Stuart Evans
The impacts of the dust radiative effect on vegetation growth in the Sahel
Figure. Annual mean values for the modern day experiment for dust optical depth (left), precipitation (middle), and leaf area (right). The black box denotes the Sahel region, from 15 °W to 35 °E and 8 to 18 °N. The value at the top of the box indicates the area weighted average value within the Sahel region.
Stuart Evans
Department of Geography
Many studies have been conducted on the effects of dust on rainfall in the Sahel, and generally show that African dust weakens the West African Monsoon, drying the region. This study tested how this drying impacts vegetation in the region by using a model that explicitly simulates vegetation growth and its impact on dust emission. There are several competing effects of dust that affect plant growth: changes to rainfall, downwelling solar radiation, surface temperature, and resultant changes in surface fluxes. Our model finds that the combined effect of these processes decreases vegetation cover and productivity of the Sahel and West Africa. In modern conditions, the dust radiative effect decreases leaf area by 12%, productivity by 14%, and increases bare soil area by 3% across the Sahel, and by much higher amounts locally. In preindustrial conditions the vegetation response is weaker, despite the dust-induced rainfall and temperature anomalies being similar. We interpret this as the vegetation being less susceptible to drought in a less evaporative climate. These vegetation responses to dust are evidence of a dust-vegetation feedback loop whose strength varies with the mean state of the climate, and which may grow stronger in the future. This research has been funded by the Princeton Environmental Institute at Princeton University through the Carbon Mitigation Initiative and supported by the RENEW Institute at the University at Buffalo.