A COMPARATIVE MODELING STUDY OF SOIL-WATER DYNAMICS IN A DESERT ECOSYSTEM

Citation
Pr. Kemp et al., A COMPARATIVE MODELING STUDY OF SOIL-WATER DYNAMICS IN A DESERT ECOSYSTEM, Water resources research, 33(1), 1997, pp. 73-90
Citations number
103
Categorie Soggetti
Limnology,"Environmental Sciences","Water Resources
Journal title
ISSN journal
00431397
Volume
33
Issue
1
Year of publication
1997
Pages
73 - 90
Database
ISI
SICI code
0043-1397(1997)33:1<73:ACMSOS>2.0.ZU;2-X
Abstract
We compared three different soil water models to evaluate the extent t o which variation in plant growth form and cover and soil texture alon g a topographic gradient interact to affect relative rates of evaporat ion and transpiration under semiarid conditions. The models all incorp orated one-dimensional distribution of water in the soil and had separ ate functions for loss of water through transpiration and soil evapora tion but differed in the degree of mechanism and emphasis. PALS-SW Pat ch Arid Lands Simulator-Soil Water) is a mechanistic model that includ es soil water fluxes and emphasizes; the physiological control of wate r loss by different plant life forms along the gradient. 2DSOIL is a m echanistic model that emphasizes the physical aspects of soil water fl uxes. SWB (Soil Water Budget) is a simple water budget model that has no soil water redistribution and includes simplified schemes for soil evaporation and transpiration by different life forms. The model predi ctions were compared to observed soil water distributions at five posi tions along the gradient. All models predicted soil water distribution s reasonably well and, for the most part, predicted similar trends alo ng the transect in the fractions of water lost as soil evaporation ver sus transpiration. Transpiration was lowest (about 40% of total evapot ranspiration (ET)) for the creosote bush community, which had the lowe st plant cover (30% peak cover). The fraction of ET as transpiration i ncreased with increasing plant cover, with 2DSOIL predicting the highe st transpiration (60% of total ET) for the mixed vegetation community (60% peak cover) on relatively fine textured soil and PALS-SW predicti ng highest transpiration (69% of total ET) for the mixed vegetation co mmunity (70% peak cover) on relatively coarse textured soil. The commu nity type had an effect on the amount of water lost as transpiration p rimarily via depth and distribution of roots. In this respect, PALS-SW predicted greatest differences among stations as related to differenc es in plant community types. However, since FALS,SW did not provide as good of fit with the soil moisture data as did 2DSOIL, the difference s in the morphology and physiology of the life-forms may be secondary to the overall control of water loss by the primary factors accounted for in 2DSOIL: vertical distribution of soil moisture. degree of canop y cover, and evaporative energy budget of the canopy. Soil texture int eracted with the amount and type of plant cover to affect evaporation and transpiration, but the effect was relatively minor.