Burundi is a small, landlocked country of which only 36 percent is arable. The country has two rainy seasons, which run from February to May and from September to November, as well as a short rain period for two weeks in January. The rainfall varies from 2,000 mm in higher altitudes to 1,000 mm in low-lying areas. The main staple crops are bananas, cassava, sweet potatoes, and beans. Bananas alone accounted for 29 percent of total cultivated area and 44 percent of the total value of crop production between 2006 and 2008. The malnutrition rate for children under five years is high; thirty-nine out of every 100 children weigh less than is normal for their age. Life expectancy at birth has improved from 40 years in the 1980s to 50–52 years in the 2000s. Although the infant mortality rate declined from more than 250 cases per 1,000 births in the 1960s to fewer than 200 per 1,000 in the 2000s, it remains very high. The main causes of death are malaria (40 percent), which predominately affects pregnant women and children under five years, diarrhea (3 percent), acute respiratory infections (19 percent), malnutrition, and HIV/AIDS. Burundi’s population of 8 million is young and growing rapidly: Nearly 7 out 10 Burundians are under the age of 15, and the annual growth rate is 2.8 percent. The growth rate in cities is generally higher than in rural areas, having risen sharply in the latter part of the last decade as more than 500,000 Burundians returned home following the cessation of war. Poverty is widespread, with 90–95 percent of the population living on less than $2 per day, particularly in rural areas.