you ask me to advise a young hydrologists. I just think that he/she needs a master, first. I had the fortune to work at the beginning with Alessandro Marani, and subsequently Andrea Rinaldo and Ignacio Rodriguez-Iturbe. They had strong ideas on what is “the gold medal” that we have to gain, and had their own methods to pursue it (get ideas, get methods!). So, at least for me, the matter was to follow their own inclination, challenging myself to follow them, and see how much I liked it.
So my first hint is: look for (one) some masters. You soon realise that some guys (or some places) are far far beyond the present state-of-art of the topic you are caring about. Try to work with them. If you cannot, try to follow them and see what they do, and understand what they think it is important.
Copying from “smart people, can help you to save a lot of time, and avoid to spend huge time resources following unimportant topics. In my academic life I saw very many “brilliant” guys (gals) spending their youth and hundreds of hours on irrelevant problems. However, if you do not give up, you will get the hot topic (and the people) that copes with you. The research company you get along, is going to stick with you for all of your life, and change you, especially if you start an Academic path.
Not very much, indeed (meet the right people!), as an advise, but in a previous post you can find my decalogue for a hydrologist that can complete the topic.