Global Retrospective Estimation of Soil Moisture Using the Variable Infiltration Capacity Land Surface Model, 1980–93

Abstract

A daily set of surface meteorological forcings, model-derived surface moisture fluxes, and state variables for global land areas for the period of 1979?93 is described. The forcing dataset facilitates global simulations and evaluation of land surface parameterizations without relying heavily on GCM output. Daily precipitation and temperature are based on station observations, daily wind speeds are based on National Centers for Environmental Prediction?National Center for Atmospheric Research reanalysis data, and the remaining meteorological forcing variables (shortwave radiation, longwave radiation, and vapor pressure) are derived from the precipitation and temperature series. The Variable Infiltration Capacity (VIC) land surface model is used to produce a set of derived fluxes and state variables, including snow water equivalent, evapotranspiration, runoff, and soil moisture storage. The main differences between the new dataset and other, similar datasets are the daily time step, the use of a specified simulation period as opposed to climatological averages, the length of the simulation period, the use of observed meteorological data, and the use of a more realistic hydrological model. Comparison with observations and existing climatologies shows that 1) the interannual variation in simulated snow cover extent is similar to observations in Eurasia but is somewhat underpredicted in North America; 2) the components of the global and continental water balance are similar to those in previously produced climatologies, although runoff is somewhat lower; 3) patterns of simulated soil moisture storage are similar to the climatology of Mintz and Serafini, but the more sophisticated VIC hydrological model produces a larger range in soil moisture; and 4) the annual cycle and spatial patterns in soil moisture compare well with soil moisture observations in Illinois and in central Eurasia, but mean modeled soil moisture is somewhat lower than observed, and observed soil moisture shows a greater interannual persistence than do the simulations.