Abstract:
Plant-available water in the root zone is the key variable in many applications, as it controls the plant-physiological activity in semi-arid regions. It therefore plays a role in drought development and persistence, and the planning of agricultural practices, in particular timing of sowing and irrigation. However, in most parts of Australia, the root zone water content is often poorly known and generally quantified using land surface models driven by atmospheric predictions. The inclusion of space-borne surface soil moisture observations allows to constrain the model trajectories, reducing potential errors due to model parameterization and uncertainties in the forcing data. The advantage of using remotely sensed products is that areas with high uncertainty in rainfall input can be better monitored in terms of their soil water content, in particular in remote locations throughout inland Australia. This paper first evaluates the products obtained from three satellites, namely ASCAT, SMAP, and Sentinel-1A at varying spatial resolutions (25 km, 9 km, and 1 km, respectively) over an 18-month period, starting in April 2015. The products are compared against in situ monitoring stations across the Australian wheatbelt, located within different climate regimes, from the high-rainfall zones to arid regions, and also including a range of soil and land use types. Their differences and similarities are then assessed across the entire continent, in terms of their spatio-temporal performance, and their ability to reproduce overall seasonal trends, including extreme events, such as droughts.