In order to answer these questions we need data, and I dealt with some of the data requirements for solving hydrological problems. Collecting data and making them available is a relatively less expansive action than doing work and can save a lot of efforts and money.  Furthermore there are social aspects of the question that cannot be overlooked. We made the experience of LIFE FRANCA that opened our view on this this topic. Clicking on the figure above, please find the presentation. At least, I think it is a nice overview covering some recent studies on the island. From them you can have more detailed information. 

Other presentation and information can be found at the TAIEX website.