This is a new concept that I just heard on Thursday (5 May), and I have a strong feeling that I’m gonna embark on it.
The key idea is to reconstruct climate conditions of the past via proxies such as tree rings, speleothems (loosely speaking, those pointy structures that you often see in caves) and so on.
Why is this important to water resources management? In planning for the future, we always rely on past data. For example, to build flood control structures, engineers rely on past streamflow data. However, in most places, such data are available for only about less than a hundred years. If we want to predict something of a longer (e.g. multi-century) scale, that is not enough, mainly because extreme events are unlikely to be captured in such short period. So the rising trend in literature is to reconstruct hydrological data via proxies (as listed above). With this technique, extreme events in the past can be observed, and probability calculations can be done more accurately.
I’ll take a deeper look at some papers relating to this. I think this is quite fascinating.