November’s big dry breaks rainfall records
News media release
For immediate release – 1 December
2017
November’s big dry
breaks rainfall records
What astonishing November
weather. Rainfall records for the month throughout the
region fell faster than the rain as the region’s big dry
really started to bite and summer made a grand
entrance.
In most parts of the region you’d have to go back decades to match the low rainfall, and in parts of Otaki and Wainuiomata you’d need a time machine to match records set in 1890 and 1893.
In fact, it was so dry that there were only four days with any recordable rain at Karori and Wainuiomata. These are both the record lowest for November since 1879 and 1890 respectively. Otaki had five days with rainfall which is the lowest there for November since 1893.
Here’s a regional round up of the big dry, collected by Greater Wellington Regional Council.
Exceptionally dry in (most of) the
Wairarapa
November rainfall
across the Wairarapa was exceptionally low. Only 8mm of rain
was recorded at Masterton (14% of average) making it the
driest November since at least 1992. At the Tauherenikau
Racecourse there was just 14mm which makes it the lowest
November total since records began in 1963. Across most of
the Wairarapa monthly rainfall was less than 25% of the
November average.
Isolated thunderstorms over the last week brought some intense downpours to some areas. Rainfall at Carterton and Greytown had been looking very low with 7mm and 9mm recorded respectively until the 26th when Carterton received 74mm of rain in three days, which included a very intense downpour of 45mm that occurred over just two hours on the 29th. The monthly rainfall that had been heading towards 12% of average ended up being 140% of average.
Wellington, Hutt and Kapiti hit by big
dry
Rainfall records have
been plundered across Wellington, Hutt valley and the Kapiti
Coast with monthly averages barely reaching 25% of normal.
The November rainfall total of 17.5mm recorded at Karori
Reservoir (Zealandia) is the second lowest November total
since records began in 1879. The only lower November total
was 72 years ago in 1945. At Wainuiomata the 27mm total is
the lowest November rainfall since records started in 1890.
The headwaters of the Wainuiomata, Orongorongo and Hutt rivers are key water supply collection areas and have been hit hard by the dry conditions. Rainfall recorded during October and November shows that period to be the driest on record (since 1980) in the Orongorongo valley and the second driest at Kaitoke since 1951.
Otaki and Waikanae received
November rainfall of 21mm and 26mm respectively – both 25%
of normal. Rainfall has been measured within Otaki township
1893 and this is the lowest November total that has been
recorded since then. Waikanae rainfall was the lowest for
November since 1969.
Other November totals around the
region include; Miramar 8mm, Hataitai 11mm, Berhampore 14mm,
Khandallah 15mm, Woodridge and Paparangi 20mm, Plimmerton
and Whitby 19mm, Lower Hutt 21mm, Pinehaven 33mm, Belmont
25mm, Maymorn 26mm, Te Marua 44mm, Paekakariki 17mm, Te Horo
19mm, Mauriceville 32mm, Longbush 11mm, Tanawa Hut (near
Tinui) 13mm, Masterton 8mm, Lake Wairarapa
13mm.
Even the Tararua ranges were dry
The normally soaking
Taraura ranges were also bathed in uncharacteristic
sunshine.
The network of rain gauges high within the Tararua Range shows the low November rainfall extended into the mountains. In the headwaters of the Otaki River catchment 120mm of rain was recorded, this being 24% of average and the lowest November total since 1991. The region’s wettest spot – the Angle Knob rain gauge (average yearly rainfall of 7000mm) – high in the headwaters of the Waingawa River only received 200mm, which is 30% of average and the lowest November total there since 1985.
Rivers receding
rapidly
River flows across
the region have been very low during November with most
monitored sites being around 20% to 40% of average. The Hutt
River and tributaries saw only 25% of the normally expected
November flow. Other monthly flow percentages include:
Wainuiomata River (30%), Porirua Stream (40%), Waikanae and
Otaki rivers (35%), Ruamahanga River (30%), Waiohine and
Waingawa rivers (30%), Pahaoa River (20%).
The very
lowest flow measured in the Hutt River towards the end of
the month was quite significant, with a frequency of
occurrence around 1 in 30-years (3%) during November. River
flow will typically drop lower than this during summer but
to see the river this low during November is rare. The
Wainuiomata, Waiohine, Tauherenikau and Ruamahanga rivers
also recorded very low flows falling to levels expected once
in 20-years during November.
Along with stress on the public water supplies, low flow restrictions on irrigators may begin to bite earlier than normal if the dry conditions continue.
Topsy turvy rainfall
rollercoaster………
2017
has been a highly variable year for rainfall. Since rainfall
records began in 1980 at Orongorongo range: April was the
wettest; June the 2nd driest; July the 3rd wettest; August
the 4th wettest; October the driest; and November the
driest.
Highlights - a showcase of broken
records
Location Rainfall Lowest
since
Masterton 08mm 1992
Karori (at Zealandia)
15.5mm 1945
Wainuiomata 27mm 1890
Otaki
21mm 1893
Tararua (Otaki River
catchment) 120mm 1991
Waikanae 26mm 1969
ENDS – more information GW mediaphone on 021 914 266