Landlocked between China and India, two of the most populous and fastest-developing countries in the world, Nepal is a geographically diverse nation roughly the size of Arkansas. It possesses the greatest altitude variation of any country, ranging from 59 meters (194 ft) in the tropical Terai, to the peak of Mount Everest at 8,850 meters (29,035 feet). Nepal is home to 90 peaks over 7,000 meters (22,966 ft), including eight of the world’s ten highest mountains.
Along a south-to-north transect, Nepal can be divided into five belts, described below: Terai, Siwalik, Middle Hills, High Mountains, and High Himalaya (some sources identify only three belts: Terai, Hill, and Mountain regions). In the other direction, the country is divided into three major river systems, from east to west: Koshi, Gandaki/Narayani and Karnali (including the Mahakali/Sarda along the western border), all tributaries of the Ganges. In all, Nepal has more than 6,000 rivers and rivulets, totaling 45,000 km (almost 28,000 miles) in length.
- Terai: This is the northern part of Indo-Gangetic plain. The Terai extends nearly 800 km from east to west and about 30-40 km from north to south. The average elevation is below 750 meters.
- Siwalik: Commonly referred to as the Churia Hills, the elevation in the Siwalik ranges from 700 to 1,500 meters. Due to its loose friable nature and extensive deforestation in past decades, this region experiences frequent landslides that contributes largely to the sediment load in many Nepali rivers.
- Middle Hills or Middle Mountains: Also known as the Mahabharat range, the elevation of this range is from 1,500 to 2,700 meters. The Middle Hills are cut in many places by rivers such as the Kosi, Gandaki (Narayani), Karnali, and Mahakali. These hills are the first great barrier to monsoon clouds and the highest precipitation occurs on the southern slope of this range.
- High Mountains: Ranges from 2,200 to 4,000 meters. This region consists of phyllite, schists, and quartzite, and the soil is generally shallow and resistant to weathering. The climate is cool temperate.
- High Himalaya: Ranges from 4,000 to above 8,000 meters. Eight of the highest peaks in the world and the world’s deepest gorge, 5,791 meters in the Kali Gandaki Valley, are located in this region. The climate is alpine and the snowline lies at 5,000 meters in the east and at 4,000 meters in the west. The area lying to the north of the main Himalayan range is the Trans-Himalayan region, which restricts the entry of monsoon moisture and therefore the region has a dry desert-like climate.