in Vietnam are lower than other countries located at the same latitude in Asia. The highest temperatures normally occurs in March–May in the south and May–July in the north. Temperatures in summer are relatively equal among the northern and southern parts of the country with differences being mostly due to altitude (the decrease in temperature is predominantly due to altitude). Mean annual rainfall in the country ranges from although most places in Vietnam receive between . The majority of rainfall occurs during the rainy season, which is responsible for 80%–90% of the annual precipitation. Generally, northern parts of the country receive more rainfall than southern parts of the country. Drizzle is a weather phenomenon that is characteristic of the weather in winter in the north and north central coast. Depending on the region, the onset of the rainy season (defined as when the monthly average precipitation exceeds ) differs. Area and boundaries Area: Total: Land: Water: Area – comparative: Slightly larger than the state of New Mexico in the United States. Somewhat less than half as big as New South Wales, Australia. About 1⅓ times the United Kingdom's size. Land Boundaries: Total: Border countries: Cambodia , China , Laos Coastline: (excludes islands) Maritime Claims: Contiguous zone: Continental shelf: or to the edge of the continental margin Exclusive economic zone: , Territorial sea: Elevation extremes: Lowest point: South China Sea 0 m Highest point: Fansipan Rivers: Longest river: Đồng Nai river (longest inland river) Lakes: Biggest lake: Ba Bể Lake Resources and land use Natural resources: phosphates, coal, manganese, rare earth elements, bauxite, offshore oil and gas deposits, timber, hydropower Land use: Arable land: 19.64% Permanent crops: 11.18% Other: 69.18% (2011) Irrigated land: 45,850 km2 (2005) Total renewable water resources: 864.1 km3 (2011) Freshwater withdrawal (domestic/industrial/agricultural): total: 82.03 km3/yr (1%/4%/95%) per capita: 965 m3/yr (2005) Environmental concerns Natural hazards: occasional typhoons (May to January) with extensive flooding, especially in the Mekong Delta. Environment – current issues: Logging and slash-and-burn agricultural practices contribute to deforestation and soil degradation; water pollution and overfishing threaten marine life populations; groundwater contamination limits potable water supply; growing urbanization and human migration are rapidly degrading environment in Hanoi and Hồ Chí Minh City Environment – international agreements: party to: Biodiversity, Climate Change, Climate Change-Kyoto Protocol, Desertification, Endangered Species, Environmental Modification, Hazardous Wastes, Law of the Sea, Ozone Layer Protection, Ship Pollution (MARPOL 73/78), Wetlands Climate change See