A brief summary of climate and hydrological conditions in the region.
This service is regularly 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. Outside of dry periods, less frequent updates synchronise with our latest seasonal outlooks.
Updated 27 March 2024
Next update due when there is a significant change of conditions or a new seasonal outlook.
Background
The current El Niño/Southern Oscillation (ENSO) event is almost over. This has been a highly unusual, or ‘non-traditional’ El Niño. On the diagram below we can see that normally El Niños are associated with cooler oceanic temperatures around New Zealand. However, the waters remained very warm with high evaporation for most of summer. The weather patterns have been a mixed bag with alternating flows, and severe thunderstorms which would not normally occur in El Niño years.
Current situation
The total summer rainfall in the region was about half the long-term average for most places, but rainfall was closer to normal for Upper Hutt, Kāpiti and the northwestern part of the Tararua Ranges. The eastern Wairarapa was one of the driest spots, with total accumulations only between 20 and 40% of the seasonal average. This pattern has remained mostly unchanged throughout March. The national drought index, which is updated daily (see below), is indicating most of the region to be very dry (except the Kāpiti Coast). Thanks to regular (albeit modest) showers and reduced evapotranspiration as we passed the equinox with cooler temperatures, the more severe areas previously classed as ‘extremely dry’ have eased slightly. Soil moisture deficit levels are comparable to 2020 and 2021, but not as severe as 2020 for the most part.
After maintaining relatively good baseflows throughout summer, several larger rivers in the Wairarapa (including the Ruamāhanga, Waingawa, Pahaoa and Mangatarere) have fallen below minimum flows in the past week, meaning restrictions for irrigators and other water users have come into force. Several other rivers are close to minimum flow and most of the valley floor streams have been at very low flow (with water users under restriction) for several months now. Given the time of year and forecast for the next couple of weeks, restrictions in the larger (Tararua-fed) rivers may not be prolonged or sustained. However, the broader meteorological outlook (see below) suggests a good likelihood of dryness in the Wairarapa persisting for some time yet, especially to the east; this means the valley floor streams and eastern hills rivers could remain low.
Meteorological outlook
International climate models are predicting that the current El Niño will dissipate towards the end of autumn. A La Niña might start forming during winter (about 60% chance according to NOAA), but it’s still too early to make a firm prediction considering typically poor skills of most ENSO models this time of the year. Regardless, there is usually a lag in the atmospheric response to the climate drivers. It’s looking likely that the Region will remain drier than average for a little longer before returning to normal. The extended climate projections are currently suggesting a 40-50% chance that rainfall could remain below average in the eastern Wairarapa until May-June, before progressively returning to normal into winter and beyond.
Climate change
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 were to 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 more unreliable climate patterns with both extreme dry and extreme wet periods. We note that the warming of the land also means that evapotranspiration will greatly increase, so the soil will likely need more ongoing rain to maintain ideal moisture levels, compared to what it has needed in the past.
While the last three years have been incredibly wet thanks to a persistent La Niña, there is some evidence that our soils are getting drier, and groundwater storage may be decreasing, in the long-term.
View the latest national drought index state
View the national drought forecasting dashboard
View the latest seasonal report:
Climate drivers and seasonal outlook for the Wellington Region - Summer 2023-24 summary Autumn 2024 outlook
date_range Published 26 Mar 2024
Download now (PDF 2.3 MB) get_appBrowse the data
Anomaly Maps
How different has recent rainfall/soil moisture been compared with the same time in previous years?
Site-specific graphs
Area | Rainfall | Soil Moisture |
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 |
Get in touch
- Phone:
- 0800496734
- Email:
- info@gw.govt.nz