Abstract
In Madagascar, soil erosion is significant even when it is compared to world averages. A resulting special geomorphic feature is a form of gully erosion known as lavaka that appears in the highlands of the country. Lavakization (the generation and development of these features) is due to rather unique multifactorial environmental conditions. Among many factors (geology, soil composition, human activities, etc.), the spatial and temporal distribution of precipitation is a key factor influencing the behaviour of lithology and the vegetation cover of the island. The inter-annual variability in precipitation seems to be responsible for the enhanced generation of small cracks that might eventually lead to the development of a gully. However, the way of the development of such gullies is unknown. To what extent the actual precipitation pattern contributes to the aforementioned phenomenon has not yet been studied in great detail.This paper aims to analyze lavaka distribution with GIS methods and to study the relation between lavaka density and climatic conditions. Study areas have been designated throughout the country and lavakas have been identified using satellite imagery. Archive climate data of the study areas have been used to understand the influence of the weather on gully density. Data show that the spatial distribution of precipitation is connected to the appearance of lavakas to a given extent and its effect is further strengthened by the tropical cyclones. However, neither the amount of the precipitation, nor its variability alone can explain the high variation found in the spatial distribution of lavakas. Further multidisciplinary studies are necessary to draw conclusions about lavaka formation and to describe the process of lavaka development.
Highlights
Madagascar, the fourth biggest island of the world, is unique in many respects.Among others, its wildlife diversity and numerous endemic species are well known.it is quite special in terms of erosional processes
Numerous publications mention that climate is controlling the process of lavakization because of the occurrence of heavy rainfalls followed by dry seasons (e.g. Mietton, 2014; Voarintsoa et al, 2012). We considered this aspect in our study, in order to understand to what extent the precipitation intensity contributes to the initiation and acceleration of gully formation and development
Visualization of imagery showed that the studied areas have lavaka densities between 0 and 4.3 km-2
Summary
Madagascar, the fourth biggest island of the world, is unique in many respects.Among others, its wildlife diversity and numerous endemic species are well known.it is quite special in terms of erosional processes. Lavakization in the light of archive precipitation data in the island (Cox et al, 2010) is attributed to a landform type found throughout the island known as lavaka (Riquier, 1955; Cox et al, 2010). The study of this landform and its development has special importance, since it causes several problems for the local inhabitants (Bakoariniaina et al, 2006). Beside the study of this unique landform, Madagascar is an important place to study erosion processes (Cox et al, 2010), because of the long-term erosion rates due to lavakas might be significant as well
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