Rainfall characteristics (delta O-18, delta H-2, Delta T and Delta H-r) in western Africa: Regional scale and influence of irrigated areas

摘要

A summary of previous isotopic studies of rainfall in western Africa (0 degrees-17 degrees N; 0 degrees-15 degrees E) together with the isotopic analyses of rainfall events front 15 stations in 1989 shows that (I) the Gulf of Guinea is the nlain source of watel vapor in the SLldan-Sahelian zone (minimum of monthly mean of delta(18)O contemporaneous with the heart of the monsoon), (2) the reevaporated water from previous local rainfalls is an important source of water vapor of subsequent rainfalls (lack of continental effect, where the majority of rain events present isotopic signature either evaporated or fed by evaporated water), and (3) no isotopic data support the Indian Ocean as a source of vapor. Isotopic ratios combined with variations of temperature and relative humidity associated with rain events in 1989 mirror the increasing aridity From south to north and from west to east. However, a Sahelian station, Birni N'Konni, presents all the features of a humid station with a large contribution of continental vapor (60% of min events with ch d >10 parts per thousand, -2 K