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Soil moisture introduction
Soil moisture is a key variable in climate and hydrological science through its impact on the energy and water balance. There has been a great discussion about the role of soil moisture in the land water and energy balance. In the land water balance, soil moisture is a source of water for the atmosphere as the evapotranspiration. The previous study noted that about 60 % of the land precipitation returns to the atmosphere. In the land energy balance, soil moisture constrains Bowen ratio, which is the partitioning ratio of incoming solar radiation into sensible heat flux and latent heat flux. This energy partitioning is important for land surface climate processes as well as that of the global.
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Ground-based observation data
Three automatic weather stations (AWSs) and 13 automatic stations for soil hydrology (ASSHs) have been monitoring soil moisture and meteorological elements since 2001 and 2000, respectively. The location of these observation sites are shown in Table 2.1 and Figure 2.2. AWSs measure some of meteorological elements and soil moisture at four depths with a time interval of 30 minutes. ASSHs observe soil moisture and soil temperature at the depth of 3cm and 10cm. The time interval of the measurements at ASSHs is one hour until October 2004, after which it has been 2 hours due to electric problem. Because of different time interval between the instruments, the hourly soil moisture and meteorological variables were calculated using linear interpolation.
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The target area
Mongolia is located over mid-latitude in the Northeastern Asia and has an arid and cold climate. The study area is the validation site in Mongolian grassland near Mandalgobi city at the Mongolia Plateau. The area was approximately 160 km by 120 km in size and topography is mostly flat. Annual precipitation is approximately 70-150 mm, and concentrated in summer. Vegetation is pasture grass and sparse shrubs. Land use is largely dominated by rangeland, and there are no major rivers within this area.
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