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.
After a very wet spring last year, most of 2021 so far has been predominantly dry in the Wairarapa, with rainfall just over half of what would be climatologically expected, in some areas.
In particular, April and May were very dry in the east, and the Wairarapa largely missed out on the significant rainfall that fell in Wellington at the end tail of the Canterbury storm, during the last few days of May.
The drought monitoring index from NIWA shows that the eastern Wairarapa remains classed as dry, from a combined meteorological and soil perspective. The standard precipitation index (SPI) indicates that the Wairarapa has been oscillating between moderately and severely dry from April onwards.
As a result, the soil moisture also remains drier than normal for this time of the year for most of the Wellington region, except in the west where the soil moisture replenishment is regarded as normal.
The ENSO (El Niño/Southern Oscillation) phenomenon in the Equatorial Pacific Ocean is now neutral, and is expected to remain so over the next six months. The Sea Surface Temperatures (SST) around New Zealand are largely above average, especially to the east and northeast of the country. The Indian Ocean Dipole (IOD) is expected to remain borderline between negative and neutral, while the Southern Annular Mode (SAM) is predicted to remain mostly positive.
Due to the combined effect of these drivers, climate models are predicting that the remaining of the winter season should continue to be wet in the west and dry in the east on average. However, the warm SSTs mean that the possibility of heavy rainfall events in the east remain high, such as witnessed for the Canterbury storm.
As warmer than average air temperatures are largely predicted for the season, there is the expectation that the Wairarapa will remain dry overall, with deficient hydrological replenishment which could lead to a dry start to spring. Single extreme events could, however, abruptly alter these conditions, such as seen in the exceptional Canterbury event.
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.
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|