and also spatially across the region.
With climate change, droughts are expected to become more severe and frequent 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 evapotranspiration is greatly increased. There is some evidence that our soils are getting drier, and ground water storage may be decreasing, in the long-term.
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|