Agrometeorological aspects of agriculture and forestry in the arid zones

The arid zones of the world are all characterized by a large deficit of rai nfall in relation to the potential evapotranspiration. Their distribution a round the world is governed by the interaction of global atmospheric circul ation patterns, the distribution of land and sea, and local topography. Cou ntries that have substantial areas with arid conditions belong to very diff erent groups in terms of resource availability, agricultural productivity, population density and wealth. Most are poorly endowed with good agricultur al land. Water resources vary tremendously, both in terms of reserves and c onsumption. Agriculture is in most cases the main consumer of water. Most a rid zone countries have high population growth, and rural population densit ies are generally much higher than overall population densities. They have a wide disparity in wealth. The arid zones have a surprising diversity of a groecological niches, with edaphic conditions that can deviate substantiall y from those of surrounding areas. These niches often have a higher biomass or agricultural productivity. At the same time they are vulnerable to natu ral processes such as primary salinization, wind and water erosion. Increas ing pressure of human and livestock population make that these natural envi ronmental stresses lead to accelerated degradation and depletion of soil an d water resources. As they exploit the various agroecological niches, the p roduction systems of the arid zones are equally diverse, and cover the full spectrum of land use intensification from pastoral or transhumant livestoc k systems to rainfed or irrigated cropping systems. These production system s show rapid change under the pressures of environmental degradation, incre asing land and water shortage, and the needs of expanding populations. With the exception of irrigation management, the agrometeorological needs of th e arid zones have been insufficiently addressed in the past. Perceptions of homogeneity, low agricultural potential, low population density and the lo gistical problems of providing maintenance and collecting data from remote stations are largely to blame for this situation. Agrometeorological resear ch can have a positive impact on the productivity, resource-efficiency and environmental sustainability of the arid zones by supporting a better chara cterization of the agricultural environments. Research targeted towards dat a spatialization and integration of meteorological and remote sensing infor mation will help to alleviate the handicap of sparse meteorological data ne tworks. At the same time these networks will need to be improved through in stallation of automatic stations and by establishing new partnerships with land users. (C) 2000 Elsevier Science B.V. All rights reserved.