A mechanism for the low-frequency variability of the Sahel rainfall

Historical records and recent observations have shown that rainfall variability in the Sahel region is dominated by the low-frequency component at decadal time scale. To study the physical mechanism behind this long-term rainfall fluctuations, we carried out simulations of 100 years using a synchronously coupled biosphere-atmosphere model, with the sea surface temperature (SST) in the Atlantic ocean varying from 1898 to 1997. Our study show that ecosystem dynamics regulate the response of the biosphere-atmosphere system in West Africa to the SST forcings over the Atlantic Ocean. Based on our results, we argue that the natural ecosystem dynamics play a critical role in enhancing the low-frequency rainfall variability over the Sahel region.