EFFECT OF A CANOPY INTERCEPTION RESERVOIR ON HYDROLOGICAL PERSISTENCEIN A GENERAL-CIRCULATION MODEL

Using decadal GCM simulations, the effects of a SVAT (Surface-Vegetati on-Atmosphere-Transfer) and a ''bucket'' land surface parameterization on simulated hydrological persistence are contrasted. The bucket mode l promotes persistence, as measured by the one-month-lagged autocorrel ations of precipitation and evaporation, relative to the SVAT model, p articularly in the Tropics. An additional simulation shows that despit e the many complexities incorporated into the SVAT model's evaporation formulation, it is the canopy interception reservoir alone that expla ins most of the difference. Water that evaporates from this reservoir bypasses bare soil and stomatal resistances. The interception reservoi r thus acts as a short circuit in the soil and vegetation resistance n etwork that decreases hydrological persistence by reducing the residen ce time of surface moisture.