Adianto P. Simamora, Jakarta – A recent study has predicted less rainwater will flow to the Citarum river basin in West Java as a result of warmer temperatures and vast changes in land use.
Citarum, the largest water basin on the island of Java, is the key source of water for both West Java and Jakarta.
The study, conducted in April by WWF Indonesia and the Meteorology Laboratory of the Bandung Institute of Technology (ITB), found that temperatures in the Citarum river basin would significantly increase by 2020, both in the rainy and dry seasons.
The study predicts the average temperature in the rainy months will be 26.1 degrees Celsius in 2020, up from 24.7 degrees in 2001. During the dry season, the average temperature will soar to 30.7 degrees, up from 27.1 degrees in 2001.
"This increase in temperature will be caused by global warming," the head of the study, Armi Susandi of the ITB, told The Jakarta Post on Saturday.
It was predicted the level of rainfall during the rainy season will jump to between 239 millimeters and 1,377 mm in 2020, up from between 249 mm and 746 mm in January 2001.
"Such big downpours could be a blessing and solve water scarcity problems. But on the other hand, it would lead to more natural disasters such as floods and landslides, especially if there is no effort made to replant the forest area around Citarum so as water can be retained," he said.
Armi said ongoing rapid land use changes in the Citarum area would further prevent rainwater from reaching the basin. The study said the direct runoff of rainwater was between 337 mm and 414 mm in 2001. "Thus, with rainfall of 420 mm in January 2001, over 70 percent of rainwater became runoff," he said.
The study predicts the runoff rate may reach 651 mm due to rapid deforestation for urban development around the Citarum basin. "This will cause huge floods, landslides, the overflow of rivers and harvesting failures," he said.
The Citarum river basin takes up 6,080 squares kilometers of land, with the river stretching 269 kilometers. Data from the West Java administration shows about 11 million people live in the basin, with over 1,000 companies operating in the area. The Citarum river basin is a water source for the Jatiluhur, Cirata and Cikumpay reservoirs.
Jakarta's tap water operators have complained in recent times of a decrease in the supply of water from the Jatiluhur reservoir in Purwakarta, West Java. The Jatiluhur reservoir supplies 80 percent of water to over 700,000 water consumers across the city.
The study predicted the Cirata reservoir, located in the southern part of Citarum, would be affected the most by the changes. The water from the Citarum river basin is used primarily for irrigation, agriculture, fishery, industry and hydropower purposes.
The West Java environmental agency reported that some 54 percent of forest in the Citarum area had been converted in the period between 1983 and 2002. The agency also said vast areas of agricultural land had been converted into housing complexes or industrial land, further contributing to the decease in water catchment areas.
The agency said the number of housing complexes jumped by 233 percent between 1983 and 2002, with industrial land use increasing by 868 percent during the same period.
WWF Indonesia's climate change coordinator Ari Muhammad said stakeholders in the Citarum river basin needed to make efforts to adapt to minimize the impact of global warming in the area. "It is urgent that stakeholders make an effort to re-green the area and improve spatial planning," he said.