An analytical model for soil-atmosphere feedback

摘要

Soil-atmosphere feedback is a key for understanding the hydrological cycleand the direction of potential system changes. This paper presents ananalytical framework to study the interplay between soil and atmosphericmoisture, using as input only the boundary conditions at the upstream end oftrajectory,assuming advective moisture transport with average wind speed alongthistrajectory and vertical moisture exchange with the soil compartment ofuniform vertical properties. Precipitation, evaporation from interception andrunoff are assumed to depend through simple functional relationships on thesoil moisture or the atmospheric moisture. Evaporation from soil moisture(including transpiration) depends on both state variables, which introduces anonlinear relationship between the two compartments. This nonlinearrelationship can explain some apparently paradoxical phenomena such as alocal decrease of precipitation accompanied by a runoff increase.The solutions of the resulting water balance equations correspond totwo different spatial moisture regimes showing either an increasing or adecreasing atmospheric moisture content along a trajectory starting at the coast, depending on boundaryconditions and parameters. The paper discusses how different model parameters(e.g. time scales of precipitation, evaporation or runoff) influence theseregimes and how they can create regime switches. Such an analysis haspotential to anticipate the range of possible land use and climate changes orto interpret the results of complex land-atmosphere interaction models. Basedon derived analytical expressions for the Horton index, the Budyko curve anda precipitation recycling ratio, the analytical framework opens newperspectives for the classification of hydrological systems.