Soil moisture memory in climate models

Water balance considerations at the soil surface lead to an equation that relates the autocorrelation of soil moisture in climate models to 1) seasonality in the statistics of the atmospheric forcing, 2) the variation of evaporation with soil moisture, 3) the variation of runoff with soil moisture, and 4) correlation between the atmospheric forcing and antecedent soil moisture, as perhaps induced by land-atmosphere feedback. Geographical variations in the relative strengths of these factors, which can be established through analysis of model diagnostics, lead to geographical variations in simulated soil moisture memory. The use of the equation to characterize controls on soil moisture memory is demonstrated with data from the modeling system of the National Aeronautics and Space Administration Seasonal-to-Interannual Prediction Project.