Identifying Climate Change Driven Critical Weather Conditions that Result in Dramatic Shifts in Lakes

Lakes provide important ecosystem services to society and are showing alarming responses to ongoing climate change worldwide. Apart from long-term changes, events on a shorter time scale can also have medium- to long-term impacts on lakes. Therefore, we aim to investigate to what extent short- to medium-term weather conditions together with long-term climatic changes have critical impacts on lakes. To accomplish this, we are jointly advancing our methods for stochastic weather generation and lake modeling so that we can combine them to a model chain. This model chain will allow us to iteratively model inversely which weather events can cause predefined, dangerous changes in lake state, i.e. identify critical weather conditions. As a specific example of a lake, we use Lake Kinneret in Israel, which is already subject to pressure from changing climatic conditions and is located in a region for which strong changes are projected to continue. Our approach will allow us to combine identified critical weather conditions with long-term changes so that we can assess the relative importance of the two influences. This will further allow us to evaluate if weather events that have a critical impact on the lake under current climatic conditions become even more dangerous due to climate change, and if weather conditions that would have been irrelevant in the past only become dangerous when combined with long-term climatic changes.

In the second phase of the project, in order to expand assessing the impact of climate change and critical weather conditions, we plan to extend the model chain to include catchment-scale processes and resolve three-dimensional flow patterns in the lake. This extension will allow us to include river discharge and nutrient loading that consistent with the generated weather and to model flow patterns like breaking internal waves which may become a crucial contributor to mixing under future conditions. Since these models will be driven by the same stochastically generated weather, it is necessary to further develop the corresponding weather generator to produce spatially resolved values. In the second phase of the project we will not only be able to refine the results of the first half, but also determine to what extent targeted water management actions can counteract the identified critical weather conditions.