Implications of Decadal Changes in Precipitation and Land Use Policy to Soil Erosion in Basilicata, Italy

Catena 65 (2006) 138 – 151 www.elsevier.com/locate/catena Implications of decadal changes in precipitation and land use policy to soil erosion in Basilicata, Italy M. Piccarreta a, D. Capolongo a,*, F. Boenzi a, M. Bentivenga b a Dipartimento di Geologia e Geofisica, Universita`di Bari, via Orabona 4, Bari, Italy b Dipartimento di Scienze Geologiche, Universita`della Basilicata, Contrada Macchia Romana, Potenza, Italy Abstract This paper examines the implications of changes in precipitation and land use to soil erosion from 1955 to 2002 in Basilicata, a hilly portion of southern Italy. Analysis of daily precipitation records reveals statistically significant trends using both non-parametric and parametric approaches. The inter-annual variability of precipitation increases in intensity; primarily between October and January. From 1955 to 2000, the length of dry spells greatly increased, while wet days decreased. A land use change map was produced for the three study areas using aerial photos (1955) and orthophotos (1997 and 2002), integrated with field surveys. Results show that land use is highly dynamic in Basilicata, especially due to the application of the European Union’s Common Agricultural Policy (CAP) measures. The EU policies resulted in reclamation of badlands and degraded grasslands for agriculture, principally the cultivation of durum wheat. This farming practice and the abandonment of some of the remodeled areas have increased the risk of soil erosion and desertification processes, and is manifest in land degradation by rill networks and gullying. D 2005 Elsevier B.V. All rights reserved. Keywords: Soil erosion risk; Land degradation; Rainfall pattern; Land use change; Mediterranean; Southern Italy 1. Introduction their attention on the relationships between human activity and soil quality (loss in biodiversity, percentage in organic Land degradation, initiated by natural and human matter and nutrients). Technological development and processes, is responsible for environmental and socio- commercial strategies, as well as the European and national economic problems and has long been of great concern to policies, have led to production based on soil intensive the Mediterranean region. Changes in rainfall patterns exploitation and monoculture in the Italian countryside. (annual precipitation, intensity and inter-annual variability) Moreover, the improper use of production means intense and in land use have frequently been found as the agricultural systems and improper forest management have mechanisms responsible for triggering land degradation. initiated land degradation in many regions (INEA, 1999), Many studies in the Mediterranean region (Kosmas et al., including Basilicata. 1997; Renschler et al., 1999; Torri et al., 1999; Faulkner et Agricultural soils in Basilicata underwent continuous al., 2003) have shown that extreme events, severe drought, degradation during the last century, with acceleration in the high wind and farming practices are powerful causes of last 30 years due to the introduction of Common Agricul- erosion in bare or poorly vegetated areas (soils), and tural Policy (CAP) measures (Rendell, 1986; Sonnino et al., influencethedevelopmentofgeomorphicfeatures.Lately 1998), such as Reg. CEE 1765/92 concerning the subsidies some authors (Dumansky and Pieri, 2000) have focused to cultivate durum wheat (first on production and then on cultivated areas) and Reg. CEE 2078/92 regarding the F measure (20 years – set-aside). * Corresponding author. Fax: +39 080 5442471. E-mail addresses: [email protected](M.Piccarreta), InBasilicatathefirstCAPmeasurefavouredthe [email protected](D.Capolongo),[email protected](F.Boenzi), reclamation of bushy lands and badlands for durum wheat [email protected](M.Bentivenga). cultivation owing to the great economical advantages. 0341-8162/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2005.11.005 M. Piccarreta et al. / Catena 65 (2006) 138–151 139 Reclamation of badlands is known as ‘‘remodelling’’ and piping and tunnel erosion (Alexander, 1982; Faulkner et al., implies the flattening of the landforms, reduction of slope 2000). The seasonal rainfall distribution, high relative relief, angles (¨20-) and breaking up of the soil surface. The and dispersive nature of clays have contributed to create exposed larger surface area results in more rapid wetting, high drainage densities in both areas, resulting in a typical increased slaking and an increased tendency for soils to badland landscape. chemically disperse (Phillips, 1998). Subsequently the second measure has determined the abandonment of several remodeled areas, especially of 3. Materials and methods badlands, which are characterized by low productivity. The seasonal cultivation of durum wheat and cereals and 3.1. Data collection the frequent abandonment of some of these areas, deeply increased the erosion effectiveness of natural processes Pluviometric data from 1955 to 2000 relative to the over these lands, causing degradation conditions, as in stations of Aliano and Pisticci were obtained from the other Mediterranean areas (Kosmas et al., 2000; Dunjo´et National Hydrographic Service (SI). Time series were al., 2003). Rills, gullies, debris flows, mudflows, soil homogenized with single and multiple linear regression creep and occasionally small landslides are the main performed to fill data gaps. More details on pluviometric features of what was once a remodeled area. Previous trends in Basilicata as well as on the methods of data studies relative to Basilicata have dealt with this topic in a management are supplied in Piccarreta et al., 2004. Land use qualitative way, showing in which way recent land use changes have been deduced using aerial photography taken changes have contributed to exacerbate the soil erosion in 1955, 1997 and 2002. Field work was supplementary to processes. the mapping of land use change. Thus, the aim of this paper is to make predictions of the impacts of changes in rainfall regime and land use on land 3.1.1. Pluviometric data degradation in Basilicata across a range of temporal and Total annual and monthly precipitation data have been spatial scales, through analysis of precipitation and land-use computed to evaluate the inter-annual variability of dynamics in three selected areas from 1955 to 2002. rainfall and its concentration during the year. To define pluviometric thresholds responsible for the main erosive processes on the slopes, the authors have verified directly 2. Study area to what extent pluviometric events having different intensity have affected the soil. Moreover, a detailed The study areas are located within the hydrographical bibliographic analysis has been carried out on the dates basins of Agri and Salandrella–Cavone river catchments when alluvional and landsliding events occurred in the between 40-16Vand 40-23VN and 16-12Vand 16-35VE(Fig. investigated areas during the last century. Accordingly, 1). The Aliano area (1) covers a surface of about 45.24 km2, three classes of pluviometric events have been considered: the Craco area (2) is 13.10 km2 and the Pisticci area (3) number of rainy events >2.0, >10.0 and <30.0 mm, and 16.35 km2. >30.0 mm. In this paper, events >2.0 mm, are considered The climate is typically Mediterranean, characterized by as rainy days. hot dry summers and mild wet winters. The yearly average Several authors (Mannaerts and Gabriels, 2000, Board- rainfall ranges between 737.83 mm and 580.73 mm, and is man et al., 2003) consider that an amount of daily rainfall concentrated from November to January; the yearly average >10.0 mm to be an approximate threshold at which runoff temperature ranges from 16- to 17.5-, with an average commences in semi-arid environments, while Canton et al. maximum between 24- and 25.5- during summer and an (2001) have found that in the semi-arid region of Almeria average minimum ranging between 8- and 9.5- during (Southern Spain) the threshold rainfall required to produce winter. runoff ranges between 3.5 mm and 14.2 mm. Based on field The Plio-Pleistocene clays, with a thickness from 500 m surveys, the authors have concluded that erosion occurs to 900 m (Lentini and Vezzani, 1974; Clarke and Rendell, when daily rainfall exceeds 10.0 mm. 2000), are the most widespread lithology in the studied The literature relative to the alluvional and landsliding areas. They consist of marly and silty clays with middle– events (Caloiero and Mercuri, 1982; AVI project) has shown high plasticity (Pieri et al., 1994; Clarke and Rendell, 2000). that 30.0 mm might be considered as a threshold after which They include illite, kaolinite and montmorillonite. The high the geomorphic work effected by precipitation on slopes in Na-contents of these deposits imply a great tendency to Basilicata clays produces both severe rill erosion and mass disperse rapidly when wetted. The calculated ESP (ex- movements. changeable sodium percentage) ranges from 36% to 45% Then, rainfall intensity, max number of consecutive dry (Alexander, 1982; Rendell, 1986; Del Prete et al., 1994; days, max number of consecutive wet days, mean dry spell Phillips, 1998; Farifteh and Soeters, 1999). It is worth lengths (days) and mean wet spell lengths (days), have been noting that ESP15% induces deflocculation favouring computed for the two pluviometric stations. For all 140 M. Piccarreta et al. / Catena 65 (2006) 138–151 Fig. 1. Lithology of the Aliano (a), Craco (b) and Pisticci (c) areas. M. Piccarreta et al. / Catena 65 (2006) 138–151 141 Table 1 Results of the application of the Mann–Kendall test (u) and of least-squares linear fitting (b Tr) to all the pluviometric parameters for Aliano and Pisticci from 1955 to 2000 Aliano Pisticci u bTr u bTr Year À0.64 À1.60T775.35 À3.16** À6.79T745.57 Rainy days >2 mm À1.68* À0.22T72.90 À2.85** À0.34T56.61 Rainy days >10–30 mm À0.06 À0.003T22.38 À2.67** À0.16T17.36 Rainy days >30 mm 0.08 À0.01T3.72 À2.35* À0.07T5.64 Intensity (mm/rainday) À0.44 0.01T10.59 À0.57 À0.04T12.89 Max annual no.

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