Abstract
Abstract. Mediterranean ecosystems are commonly heterogeneous savanna-like ecosystems, with contrasting plant functional types (PFTs, e.g. grass and woody vegetation) competing for water. Mediterranean ecosystems are also commonly characterized by strong inter-annual rainfall variability, which influences the distributions of PFTs that vary spatially and temporally. An extensive field campaign in a Mediterranean setting was performed with the objective to investigate interactions between vegetation dynamics, soil water budget and land-surface fluxes in a water-limited ecosystem. Also a vegetation dynamic model (VDM) is coupled to a 3-component (bare soil, grass and woody vegetation) Land surface model (LSM). The case study is in Orroli, situated in the mid-west of Sardegna within the Flumendosa river basin. The landscape is a mixture of Mediterranean patchy vegetation types: trees, including wild olives and cork oaks, different shrubs and herbaceous species. Land surface fluxes, soil moisture and vegetation growth were monitored during the May 2003–June 2006 period. Interestingly, hydrometeorological conditions of the monitored years strongly differ, with dry and wet years in turn, such that a wide range of hydrometeorological conditions can be analyzed. The coupled VDM-LSM model is successfully tested for the case study, demonstrating high model performance for the wide range of eco-hydrologic conditions. Results demonstrate also that vegetation dynamics are strongly influenced by the inter-annual variability of atmospheric forcing, with grass leaf area index changing significantly each spring season according to seasonal rainfall amount.
Highlights
Mediterranean semi-arid ecosystems are characterized by water-limited conditions
In the model the vegetation dynamic model (VDM) provides the grass leaf area index (LAI) evolution through time, and the Land surface model (LSM) uses this to compute the land surface fluxes and update the soil water contents. They successfully tested the coupled model for two case studies of water-limited grass fields in California (USA) and North Carolina (USA). Even in such “simple” ecosystems characterized by only one PFT, they demonstrated the significant role of vegetation dynamics on soil water balance modeling in water-limited conditions, and the importance of including the VDM for correctly predicting land surface fluxes and soil water balance
The coupled VDM-LSM is tested for predicting energy balance terms, soil moisture and LAI of both PFTs
Summary
Mediterranean semi-arid ecosystems are characterized by water-limited conditions. These ecosystems and the goods and services that they provide are increasingly threatened by the broad desertification processes produced by both natural (climate variation, fires, etc.) and human (deforestation, overgrazing, urbanization, pollution, fires, etc.) influences (e.g. Brunetti et al, 2002; Lelieveld et al, 2002; Moonen et al, 2002; Ventura et al, 2002; Ceballos et al, 2004). In the model the VDM provides the grass leaf area index (LAI) evolution through time, and the LSM uses this to compute the land surface fluxes and update the soil water contents They successfully tested the coupled model for two case studies of water-limited grass fields in California (USA) and North Carolina (USA). Even in such “simple” ecosystems characterized by only one PFT, they demonstrated the significant role of vegetation dynamics on soil water balance modeling in water-limited conditions, and the importance of including the VDM for correctly predicting land surface fluxes and soil water balance. Development of a 3-component (bare soil, grass and woody vegetation) coupled VDM-LSM for modeling land surface dynamics of a water-limited Mediterranean heterogeneous ecosystem; 3. This paper addresses the following objectives: 1. pointing out the dynamics of land surface fluxes, soil moisture and vegetation cover for years with different hydro-meteorological conditions of the Sardinian heterogeneous ecosystem; 2. development of a 3-component (bare soil, grass and woody vegetation) coupled VDM-LSM for modeling land surface dynamics of a water-limited Mediterranean heterogeneous ecosystem; 3. assess the influence of key environmental factors on the vegetation dynamics for the different annual hydrologic conditions
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