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Drought check

https://www.gw.govt.nz/drought-check

Drought check

Updated 22 December 2020 10:54am

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.

Situation Statement

Updated 22 December 2020
Next update due when there is a significant change of conditions, as the situation evolves 

Background

 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.

 

Current situation

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.

 

Meteorological outlook

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.

 

Climate change

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.

See the latest national drought index state.

Browse the data

Anomaly Maps

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

Site-specific graphs

Cumulative rainfall/soil moisture totals for indicator sites compared with historical averages and other recent years

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