Farming is mainly on a subsistence level, although its importance is diminishing. The principal agricultural crops are coconuts, bananas, betel nuts, cassava, and sweet potatoes. The agricultural sector contributed 19 percent of GDP in 1996 and engaged 27 percent of the total labor force in 1994. Exports of agricultural products (excluding fish) accounted for 6 percent of export earnings in 1996, while exports of marine products accounted for 84 percent of total export revenues in that year. The annual rainfall received each year varies from 2,500 millimeters (98 inches) in Yap to 4,500-7,500 millimeters (177-295 inches) in Pohnpei. The limited water reserves in both Chuuk and Yap are a source of concern for the long term.