Initial Outlook for Waikato Winter and Summer Seasons: Slight shift in seasonal timing with cool and relatively dry winter, cool and average rainfall for the spring and delayed warming up in mid-summer with dry conditions in February but near normal in January and possibly slightly drier than normal March.

When it comes to climate risks in New Zealand, the bluster and rage of tropical storms can steal the stage. But what has really garnered attention over the last ten years are the recurring droughts some of which have affected not just regional New Zealand but the whole country. These events can flare up quickly, and can cause considerable economic damage and stress to farmers and the ecosystems under their stewardship.

Drought is often insidious and creeping, intensifying over many months, stunting or killing crops and limiting grass growth and quality as it develops, reducing groundwater levels and river flow and drying out water supplies. It represents a more frequently occurring and persistent climate hazards faced by New Zealand. Conversely, extended rainy periods and the occasional extreme rainfall event characterised by excessively high rainfall totals over a short duration and typically covering small geographical areas can lead to their own set of problems for the country.

For New Zealand droughts can wreak havoc, especially to the diverse range of farming communities. The agriculture sector accounts for about 5 percent of New Zealand’s gross domestic product and employs less than 7 percent of the workforce.

But agriculture is particularly vulnerable to climate variability and drought. New Zealand has many farms that rely heavily on rainfall for their grass growth and crop, horticulture and viticulture productivity. In 2013 one of the worst droughts since 1945 occurred and in 2015 a pan-national drought developed.

In the future early warning of droughts will improve through the application of a new modeling system called ExtendWeather deployed by CLIMsystems based in Hamilton. After three years of development the system is up and running and producing some very good predictive results. The forecast is innovative as it relies on the latest CFSv2 data supplied by NOAA for the globe. What is different about this data is that CLIMsystems downloads and processes through a propriety downscaling method the data every ten days. The atmosphere is dynamic so changes are reflected in a new series of high resolution maps that are produced for New Zealand from an ensemble of forty model runs over the previous ten days. The system generates outputs three times each month. The new CFSv2 system is the latest generation of seasonal and sub seasonal forecast model and the downscaling abilities of CLIMsystems climate scientists bring the large datasets down to a very local scale to assist New Zealand’s primary producers in decision making. The variables available include anomalies for rainfall, temperature and potential evapotranspiration deficit. CLIMsystems also processes monthly wind data for those that require it. The group also generates extreme temperature and precipitation forecasts and monthly sea surface temperature forecasts that are so important to the understanding of the evolution of ENSO events. All the results are available as high resolution maps which mean interpretation is easy.

What Might the Summer Be Like?

The latest ten days forecast for New Zealand has been recently processed and it now extends through the summer season. For the dairy engine room of the country - the Waikato - the forecast looks interesting.

In general, July temperatures look like they will be slightly above average but from August through December the recent forecast is for cooler than normal conditions. With warmer than normal conditions returning in January, with February near normal and March warmer than normal.

More importantly, the precipitation forecast is for a slightly drier than normal July except in the Coromandel where it should be near normal. August is currently forecast to be moderately drier than normal across the Waikato region. September could remain drier than normal for most of the region except the North Waikato which may be near normal. As the soil warms and grass growth kicks off in October precipitation is expected to be near normal. The same should prevail in November except for the southern part of the region that could be slightly drier than normal. In December only the western part of the region could be normal with the rest of the region slightly drier than normal yet January is currently forecast to be near normal. However February is forecast to be moderately drier than normal with March precipitation returning to near normal expect in the Hauraki Plains area that could remain slightly drier than normal.

Soil moisture as represented by the potential evapotranspiration deficit is below normal for the next eight months against the 30 year average ranging between -20 to -50 percent of that long term average. With the current forecast showing only March with a 20 to 50 percent anomaly above the 30 year average.

Other regions of the country have different forecast outlooks. As noted these maps and forecasts are updated every ten days. As a result trends in changes in the forecast can be discerned and as would be expected the accuracy of the forecast improves the closer one gets to the present however the general direction of the forecast often does not change markedly while the strength of the signal - wetter, drier, hotter, cooler can shift. It is therefore recommended that the regular updates be examined in the context of previous updates.

You can get free access to the forecast for one month by signing up for an account at www.extendweather.com http://www.extendweather.com and selecting ‘free trial’. There are various plans available for regular delivery of the maps and a written synopsis for precipitation and temperature for each region. An account will also provide access to periodic extreme event updates and other news and views on the seasonal outlook for the country.