The Temporal And Spatial Characteristics Of Spring Soil Moisture Over Eastern China And The Intercomparison Among Multiple Reanalysis Datasets

Statistical characteristics of spring soil moisture in different reanalysis datasets of ERA-Interim, MERRA, JRA-25, CFSR and NCEP/NCAR-R1are intercompared with each other and with the observations over China. The spring soil moisture is largest in southeastern China and smallest in northwestern China in climatology. It exhibits pronounced interannual variability with opposite variation in the mid-latitude zone and northeastern China. There exist a wet trend at mid-latitudes and a dry trend in northeastern China. The intercomparison shows that, except NCEP/NCAR-R1, the reanalyses can reproduce the observed gradual increases of climatological soil moisture in China from the northwest to the northeast and to the southeast. MERRA presents the best climatological soil moisture. Only ERA-Interim can well represent the interannual variations of observed soil moisture. The first EOF mode of observed soil moisture demonstrates that the variability of soil moisture is most robust in the mid-latitude zone of eastern China and the ERA-Interim is the best in reproducing the spatial and temporal features. The reasons causing differences between reanalyses of soil moisture are also investigated in terms of two main factors affecting soil moisture, precipitation and evaporation. The ERA-Interim can well reproduce the precipitation and evaporation from observations as well as their relations to soil moisture, resulting in a preferable ability to represent the spatial and temporal characteristics of observed soil moisture. Although the other four reanalysis datasets reproduce precipitation well, their poor ability to describe the evaporation causes large differences of soil moisture between their simulations and observations.Based on the evaluation above, we analyzed the periodic variation of soil moisture in the ERA. The results show that:In the east, there is a periodic variation of2～4years. The time scales of soil moisture show that:The values of residence time in observations are highest in the mid-latitude and Nanling area, which are2～3months and2～5months respectively. The residence time of ERA increases from south to north and the top soil moisture memory in northeast China are longer than observations, when it is shorter than observations in middle latitude and south areas. In addition, the soil moisture memory increases as the soil get deeper. When it comes to the seasonal distribution, the residence time is longer in winter than other seasons.We also analyzed the relation between vegetation and soil moisture in the different soil types. The results show that:the vegetation has significant positive correlations with soil moisture at the same period in the clay. However, the vegetation is negatively correlated with the soil moisture with one month lag in sand. The influence of vegetation on residence time of soil moisture demonstrated our results. The more (less) vegetation results in the longer (shorter) residence time of soil moisture in clay, indicating that the vegetation in clay is beneficial to the maintaining of soil moisture. On the other hand, the more (less) vegetation results in the shorter (longer) residence time of soil moisture in sand, indicating that the vegetation in sand goes against the maintaining of soil moisture.