Floods

Although torrential rainfalls are quiet common during Indonesian's rainy season, more and more floods especially in cities have been reported in the last years.It is not yet proofed which role global warming plays in this trend, but it is sure that the high percentage of sealed ground in urban areas that prevents the water from infiltrating the soil, is accelerating the problem.
In rural areas landuse changes towards less dense vegetation-covers often generate surface runoff, which is a major cause for floods, landslides, mudflows and soil erosion. This characteristic combination often causes high damages to whole regions, like in April 2003 on Flores . So especially these kinds of disasters, normally referred to as "natural" are manmade in many cases. Besides this problem, in some areas of Indonesia there is another rather unusual reason for floods:

Unconsolidated costal sediments are compressed and the affected areas gradually subside below see-level. Even if dams are built, rainwater cannot flow out and generates swampy conditions. Although there is no high mechanical pressure by rapidly flowing water and therefore no danger to live, the structures of buildings are weakened, diseases may spread out and the water supply polluted. Especially some areas ofJakarta and Semarang are affected by this problem. A research team of the Directorate General of Geology and Mineral Resources found out, that the soil compression is not only due to natural consolidation but also to the up-weight of buildings and the extraction of drinking water.