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.
Updated 20 December 2022.
Next update due when there is a significant change of conditions, as the situation evolves.
After a very wet year overall, spring rainfall remained above average over the Wairarapa. Even though December entered a drier and more mixed pattern, soil moisture levels remain within normal, with significant thunderstorms developing in the lead up to Christmas.
The global climate remains ‘phase-locked’ into a mature La Niña, coupled with a positive Southern Annular Mode. This translates into more frequent marine heatwaves around New Zealand, with a predominantly warm and humid north-easterly flow. This pattern helps explain the positive rainfall anomalies in the Wairarapa observed during most of 2022, with significant ‘atmospheric river’ events.
Most dynamical climate models are predicting the persistence of high pressures south-east of New Zealand into summer, which will lead to continuing warmer than average seasonal temperatures. A prevailing La Niña easterly flow is expected to alternate with westerlies at times. Humidity corridors (atmospheric rivers) under the influence of moist tropical air masses are expected to continue to affect the region over summer.
There is a high likelihood that at least two ex-tropical cyclones will affect the country during the warm season. For the Wairarapa, the total rainfall accumulation during the warm season will also largely depend on the formation of localised thunderstorm activity, which is typical of humid summers under north-easterly flows.
The ‘normal’ longer-term water balance is becoming increasingly hard to maintain quite possibly due to climate change influences, and increased high frequency climate variability, with more unreliable weather patterns.
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 enhance our 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 will greatly increase. There is some evidence that our soils are getting drier, and groundwater storage may be decreasing, in the long-term.
Browse the data
How different has recent rainfall/soil moisture been compared with the same time in previous years?
|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|
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