Analyzing The Characteristics Of Soil Moisture In Jiangsu Coastal Zones

In this paper,we use GLDAS(Global Land Data Assimilation System)data,temperature and precipitation observation data to analyze the characteristics of soil moisture in the eastern region of China.We find that the temperature and precipitation in different seasons have different degrees of influence on the characteristics of soil moisture in each layer.The results show that over the last 50 years,the soil moisture in eastern China has a tendency to dry out,especially between the late 1970s to the early 1980s.The change of soil moisture with the depth of soil layer has similar inter-annual and seasonal patterns.Soil moisture in different depths(0-200 cm)positively correlates with the air temperatures of spring,summer and autumn,but negatively correlates with the air temperature in winter at 0-10 cm,40-100 cm and 100-200 cm.Similarly,soil moisture is positively related to the precipitation in spring,summer and autumn,and the opposite is true in winter.The results also show that precipitation has a significant effect on the shallow soil moisture,while air temperature most affects the deep soil moisture.Then,we choose MODIS vegetation index data(MOD13A2)and land surface temperature data(MOD11A2)in Jiangsu coastal zone to build the NDVI-Ts and EVI-Ts feature space.From the feature space,we get the wet and dry side equation,and calculate the temperature vegetation drought index(TVDI)to analyze the Jiangsu region spatial distribution of soil moisture.We analyze quantitatively the differences between NDVI and EVI,The inversion results show that the soil moisture value in the eastern coastal zone of Jiangsu is higher than that in the non-coastal areas.Finally,based on the surface soil moisture data of GLDAS from 1961 to 2011 and the COBE-SST(sea surface temperature)reanalysis data,we use the correlation analysis,time-delay correlation analysis and time series causality analysis methods to analyze the relationship between the annual change of soil moisture in the coastal zone of Jiangsu and SST in coastal waters of China.The analysis results show that SST in coastal waters of China shows a warming trend in the long time series,especially since 1987.However,the soil moisture in coastal areas of Jiangsu showed a drying trend,which was obvious after 1978.Before 1974 and after 2002,SST and soil moisture changed in the same phase,while from 1974 to 2002,they changed in the opposite phase.Regional correlation analysis shows that the Yellow sea,the East China Sea and the South China Sea adjacent to the coast of Guangdong province are significantly correlated areas,and time-series causal analysis proves that SST and soil moisture are correlated,the effect of SST on soil moisture is greater than soil moisture on SST.SST in spring,summer and winter was negatively correlated with soil moisture in spring and autumn,and positively correlated with soil moisture in summer and winter.The SST in autumn and the soil moisture in four seasons are contrary to above conclusion.These phenomena indicate that the thermodynamic state of SST in coastal waters of China will affect the soil moisture in the coastal zone of Jiangsu.