HYDROLOGICAL APPROACH FOR ASSESSING DESERTIFICATION PROCESSES IN THE

Land degradation, which affects the conservation of soil and water in adequate places, amounts and qualities, is the main direct cause of desertification. It is related to climate and soil characteristics, but mainly to deforestation and inappropriate use and management of natural resources including soil and water. The main effects are a decrease in water supply, a non sustainable agricultural and food production, and increased risks of catastrophic flooding, sedimentation, landslides, etc. In the medium or long term, the previewed global climatic changes may contribute to accelerate the processes of desertification in the Mediterranean Region, but in the short term, land use practices leading to soil degradation processes would increase the negative influence of those changes. The processes of soil and water degradation, leading to desertification, are strongly linked to unfavourable changes in the hydrological processes responsible for the soil water balance and for the soil moisture regime. These are affected by the climate conditions and variations, and by the changes in the use and management of soil and water resources. In the arid and semiarid Mediterranean climates, the rainfall is highly variable among years and during the year, and usually occurs in erratic storms of short duration and high intensities. This factor increases the risks of land degradation leading to desertification processes. In N Mediterranean countries, agricultural production patterns and practices have been drastically changed in the last decades, emphasizing labour- substituting technologies in some cases, with abandon of traditional soil and water conservation practices, and leading to the abandonment of agricultural lands in others. By contrast, in most of the S Mediterranean countries, population growth and lack of resources have obliged to intensify the use of marginal lands without appropriate conservation practices. Both situations frequently lead to accelerated land degradation and desertification processes, although in N Mediterranean countries, if resources are available, these processes and effects are usually masked by technological external inputs of energy, irrigation water, nutrients, and other control measures. Any break in these artificial measures, generally causes a complete loss of productivity and leads to accelerated desertification processes. Hydrological approaches would be essential to identify and assess the causes and processes of desertification. The evaluation of the hydrological processes, under different scenarios of changing climate, soil properties, and land use and management, with flexible simulation models based on those processes, may help to predict and to identify the biophysical causes of desertification at local, national and regional levels. This is a required previous step for a rational land use planning, and for the selection and development of short and long term strategies and technologies to reduce or to control land degradation processes leading to desertification, and to the related social economic and security problems. There is proposed an integrated framework for the development of this kind of approach, with potential application under Mediterranean conditions.