Summary and discussions

There are obvious seasonal variations for soil moisture. It increases significantly in spring in the northern of eastern China due to snow melting. In autumn, soil moisture increases due to less evapotranapiration and reaches its highest value in November. In the mid-latitude of eastern China, the soil water content is lowest in spring and highest in autumn and winter. For the southern of eastern China, in area to the west of 110°E soil is driest in spring and wettest in autumn and winter, while in the area to the east of 100°E soil moisture has opposite seasonal variation. Spatial distribution of soil moisture is highly heterogeneous; the accumulated soil water storage at 100cm ranges from 130mm to 400mm. In general, soil water content increases with the depth; however, in North China the spring soil water has reached its maximum at 10-20cm layer due to snow-melt.

Soil moisture is positively correlated to precipitation and negatively surface air temperature. The correlation coefficients however have significant seasonal variations. The interaction between soil moisture and surface climate is more obvious for drier soil, in the region to the south of 40°N, in-terannual variability shows drying trends for both surface and deep layer soil. Analysis indicates that combination of less precipitation and warmer temperature may cause the drying tendency in soil water, in addition to excessive use of groundwater. Time lag correlation analysis shows that show that the positive correlation between soil moisture and precipitation is significant with lag time exceeds one year. Analysis also shows precipitation has longer influence time on soil moisture and not opposite.

The surface climate is closely connected to soil moisture in both prior and lag correlation analyses. It is obvious that there are close correlations among soil moisture, surface air temperature and the precipitation for both preceding and lagged. Obviously soil moisture is one of essential components in the climate change study, and how to couple soil moisture variations into climate change prediction study requires more efforts.

SRSM is proven to be a reliable and feasible tool to retrieve soil moisture in Eastern China, and the retrieved soil moisture can reproduce the spatial and temporal variations of observed soil moisture.

Remote sensing is another useful way to retrieve soil moisture. SWI is derived from Earth Resources Satellite (ERS) scatterometer observation and can help to reduce the difficulty of lacking soil moisture observation in large scale and high spatial resolution. The retrieved soil moisture can be used as initial conditions in regional climate simulations in Eastern China monsoon regionl, as well as the validation data for land surface model.

The surface climate is closely connected to soil moisture in both prior and lag correlation analyses. It is obvious that there are close correlations among soil moisture, surface air temperature and the precipitation for both preceding and lagged. Obviously soil moisture is one of essential components in the climate change study, and how to couple soil moisture variations into climate change prediction study requires more efforts.

Progresses have been made on the relationship between soil moisture and climate change, still there exists many problems which need further attention, for example, the annual and interannual variations of soil moisture and temperature, and their interactions with regional climate, the design of initial soil moisture scheme in climatic model, soil moisture and temperature anomalies and their impact on regional climate, and the effect of regional drying tendency on climate and environment in middle latitude of Eastern China.

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