Evaluation of Reanalysis Soil Moisture Simulations Using Updated Chinese Soil Moisture Observations

Using 19 years of Chinese soil moisture data from 1981-1999, we evaluate soil moisture in three reanalysis outputs: ERA40, NCEP/NCAR reanalysis (R-1), and NCEP/DOE reanalysis 2 (R-2) over China. R-2 shows better interannual variability and seasonal patterns of soil moisture than R-1 as the result of incorporation of observed precipitation. ERA40 produces a better mean value of soil moisture for most Chinese stations and good interannual variability. Limited observations in the spring indicate a spring soil moisture peak for most of the stations. ERA40 generally reproduced this event, while R-1 or R-2 generally did not capture this feature, either because the soil was already saturated or the deep soil layer is too thick and damps such a response. ERA40 and R-1 have temporal time scale comparable to observations, but R-2 has a memory of nearly 8 months, 3 times the temporal scale of observations. The unrealistic long temporal scale of R-2 can be attributed to the deep layer of the land surface model, which is too thick and dominates the soil moisture variability. R-1 has the same land surface scheme as R-2, but shows a temporal scale close to observations. This, however, actually is a response to the effects of soil moisture nudging. This new long time series of observed soil moisture will prove valuable for other studies of climate change, remote sensing, and model evaluation.