Recent evolution and erosion risk of the Molise coast (southern Italy).

As documented by various recent studies (AUCELLI et alu, 2004, FAILLACE, 2004. IANNANTUONO et alu, 2005, GRUPPO NAZIONALE PER LA RICERCA DELL'ANIBIENTE COSTIERO, 2006a, ACLLI e abi, 2007, IANNANTLIONO, 2007), the evolution of the 36 km long Molise coast during the last fifty years is characterised by a prevailing tendency to shoreline retreat The aim of the present paper is to provide a precise description of the Molise coast with reference to its coastal morphology along with a detailed frame of the evolution of its shoreline and first indications on the potential erosion risk The Molise coast that includes ca 13 km of high coast behaves at as a low coast system, because the cliffs limiting the high coast to the sea are located, except for the promontory of Termoh, at variable distance from the shoreline Beaches are present nearly all along the coast and anthropic structures frequently are located along their inner edges To analyse shoreline variations in detail, the Molise coast was subdivided nine reaches (T1-T9) of different lengths and characters Quantitative analyses on linear shoreline variations and related surface changes were carried OM for the 1954-2003 time interval and relative sub-periods 1954-1992 and 1992-2003 From 1954 to 2003, the general shoreline retreat caused a total loss of ca 1 090 000 m(2) of coastal area (beaches, clones, deltaic and retro-dune areas) The most sensible reaches to erosion are TI and T7 that respectively comprise the mouths of the Trigno and Biferno rivers, which experienced in this period a retreat of ca 230 and 350 metres, respectively A acceleration of shoreline retreat with shown by the comparison sub-periods 1954-1992 and 1992-2003 Though the second period is much shorter (11 years vs 38 years), TI and T7, in particular, totalize nearly 50% of the surface losses that occurred during the precedent periocl Due to such an acceleration. during the second periocl ca 32% of the total erosion occurred. giving rise to a loss of ea 348 609 m(2) For reaches T1 and 17, the average annual retreat rates changed from respectively 2 37 and 3 24 m/y to 4 24 and 4 74 during the second penocl, when reach T7 underwent a maximum reti-eat of about 231 men-es which corresponds to an average annual retreat of 21 m/y The reconstructed acceleration of erosion is in net contrast to the increasing protection of the coast by defense structures as evident above all for reach 17 In order to better understand this apparent inconsistency, and the consequent hypothesis for a possible meteochmanc influence (already outlined for part of the Molise coast by AUCELLI et alit, 2007), a detailed analysis of the period 1992-2003, subdivided therefore into sub-periods 1992-1997, 19972000, 2000-2003, was carried out This analysis showed consistent differences between the distinguished sub-periods in relation to average annual shoreline variations zind the percentage with which each reach contributed to erosion The observed differences strongly support the hypothesis that variations of meicomarine conditions have strongly favoured erosion during the second period, and in particular durme sub-period 2000-2003. thus outImmg the need to adequately consider such climatic influence when developing potential erosion scenaries related to climate change Starting from the basic morphological and topographical features of the Molise coast, in order to examine the potential erosion risk, the rates of annual average linear shoreline variations for periods 1954-992 and 1992-2003 were examined on the basis of the risk scheme developed by (1994) Such an examination allowed to evaluate the degree of erosion risk for each reach and to attribute, in particular, a very high erosion risk to reaches TI and 17, which, indeed, are the main responsible for the observed shoreline instability Further analyses carried out on coastal sectors characterised by the occurrence of constructions located up to ca 200 m from the current shoreline along the inner edges of the beaches, allowed to calculate the potential time span required by marine erosion to possibly affect the constructions Said calculations point out for the northern sectors of reaches T1 and T7 time spans of 13,5 and 22 years, respectively, and therefore a real, and very high erosion risk