Geomorphology of the Anthropocene in Mediterranean urban areas

Abstract

Urban-geomorphology studies in historical cities provide a significant contribution towards the broad definition of the Anthropocene, perhaps even including its consideration as a new unit of geological time. Specific methodological approaches to recognize and map landforms in urban environments, where human-induced geomorphic processes have often overcome the natural ones, are proposed. This paper reports the results from, and comparison of, studies conducted in coastal historical cities facing the core of the Mediterranean Sea – that is, Genoa, Rome, Naples, Palermo (Italy) and Patras (Greece). Their settlements were facilitated by similar climatic and geographical contexts, with high grounds functional for defence, as well as by the availability of rocks useful as construction materials, which were excavated both in opencast and underground quarries. Over centuries, urbanization has also required the levelling of relief, which was performed by the excavation of heights, filling of depressions and by slope terracing. Consequently, highly modified hydrographic networks, whose streams were dammed, diverted, modified in a culvert or simply buried, characterize the selected cities. Their urban growth, which has been driven by maritime commercial activities, has determined anthropogenic coastal progradation through port and defence or waterfront works. Aggradation of artificial ground has also occurred as a consequence of repeated destruction because of both human and natural events, and subsequent reconstruction even over ruins, buried depressions and shallow cavities. As a result, the selected cities represent anthropogenic landscapes that have been predominately shaped by several human-driven processes, sometimes over centuries. Each landform represents the current result, often from multiple activities with opposing geomorphic effects. Beyond academic progress, we believe that detecting and mapping these landforms and processes should be compulsory, even in risk-assessment urban planning, because of the increase of both hazards and vulnerability as a result of climate-change-induced extreme events and extensive urbanization, respectively.

Urban geomorphology of a historical city straddling the Tanaro River (Alessandria, NW Italy)

“…Thus, urban geomorphology investigates the human impact on landscape during the Anthropocene in many various geographical settings (Brandolini et al, 2019;Brown et al, 2017;Cooke et al, 1982;Douglas, 2005;Espinosa et al, 2018;Jeong et al, 2018;Knight, 2018;Martín-Díaz et al, 2015;Thornbush, 2015;Waters et al, 2016;Zwoliński et al, 2018).…”

“…Some very recent researches concerning urban geomorphology were carried out in a number of Mediterranean cities, in terms of geomorphological mapping, geomorphological heritage and characterization of anthropogenic landforms (Brandolini et al, 2018(Brandolini et al, , 2019Del Monte et al, 2016;Luberti et al, 2018Luberti et al, , 2019Mozzi et al, 2018). Most of these case studies are located in alluvial-coastal areas with more or less pronounced hills behind them (Brandolini et al, 2017(Brandolini et al, , 2018Luino et al, 2019;Roccati et al, 2019).…”

Short-Term GIS Analysis for the Assessment of the Recent Active-Channel Planform Adjustments in a Widening, Highly Altered River: The Scrivia River, Italy

“…However, aiming to precisely define the ongoing morphological dynamics, the most suited time span to consider for analyzing the riverbed adjustments ranges from the present-day to approximately 10-25 years ago [11,22,23].Previous studies concerning the morphological evolution of Italian rivers outlined their main morphological tendencies over the last two centuries, that is substantially before the occurrence of the most intense and widespread anthropic interventions on fluvial systems. As reported by several authors [18,[24][25][26][27][28], three evolutionary phases can be recognized: (i) the first one, from the last decades of the 19th century to the 1950s, is generally characterized by gentle narrowing and incision albeit, in some cases, no large-scale dominant processes are recognizable up to the beginning of the 20th century [18]; (ii) the second one, from the 1950s to the 1990s, presents the most relevant channel adjustments related to fast, severe and generalized narrowing and incision processes, coupled with a reduction in braiding degree and with an increase of sinuosity; (iii) the third one, from the 1990s onwards, shows a reversal trend since it is characterized by active-channel widening and by an overall slight aggradation or bed-level stability; however, this latter phase is documented only along some rivers [25,29,30].The causes behind the 20th century channel changes are now widely documented [18,21] and have been recognized in the reduction of the sediment budget due to in-channel quarrying activity [19,31], occupation of areas of fluvial pertinence [21,32], channelization [19,33,34], land-use changes at catchment scale [16,30,[35][36][37][38] and building of cross works such as weirs and dams [39][40][41]. On the contrary, the triggering factors of the most recent phase are still quite debated in the scientific literature…”

“…The causes behind the 20th century channel changes are now widely documented [18,21] and have been recognized in the reduction of the sediment budget due to in-channel quarrying activity [19,31], occupation of areas of fluvial pertinence [21,32], channelization [19,33,34], land-use changes at catchment scale [16,30,[35][36][37][38] and building of cross works such as weirs and dams [39][40][41]. On the contrary, the triggering factors of the most recent phase are still quite debated in the scientific literature [29,30] and according to previous research could be related to: (i) the end of the in-channel sediment mining for commercial purposes, which is dated back around the late 1980s-early 1990s [20,42,43], (ii) changes in the riverbed geometry resulting in an increase of unit stream power [44], and/or (iii) the occurrence of large flood events [21,24,25,29,30].…”

Large-scale geomorphology of the Entella River floodplain (Italy) for coastal urban areas management

“…Geomorphological mapping in the urbanized landscape is a relatively recent topic (Bathrellos, 2007), but it has been rapidly developing in recent years. In particular, in the research field of the Anthropocene (Brandolini et al, 2019;Tarolli & Sofia, 2016;Thornbush, 2015), i.e. the current geological time in which the intensive changes in landscape, climate and Earth surface processes are mainly ascribed to human activities (Brown et al, 2017;Crutzen, 2002;Waters et al, 2016).…”