| Mongolia plateau is located at a semi-arid and arid climate region, and the fragile ecological environment makes it sensitive to climate change. Soil moisture is an important component of the hydrologic cycle in terrestrial ecosystems and it is critical for predicting and understanding various hydrological processes, including changes in weather conditions, precipitation patterns, runoff generation and irrigation scheduling. Soil moisture is a function of the total effect of environmental factors. Thus, a soil moisture retrieval model for the Mongolia Plateau was built using microwave radiance transfer function and Qp model based on AMSR-2 brightness temperature and SPOT normalized difference vegetation index (NDVI) data. Soil moisture was retrieved, and the retrieval precision was verified during vegetation growth period from April to October 2013 in the Mongolia Plateau. Meanwhile, by introducing an idea of spatial-temporal stability to explore the spatio-temporal variability of surface soil moisture. Combination with TRMM 3B43 precipitation and air temperature data acquired by meteorological stations, the study explored response characteristics between soil moisture, meteorological factors and vegetation. The results showed that:(1) The coefficient of Pearson between retrieved and ground-based was 0.825, with a root-mean square error of 0.0316cm3-cm-3, and the model passed two-tailed test under the significant levels 0.01. The retrieval result was much better than soil moisture product data of JAXA (RMSE= 0.0441cm3·cm-3). The developed model had a high accuracy and was applicable in surface soil moisture estimation. The regression coefficient of the linear fit of the TRMM 3B43 precipitation measure (rainfall) was 0.8598 and with a slope line of 0.9415, which suggested that TRMM 3B43 data were applicable in the Mongolia Plateau.(2) The average value of surface soil moisture lies between 0.047 cm3·cm-3 and 0.234cm3·cm-3, and spatial distribution has local difference which gradually decreases from north to south, from northeast to southwest. The distribution of high value area, transition zone and low value zone of soil moisture is obvious. RMSE?s results showed that In Mongolia Sayan Mountains east, Kent hill north surrounded intermountain basin, Inner Mongolia Daxinganling forest region, spatial variation of the soil moisture in the study area with the average soil moisture condition is more severe. In Mongolia Zavkhan Province in the west, Kent Province in central and Western Inner Mongolia eastern edge of Tengger Desert-in the Ordos Plateau-Wulanchabu plateau-Xilin Gol League in Hunshandake sandy land area, the average change in soil moisture variation in soil moisture with the whole study area consistent.(3) Soil moisture has an obvious change with season, the soil moisture in the peripheral area of the whole plateau is relatively high, while the soil moisture in the plateau is relatively low. With the arrival of the rainy season, soil moisture high value area gradually extended to the interior of the plateau and northwest region. RMSEst results showed that in plateau periphery soil moisture was higher in the area, the time stability of the weaker, and in plateau internal soil water low value area, especially in desert steppe region, the time stability of the strongest, with the seasonal variation of soil moisture fluctuation is not obvious.(4) Total precipitation, mean NDVI and soil moisture during the growing season decreased gradually from north to south and from northeast to southwest. The response characteristics of soil moisture to rainfall, temperature and vegetation were significant difference in different climatic sub regions. In the arid region of the study area, soil moisture was significantly and positively correlated with temperature. Compared to the precipitation, soil moisture is more sensitive to air temperature. In the semi-arid region of the study area, the effect of vegetation on soil moisture showed a trend of increasing first and then decreasing, and the effects of temperature and precipitation on soil moisture showed seasonal variations. The response of soil moisture to the three factors was in the order of vegetation> precipitation> temperature in the semi-humid region of the study area. In conclusion, the response of soil moisture to both environmental factors and vegetation could provide scientific basis for constructing healthy regional eco-environments with reducing disasters risk. |
PDF Full Text Request