The relative roles of climate, soil, vegetation and topography in determining seasonal and long-term catchment dynamics

This paper develops and demonstrates a preliminary set of coupled analytical models for the seasonality and annual water balance of catchments. We include the effects of temporal variability of atmospheric forcing and the interaction of nonlinear catchment processes, while assuming that climate, soil and vegetation are effectively uniform over the catchment. The models make predictions for the water balance of the canopy, root zone, saturated zone and catchment system, as functions of 6 dimensionless similarity parameters. These parameters quantify: (i) climate dryness; (ii) interception capacity relative to rainfall; (iii) combined climate seasonality and rootzone storage; (iv) subsurface flow responsiveness; (v) saturated subsurface flow capacity, relative to mean annual rainfall rate; and (vi) a geomorphological exponent controlling the expansion of saturated area fraction. The model can provide estimates of throughfall, evaporation, drainage, subsurface flow, saturated area and catchment yield. Testing of these estimates is in progress. The coupled models can be used to predict hydrological differences between catchments using differences in the dimensionless parameters. The sensitivity of water balance to each of the similarity parameters can be presented graphically or analytically, so that dominant controls on water balance can be identified as functions of climate and catchment properties. The principal application we envisage is as a simple method to transfer measurements to ungauged catchments