Abstract
In the tropical and subtropical regions, extensive semi-arid regions exist. Recent researches on the atmospheric circulation and climatic change in West Africa and Northeast Brazil are reviewed. In West Africa, the recent decrease in the rainfall since the rainy decade of 1950s accelerated the desertification caused by the rapid increase in population. An investigation on the atmospheric circulation shows that the 850 mb African Monsoon winds are weak (strong) in the dry (rainy) August.
In Northeast Brazil, the recurrent drought in the 20th century were found to occur in ENSO year or one year after ENSO year. In the dry years, the South Atlantic high pressure is strong and extends its influence over Northeast Brazil compared to the average year. Consequently, the ITCZ is located in the Northern Hemisphere. In the rainy years, the ITCZ is displaced south toward Northeast Brazil in the March-April rainy season.
In both of these semi-arid regions, the rainfall were found to be controled by the large-scale atmospheric circulation. Hence the local desertification has little influence on the climatic change. On the other hand, the climatic change toward increased aridity in West Africa accelerates the process of desertification.
