Dennis Fox

University of Nice, Geography, Faculty Member

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Dormant categories and spatial resolution affect the perception of land cover change model performance

Cybergeo, 2016

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Spatial dynamics of land cover change in a Euro-Mediterranean catchment (1950–2008)

Journal of Land Use Science, 2014

ABSTRACT The Euro-Mediterranean area has experienced widespread land cover change since 1950, but... more ABSTRACT The Euro-Mediterranean area has experienced widespread land cover change since 1950, but few studies of land cover change explicitly explore spatial constraints on land cover change patterns. The main objective of this study was to analyze the spatial dynamics of land cover change from 1950 to 2008 in a French Mediterranean catchment. Aerial photographs (1950, 1982, and 2008) were screen digitized, and surfaces were classified into five categories: forest, vineyard, grassland, urban, and suburban. Land cover changes were concentrated mainly in the alluvial plain. Although forest remained the dominant land cover in the catchment (&gt;85.0%), it underwent significant swapping with vineyard and grassland. Vineyard decreased (34% of initial loss) while grassland increased (43% of initial). Urban and suburban areas remained minor in the catchment (0.2% in 1950 and 3.0% in 2008), but showed a dramatic relative increase (about 20×). Changes occurred mainly at low altitudes and slopes. Vineyard located near streams was converted mainly to grassland. Built areas were dependent on roads and former built areas for expansion but expanded little near streams due to flooding risks. The rate of change was greater during the latter part of the study (1982–2008) than in the earlier phase (1950–1982).

Crusting, runoff and sheet erosion on silty loamy soils at various scales and upscaling from m2 to small catchments

Soil and Tillage Research, 1998

Water erosion is one of the most active processes in soil genesis and dynamics. It is also at the... more Water erosion is one of the most active processes in soil genesis and dynamics. It is also at the origin of significant environmental problems. Soil surface state is one of the most important factors for erosion risk assessment. However, it is not easy to determine the effect of this factor at a large scale. A field experiment was held in Pays de Caux (Normandy, France) in order to study and quantify crusting, runoff and sheet erosion at the cultivated field and catchment scales. We measured crust formation, runoff and erosion during two seasons on 1-m 2, 20-m z and 500-m 2 experimental plots and on a small catchment. Results allow a ranking of the most important factors influencing crusting and erosion at the different scales. They also enable the development of relationships for upscaling from small plot results to the cultivated field and catchment for specific conditions. However, upscaling from plots to catchments is generally difficult and needs to take catchment spatial structures into account. We distinguish between runoff and erosion scale transfer, the latter being at the origin of specific problems that need further research to be solved.1998 Elsevier Science B.V. All rights reserved.

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Modelling complex systems in Archaeology: general issues and first insights from the ModelAnSet project

by Frédérique Bertoncello, Marie-Jeanne Ouriachi, Andrea G B Tettamanzi, Daniel Contreras, and Dennis Fox

Proceedings of the Complex Systems Academy of Excellence, 2018

Complexity theory provides useful concepts for archaeological issues related to the understanding... more Complexity theory provides useful concepts for archaeological issues related to the understanding of past societies and their environment. More specifically, Agent-Based Modelling is a relevant tool to explore scenarios and to test hypotheses about the impacts of complex socioenvironmental interactions on the transformations of ancient settlement systems evident in archaeological records. After a short historiography of complex systems modelling in Archaeology, this paper focus on the mains issues of archaeological simulation models. As a case study, we briefly present the model under development within the ModelAnSet project supported by UCAJEDI Complex Systems Academy of Excellence. Agent-Based Modelling is used to explore the respective impacts of environmental and social factors on the settlement pattern and dynamics during the Roman period in South-Eastern France.

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Comparing post forest fire erosion to erosion in vineyards in a Mediterranean environment

Egu General Assembly Conference Abstracts, May 1, 2010

In Mediterranean France, severe soil erosion can occur in two environmental contexts: on forested... more In Mediterranean France, severe soil erosion can occur in two environmental contexts: on forested slopes shortly after a forest fire and in vineyards. Soils are particularly vulnerable to erosion during the first year after a fire. Vineyards tend to occupy gentler slopes in alluvial plains and the first foothills of steeper landscapes. They can be exposed to erosion throughout the year depending on storm characteristics and inter row grass cover which is variable both spatially and temporally. The objective of this case study was to compare estimated rates of erosion and potential inputs of sediments into stream channels from post forest fire and agricultural contexts. The studied catchment has a surface area of about 234 km2, where about 199 km2 are forested, 18 km2 are vineyards, and the remaining 17 km2 are mainly grassed or urban. Forest fire records are too recent to calculate return periods for large fires but it is estimated at about 25-35 years in the study catchment. In 2003, a 2,000 ha fire burned through the catchment, and sediment traps on a N facing slope were used to estimate erosion rates during a period of about 2.5 years after the fire. Total event erosion for the burned area was estimated using non-linear curves where erosion decreased exponentially with time according to slope orientation: vegetation on N facing slopes recovers more quickly than on S facing slopes so erosion rates tend to remain greater for a longer period on the latter. Soil erosion in vineyards was estimated by adapting the Revised USLE. Conservation practises (P) were modified to account for terracing and vine row orientation with regards to slope orientation. Vegetation cover (C) was modified to account for seasonal variations in inter row grass cover. The other factors in the equation were not altered. In this case study, post forest fire erosion rates were particularly low due to an absence of significant storms during the first post fire winter. Mean soil erosion rate for the first year was about 2.7 T ha-1, and total event erosion was estimated at 5.4 T for the first year and 8.4 T over a 6 year period. Assuming a return period of 25 years for a fire of similar magnitude, this would represent the 25 year sediment input value. Mean annual vineyard erosion rate was 5.5 T ha-1. This corresponds roughly to about 9,900 T during any typical year and to about 247,500 T over a 25 year period. Several factors affect post fire erosion estimation, including return period, burned surface area, and rainfall intensities during the first year after a fire. The 2,000 ha fire used in the case study is considered a large fire in a region where fires rarely surpass 6,000 ha due to agricultural and urban densities. Post fire erosion is particularly sensitive to rainfall characteristics and the unusually low rainfall during the year of study underestimates long term post fire erosion rates. Actual long term rates may be 5 to 10 times greater for a normal rainfall year. Reasonable increases in surface area and rainfall would provide a very rough long term average estimate of about 100 T ha-1 for the first post fire year and about 150 T ha-1 for the entire forest fire event. Hence, typical sediment input from the burn scar may be as much as 10 times greater than input from vineyards the first year after a fire, but long term vineyard erosion rates may be as great as 1,000-2,000 times greater than from forest fires.

The effect of ponding depth on infiltration in a crusted surface depression

Catena, 1998

Over the past few decades, the influence of surface sealing on infiltration has been the subject ... more Over the past few decades, the influence of surface sealing on infiltration has been the subject of numerous publications. However, very few of these experiments have considered the effect of spatial variability in seal hydraulic characteristics on infiltration. Field and laboratory observations have demonstrated that seal characteristics vary considerably within a range of a few cm, and the changes are often related to microtopography. The objective of this experiment was to investigate the influence on infiltration of a seal with varying hydraulic properties in a surface depression. Two soils of different aggregate stability were used in the experiment: Blosseville silt loam and Villamblain silty clay loam. Soil columns (23 cm diameter by 30 cm length) were packed with aggregates of <2.0 cm and a 6 cm depression was formed in the soil surface. A sedimentary crust was formed in the centre of the depression, and the sample was rained upon for 60 min at a rainfall intensity of 35 mm h−1. Subsequently, water outflow at the base of the column and pressure heads in the column were measured during two ponding periods corresponding to depths of 0.5 and 4.0 cm. Water outflow rates increased with ponding depth substantially more than could be attributed to the increases in ponding pressure head and submerged area for both soils. The experiment demonstrated that where seal hydraulic conductivity varies with microtopography, a significant increase in infiltration rate occurs as areas of greater hydraulic conductivity are submerged. The increases in ponded pressure head and submerged area are negligible compared to the influence of spatial variability in seal hydraulic conductivity.

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Increases in fire risk due to warmer summer temperatures and wildland urban interface changes do not necessarily lead to more fires

ABSTRACT Historical changes in the wildland urban interface between about 1960 and 2009 indicate ... more ABSTRACT Historical changes in the wildland urban interface between about 1960 and 2009 indicate a moderate increase in forest fire risk.•Mean minimum and maximum summer temperatures have increased by about 1.4 °C–1.8 °C over the same period.•Fire risk has increased significantly but the number of fires and burned area have both decreased.•Fire-fighting strategies have reduced the number of fires despite greater fire risk.

The Influence of Slope Angle on Infiltration Rate and Surface Seal Characteristics

Geoderma

Une méthode de cartographie du risque érosif : exemple d'application aux collines du Terrefort lauragais

Une carte du risque érosif est un outil indispensable dans une démarche de lutte contre l'éro... more Une carte du risque érosif est un outil indispensable dans une démarche de lutte contre l'érosion. Elle permet en effet d'avoir une vue d'ensemble des problèmes et donc de localiser les secteurs nécessitant une intervention prioritaire. La carte des risques réalisée dans cette étude résulte de la spatialisation de la « Revised Universal Soil Loss Equation » (RUSLE). Le but de cet article est de montrer les différentes étapes nécessaires à la spatialisation de ce modèle et à la réalisation de la carte.

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Relation au champ entre pertes en terre et inclinaison de la pente en situation d'érosion diffuse

Les mesures de pertes en eau et en terre, réalisées dans un contexte de région limoneuse intensiv... more Les mesures de pertes en eau et en terre, réalisées dans un contexte de région limoneuse intensivement cultivée du Nord-Ouest de la France à l'échelle de 1 m2, sont présentées et commentées. L'érosion hydrique est l'un des processus majeurs dans la redistribution des particules solides du sol au sein des paysages. Aussi, afin d'estimer dans un premier temps les zones sensibles et ensuite de lutter contre les exportations de terre par des mesures agro-environnementales, il est important de pouvoir apprécier l'effet de l'inclinaison de la pente. Malgré de nombreuses études sur le sujet, l'influence de l'angle de la pente sur le niveau d'érosion inter-rigole n'est pas clairement établi. L'objectif de l'étude est de déterminer au champ, sur une surface uniformément battue, l'influence de l'angle de la pente (2, 4, 8%) sur les pertes en terre. L'expérimentation, menée à la fois sous pluies naturelles et simulées, nous a permis d...

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Hydrological Modeling of the Potential Impact of a Forest Fire on Runoff in a Mediterranean Catchment (peer reviewed)

Forest fires are a recurrent phenomenon in Mediterranean environments around the world. Each year... more Forest fires are a recurrent phenomenon in Mediterranean environments around the world. Each year, hundreds of thousands of hectares are burned, leaving the soil bare and unprotected against rainfall. Runoff and soil erosion risks are therefore greatly increased during the first year after a fire. This study used a partially distributed hydrological model to examine the potential effect of forest fire on runoff in a Mediterranean Catchment in SE France. The Hydrological Engineering Center’s Hydrological Modeling System (HEC-HMS) was used for this purpose. Daily discharge and rainfall data from 1975 to 1991 were available. Different short events were selected and two representative storms were modelled with and without a fire scar. The model was calibrated and validated with the observed data and was employed to simulate the after fire scenario. The model revealed that, after forest fire, the peak discharge in the stream can rise from 10% to 50 % while the general pattern of discharg...

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Cartographie des chemins de l'eau dans un paysage semi-aride de la Dorsale Tunisienne

Comprendre l'organisation spatiale du milieu naturel est d'une grande importance en hydro... more Comprendre l'organisation spatiale du milieu naturel est d'une grande importance en hydrologie puisque c'est son agencement qui impose les mécanismes qui génèrent et dirigent les flux hydriques. En cela, une cartographie des chemins de l'eau dans le milieu naturel s'avère être un outil intéressant pour expliquer le devenir de l'eau dans un bassin versant. Etablie à partir des règles de l'analyse paysagère, cette carte montre comment s'organisent, latéralement et verticalement, les différents matériaux qui composent milieu naturel et permet de comprendre ce qu'il advient aux flux hydriques lorsqu'ils rencontrent ces diverses organisations. L'établissement de cet outil requiert la définition d'unités spatiales, nommées "segments de paysage", déduites de l'analyse conjointe de toposéquences caractéristiques du paysage et de la cartographie fine des états de surface et des directions d'écoulements par unité topographique ...

Une méthode de cartographie du risque érosif: application aux collines du Terrefort lauragais

A soil erosion risk map is an essential tool for soil conservation planning. It provides a genera... more A soil erosion risk map is an essential tool for soil conservation planning. It provides a general view of erosion problems and makes it possible to identify sectors requiring emergency action. The erosion risk map produced for this study was achieved by spatialising the Revised Universal Soil Loss Equation (RUSLE). The aim of this article is to demonstrate the steps involved in developing a soil erosion risk map.

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Genèse du ruissellement et de l'érosion diffuse sur sols limoneux : analyse du transfert d'échelle du m2 au bassin versant élémentaire agricole/Runoff and interrill erosion on silty loamy soils: analysis of scale tranfer from m2 to small cultivated catchments

Géomorphologie : relief, processus, environnement, 1996

Process-Based Analysis of Aggregate Stability Effects on Sealing, Infiltration, and Interrill Erosion

Soil Science Society of America Journal, 1998

ABSTRACT Aggregate stability indices are correlated with soil erosion rates. Although aggregate s... more ABSTRACT Aggregate stability indices are correlated with soil erosion rates. Although aggregate stability influences soil erodibility and aggregate breakdown product size distributions, these indices are usually unsatisfactory because of interacting physicochemical considerations affecting infiltration and erosion. We examined the spatial variability in structural and depositional seal composition, and the influence of breakdown fragment size distribution on seal hydraulic resistance and interrill erosion. Two Alfisols, Villamblain clay loam and Blosseville silt loam, were sieved to retain &lt;2.0-cm aggregates and packed in 0.25-m2 soil trays. Soil trays were rained upon for 4 h at 23 mm h-1. Infiltration, runoff, and subseal pressure head were measured throughout the experiment, and surface roughness and depositional seal area were measured at selected times during the event. Aggregate stability, hydraulic resistance, and fragment size distribution of the seal matrix were also determined. Mean weight diameter (MWD) of aggregates after mechanical breakdown by stirring was greater for Villamblain (1.70 mm) than for Blosseville (0.92 mm) (r2 = 0.94, P&lt;0.001). Blosseville seals had finer fragments than those of Villamblain (r2 = 0.82, P&lt;0.001): fewer than 28% of fragments &gt;1 mm and more than 40% &lt;0.1 mm, compared with 60 and 15% for Villamblain. Depositional seals had finer fragments than structural seals for both soils. For the same runoff rate (15 mm h-1), soil loss was greater for Blosseville (2 g m2 min-1) than for Villamblain (0.4 g m2 min-1) since breakdown products were finer and more transportable. Seal hydraulic resistance was correlated (r2 = 0.53, P&lt;0.01) with MWD of seal fragments.

Upscaling a simple erosion model from small areas to a large region

Soil and Water Quality at Different Scales, 1998

Upscaling from a catchment scale to a regional scale is generally rendered difficult by the lack ... more Upscaling from a catchment scale to a regional scale is generally rendered difficult by the lack of relevant and precise data at the larger scale. In this case, a winter rill erosion hazard map was produced for the Nord-Pasde-Calais region using a linear regression erosion model originally designed for the catchment scale. Upscaling entailed adapting and applying the model at the county scale for all of the counties within the region. In upscaling the model, the difficulties associated with the nature of the data were dealt with in three stages: (1) the modification of the model for the county scale as a function of the nature of the data available, (2) an analysis of the influence of the spatial distribution of the data, (3) an analysis of the effect of the loss in precision of the data on the model output. Reference areas were used to verify the accuracy of the upscaling process before applying it to all of the counties in the region. In this case, the most significant limitation was the spatial coverage of the data: the basic administrative unit for which data is collected is the county, and it does not correspond to the erosion process scale which is the catchment. Defining erosion risk in terms of hazard categories rather than estimated erosion rates overcomes this difficulty to some extent. The use of reference areas provides several advantages in an upscaling procedure: these are mainly related to minimizing data collection and obtaining a reliable estimate of the accuracy of the predicted output.

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Increases in fire risk due to warmer summer temperatures and wildland urban interface changes do not necessarily lead to more fires

Applied Geography, 2015

Comparing post forest fire erosion to erosion in vineyards in a Mediterranean environment

Étude et Cartographie De L'Érosion Des Sols Dans Un Vignoble Du Sud-Est De La France

In South-East France, soil erosion is common in vineyards and a suitable strategy to combat erosi... more In South-East France, soil erosion is common in vineyards and a suitable strategy to combat erosion depends on accurate knowledge of its spatial distribution within a catchment. Soil erosion risk was mapped by measuring rill erosion within a reference zone and the relationships identified were then extrapolated to all the vineyards in the catchment.

Evaluation of two soil conditioners for limiting post-fire erosion as part of a soil conservation strategy

Soil Use and Management, 2008

Soil conservation is a major concern for catchments affected by forest fires. The lack of vegetat... more Soil conservation is a major concern for catchments affected by forest fires. The lack of vegetation cover and the development of soil water repellency increase the risk of topsoil erosion. This paper evaluates two soil conditioners (a wetting agent and a polyvinyl acetate) for limiting overland flow and erosion in inter-rill areas. Unburned and burned soil samples were treated with one or both soil conditioners. The effects of these treatments on run-off, water retention, erosion and plant growth were assessed using laboratory rainfall simulations. Polyvinyl acetate had little impact on water retention but was effective in reducing soil loss. The surfactant had little impact on water run-off or soil loss but substantially improved water retention and plant biomass production. Application of soil conditioners on post-fire areas could be a valuable technique in a soil conservation strategy. To maximize their benefits, soil conditioners could be applied with seeding using hydroseeding techniques and be limited to particular areas, such as paths and roadsides. Laboratory results indicate that field testing should also be carried out.

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