Influence of Future Climate Scenarios on Stratification in Sub-tropical Water Supply Lakes

Numerical models of lake hydrodynamics and heat exchange have been used in past investigations to examine the potential changes to physical and bio-geochemical processes under future climate scenarios. Results suggest climate warming can induce changes to thermal stratification with a general trend of earlier onset of stratification and greater stratification intensity. There are numerous ways to represent future climates in lake models however there are relatively few investigations that examine the choice of method used to represent future climates on the simulation outcomes. In this study we explore the influence of choice of simple approaches to representing future climates on the annual stratification/de-stratification cycle in subtropical water supply lakes.

A large sub-tropical Australian water supply lake, Lake Wivenhoe (latitude -27.394314°, longitude 152.609220°), was used as a case study. The General Lake Model platform was applied to simulate one-dimensional mixing and heat exchange within the lake. The model was calibrated and validated against water temperature measurements collected over a 6 year period (2009 to 2015). A scenario based approach was then used to examine changes due to warming suggested by the IPCC’s RCP6.0 and RCP8.5 scenarios over a 90 year period (2009 to 2099). Time series data for the key meteorological model inputs were adjusted to represent each climate scenario by step-change and progressive linear adjustment of past time series data. An approach that adjusted the frequency of extreme events within each of the scenarios was also implemented.

Simulation results were broadly consistent with past investigations in terms of earlier onset and greater intensity of stratification. Interestingly the choice of method used to develop the representative meteorological time series data was found to produce a greater variation in results when compared to different climate scenarios. These results seem to offer little insights for water resource managers other than to consider a wide range of variability when planning for future conditions. These results also suggest that additional research is required to better understand how to implement future climate scenarios and interpret their results in decision making frameworks. A discussion of the implications of the variation in simulation outputs for water resource managers is also included.