The drought of summer–autumn 2003
The effects of the severe drought which struck much of New Zealand during summer and autumn are already evident in reduced earnings for the pastoral industry (see MAF media release) and the ‘Target 10%’ campaign to reduce electricity consumption. Our growth in GDP is likely to be slowed too – a drought-induced electricity shortage in 1992 caused a drop in GDP of 1.5%, and the 1997–98 and 2001–02 droughts each cost the nation several hundred million dollars.
In January and February 2003 much of the country had low rainfalls, and soil moisture deficits were more widespread than normal. Drought persisted through March and April in central and southern North Island, and in much of the South Island. Recent rain has relieved North Island conditions, but parts of Canterbury and Otago are still vulnerable to the rapid onset of drought next spring.
Streamflows have been very low over much of the country. The maps show the measured streamflows during the drought in comparison with flows recorded for these months in previous years. They show record low flows (red) or extremely low flows (orange) across much of the country, notably in the hydroelectric catchments of both islands.
Rivers reached record lows in Taranaki, Wellington, Marlborough, Otago, Southland, and the West Coast. By the end of May, rivers in most regions began to recover, except for Wellington and parts of Otago and Southland. This drought was the most widespread of any in the last 25 years. Paradoxically, there were exceptionally high flows in Northland, Coromandel, and East Cape.
As a result of the prolonged below-average rainfall, groundwater levels were also very low throughout most of the South Island and southern North Island, with wells reaching record low levels in some parts of Canterbury. Autumn rain in the north and east of the North Island has allowed groundwater systems there to recover well from their low levels last summer.
The environmental and human consequences of this drought were widespread. The Target 10% campaign was initiated to reduce demand for electricity as hydro reservoir levels fell. There were widespread restrictions on irrigation pumping in Canterbury and Otago, and this will have reduced productivity. Water restrictions (no watering of lawns and gardens, no washing of cars and boats) were used on the Kapiti Coast to reduce demand on the Waikanae River, and night patrols checked for illegal water use. In the Waikato, the low flows, warm temperatures, and low winds provided favourable conditions for algal blooms, and health warnings were issued advising people to avoid swimming in some lakes and rivers.
What will happen next? It seems unlikely that another El Niño will develop in the coming spring and summer, and so it is likely that more normal rainfall conditions will prevail. As a result, we are expecting a return to more normal conditions in most of New Zealand for river flows, water quality, and lake levels. However, groundwater storages on the east coasts of the North Island and South Island are likely to be average or below average at the beginning of spring, and some regions may again face pressures on their groundwater resources over summer.
Alistair McKerchar [ [email protected] ]