On the spatial and temporal sampling of soil moisture fields

Recent work by Isham et al. and Rodrìguez-Iturbe et al. has characterized the space- time variability of soil moisture through its analytically derived covariance function which depends on soil properties, vegetation structure, and rainfall patterns typical of a region. This paper uses such characterization to address the strategies and methodologies for the sampling of soil moisture fields. The focus is on the estimation of the long-term mean soil moisture and the daily soil moisture averaged over a given area as a function of the network geometry, number of stations, number of sampling days and landscape heterogeneity. It is found that the spatial geometry of the network has a significant impact on the sampling of the average soil moisture over an area in any particular day, while it is much less relevant for the sampling of the long-term mean daily soil moisture over the region. In the latter case, the length of the record is a commanding factor in what concerns the variance of estimation, specially for soils with shallow rooted vegetation. Spatial vegetation heterogeneity plays an important role on the variance of estimation of the soil moisture, being particularly critical for the sampling of the average soil moisture over an area for a given day.

How to cite: Manfreda, S. and I. Rodrìguez-Iturbe, On the Spatial and Temporal Sampling of Soil Moisture FieldsWater Resources Research, 42, W05409, (doi:10.1029/2005WR004548), 2006. [pdf]

Space-time modeling of soil moisture: Stochastic rainfall forcing with heterogeneous vegetation

The present paper complements that of Isham et al. (2005), who introduced a space-time soil moisture model driven by stochastic space-time rainfall forcing with homogeneous vegetation and in the absence of topographical landscape effects. However, the spatial variability of vegetation may significantly modify the soil moisture dynamics with important implications for hydrological modeling. In the present paper, vegetation heterogeneity is incorporated through a two dimensional Poisson process representing the coexistence of two functionally different types of plants (e.g., trees and grasses). The space-time statistical structure of relative soil moisture is characterized through its covariance function which depends on soil, vegetation, and rainfall patterns. The statistical properties of the soil moisture process averaged in space and time are also investigated. These properties are especially important for any modeling that aggregates soil moisture characteristics over a range of spatial and temporal scales. It is found that particularly at small scales, vegetation heterogeneity has a significant impact on the averaged process as compared with the uniform vegetation case. Also, averaging in space considerably smoothes the soil moisture process, but in contrast, averaging in time up to 1 week leads to little change in the variance of the averaged process.

How to cite: Rodríguez-Iturbe, I., V. Isham, D.R. Cox, S. Manfreda, A. Porporato, Space-time modeling of soil moisture: stochastic rainfall forcing with heterogeneous vegetationWater Resources Research, 42, W06D05, (doi:10.1029/2005WR004497), 2006. [pdf]

Analysis on flood generation processes by means of a continuous simulation model

In the present research, we exploited a continuous hydrological simulation to investigate on key variables responsible of flood peak formation. With this purpose, a distributed hydrological model (DREAM) is used in cascade with a rainfall generator (IRP-Iterated Random Pulse) to simulate a large number of extreme events providing insight into the main controls of flood generation mechanisms. Investigated variables are those used in theoretically derived probability distribution of floods based on the concept of partial contributing area (e.g. Iacobellis and Fiorentino, 2000). The continuous simulation model is used to investigate on the hydrological losses occurring during extreme events, the variability of the source area contributing to the flood peak and its lag-time. Results suggest interesting simplification for the theoretical probability distribution of floods according to the different climatic and geomorfologic environments. The study is applied to two basins located in Southern Italy with different climatic characteristics.

How to cite: Fiorentino, M., A. Gioia, V. Iacobellis, S. Manfreda, Analysis on flood generation processes by means of a continuous simulation modelAdvances in Geosciences, 7, 231-236, (SRef-ID: 1680-7359/adgeo/2006-7-231), 2006. [pdf]

DREAM: a distributed model for runoff, evapotranspiration, and antecedent soil moisture simulation

The paper introduces a semi-distributed hydrological model, suitable for continuous simulations, based upon the use of daily and hourly time steps. The model is called Distributed model for Runoff, Evapotranspiration, and Antecedent soil Moisture simulation (DREAM). It includes a daily water budget and an “event scale” hourly rainfall-runoff module. The two modules may be used separately or in cascade for continuous simulation. The main advantages of this approach lay in the robust and physically based parameterization, which allows use of prior information and measurable data for parameter estimation. The proposed model was applied over four medium-sized basins in southern Italy, exhibiting considerable differences in climate and other physical characteristics. The capabilities of the two modules (daily and hourly) and of the combined runs were tested against measured data.

How to cite: Manfreda, S., M. Fiorentino, V. Iacobellis, DREAM: a Distributed model for Runoff, Evapotranspiration, and Antecedent Soil Moisture SimulationAdvances in Geosciences, 2, 31-39, (SRef-ID: 1680-7359/adgeo/2005-2-31), 2005. [pdf]

Dynamic response of grass cover to rainfall variability: implications for the function and persistence of savanna ecosystems

Savanna grass cover is dynamic and its annual extent resonates with wet season rainfall, as shown by satellite observations of normalized difference vegetation index (NDVI) time series for the Kalahari Transect (KT) in southern Africa. We explore the hydrological significance of the dynamic grass cover by applying a soil moisture model to the water-limited portion of the KT, which spans a north-south gradient in mean wet season rainfall, r’, from approximately 700 to 300 mm. Satellite-derived tree fractional cover, xt, is shown to be highly correlated with ground meteorological measurements of r’ (R2 =0,94) in this region. By implementing a simple expression for grass growth and decay in the model that factored in only xt and near-surface soil moisture, we were able to effectively reproduce the satellite-derived fractional grass cover, xg , along the transect over a 16-year period (1983–1998). We compared the results from dynamic grass model with those yielded by a static grass cover model in which xg was set to its 16-year average for each simulation. The dynamic quality of the grass was found to be important for reducing tree stress during dry years and for reducing the amount of water that is lost from the overall root zone during the wet years, relative to the static grass case. We find that the dynamic grass cover acts as a buffer against variability in wet season precipitation, and in doing so helps to maximize ecosystem water use. The model results indicate that mixed tree/grass savanna ecosystems are ideally suited to reach a dynamic equilibrium with respect to the use of a fluctuating limiting resource (water) by having functional components that respond to variability in rainfall over long timescales (trees) and short timescales (grasses).

How to cite: Scanlon, T.M., K.K. Caylor, S. Manfreda, S.A. Levin, I. Rodríguez-Iturbe, Dynamic Response of Grass Cover to Rainfall Variability: Implications the Function and Persistence of Savanna EcosystemsAdvances in Water Resources, 28(3), 291-302, (doi: 10.1016/j.advwatres.2004.10.014), 2005.  [pdf]

MEDCLUB—starting line and first activities

The working group MEDCLUB, proposed by Fiorentino and Iacobellis (2005), is aimed at developing a wide range of activities dealing with Climate-Soil-Vegetation (CSV) interactions in Mediterranean basins. The goal of the project is to reduce uncertainty in predictions regarding hydrological extremes, soil water balance and ecosystem response to hydrological fluctuations. The research will focus on the controlling or dominant processes acting at basin or local scale that may allow model classification in terms of temporal and spatial scales, local climate, data requirements and type of application. In the present work, we briefly present the main framework of the project and its future perspective.

How to cite: Fiorentino, M., D. Carriero, V. Iacobellis, S. Manfreda, I. Portoghese, MEDCLUB – starting line and first activities, In: Predictions in Ungauged Basins: Promises and Progress edited by Murugesu Sivapalan, Thorsten Wagener, Stefan Uhlenbrook, Erwin Zehe, Venkat Lakshmi, Xu Liang, Yasuto Tachikawa & Praveen Kumar,  IAHS Publ. 303, (ISBN 1-901502-48-1), 2006. 

Localization of Buffer Strips by using IFF field data and Landsat-TM satellite data

In recent years the need to restore impacted habitats has become a fundamental aspect of environmental management in order to match sustainable development requirements. This is particularly important for fluvial habitats because of their role in the landscapes as environmental corridors. For these reasons the correct management of the restoration ecology interventions is mandatory and the ecosystem characteristics, as well as the influence of its landscape, have to be taken into account. In order to correctly realize buffer strip intervention, one of the most used restoration techniques, we propose an approach which uses field measurements for fluvial functionality and satellite data integrated with hydrological models to obtain information on the landscape influence on the river system. The investigation involved the high valley of the Agri River located in the Basilicata region, Southern Italy. The first step to the analysis involves the investigation of the fluvial ecosystem quality by using the Italian IFF Index (Fluvial Functionality Index), which differentiates various river segments in different levels of functionality. Meanwhile, by using a multispectral satellite image (LANDSAT TM 5) a land use map of the area of interest was performed. This land use map represented an important input for the hydrological simulation, which identified fluvial segments receiving the highest amount of landscape surface runoff, which is the most important cause of pollutant transporting from surrounding areas. All the results have been recorded and integrated in a Geographical Information System to define the final prediction for the localization of the buffer strips. The results obtained underline that the identification of the intervention sites realized by using the IFF field measurements and satellite-based hydrological analyses are complementary since critical segments respectively identified are not completely overlapped. Therefore, an integrated approach is fundamental to better plan the management of restoration ecology interventions.

How to cite: Carone, M.T., S. Manfreda, T. Simoniello, & M. Macchiato, Localization of Buffer Strips by using IFF Field Data and Landsat-TM Satellite Data, Proceedings of River Basin Management III,  WITPress, Vol. 83: 193-201, 2005. [Link]

On the coupled geomorphological and ecohydrological organization of river basins

This paper examines the linkage between the drainage network and the patterns of soil water balance components determined by the organization of vegetation, soils and climate in a semiarid river basin. Research during the last 10 years has conclusively shown an increasing degree of organization and unifying principles behind the structure of the drainage network and the three-dimensional geometry of river basins. This cohesion exists despite the infinite variety of shapes and forms one observes in natural watersheds. What has been relatively unexplored in a quantitative and general manner is the question of whether or not the interaction of vegetation, soils, and climate also display a similar set of unifying characteristics among the very different patterns they presents in river
basins. A recently formulated framework for the water balance at the daily level links the observed patterns of basin organization to the soil moisture dynamics. Using available geospatial data, we assign soil, climate, and vegetation properties across the basin and analyze the probabilistic characteristics of steady-state soil moisture distribution. We investigate the presence of organization through the analysis of the spatial patterns of the steady-state soil moisture distribution, as well as in the distribution of observed vegetation patterns, simulated vegetation dynamic water stress and hydrological fluxes such as transpiration. Here we show that the drainage network acts as a template for the organization of both vegetation and hydrological patterns, which exhibit self-affine characteristics in their distribution across the river basin. Our analyses suggest the existence of a balance between the large-scale determinants of vegetation pattern reflecting optimality in the response to water stress and the random small-scale patterns that arise from local factors and ecological legacies such as those caused by dispersal, disturbance, and founder effects.

How to cite: Caylor, K.K., S. Manfreda, I. Rodríguez-Iturbe, On the Coupled Geomorphological and Ecohydrological Organization of River BasinsAdvances in Water Resources, 28(1), 69-86, (doi: 10.1016/j.advwatres.2004.08.013), 2005.  [pdf]

Representation of space–time variability of soil moisture

A simplified spatial-temporal soil moisture model driven by stochastic spatial rainfall forcing is proposed. The model is mathematically tractable, and allows the spatial and temporal structure of soil moisture fields, induced by the spatial-temporal variability of rainfall and the spatial variability of vegetation, to be explored analytically. The influence of the main model parameters, reflecting the spatial scale of rain cells, the soil storage capacity, the rainfall interception and the soil water loss rate (representing evaporation and deep infiltration) is investigated. The variabilities of the spatially averaged soil moisture process, and that averaged in both space and time, are derived. The present analysis focuses on spatially uniform vegetation conditions; a follow-up paper will incorporate stochastically heterogeneous vegetation.

How to cite: Isham, V., D.R. Cox, I. Rodríguez-Iturbe, A. Porporato, S. Manfreda, Representation of Space-Time Variability of Soil MoistureProceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 461(2064), 4035 – 4055, (doi:10.1098/rspa.2005.1568), 2005. [pdf]

The effects of soil properties on floods in the Agri basin (southern Italy)

The spatial distribution of soil properties is directly involved in the fluctuation of soil moisture conditions and in the runoff generation mechanisms. In this work, the influences of the physical characteristics of the contributing area to the peak flow were widely investigated with the aim of understanding the influences of each physical parameter. The study was conducted by means of a hydrological distributed model (Manfreda et al. [7]), applied on the study area of the Agri river basin at Tarangelo (507 km2), in the region of Basilicata, Italy. Two different time scales were used: the first with higher temporal resolution (1-hour) dedicated to the superficial routing, the latter at daily scale used for local water balances and subsurface flow evaluation. Using the model at daily scale, daily soil moisture maps and the river discharge at the outlet are obtained. These results were used as input for the model at the hourly scale in order to describe the initial conditions in the watershed for event simulations. The simulation was carried on by using a synthetic hourly rainfall series generated by using the IRP model proposed by Veneziano & Iacobellis [9]. By using the rainfall-runoff model it was possible to simulate a large number of extreme events and consequently evaluate the relative contributing area to the peak flow. Specifically, every cell of these areas was classified for its vegetational, pedological and morphological characteristics with the aim of interpreting the relationship between physical properties and potential contribute to flow peaks.

How to cite: Manfreda, S., D. Carriero, V. Iacobellis, A. Sole & M. Fiorentino, The Effects of Soil Properties on Floods in the Agri Basin (Southern Italy), River Basin Management II (edited by C.A. Brebbia), WITpress, pp. 321-330, (ISBN 1-85312-966-6), 2003.