Vegetation dynamics and soil water balance in a water-limited Mediterranean ecosystem on Sardinia, Italy

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.

Development and testing of a large, transportable rainfall simulator for plot-scale runoff and parameter estimation

“…We use these two values rather than one K s value to separate the behavior of the soil surface, which determines the amount of water that infiltrates, from that of the bulk soil, which determines overall soil water content. Based on previous work for this site (Montaldo et al, 2008), the estimated saturated hydraulic conductivity for this soil is approximately 18 mm h −1 , and since land use and vegetation cover have not changed at the site, the estimate is still considered accurate to an order of magnitude. Therefore, if K s values obtained from model fitting are close to this previous estimate, then the rainfall simulator indeed performs as intended.…”

“…However, examining the spatial variability within the plot allows for a better understanding of each experiment. According to previous fieldwork at this site (Montaldo et al, 2008) and examination of the measured soil moisture at saturation, the soil has an average porosity of θ s = 0.568. However, the saturation value at each individual probe location varies.…”

“…The soil is a silt loam with bulk density of 1.38 g cm −3 (Montaldo et al, 2008). The choice of a vegetated plot is intentional, as future work with this rainfall simulator will be to assess the effect of vegetation on the estimated soil parameters.…”

Distributed hydrologic modeling of a sparsely monitored basin in Sardinia, Italy, through hydrometeorological downscaling

“…We used the Penman-Monteith (PM) equation (Allen et al, 1989(Allen et al, , 2006 to compute ET 0 (h, d, m, y)| H with meteorological data in the period 1995-2010 (Table 3) and values of stomatal resistance and albedo from a study by Montaldo et al (2008) in Sardinia. From the hourly estimates, we derived ET 0 (d, m, y)| D by summing over the 24 h of each day.…”

“…The values of K s and f were modified within the ranges typical for the corresponding soil texture classes (Fig. 2), while, for the other parameters, we adopted literature values for similar soil and vegetation properties (Rawls et al, 1983;Noto et al, 2008;Montaldo et al, 2008;Vivoni et al, 2010). Table 8 presents the parameter values in the main classes.…”