GLOBAL DISTRIBUTION OF PLANT-EXTRACTABLE WATER CAPACITY OF SOIL
Article first published online: 4 DEC 1998
Copyright © 1996 The Royal Meteorological Society
International Journal of Climatology
Volume 16, Issue 8, pages 841–859, August 1996
How to Cite
DUNNE, K. A. and WILLMOTT, C. J. (1996), GLOBAL DISTRIBUTION OF PLANT-EXTRACTABLE WATER CAPACITY OF SOIL. Int. J. Climatol., 16: 841–859. doi: 10.1002/(SICI)1097-0088(199608)16:8<841::AID-JOC60>3.0.CO;2-8
- Issue published online: 4 DEC 1998
- Article first published online: 4 DEC 1998
- Manuscript Accepted: 9 NOV 1995
- Manuscript Received: 5 DEC 1994
- NASA & GEOPHYSICAL FLUID DYNAMICS LABORATY OF NOAA. Grant Numbers: NAG5-853, NAGW-1884
- plant-extractable water capacity of soil;
- soil moisture;
- available water capacity;
- global soil moisture;
- global water budget
Plant-extractable water capacity of soil is the amount of water that can be extracted from the soil to fulfill evapotranspiration demands. It is often assumed to be spatially invariant in large-scale computations of the soil-water balance. Empirical evidence, however, suggests that this assumption is incorrect. In this paper, we estimate the global distribution of the plant-extractable water capacity of soil.
A representative soil profile, characterized by horizon (layer) particle size data and thickness, was created for each soil unit mapped by FAO (Food and Agriculture Organization of the United Nations)/Unesco. Soil organic matter was estimated empirically from climate data. Plant rooting depths and ground coverages were obtained from a vegetation characteristic data set. At each 0.5°×0.5° grid cell where vegetation is present, unit available water capacity (cm water per cm soil) was estimated from the sand, clay, and organic content of each profile horizon, and integrated over horizon thickness. Summation of the integrated values over the lesser of profile depth and root depth produced an estimate of the plant-extractable water capacity of soil.
The global average of the estimated plant-extractable water capacities of soil is 8ċ6cm (Greenland, Antarctica and bare soil areas excluded). Estimates are less than 5, 10 and 15 cm—over approximately 30, 60, and 89 per cent of the area, respectively. Estimates reflect the combined effects of soil texture, soil organic content, and plant root depth or profile depth. The most influential and uncertain parameter is the depth over which the plant- extractable water capacity of soil is computed, which is usually limited by root depth. Soil texture exerts a lesser, but still substantial, influence. Organic content, except where concentrations are very high, has relatively little effect.