Effects of climate change on water quality for urban water supply of Valencia (Spain).

Climate change can cause distinct impacts on the environment and natural sources. Water resources are essential for social and economic development of cities and it will be affected by climate changes. The major part of research is focused in the impacts on water quantity. However, in water quality is also important because it can influence on purify process. The city of Valencia (Spain) has experimented recently a worsening in last years, with increasing warming trends and precipitation shifts. Water resources on the two river basins from which Valencia takes its supply are predicted to decrease during the 21^st century. It is necessary to explore how these trends may affect the city in order to develop new adaptation and mitigation strategies if necessary.

The aim of this contribution is to analyze the effects on different climate scenarios on raw water quality of Valencia, combining different models, like sadistic and process model. A water quality model has been developed using GESCAL (DSS AQUATOOL), for the Tous reservoir, where raw water is accumulated before being distributed to the water treatment plants. It assesses the effects of increased temperatures and a change in rainfall pattern on raw water quality. On the one hand, changes in stratification and nitrogen compounds oxidation process are evaluated. On the other hand, climate change impacts are evaluated on the system trophic process by means of phytoplankton dynamic model.

All the climate change scenarios considered showed a decrease of water resources in Tous reservoir, a concentration of nutrients and polluters in the water is foreseen. Also, high temperatures and nutrients concentration will work out well for phytoplankton proliferation and a worsening of water quality. The future climate conditions present an ideal scenario to cyanobacteria development and a detriment to another phytoplankton groups, like diatoms and clorophytes. The appearance of taste and odor metabolites, as geosmin and 2-methylisoborneol (MIB), is predictable and they will be more frequents. In fact, these metabolites force to water treatment plants to adapt their process to guarantee the urban water supply. Finally, this research will allow studying future treatment process in a pilot plant and adapting the water treatment plants to future scenarios.