Water Freedom System

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Because ENSO modulates the climate throughout the Pacific, this leads to much wetter and drier seasons respectively and often floods and drought, tte consequences of these place challenges to agriculture and forestry, demonstrated by examples in this section.

tte impact of ENSO climate variability on Australia has been highlighted by events during the early 1990s. In 1990-91 the wet season produced abundant rains, yet it failed almost completely the following year as drought set in across Queensland and New South Wales. While drought continued in some areas through 1992 and 1993 in southeast Australia there were the floods of spring 1992 and spring 1993, and the cool summers which followed, ttese were all connected with the Southern Oscillation. Rural productivity, especially in Queensland and New South Wales, is linked to the behaviour of the Southern Oscillation. Australian wheat yield (trend over time removed) have fluctuated with variations in the Southern Oscillation. Negative phases in the oscillation (drier periods) tend to have been linked with reduced wheat crops, and vice versa (Figure 7.5).

tte relationships between wheat yields and the SOI are directly a consequence of ENSO effects on the Australian climate. ENSO tends to be accompanied by less rainfall and often droughts in Australia, especially during the winter in the interior of eastern Australia, and during the northern Australian monsoon. La Niña years are often wetter, with floods. For instance the 1998-99 La Niña brought record level rains to parts of central Western Australia. Lake Eyre in the northeast of South Australia is dry except for occasional major flooding, usually during La Niña years, due to extra rainfall in southwestern Queensland.

El Niño events produce widespread impacts on communities across the Southwest Pacific, as instanced by the 1997-98 event (Shea et al. 2001). Drought severely affected Fiji, Papua-New Guinea, the Solomon Islands, Tonga and the Marquesas Islands of French Polynesia. In Fiji, by October 1998, 54,000 people were receiving food supplies and 400,000, half the population, were receiving water deliveries (Hamnett et al. 2002, Lightfoot 1999). In contrast Kiribati was wetter than normal. Fisheries were impacted with a general shift of the catch to the east, followed by a shift westwards (Lehodey et al. 1997, Lefale et al. 2003). Catches declined for Papua-New Guinea and the Solomon Islands, and increased for Kiribati. Extended drought conditions were recorded in Niue in the 1982/83 ENSO event, which lasted

Fig. 7.5. Australian wheat yields and the Southern Oscillation Index (Rimmington and Nicholls, 1993).

Australian Wheat Yields Versus SOI Index

LflWheit Yield — soi

Fig. 7.5. Australian wheat yields and the Southern Oscillation Index (Rimmington and Nicholls, 1993).

18 months from July 1982 to December 1983. During this event exports went down, and local cows were slaughtered for food and imports of farm produce increased, tte drought also created conditions of leafaopper and aphid invasions on important exports such as taro (Government ofNiue 2000).

In El Niño years, New Zealand tends to experience stronger or more frequent winds from the west in summer, leading to drought in east coast areas and more rain in the west. In winter, the winds tend to be more from the south, bringing colder conditions to both the land and the surrounding ocean. In spring and autumn southwesterlies tend to be stronger or more frequent, providing a mix of the summer and winter effects, tte La Niña events which occur at the opposite extreme of the Southern Oscillation Index cycle have weaker impacts on New Zealand's climate. New Zealand tends to experience more northeasterly winds, which bring more moist, rainy conditions to the northeast parts of the North Island, tte impacts are instanced by the 1997-98 event (Basher 1998). It was much drier than normal in the east from July 1997 onwards - with drought very extensive throughout eastern areas up to the end of March 1998. In late April 1998 the New Zealand Ministry of Agriculture and Forestry estimated the likely cost of the drought on farm gate returns would be NZS256 million for the year ending June 30 1998, and NZS169 million for the following year, giving a total of NZS425 million. Given the impact on downstream value-added agricultural production, the likely total cost to the country was estimated to be in excess ofNZSl billion.

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