On hydrological predictability

Have you ever been flabbergasted, after the fact, by how far your predictions were off the observed data? An underestimation of pesticide arrival time by a factor of 10, or an overestimation of flood peaks by a factor of two or more—all this with models that have apparently been well calibrated with data from the past. Of course, there is always an explanation, after the fact. The media characteristics may have been slightly different from what we initially assumed, perhaps preferential flow occurred where we did not expect it to occur, there was inaccuracy in the assumed initial conditions and, of course, in the boundary conditions as well, and the events were larger than what we thought could reasonably occur. It seems that small uncertainties can easily amplify under certain conditions and will limit predictability. In this commentary, we argue that there is a pattern to this.