Bangladesh is a densely-populated, low-lying, mainly riverine country located in South Asia with a coastline of on the northern littoral of the Bay of Bengal. The delta plain of the Ganges (Padma), Brahmaputra (Jamuna), and Meghna Rivers and their tributaries occupy 79 percent of the country. Four uplifted blocks (including the Madhupur and Barind Tracts in the centre and northwest) occupy 9 percent, and steep hill ranges up to approximately high occupy 12 percent in the southeast (the Chittagong Hill Tracts) and in the northeast. Straddling the Tropic of Cancer, Bangladesh has a tropical monsoon climate characterised by heavy seasonal rainfall, high temperatures, and high humidity. Natural disasters such as floods and cyclones accompanied by storm surges periodically affect the country. Most of the country is intensively farmed, with rice the main crop, grown in three seasons. Rapid urbanisation is taking place with associated industrial and commercial development. Exports of garments and shrimp plus remittances from Bangladeshis working abroad provide the country's three main sources of foreign exchange income.