26.1 Soil moisture
Soil moisture in the Adelaide region was 1,254,741 ML at 30 June 2010 (opening balance) and 1,365,350 ML at 30 June 2011 (closing balance). Soil moisture represents the water stored in the soil. Not all this moisture is available to plants as it is held too tight for plants to extract.
Soil moisture for the Adelaide region was estimated based on the AWRA-L version 1.0.0 (Van Dijk 2010) surface soil, shallow soil and deep-soil moisture model outputs.
Using climate grid data for the Adelaide region (including precipitation, temperature and solar radiation data), AWRA-L was used to estimate the soil moisture for each soil layer at each grid point within the region. Only soil moisture within the landscape was considered; therefore, the surface areas of the major storages and off-channel water storages (farm dams) were excluded from the analysis.
The total water depth in all three layers of the soil column at each grid point was extracted. This depth was then multiplied by the surface area represented by each individual grid point to give a volumetric estimate for every grid point. The volume for each grid point was summed up to provide an estimate of soil moisture for the entire landscape within the Adelaide region.
Assumptions, Limitations, Caveats and Approximations
- These estimates have not been compared to any real-time measured data for the 2010–11 year.
- The soil moisture estimates are subject to the assumptions of the AWRA-L v1.0.0 model detailed in Van Dijk (2010).
- AWRA-L was balanced according to the supply of water to the landscape via precipitation and therefore does not account for application of water via irrigation and lateral flow.