Relationships between land degradation forms and historical development of malaria in Calabria

The present paper deals with the correlation between the malaria diffusion in Calabria during the past centuries and the different forms of land degradation on slopes and alongside the river network. It also describes the regional distribution of land degradation processes within the altimetric limits in which environmental conditions are suitable for the development of Anopheles mosquitoes (0 to 500 m). Calabria, the southernmost region of the Italian peninsula, has an area of about 15000 km2: more than 60% of its surface lies at an elevation greater than 500 m a.s.l. A great deal of such territory, composed of weathered and tectonized rocks, is involved in active geodynamic processes. Land degradation on slopes occurs mostly as mass movement and badland erosion: they both contribute to continuously model the Earth's relief. Such processes are very common throughout the region, except on alluvial plains and flat areas at the top of major mountain ranges. In many cases, rock types cropping out in the hilly areas are both prone to instability and intensive erosion. Small lakes and ephemeral ponds can form on the surface and flanks of landslide bodies, or as a result of river blockage, or, to a lesser extent, in the badland areas (Fig. 1). These impoundments can be long lasting and be colonised by several forms of life such as reeds, sphagnum, frogs and, above all, mosquitoes. Because of the short distance between mountain chains and sea, the size of many catchment basins ranges between 50 and 200 km2. The drainage network is composed of short branches with steep mountain reaches and a wide terminal braided branch characterised by coarse debris (Fig. 2). The fluvial regime of these rivers, called fiumare (Fairbridge, 1979), is tied to the Mediterranean climate of Calabria, characterized by hot dry summers and rainy winters. During the dry season the stream flow is mainly base flow, but occasionally, in autumn and winter disastrous floods can occur. The spreading of debris transported by water causes the greatest part of damage for settlements located on flood plains. After the flood peak, along the irregular braided channels, water can locally form swampy areas.