HR: 1340h
AN: B33D-1059    [Abstracts]
TI: Horizontal Precipitation in a Semiarid Cloud Forest: A Feedback Between Vegetation and Water Availability
AU: * Hildebrandt, A
EM: hildebra@alum.mit.edu
AF: UFZ Centre for Environmental Research Leipzig-Halle GmbH, Permoserstr. 15, Leipzig, 04318 Germany
AU: Eltahir, E A
EM: eltahir@mit.edu
AF: Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 77 Massachussetts Avenue 48-207, Cambridge, MA 02139 United States
AB: We investigate the particular hydrology of an endangered semiarid cloud forest in the governorate of Dhofar (Oman). This forest is currently overexploited by browsing cattle feeding on tree canopies, leading to degradation of forest into grassland. In this region the forests survive in a relatively dry climate (annual rainfall below 250mm/year, annual temperature 21degC) as a result of the microclimate provided by annual reoccurrence of seasonal cloud immersion, which coincides with the wet summer season. Besides decreasing incoming radiation, the cloud cover provides for an additional water source besides rainfall. Due to turbulent exchange cloud droplets are mixed from surrounding clouds into the vegetation canopy, where they are captured by leaves, and eventually drip down to the ground (horizontal precipitation). In Dhofar, horizontal precipitation was estimated to account for up to two times the rainfall amount, based on results of a field experiment in 2004. Horizontal precipitation, and therefore plant available water, depends on the surface roughness, which is greatly enhanced by the presence of tall vegetation. On the other hand, water availability determines vegetation height in a water limited environment. We included a model for horizontal precipitation into a dynamical vegetation model (IBIS) to investigate, if the degradation of forest into grassland leads to a decrease in plant available water that is strong enough to substantially limit net primary productivity and vegetation height. Our model results suggest that tree removal triggers a feedback leading to substantially smaller water gain by the vegetation, resulting in an overall drier environment that prevents re-establishment of tree vegetation, and sustains the landscape in a degraded state.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1809 Desertification
DE: 1813 Eco-hydrology
DE: 9320 Asia
SC: Biogeosciences [B]
MN: Fall Meeting 2005