No weather drama on horizon
Pastoral farmers, croppers and horticultural growers can take heart that the long-range climate outlook for the Gisborne-East Coast area is for nothing dramatic.
The National Institute of Atmospheric and Water Research (Niwa) says guidance from all the major climate institutions indicates the chance of an El Nino developing the next three months has dropped further and if one does develop, it is thought it will only be of weak or moderate strength.
Data from Gisborne District Council’s hydrological section shows the district is in good shape for groundwater resources for the summer ahead.
Monitoring of wells around the key Poverty Bay Flats area shows that the groundwater aquifers have replenished over winter and are ready to meet normal summer demands for irrigation.
Rivers and streams are running at normal levels for the time of year.
Niwa’s outlook for the September to end of November period indicates temperatures, rainfall, soil moisture and river levels are all equally likely to be near average or slightly above average.
Sea surface temperatures are likely to be near average.
Rainfall for Gisborne for the year to date is running ahead of last year, despite five months of below-average rainfall — January, February, March, May and July.
However, the dry spells have been punctuated by a number of heavy rainfall events that resulted in the present sloppy and saturated soil conditions.
There have been only five prolonged or heavy rainfall events in Gisborne this year — April, end of May and June, August and this month.
Groundwater plots for monitor wells around the Flats over the past 18 years show irrigation demand has extended to earlier and later in the season.
This has been encouraged by a gradual change away from distinct cold and wet winters and hot dry summers, towards a more moderate climate all year round.
The winters are now warmer than they were, the summers generally less fierce, and the rainfall is more spread throughout the year — fulfilling climate projections made by New Zealand’s scientific institutions over the past 30 years.
The bores at Kirkpatrick Road and Nelson Road hint at a small but noticeable decline in replenishment since 1996, with the Kirkpatrick Road bore showing a big drawdown last year.
The Flats groundwater has two main recharge mechanisms — the Waipaoa River and ancient water flowing cross-country through the underground rock layers — both of which occur at a fixed rate, independent of rainwater on the surface.
Long-term groundwater recharge is affected by major climate patterns such as ENSO (El Nino Southern Oscillation).
This year, earlier fears of a strong El Nino have been watered down as the expected coupling of ocean and atmosphere has stalled.
However, Anthony Barnston, a seasonal climate forecaster at Columbia University in New York City, says the latest data show that winds from the west are again forming — a second chance for a full-blown El Nino.
His team now estimates that there is a 75 percent chance that a weak to moderate event will form by the end of this year, just a bit later than researchers had thought.
The predictions are in line with those from the US National Oceanic and Atmospheric Administration.
The next few months will be an important test for the latest generation of seasonal forecast models.
¦ The past week has been a wet one for some parts of the district, with silt washed from the hills turning the bay brown over the weekend.
Rain has not been been particularly heavy — it is just that it has rained on almost every day since the 19th of last month, over most of the district.
Gisborne itself has had 17 rain days out of the past 20.
In the past week, varying amounts have fallen over the district — from 30mm to 100mm.
Mount Arowhana has copped the heaviest falls, gathering rain from east and west for almost 260mm in the past three days, and almost 340mm in the past week.
The Wharerata rain gauge has seen 260mm over the past seven days, while Mangapoike has had 100mm in the same period.