Lake stratification and temperature profiles simulated using downscaled GCM output

A mathematical in-lake water temperature model (WATEMP-Lake) was developed to investigate future responses of lake stratification and temperature profiles to future climate change due to rising concentrations of atmospheric greenhouse gases (GHGs). The model was used to simulate daily water temperature profiles and stratification characteristics in summer (June, July, and August-JJA) for Suwa Lake in Japan as a case study. For future assessments, the model uses surface climate variables obtained from a downscaling method that was applied to the UK Hadley Centre's coupled ocean/atmosphere model forced by combined CO₂ and sulphate aerosol changes (HadCM2SUL). The downscaling method employed mean sea level surface pressure to derive three airflow indices identified as: the total shear vorticity (Z) -a measure of cyclonicity -, the strength of the resultant flow (F), and the overall flow direction (D). Statistical relationships between these indices and seven daily meteorological time series were formulated to represent climate variable series at sites around Suwa Lake. These relationships were used to downscale the observed climatology of 1979-1995 and that of 2080-2099 using HadCM2SUL outputs.