The impact of climate change on geomorphology and desertification along a Mediterranean-arid transect

H. Lavee, A. C. Imeson, P. Sarah

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266 Scopus citations

Abstract

From the perspective of gemorphology, three important aspects of climate should be considered if conditions become more arid: a) any decrease that might occur in the annual rainfall amount; b) the duration of rainfall events; and c) any increase in the intervals between rainfall events. These, together with increasing temperature, lead to less available water, less biomass and soil organic matter content and hence to a decrease in aggregate size and stability. As a consequence, the soil permeability decreases, soils develop surface crusts and infiltration rates decrease dramatically. Such changes in vegetation cover and soil strucure lead to an increase in overland flow and in the erosion of the fertile topsoil layer. Positive feedback mechanisms may reinforce these effects and lead to desertification. This paper considers the results of field investigations into the spatial variability of a number of 'quick response' variables at two scales: the regional and the plot scales. Concerning the regional scale spatial variability, results of experimental field work conducted along a climatic transect, from the Mediterranean climate to the arid zone in Israel, show that: 1) organic matter content, and aggregate size and stability decrease with aridity, while the sodium adsorption ratio and the runoff coefficient increase; and 2) the rate of change of these variables along the climatic transect is non-linear. Steplike threshold exists at the semiarid area, which sharply separates the Mediterranean climate and arid ecogeomorphic systems. This means that only a relatively small climatic change would be needed to shift the borders between these two systems. As many regions of Mediterranean climate lie adjacent to semiarid areas, they are threatened by desertification in the event of climate change. Concerning spatial variability at the plot scale, different patterns of overland flow generation and continuity characterize hillslopes under different climatic conditions. While in the Mediterranean climate area infiltration is the dominant process all over the hillslope, in the arid area overland flow predominates. In contrast to the uniform distribution of proceses in these two zones, a mosaic-like pattern, consisting of locally 'arid' water contributing and 'moist' water accepting patches is typical of the transitional semiarid area. Such pattern is strengthened by fires or grazing which are characteristic of this area. The development of such mosaic pattern enables most rainfall to be retained on hillslopes. Changes in the spatial pattern of contributing versus accepting water areas can be used as an indicator of desertification and applied to developing rehabilitation strategies.

Original languageEnglish
Pages (from-to)407-422
Number of pages16
JournalLand Degradation and Development
Volume9
Issue number5
DOIs
StatePublished - Sep 1998

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