Vietnam has a tropical, hot and wet monsoon climate. Based on climatic conditions Vietnam can be divided into two regions, separated by the Hai Van Mountain pass, which is located between Hue and Da Nang cities. In the areas North from Hai Van Mountain pass it is cold in the Winter and hot and wet in the Summer, with average annual temperature of 22-24oC. The average temperature of the coldest month is 15- 19oC, and average temperature of the hottest month is 32-34.4oC. In the areas from South of the Hai Van Mountain pass, it is hot all the year round, with average annual temperature of 25- 27oC (except Tay Nguyen Plateau with annual average temperature of 20-22oC), and average temperature in coldest month of 21- 26oC, and average temperature in hottest month of 32-34.5oC.
The average annual rainfall of Vietnam is from 1,500 to 2,500 mm and the annual average humidity is 80-85%. The total amount of annual solar radiation is 95-150 Kcal/cm2.
Vietnam has a total land area of 332,000 km2, of which the area of plains is only 7 millions ha and the remainder is mountains, hills and plateau. According to the 1997 statistics from the General Department of Land Administration, the proportion of cultivated land to total land area is 25%, forestland is 34.8%, land for specialised use is 4% and uncultivated land is 34%. Most of the uncultivated lands are bare hills, denuded land, steep slope land (63.6% of those land have the steepness of over 25o) arid areas, hard, unfertile land and land with unbalanced nutrients.
During the past several years, the area of cultivated land has increased gradually. In 1990 it was 7,111 million ha, in 1995 it was 7,972 million ha and by 1998 it had increased to 8,416 million ha. It is estimated that the maximum area over which agriculture could be extended is only 11 million ha. If the rate of demographic increase is still 1.7%/year, the average area of cultivated land per capita will not exceed the threshold of 1,300m2/person. This threshold is very low as compared with the average global value. Coefficient of agricultural land used attains only 1.5-1.6 crops/year. Because of industrialisation, urbanisation and transportation development, the proportion of land for special use has increased gradually.
Surface water: Vietnam has a high rainfall and a dense rivers-streams system, therefore, surface water resources are very abundant. There are 16 river basins with an area of over 2,000 km2, of which 9 basins are over 10,000 km2 in area. These 9 basins contribute more than 80% of the total area of basins in the whole country. The total annual average volume of surface water is 880 billion m3. Of which, 75% of the said volume is contributed from Red River and Cuu Long River basins, while the water volume generated within Vietnam is 325 billion m3. Rainfall in Vietnam, however, is irregularly distributed during the year and over different regions of the country. Therefore, there are frequent droughts in the northern midland provinces, in provinces of central land (particularly in south of central land) and in Tay Nguyen plateau.
As non-treated industrial waste water and urban waste water is discharged into the waterways, organic water pollution is a serious problem in some rivers such as Cau river (in the north), Thi Vai, Sai Gon and Vam Co Dong rivers (in the South) and to a lesser extent in Dong Nai river.
Ground water: Ground water is mainly present in loose, disconnected sediment layers generated in Fourth Period or layers embracing carbonate stones or carbonate stones alternated with young basalt or with other mixed components. It has been estimated that the potential reserve of ground water can be 48 billion m3/year (17-20 millions m3/day). At present, every year about 1 billion m3 (approximate 2.3 millions/day) of ground water is being exploited.
The forests in Vietnam are tropical moist forests, very abundant in the variety and numbers of species of flora and fauna, including micro-organisms.
Because of the devastation caused by war, as well as the impact of former socio-economic development strategy that lacked adequate concern for environmental protection, the forest area has undergone serious degradation. The forest coverage has decreased from 43% in 1943 to 33% in 1976 and to only 27% by 1990. Since 1994, however, as a result of the national "327" afforestation program, the governmental policy of forest land allocation to people, as well as better protection, the forest coverage has increased gradually and reached 28.8% in early 1999. The target is to reach the forest coverage of 45% by 2010 through the 5 million hectare afforestation program.
Vietnam is considered as one of 10 major or mega biodiversity centres in the world. The range of biodiversity is evident from the rich communities of biological species as well as the diversity of landscapes and ecosystems.
- Terrestrial flora: Research on the flora in Vietnam (Nguyen Huu Thua, 1999) shows a total of 13,766 botanical species in Vietnam. These include 2,393 species of lower plants and 11,373 species of higher plants that are divided into 2,524 groups belonging to 378 families. Within the 378 families of higher plants there are 24 families having more than 100 species each, such as orchid family with 800 species, three-pods family with 422 species; bean family with about 400 species; rice family with 400 species; and coffee family with 400 species. Scientists have concluded that nearly 10% of Vietnam's flora is endemic.
- Terrestrial fauna: Currently, scientists have been able to identify in Vietnam 300 species of nematode, 200 species of oligochaeta, 145 species of acartia, 144 species of arthropods, 113 species of collembola, 5,155 species of insecta, 258 species of reptilia, 83 species of amphibia, 828 species of aves, 257 species and sub-species of mammalia. Vietnam is one of the centres of origin of many species of primates and phasianidae.
- Aquatic ecosystem: The aquatic ecosystems in Vietnam are rich in both flora and fauna. So far, it has been possible to describe 1,402 species of algae, 782 species of invertebrates (among 48 species of crustacean, 52 species of lobster and crab, 141 species of oyster and shellfish, and 544 species of fresh-water fish.
- Marine and coastal ecosystems: The research results in the marine environment has revealed 10,837 species, including 537 species of floating vegetation, 662 species of pelagic animals; 6,377 species of benthic animals; 225 species of lobster; 53 species of arthropod; 298 species of hard coral; 2,038 species of sea fish; 50 species of sea snake, 4 species of sea tortoise and 16 species of marine mammals.
In recent years, however, the biodiversity of Vietnam has considerably declined. This decline has basically been brought from natural habitats loss caused by socio-economic development, from the over-exploitation of natural resources and environmental pollution. Many species have become threatened with extinction, such as the tiger whose numbers have reduced from about 1000 in 1970 to only 80-100 at present. There were an estimated 20-30 grey cows in 1970 but now they are no longer to be seen. The population of gayals was estimated at between 2,000- 3,000 before 1970, which has declined to only 80-100 at present. Similarly, there were thousands of peacock before 1970 and now only about 80-100 are believed to be left.