GENESIS OF FLOOD.

Star (Christchurch), Issue 17038, 11 May 1923, Page 9

GENESIS OF FLOOD.

MR WOOLES’S THEORY. STORM OF TROPICAL ORIGIN. An interview with Mr F. L. Wooles elicited some facts in legard to the recent storm and floods. The genesis of the storm was on ilia;* 3, when r. small storm area of tropical origin made its appearance off Cape Egmont. accompanied with a high degree of humidity and a rather unseasonably high temperature over the North Island and northern half of the South Island. This low pressure area in itaelf was not of sufficient intensity to produce anything in the nature of an abnormal rainfall. But., in addition to this particular s£.orm area, an Antarctic disturbance also made its appearance in the region of the Bluff on the same date. This combination of storm areas produced the light to moderate rains experienced on the third and fourth. Early on the fifth the centre of the Antarctic disturbance passed eastward of the Bluff bringing in its wake a cold wave of air and a high barometer in the southern districts. The low pressure off Cape F-gmont, however, still persisted. the result being that a steep barometric gradient developed between the high pressure in the south ami the tropical “ low” in the north. The result was the storm intensified, the temperature fell considerably, and the wind rose to a gale from the south and south-east. The combination of high humidity in the tropical “ low ’’ and the cold air of the Antarctic ‘'high” now began to have full play and the rainfall greatly increased, the st ol*9l reaching its height earlv on Monday morning. May 6. During the succeeding days the tropical “ low ” ttill persisted off Cape Egmont and accounted for the continued rain which, however, showed a gradual decrease as the influence of the governing factor the Antarctic “high” was modified by a westerly

low pressure area which is now slowly enveloping the country. This particular storm area is likely to produce further bail weather of the cold, squally southerly t-vpe in a dnv or two Though Christchurch received over six inches of rain during the storm, the full effects were not felt in the city owing to its situation under the lee of Banks Peninsula. The main rainfall came from the southeast quarter, the Banks Peninsula hills acting as a partial break to south-east weather as far as Christchurch and district ai*e concerned. The heaviest rains were naturally experiened along the foot of the up-country ranges .and coastal barrier to the Canterbury south-easter in like manner as the nor'-wester is robbed of moisture on the Canterbury side when passing over the Alps. Comparisons have been made between the great floods of 1868 and the recent visitation. The 'BB floods occurred in February of that year, the rains being warm with little or no snow on the ranges. During, the recent storm a tremendous body of snow has fallen on the mountains and that accounts for the fact that the Waimakariri. and other snow-fed rivers, though somewhat flooded, have not burst their banks. The floods have been disastrous over a great part of Canterbury, but it would be hard to conceive what would have happened had the visitation been experienced in the warm season of the year and rain had taken the place of the great depth of snow which must now cover the ranges.