Changes in water quality and especially water quantity will be a big problem in connection with climate change. Fortunately these questions are getting attention from scientists. A topic, which is likely to become as important as water quantity: synchronisation between discharge and other events, for example spawning of fish, hatching of fish larvae, emergence of aquatic insects - you name it.
This area of reasearch raises tricky questions, for example: what does indeed trigger spawning / emergence etc and how will the seasonal run-off patterns of rivers change with climate change. So, if you like challenges ...