Weather forecast bad for smelter

Press, 28 November 1980, Page 13

Weather forecast bad for smelter

A new element has been thrown into the debate over whether the South Island should have a second aluminium smelter. It is a forecast by a climatic researcher that the period 1983-86 will be exceptionally dry throughout New Zealand. This .is precisely the period for which fears have been expressed that New Zealand may have committed itself to using more hydro-electric power than it has available. The prediction comes from Mr A. I. Tomlinson, a scientific officer at the Christchurch Science Centre, with the Water and Soil Division of the

Ministry of Works and Development. A detailed report on his studies has been published in the “New Zealand Geographer." Mr Tomlinson studied the variability of New Zealand’s rainfall over nearly 60 years — from 1910 to 1969. Records from 20 stations were analysed. Earlier studies confirmed that the 20 stations represented areas covering the whole country.

Results from these stations were compared with known cycles of solar activity, and a correllation made. There has been an upsurge of interest .in solar influences on the weather, which has been accompanied by a worldwide effort to better understand climatic " fluctuations and trends. A close connection is now generally accepted. It was found that the records from the 20 stations were generally' consistent with each other. Given significant abberra.tions over short periods, it

was found that over long periods the whole country tended to be wet or dry consistently. Based on the work done, it was decided to extrapolate the 1910-69 records along with solar activity predictions, to'the period ending 1990. This means that once the extrapolation was completed it would be compared with the actual known rainfall for the period 1969-78, when the last confirmed readings were finished. Notable features on the extrapolated graph are the low rainfall predicted for the early 19705. and the higher rainfall predicted for the late 19705. Actual

rainfall bears out these predictions. The rainfall recorded in 1973 was the lowest since 1930 and there were four years of above average rainfall from 1974-77. The last period of similar above average rainfall occurred from 1955-57 and, like 1930, is reflected in the graph. The implications of the graph for the period 1980-90 are apparent. During the period 1983-86 the graph dips to a level not previously reached since 1932 (the period 1930-34 was extremely dry). Mr Tomlinson does not express his case any more strongly than to say: “It seems possible, then, that a very dry period may occur throughout much of New Zealand in the mid--1980s." ; The situation' will be different from that of 1978, The severe drought in the early months of that year had a devasting effect on agricultural pro-

duction, and was followed by a very wet period. April-September provided the wettest six months for more than 100 years in parts of Canterbury. What the graph does indicate is something more like the extended dry spell of 1973 when some hydrolake levels became very low. The dip in the period 1983-86 suggests one very dry year, or possibly a run of up to about four consecutive moderately dry years. The method used in the study is a smoothing procedure, so a dip in the graph does not indicate that all the years at the time of the dip will be dry

years. Rather it indicates a tendency for the years at the time of the dip to be generally, but not necessarily exclusively, dry. The inference from the graph does not discount the possibility of some wet years during 1983-86, but indicates an over-all tendency to below-average rainfall. Mr Tomlinson says that the most predictable influence of an extended period of low rainfall would be a decrease in lake and groundwater storage level. The possibility of severe agricultural drought conditions could be considered, and whether this occurred would depend on whether months of deficient rainfall occurred during the growing season. , - ■ This analysis, being concerned only ; with annual rainfall 'totals, does:' not consider the distribution of the rainfall during the year. ■

By

OLIVER RIDDELL