With diminished rice harvests, seawater seeping into aquifers and islands vanishing into rising oceans, Southeast Asia will be among the regions seeing the worst effects of global warming, according to a report released Monday by the Asian Development Bank. The rise in sea levels may force the sprawling archipelago of Indonesia to redraw its sea boundaries, the report said. All those changes would take place progressively over the next century, the bank estimated, giving countries time to improve their flood-control systems, upgrade irrigation networks and take measures to prevent forest fires, which the report predicts will become more common. "Our modeling shows that sea levels will rise up to 70 centimeters," or about 28 inches, said Juzhong Zhuang, an economist at the bank and one of the authors of the report. "That will force the relocation of many millions of people." Brackish water seeping into the water table in Jakarta and the rice paddies of the Mekong Delta is already a growing problem, the report says. Some of the 92 outermost small islands that serve as a baseline for the coastal waters claimed by Indonesia could disappear, according to the report. The accuracy of any complex projections so far into the future remains a nagging question, but the report nonetheless makes sobering reading for anyone considering buying real estate or planning long-term investments in Southeast Asian nations, which have a combined population of more than 563 million. The report focuses on Indonesia, the Philippines, Thailand, Singapore and Vietnam. A projected 30-centimeter rise in sea levels in the Philippines by 2045 would flood 2,000 hectares, or 5,000 acres, affecting 500,000 people, the report says. Under another scenario, sea levels could rise 100 centimeters by 2080, affecting 2.5 million people in the Manila Bay area. The authors urged governments to build infrastructure adapted to climate change, arguing that the current economic crisis was not incompatible with adapting to global warming. "The investment in climate change adaptation can serve as an effective fiscal stimulus," said Tae Yong Jung, another author. Southeast Asia is particularly vulnerable to global warming because of the number of people who live near coastlines and the high incidence of poverty. About 93 million, or 18.8 percent of Southeast Asians, live on less than $1.25 a day and are more vulnerable to the projected increase in typhoons, drought and floods. The region also has a high percentage of workers in the agricultural sector who will face a decline in the production of rice, corn and other crops because of extreme weather patterns, the report said. The number of fish in the oceans is also likely to decline because of changes in currents. In cities like Bangkok and Jakarta that are already stiflingly hot for several months of the year, average temperatures in 2100 could be higher by 4.8 degrees Celsius, or 9 degrees Fahrenheit, the report said, using data from the Intergovernmental Panel on Climate Change. "If that's the case," Mr. Zhuang said, "the cities will be like an oven."