Geography and Climate
Vietnam is located on the eastern margin of the Indochinese peninsula and occupies about 331,688 square kilometers. It borders the Gulf of Thailand, the Gulf of Tonkin, and the South China Sea, alongside China, Laos, and Cambodia. Vietnam is an S-shaped country that has a north-to-south distance of 1,650 kilometers and is about 50 kilometers wide at the narrowest point. With a coastline of 3,260 kilometers, excluding islands, Vietnam claims 12 nautical miles (22 km) as the limit of its territorial waters, an additional 12 nautical miles (22 km) as a proximate customs and security zone, and 200 nautical miles (370 km) as an exclusive economic zone.
Vietnam has a tropical monsoon climate, with humidity averaging 84 % throughout the year. However, because of differences in latitude and the marked variety of topographical relief, the climate tends to vary considerably from place to place. During the winter or dry season, extending roughly from November to April, the monsoon winds usually blow from the northeast along the China coast and across the Gulf of Tonkin, picking up considerable moisture. Consequently, the winter season in most parts of the country is dry only by comparison with the rainy or summer season. During the south westerly summer monsoon, occurring from May to October, the heated air of the Gobi Desert rises, far to the north, inducing moist air to flow inland from the sea and deposit heavy rainfall.
Annual rainfall is substantial in all regions and torrential in some, ranging from 120 centimeters to 300 centimeters. Nearly 90 % of the precipitation occurs during the summer. The average annual temperature is generally higher in the plains than in the mountains and plateaus. Temperatures range from a low of 5 °C in December and January to more than 37 °C in April, the hottest month. Seasonal divisions are more clearly marked in the northern half than in the southern half of the country where, with the exception of some of the highlands, seasonal temperatures vary only a few degrees, usually in the 21°C - 28°C range.