The five-year U.S.-led project brings together the Lower Mekong nations of Myanmar, Laos, Thailand, Cambodia and Vietnam, as the region faces growing challenges from the impact of climate change, in particular increasingly severe weather patterns. Environmentalists say these challenges include issues over water use, deforestation, floods and disaster mitigation. The United Nations' Office for Disaster Risk Reduction, UNISDR, says costs are rising from natural disasters…