The Wellington region has been much drier and warmer than normal since October. November rainfall was generally less than 30% of average across most monitoring sites. December totals have been between 20 and 50% of average in the west and the Tararua Range, and about normal in eastern Wairarapa with a strong west-east gradient. Very low river flows were measured before Christmas (one in a five year minimum in some cases). Thanks to a couple of significant rainfall events, and very humid air masses with severe thunderstorms forming inland on several days, January rainfall so far is tracking well above average in the Wairarapa and normal to above average in Wellington and Kapiti. The soil moisture as of mid-January was above average for most of the eastern Wairarapa, but remained well below average on the Kapiti coast, where a ‘medium-scale adverse event’ was officially declared (https://www.beehive.govt.nz/release/early-dry-declared-adverse-event) before Christmas. River levels have generally improved compared to mid-December. Most of the water take restrictions that were in place in December were lifted, but river levels remain generally low and with high rates of evaporation as a function of the elevated temperatures.
The blocking high pressure that was causing severe lack of rain early in the season has subsided, allowing a more “normal” La Niña pattern to kick in. La Niñas normally bring in hot weather and afternoon thunderstorms, especially around the ranges. Weaker westerlies are expected to continue, with more south-easterlies or north-easterly episodes with occasional bursts of very heavy rainfall either from localised thunderstorms or fuelled by cyclonic depressions intensifying over warm water. The rainfall recovery since Christmas has slightly reduced the risk of water shortages for the time being. River levels remain quite low but within what is expected for summer. The dry conditions improved in Kapiti but overall the soil remains very dry in the west. In the Wairarapa the soil is wetter than normal with favourable conditions for crops, even though the NIWA drought index still shows the region as dry because of the cumulative rainfall deficit. In short, the climate drivers suggest a mixed bag with heat waves, high humidity and potential major rainfall events, relatively cooler and wetter on the eastern coast (onshore winds), and much warmer than normal elsewhere.
For the latest national drought index state, please visit: (https://www.niwa.co.nz/climate/information-and-resources/drought-monitor)
How different has recent rainfall/soil moisture been compared with the same time in previous years?
Click on links below to bring up 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|