Searching for Simplicity in Hydrology

The use of simplification as a route to scientific insight is reviewed with examples from hydrology and analogies from other sciences. The discussion covers a number of types of simplification: (a) simplification of the governing equations; (b) reduction of the state space, i.e. the number of dependent variables; (c) reduction of the solution space, i.e. the number of independent variables; (d) reduction of the parameter space, e.g. by freezing a slowly varying parameter; (e) simplification of the driving function e.g. Fourier analysis. The importance of scale is stressed and the possibility of apparent paradoxes between differing scales is noted. The complementary nature of deterministic and stochastic approaches is also discussed.