This paper introduces a geomorphological framework that uses the channel network as a spatial template to investigate the organization of vegetation, soils and the soil water balance in a semiarid river basin. By coupling a stochastic soil moisture model with the basin area function, the authors show that mean soil moisture, transpiration and dynamic water stress all exhibit self-affine characteristics linked to the geomorphic structure of the network.

Application to the Upper Rio Salado basin reveals that the actual vegetation pattern lies within an envelope bounded by a random configuration and an “ideal” one minimizing water stress — suggesting that natural ecosystems balance large-scale optimality with random small-scale ecological legacies (dispersal, disturbance, founder effects).

@article{Caylor2005,
  author  = {Caylor, Kelly K. and Manfreda, Salvatore and Rodriguez-Iturbe, Ignacio},
  title   = {On the coupled geomorphological and ecohydrological organization of river basins},
  journal = {Advances in Water Resources},
  volume  = {28}, number = {1}, pages = {69--86}, year = {2005},
  doi     = {10.1016/j.advwatres.2004.08.013}
}

Using satellite NDVI time series along the Kalahari Transect (Angola–Botswana–South Africa), this study explores how grass cover responds dynamically to interannual rainfall variability and how this dynamic component sustains the long-term persistence of savanna ecosystems. A simple soil moisture model coupled with a grass growth/decay equation reproduces 16 years of satellite-derived fractional grass cover.

Comparison between dynamic and static grass cover shows that the temporally adaptive grass component buffers tree water stress during dry years and reduces deep drainage during wet years — a co-organization in which trees track the long-term rainfall mean while grasses follow its high-frequency variability.

@article{Scanlon2005,
  author  = {Scanlon, Todd M. and Caylor, Kelly K. and Manfreda, Salvatore and Levin, Simon A. and Rodriguez-Iturbe, Ignacio},
  title   = {Dynamic response of grass cover to rainfall variability: implications for the function and persistence of savanna ecosystems},
  journal = {Advances in Water Resources},
  volume  = {28}, number = {3}, pages = {291--302}, year = {2005},
  doi     = {10.1016/j.advwatres.2004.10.014}
}

Building on the analytical space–time soil moisture covariance, this paper develops a quantitative framework for the design of soil moisture sampling networks. Two estimation problems are addressed: the long-term mean daily soil moisture at a point (relevant for remote-sensing calibration and GCM validation) and the daily soil moisture averaged over an area (relevant for hydrological modelling).

Random and stratified random sampling schemes are compared as functions of network size, sampling duration and landscape heterogeneity. The geometry of the network plays a minor role in long-term mean estimation — where temporal sampling dominates — but a major role in instantaneous areal averages, especially in heterogeneous landscapes.

@article{Manfreda2006,
  author  = {Manfreda, Salvatore and Rodriguez-Iturbe, Ignacio},
  title   = {On the spatial and temporal sampling of soil moisture fields},
  journal = {Water Resources Research},
  volume  = {42}, number = {5}, pages = {W05409}, year = {2006},
  doi     = {10.1029/2005WR004548}
}

This paper extends the analytical space–time soil moisture framework to landscapes with two functionally different vegetation types — trees and grasses — represented as a marked Poisson process. Each species contributes its own interception, evapotranspiration and rooting parameters, propagated analytically into the soil moisture covariance.

Two regimes emerge: a small-scale decay driven by vegetation heterogeneity and a large-scale decay imposed by rainfall fields. Spatial averaging strongly smooths variability, whereas temporal averaging up to one week leaves the variance largely unchanged. The model is parameterized with rainfall data from the Basilicata region (southern Italy).

@article{RodriguezIturbe2006,
  author  = {Rodriguez-Iturbe, Ignacio and Isham, Valerie and Cox, David R. and Manfreda, Salvatore and Porporato, Amilcare},
  title   = {Space-time modeling of soil moisture: Stochastic rainfall forcing with heterogeneous vegetation},
  journal = {Water Resources Research},
  volume  = {42}, number = {6}, pages = {W06D05}, year = {2006},
  doi     = {10.1029/2005WR004497}
}

Using soil moisture maps from the VIC model within the North American Land Data Assimilation System (NLDAS) at 0.125° resolution, this paper investigates the scaling behaviour of soil moisture variance as a function of averaging area for both the surface (10 cm) and root-zone (100 cm) layers.

Variance follows a clear power-law decay with averaging area, with slopes that depend systematically on the soil moisture state: drying steepens the slope (reducing spatial correlation), wetting flattens it. The deeper layer shows greater spatial organization and time stability than the surface layer — relevant for downscaling remote-sensing products and for avoiding biases in coarse-resolution land surface models.

@article{Manfreda2007,
  author  = {Manfreda, Salvatore and McCabe, Matthew F. and Fiorentino, Mauro and Rodriguez-Iturbe, Ignacio and Wood, Eric F.},
  title   = {Scaling characteristics of spatial patterns of soil moisture from distributed modelling},
  journal = {Advances in Water Resources},
  volume  = {30}, number = {10}, pages = {2145--2150}, year = {2007},
  doi     = {10.1016/j.advwatres.2006.07.009}
}

Pot-scale and field experiments on olive plants (Olea europaea L., cv. Coratina) characterize the physiological and biochemical mechanisms by which this iconic Mediterranean species tolerates prolonged drought. Measurements include leaf water potential, gas exchange, photosynthetic efficiency, osmotic adjustment, antioxidant enzyme activity and root/canopy growth ratios.

Olive plants sustain transpiration and photosynthesis at very low leaf water potentials thanks to active osmotic adjustment (mannitol, glucose, proline), increased cell-wall elasticity, up-regulation of antioxidant enzymes and a higher root-to-canopy ratio — making the olive tree a true paradigm of drought tolerance in semiarid Mediterranean conditions.

@article{Sofo2008,
  author  = {Sofo, Adriano and Manfreda, Salvatore and Fiorentino, Mauro and Dichio, Bartolomeo and Xiloyannis, Cristos},
  title   = {The olive tree: a paradigm for drought tolerance in Mediterranean climates},
  journal = {Hydrology and Earth System Sciences},
  volume  = {12}, number = {1}, pages = {293--301}, year = {2008},
  doi     = {10.5194/hess-12-293-2008}
}

This editorial introduces the special issue Coupled Ecological–Hydrological Processes of the journal Ecohydrology, originating from an EGU General Assembly session on climate–soil–vegetation interactions. The collection is organized around four themes: soil moisture dynamics, soil–plant interactions, vegetation modelling and the effects of climate change on natural ecosystems.

Spanning field experiments, soil moisture and water-stress modelling, coupled physically based ecohydrological models and climate-change scenarios, the editorial highlights how ecohydrology operates as an inherently interdisciplinary science, building the bridges needed for sustainable management of water resources and natural ecosystems.

@article{Manfreda2010preface,
  author  = {Manfreda, Salvatore and Smettem, Keith and Iacobellis, Vito and Montaldo, Nicola and Sivapalan, Murugesu},
  title   = {Coupled ecological--hydrological processes},
  journal = {Ecohydrology},
  volume  = {3}, number = {2}, pages = {131--132}, year = {2010},
  doi     = {10.1002/eco.131}
}

This paper extends the widely-used stochastic soil moisture model of Laio et al. (2001) to include the limited infiltration capacity of soils, accounting explicitly for storm duration through Philip’s infiltration equation. The new scheme is compared with the original saturation-excess formulation across a wide range of soil textures and climatic conditions.

Differences are negligible in highly permeable soils but become substantial in less permeable soils (loam, clay) and under climates with short, intense storms — typical of arid and Mediterranean regions. Including infiltration excess generally lowers both the mean and variance of soil moisture, leading to higher predicted vegetation water stress. The choice of infiltration scheme has a magnified impact on ecological state variables relative to hydrological ones.

@article{Manfreda2010,
  author  = {Manfreda, Salvatore and Scanlon, Todd M. and Caylor, Kelly K.},
  title   = {On the importance of accurate depiction of infiltration processes on modelled soil moisture and vegetation water stress},
  journal = {Ecohydrology},
  volume  = {3}, number = {2}, pages = {155--165}, year = {2010},
  doi     = {10.1002/eco.79}
}

This paper proposes a generalized framework linking the spatial organization of individuals — described through a generalized double-Poisson distribution — to landscape-scale water balance and water stress. Plants are represented as random points with circular canopies and root systems, capturing both the facilitative effect of overlapping canopies (light interception) and the competitive effect of overlapping root systems (water uptake).

Combining global remote-sensing clumping indices, TRMM rainfall climatologies and the analytical model, the authors identify the climatic boundaries that favour clumped versus over-dispersed vegetation. Clumping emerges as a strategy to maximize stress-weighted water use under drier conditions, while over-dispersed patterns dominate in wetter climates — offering a physical interpretation of the increasing variability observed in dryland ecosystems.

@article{Manfreda2017,
  author  = {Manfreda, Salvatore and Caylor, Kelly K. and Good, Stephen P.},
  title   = {An ecohydrological framework to explain shifts in vegetation organization across climatological gradients},
  journal = {Ecohydrology},
  volume  = {10}, number = {3}, pages = {e1809}, year = {2017},
  doi     = {10.1002/eco.1809}
}