Collaborative Research: Connecting the Past, Present, and Future Climate of the Lake Victoria Basin using High-Resolution Coupled Modeling

University Of Texas At Austin, Austin TX

Investigators

Abstract

Lake Victoria, the largest lake in Africa and the second largest in the world, is big enough to make its own weather. The lake's influence on weather is evident in rainfall totals, as considerably more rain falls over the lake than the catchment around it, and in the diurnal cycle of rainfall, as the lake creates a land-sea breeze effect which causes rain to fall during the day over the land and at night over the lake. Given the lake's outsized influence on weather it is natural to ask what role it will play in climate change over the Lake Victoria Basin. The question of Victoria's role in climate change is challenging for several reasons, among them the lack of observations over the region and the difficulty of making simulations which capture the range of scales and processes that matter for the region's weather and climate. Regarding the spatial scales the range extends from the size of the mesoscale thunderstorm complexes the deliver much of the rain to the regional-scale circulation patterns that control the seasonality of rainfall. The region could also be influenced by changes in surface temperature over the Indian and Atlantic Oceans. Research conducted here takes up the challenge of Victoria Basin climate change using a nested modeling strategy in which a regional model, the Weather Research and Forecasting (WRF) model, is run with three nested grids to capture the relevant scale range. The outer grid covers all of Africa and much of the Atlantic and Indian Oceans with a 27km grid spacing while the innermost grid covers the Lake Victoria Basin at 3km, sufficient resolution to capture thunderstorm complexes. WRF is coupled to the Community Land Model (CLM), which includes a representation of Lake Victoria and its interactions with the overlying atmosphere. The work involves simulations of past, present, and projected future climate over the basin. Past climate simulations focus on a period 17 thousand years ago when the lake dried out completely, and the PIs hypothesize that the dessication of the lake was the result of changes in incoming solar radiation due to Earth's orbital cycle (which also caused the ice ages). The project also considers the more general question of how regional climate depends on the size of Lake Victoria, which can be varied in the model simulations. Changes in lake size could drive precipitation changes that cause further lake size change, as the lake receives perhaps 80% of its water input from local rainfall (rivers flowing into the lake provide the other 20%). The work is of societal as well as scientific interest given that about 40 million people live in the Lake Victoria Basin and are dependent on its water resources. Rainfall is a hazard as well as a resource given that much of the rain falls in severe storms, a particular hazard for the fishing fleet. The PIs conduct public outreach regarding climate change in the region through a traveling museum exhibit to be presented at the Mayborn Museum at Baylor University and at the National Museum of Kenya. In addition, the project provides support and training to two graduate students at the University of Texas at Austin and one at Baylor University. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.