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.