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- Title
Retrieving Soil Moisture Storage in the Unsaturated Zone Using Satellite Imagery and Bi-Annual Phreatic Surface Fluctuations.
- Authors
Ahmad, Mobin-ud-Din; Bastiaanssen, W.G.M.
- Abstract
Ongoing research into net groundwater use in Pakistan needed soil moisture storage information to compute monthly soil water balances. A methodology is developed to retrieve soil moisture storage in the complete unsaturated zone from root zone soil moisture content (based on thermal satellite imagery) and bi-annual phreatic surface fluctuations. A root mean square error in volumetric soil moisture content of 0.05 cm3 cm-3 in the root zone of irrigated fields was found for the case study in Pakistan. A new simple parameterisation of matric pressure head distribution between the root zone and the phreatic surface was developed. The absolute root mean square error in daily estimates of unsaturated zone storage for shallow (2 m) and deep groundwater tables (10 m) was found to be 7 cm (the average total storage is 110 cm). It is concluded that the spatial variation of the soil moisture storage depends on the depth of the phreatic surface, whereas the temporal variation is mainly controlled by the root zone soil moisture changes. The results show that for an area of 3 million ha, storage changes of ± 10 cm month-1 occur, which is a significant quantity for monthly water balance analysis. Conventional methods such as specific yield do not consider moisture changes in the irrigated top soil when the groundwater table is deep. The new method is, therefore, a possible alternative solution, especially in areas where hydrological data is scanty.
- Subjects
PAKISTAN; SOIL moisture; GROUNDWATER; WATER table; HYDROGEOLOGY; SOIL physics
- Publication
Irrigation & Drainage Systems, 2003, Vol 17, Issue 3, p141
- ISSN
0168-6291
- Publication type
Article
- DOI
10.1023/A:1025101217521