Articles | Volume 7, issue 1
Geosci. Model Dev., 7, 317–337, 2014
Geosci. Model Dev., 7, 317–337, 2014

Model evaluation paper 18 Feb 2014

Model evaluation paper | 18 Feb 2014

Understanding the performance of the FLake model over two African Great Lakes

W. Thiery1, A. Martynov2,3, F. Darchambeau4, J.-P. Descy5, P.-D. Plisnier6, L. Sushama2, and N. P. M. van Lipzig1 W. Thiery et al.
  • 1Department of Earth and Environmental Sciences, University of Leuven, Leuven, Belgium
  • 2Centre pour l'Étude et la Simulation du Climat à l'Échelle Régionale (ESCER), Université du Québec à Montréal, Montréal, Canada
  • 3Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 4Unité d'Océanographie Chimique, Université de Liège, Liège, Belgium
  • 5Laboratoire d'écologie des Eaux Douces, University of Namur, Namur, Belgium
  • 6Royal Museum for Central Africa, Tervuren, Belgium

Abstract. The ability of the one-dimensional lake model FLake to represent the mixolimnion temperatures for tropical conditions was tested for three locations in East Africa: Lake Kivu and Lake Tanganyika's northern and southern basins. Meteorological observations from surrounding automatic weather stations were corrected and used to drive FLake, whereas a comprehensive set of water temperature profiles served to evaluate the model at each site. Careful forcing data correction and model configuration made it possible to reproduce the observed mixed layer seasonality at Lake Kivu and Lake Tanganyika (northern and southern basins), with correct representation of both the mixed layer depth and water temperatures. At Lake Kivu, mixolimnion temperatures predicted by FLake were found to be sensitive both to minimal variations in the external parameters and to small changes in the meteorological driving data, in particular wind velocity. In each case, small modifications may lead to a regime switch, from the correctly represented seasonal mixed layer deepening to either completely mixed or permanently stratified conditions from ~ 10 m downwards. In contrast, model temperatures were found to be robust close to the surface, with acceptable predictions of near-surface water temperatures even when the seasonal mixing regime is not reproduced. FLake can thus be a suitable tool to parameterise tropical lake water surface temperatures within atmospheric prediction models. Finally, FLake was used to attribute the seasonal mixing cycle at Lake Kivu to variations in the near-surface meteorological conditions. It was found that the annual mixing down to 60 m during the main dry season is primarily due to enhanced lake evaporation and secondarily to the decreased incoming long wave radiation, both causing a significant heat loss from the lake surface and associated mixolimnion cooling.