GLM Multi-lake Comparison Project (GLM-MLCP)

Dr. Louise Bruce leads the GLM-MLCP which is a community driven initiative where numerous researchers from the GLEON and AEMON networks collectively simulate numerous lakes using a common approach to setup and assessment. More than 20 lakes have been simulated, ranging in latitude from 56oN to 38oS, in elevation from -210 to +560m above sea level, from trophic status of oligotrophic to eutrophic, depth from 12 to 253m, volume from 6.9e5 to 4.8e10 m3, mixing regimes from polymictic to meremictic and from a range of climates including warm lakes with lakes with seasonal ice cover. For each lake, standard sets of both forcing (input) data and calibration (field) data were collated.

A range of metrics were chosen to assess model performance at each site, including various error estimates of epilimnetic and hypolimnetic temperature and, where relevant, ice cover. In addition we ran both model output and observed thermistor data through Lake Analyser to compare metrics of stratification including Lake Number, Wedderburn Number, Schmidt Stability, metalimnetic thickness and thermocline depth. A sensitivity analysis was performed separately for each lake using the MCMC method.

A comparative analysis was then conducted between lake model applications and a set of statistical evaluations relates patterns of model fit and stratification metrics against lake characteristics. The outcome of the study is an improved knowledge of the strength and limitations of GLM, a standardized calibration and globally relevant parameter set, and improved understanding of characteristic drivers and forcing patterns of stratification in lakes. The analysis highlights how the ability of the model to capture stratification varies based on the lake morphometry and the prevailing climate. Having a globally validated model will allow us in the future to better undertake global change assessments of lake and reservoir systems.