Modelling the circulation and spread of pollution in Lake Rådasjön under conditions of climate change

Abstract

Climate change could degrade water quality with changes in precipitation patterns and in combination with urbanisation and further land uses, such as agriculture production. These changes could accelerate the transport of pathogens into water bodies. The aim of this study is to model the circulation and spread of pollution in Lake Rådasjön due to climate changes. Lake Rådasjön is the selected study area since it is the source of raw water for the cities of Gothenburg and Mölndal. A hydrodynamic model was set up, and impacts on circulation and spread of E. coli under climate change were evaluated to identify increased risk for the water intake. Air temperature was the most significant variable for the study. The scenarios for climate change were based on two Representative Concentration Pathways (RCP), the RCP 4.5 and RCP 8.5. The results showed that the water temperature in the lake would warm-up for the years 2040 and 2100 on average 1.5°C and 3.5°C, respectively. The major impact from climate change was observed to be the reduction of ice coverage on the lake, and based on the modelling results for water temperature, there would be a prolongation of the summer regime and shortening of the winter regime for the lake. Thus, inversion of the lake in spring would occur earlier, and inversion after summer would occur later. The results showed that during spring the pollutant E. coli could reach deeper into the lake and for a longer period due to the shorter period of ice coverage on the lake since the winter season would be warmer, increasing the risk at the water intake at that time. Whereas for the rest of the year it would be seen a longer summer, thus decreasing the risk for a much longer period and leading to an even later autumn inversion.