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 have been extremely dry since the beginning of the year. The large spatial extension of the event has been highly unusual. As a result, the Agriculture Minister has declared a large scale adverse event for the entire North Island, and parts of the South Island. The last large-scale adverse event classification for drought was in 2013.
While the dry spell continues over most of the country, the situation is slowly improving. Northland has received up to 80% of the normal monthly rain in some areas so far this month, whereas in the Wairarapa the rainfall continues to be more deficient. An upper level through of low pressure is moving into New Zealand this weekend, with a heavy rainfall warning currently in place for the Wairarapa. While there is low confidence for the exact location and magnitude of the event, there is a good chance of a significant replenishment bringing relief for farmers.
For the Wellington Region as a whole, the national drought index from NIWA shows that the level of severity of the combined meteorological dryness is slowly decreasing, i.e., conditions have been progressively improving. The entire region is still classed between dry and extremely dry. Currently, the long-term weather forecast is promising, showing that most of the region should expect at least 100mm of rain between now and into the second week of April. As mentioned earlier, there is a chance that a good portion of this rain may fall in the Wairarapa this coming weekend, depending on the movement of the upper level through and the accompanying easterly flow expected to follow the system.
The main climate influencers (i.e. “climate drivers”) such as El Niño – Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are currently neutral, and therefore having little bearing on the evolution of the autumn weather pattern.
The Southern Annular Mode (SAM) has been on the negative side over the last few months, and is currently back to neutral. This climate mode helps explain the unusually strong south-westerly flow that has persisted from late spring into summer. Strong winds promote evaporation, and are a contributing factor to drying the exposed soil.
The westerly pattern has also prevented the formation of summer thunderstorms and moisture input from the subtropics, which would normally manifest during the summer months, when the sea surface temperature is sufficiently warm.
March temperatures have been between half and a degree above average in the Wairarapa, which is closer to normal compared to February. As we move into the cold season, temperatures and solar radiation should become a lesser factor in contributing to the dry pattern. An assessment of the cumulative rainfall for key Wairarapa sites from 1 December onwards shows that the current accumulated rainfall levels are comparable to 2014/2015, 2012/2013, and the 1997/1998 El Niño event.
River flows and water restrictions
Larger rivers that originate from deep in the Tararua Range have benefited from a few small ‘freshes’ recently. This has provided periodic relief from restrictions for water users. Smaller Wairarapa rivers and streams that don’t have extensive hill country catchment have not seen any rainfall recharge and flows remain very low and restrictions widespread. There are no extreme low flows or restrictions in place in the western part of the region (Hutt Valley and Kapiti Coast).
With climate change, droughts are expected to become more severe, and to occur more frequently in the Wellington Region. 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.
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|