Abstract:

The hydrological process of the Poyang Lake Basin is a local hot topic. Soil moisture is an important state variable of the hydrological process and plays a critical role in water balance at basin scale. However, the spatial and temporal variation of soil moisture is still lack of systematic research when compared with others hydrological factors, which leads to a strong uncertainty for the research of the hydrological process. The main objectives of this paper are to illustrate the soil moisture dynamics and its influencing factors at different spatial and temporal scales of the Poyang Lake Basin. For these objectives, this paper firstly obtained the AMSRE soil moisture data set from the National Snow & Ice Data Center (NSIDC, http://nsidc.org/data/amsre/index.html) from 2003 to 2009. Then the soil moisture was downscaled to resolution of 1 km and calibrated through the time series insitu soil moisture. After that, this paper investigated the annual and monthly variations of soil moisture at the spatial scales of basin, subbasin and land cover. Finally, it analyzed the relationships between soil moisture with precipitation, air temperature and land cover to capture the controlling factors. The results show that: i) at the scale of basin, the soil moisture presenteda spatial pattern of “Funnel” with the low soil moisture in center and high around at the basin scale, whereas the spatial difference at summer and fall season wasminor. Temporally, annual soil moisture decreased significantly at both basin and subbasin scale, and the rapidest decrease rate occurredin the Lake area (-035%/year). It implies that it is vulnerable to suffer from drought at the Lake area. Furthermore, there were significant differences among the monthly soil moisture, with the variability about 3~4%. The highest soil moisture mainly occurredin April, while the lowest occurred in September or October. ii) At the scale of land cover, forest obtainedthe highest soil moisture. Annual soil moisture decreased in all land cover types, with the lowest decrease rate occurred in forest area. It implies a strong ability to control drought at annual scale. Monthly soil moisture variedwith the land cover types, but the differences were minor in June, July and October. It demonstrates that the effect of land cover was weakened under the extreme climate condition (i.e., the extreme high precipitation and air temperature). iii) With regards to the controlling factors, soil moisture was positively correlated to precipitation and negatively to air temperature. However, soil moisture was positively correlated to air temperature in the Lake area, which is mainly attributed to the irrigation in summer. Furthermore, the correlation of precipitation was higher than that of air temperature. It means that precipitation plays more important role on the soil moisture. Results of this paper would help to understand the hydrological process, but also support the water resource and drought controlling for the basin