Causes of the Desiccation of Lake Victoria at 17 ka

<title>Abstract</title> <p>The desiccation of Lake Victoria 17,000 years ago (17 ka) is simulated using a triple-nested model with a large outer domain and a convective-permitting inner domain over the Lake Victoria Basin, capturing the mesoscale circulations that are coupled with local precipitation. The 17 ka climate is distinguished from the present day by reduced greenhouse gases, cooler sea and lake temperatures, and altered insolation. Annual rainfall is 51% of present day in the 17 ka simulation in association with reduced moisture flux convergence rather than evaporation reductions. Boreal spring rains provide the largest contribution when cooler temperatures in the western Indian Ocean induce anomalous zonal geopotential height gradients and easterly flow over the basin, reducing low-level moisture convergence over the lake at night. In addition, nighttime cooling and drying over the Eastern Rift Mountains associated with reduced greenhouse gases increases dry air advection. Together, these mechanisms effectively collapse the nighttime lake precipitation maximum in boreal spring. Daytime precipitation reductions over land to the east of the lake also contribute. In the afternoon, high topography warms more than lower elevations, enhancing dry advection into the basin. Additional nighttime precipitation reductions in boreal fall are associated with the same mechanisms as for boreal spring, but there is no daytime drying since fall insolation at 17 ka is lower. This analysis indicates that the 17 ka drying in the Lake Victoria Basin that resulted in the desiccation of Lake Victoria was primarily caused by regional responses to climate forcing factors and not remote forcing.</p>