f. Indonesia/New Guinea
In Indonesia, area-average rainfall totals normally range from 180-280 mm per month throughout the year (Fig. 61). The larger totals are normally observed during October-January when the primary region of tropical convection is centered on the equator. The smaller totals are typically observed during June-September as the tropical convection shifts northward to the Indian subcontinent and southeastern Asia. Rainfall across Indonesia is strongly modulated by ENSO, with above- (below-) normal rains occurring during Pacific cold (warm) episodes. This ENSO-related interannual variability is consistent with the enhanced (suppressed) equatorial Walker circulation typical of Pacific cold (warm) episodes.
During 1997 rainfall across Indonesia from March through December was significantly below average, with area-averaged totals less than 50% of normal throughout the period. For the region as a whole, the estimated total area-averaged rainfall during March-December was 1145 mm, compared to the mean of 2215 mm. These very dry conditions were linked to the onset of El Niño conditions during March, and to the subsequent persistence of strong warm episode conditions during the remainder of the year.
The most significant dryness occurred during June-November, when area-averaged totals reached only 30%-40% of normal. This below-average rainfall reflected the previously noted dramatic shift of heavy tropical rainfall from Indonesia to the eastern half of the equatorial Pacific (see section 3a). By July and August drought conditions and continued well below-normal rainfall contributed to vast uncontrolled wild fires in Sumatra and Borneo. Although dry-season burning takes place each year to clear land for planting crops, these fires during 1997 quickly created an ecological disaster as they burned out of control due to large-scale drought. By mid-August large areas of tropical rainforest were completely engulfed. In the following three months, uncontrolled fires destroyed massive areas of tropical rainforest and killed countless thousands of animals and other rainforest creatures. Vast areas of smoke from the fires reduced visibility at times to less than 100 m, and caused serious respiratory problems hundreds of kilometers away from the smoke sources. The smoke also hindered, and sometimes completely stopped, traffic by land, sea and air, and was a primary factor in several serious accidents.
At Menado, Celebes total rainfall during the April-December period only reached 1200 mm, compared to a normal accumulation of 2100 mm (Fig. 62a). There were two prolonged periods in which no rainfall was observed. The first period of complete dryness lasted 45 days between mid-May and the end of June. The second period lasted an incredible 81 days from early July through the end of September. The time series of daily rainfall at Padana Tabing, Sumatra (Fig. 63 ) shows similar severe rainfall deficits, with many prolonged periods of dryness evident. In fact, daily rainfall totals at this location exceeded 25 mm on only 2 days between mid-July and early November. Interestingly, in the area farther north, Kuala Lumpur, Sumatra recorded slightly above-normal rainfall (300 mm above normal) for the period (Fig. 64), with most of the enhanced precipitation occurring during November.
Severe drought, in combination with devastating frosts, also impacted New Guinea during 1997. These dry and cool conditions were linked to strong subsidence and clear skies in association with the an abnormally strong subtropical ridge over the country. By November, crop losses leading to malnutrition and in some cases starvation had affected hundreds of thousands of persons. These acute impacts continued during late November and December as significantly below-normal rainfall marked the onset of the 1997/98 wet season.
