1976CLIMATE
Palaeo climate
The palaeoclimate of Sulawesi does not appear to have been studied specifically, but analyses and summaries of palaeoclimate in Southeast Asia are available (Verstappen 1980; Flenley 1980; Whitmore 1981; Walker 1982; Morley and Flenley in press).
The climates of Sulawesi and the rest of Indonesia today, are quite unlike the climates which dominated the region during most of the Quaternary and before. As was shown on page 2, the world's landmasses have moved around, joining and separating, and this has led to changes in climatic regimes. Tropical and subtropical conditions, and the animals and plants associated with them, extended further away from the equator during the Tertiary than they do now and this has influenced the present distribution of animals and plants (p. 63).
During the latter part of the Quaternary, temperatures in the temperate areas of the world repeatedly rose and fell above and below present temperatures. In the cooler periods the ice sheets of the Arctic and Antarctic extended and this took great quantities of water out of the hydrological cycle (fig. 1.9). This in turn caused sea-levels around the world to fall. The maximum fall in Southeast Asia was about 150 m below present levels. This exposed large areas of dry land beyond the present coastlines-indeed, it uncovered three times the present area of the Sunda Shelf and twice the present area of the Sahul Shelf.8 When the sea-level was only 40 m below present levels it would have been possible to walk in a straight line between Banjarmasin and Surabaya, Saigon and Kuching, Singapore and Pontianak, and Merauke and Darwin. The effective area of Sulawesi was also increased but to a much lesser extent (fig. 1.10). Examination of bathymetric contours reveals features that may have been river valleys when the sea-level was lower (fig. 1.11).
Ocean currents which now enter the Indonesian Archipelago through the Torres Straits, the South China Sea, the narrow straits between many of the Lesser Sunda Islands and the straits between Mindanao and the Sangihe/Talaud Islands would have been blocked and their buffering effect on climate would have been lost. The Sulawesi Sea (between the Philippines and Sulawesi) and the Makassar Straits would have been much more enclosed but the currents entering the Molucca Sea (between Halmahera and Sulawesi) towards and from eastern Sulawesi would have been only marginally obstructed. The main Sunda and Sahul landmasses would have experienced a more continental climate (greater diurnal temperature range, lower rainfall and humidity) but this would have been rather less pronounced on Sulawesi. The lowering of sea and land temperatures during these cool periods would also have reduced rainfall and humidity. It has been estimated that the rainfall 11,000 years ago was 30% of present values in the equatorial zone.
Figure 1.9. Hydrological cycles (a) in warm conditions and (b) in cool conditions. Note the fall in sea-level because water in the form of ice is unable to flow to the sea.
Figure 1.10. The area of Sulawesi and neighbouring land-masses exposed when the sea-level was 100 m below present levels.
After van Balgooy in press
The cooling of the whole earth during the glacial periods lowered the lowest altitudes at which ice remained all year and snow fell, and lowered the upper altitude at which montane trees grew. The maximum temperature depression during the Quaternary occurred 18,000 years ago when, in New Guinea, temperatures at 2,500 m were 10°C lower, but at sea-level only 2° or 3°C lower, than at present. The tree line (the altitude at which trees are no longer able to grow) was lowered about 1,500 m in New Guinea but only about 350-500 m in Sumatra. The sea-level changes also had considerable impact on corals (p. 215).
The zone where the curtains of rising air of the northern and southern hemisphere meet is called the Intertropical Convergence Zone (ITCZ), and in the cool, dry glacial periods this was probably south of its present position (that is roughly over the equator). It is a zone of frequent, showery rain, to the north of which is a high pressure belt with relatively low rainfall. Thus, when the ITCZ lay south of the equator, parts of northern Indonesia (including Sulawesi) would have experienced drier, more seasonal climate with lower rainfall and humidity and greater seasonal change in mean daily temperature (Verstappen 1980).
Figure 1.11. Bathymetric map of the Sangkarang Archipelago to show the deep channels that are probably drowned riverbeds.
Temperatures during the warmest parts of the Quaternary were only 1° or 2°C higher than now (at sea-level) and at this time the water released from the polar ice caps caused sea-levels to rise. There is no unequivocal evidence that shorelines have been more than 6 m higher than at present during the warm periods of the Holocene, but sea-levels could have reached up to 25 m above present levels during the Pleistocene. The most recent sea-level maxima detected off the southwest peninsula were 4,500 and 1,600 years ago when sea-level was 5 m and 2.5 m higher respectively (fig. 1.12) (de Klerk 1983). This agrees closely with evidence from elsewhere in Southeast Asia (Tjia 1980; Tjia et al. 1984). Whereas this rise had a marked effect on the long shorelines of low-lying parts of eastern Sumatra and southern Borneo, the most marked effect on Sulawesi would have been the separation of the blocks of land either side of the Tempe depression. Evidence for this has been found in the vegetation record (p. 29) and there are even stories among local people of a time when travellers did not have to sail around the southern tip of South Sulawesi but could instead sail from the Gulf of Bone, through Lake Tempe and emerge in the Makassar Straits (Sartono 1982). With the exception of the Tempe depression and a few other flat plains (such as Malengke), most of Sulawesi's coastline slopes quite sharply and minor rises in sea-level would not have had significant effects. During this period seasonality in rainfall would have been less, rainfall would have been similar to or even greater than now, and mountain zones of climate, vegetation and fauna would have been raised. However, as stated above, this period occupied only a small fraction of the Quaternary. The majority of the period was characterized by lower rainfall and humidity, greater diurnal and seasonal variations, and by more marked rain shadows. Thus, the seasonal areas of Sulawesi and elsewhere would have been more extensive and, conversely the areas subject to more stable, wetter climates would have been reduced in area.
Present Climate
The climate of Sulawesi is best described with reference to rainfall since temperature is relatively constant, and other climatic variables such as wind velocity, evaporation and humidity change within even small areas. Between September and March, cool northwesterly winds pick up moisture while crossing the South China Sea (between East and West Malaysia, Philippines and Vietnam) and arrive in North Sulawesi via the Sulawesi Sea in about November, and in the west coast of South Sulawesi via the Java Sea in late November or early December. The west coast of the central part of Sulawesi is sheltered from the effects of these winds by Borneo.
Figure 1.12. Changes in sea-level over the last 7,000 years determined from a study in the southwest peninsula.
After de Klerk 1933
After this period, variable, humid, southeasterly winds blow towards eastern Sulawesi and rainfall peaks on the southeast coast occur between April and June, and on the northeast coast somewhat later. The southeasterly winds from the dry and wintery Australian landmass become stronger and these dry winds have a significant influence on the southern tips of the southwest and southeast peninsulas. Manado experiences a short dry season from August to October, but Jeneponto in the south of the southwest peninsula is subject to a long dry season between April and November.
Areas
