Climate change and irrigation requirements in the mediterranean environment

It is nowadays widely accepted that the increasing concentration of the so-called greenhouse gases in the atmosphere is altering the earth's radiation balance and causing the temperature to rise. This process in turn provides the context for a chain of events which leads to changes in the different components of the hydrological cycle, such as evapotranspiration rate, intensity and frequency of precipitation, river flows, soil moisture and groundwater recharge. Mankind is expected to respond to these effects by taking adaptive measures including changing patterns of land use, adopting new strategies for soil and water management and looking for non-conventional water resources (e.g. saline/brackish waters, desalinated water, treated wastewater). All these problems will become more pronounced in the years to come, as society enters an era of increasingly complex paths towards the global economy. In this context, European and global environments are closely linked by global processes such as climate patterns, hydrological conditions and socio-economic factors transcending regional boundaries. Consequently, achieving sustainable development in Europe will depend on the above factors and on the basic policies adopted by our society in the decades to come. Within the Mediterranean environment, the focus of the current report, water availability and irrigation development already pose a growing problem under today's climatic conditions and antrophic pressure and will pose even more challenges under the expected future climatic trends. The present Mediterranean climate is characterised by hot dry summers and mild wet winters. The region frequently suffers from years of scant rainfall and many areas are afflicted by severe drought. Concerning irrigated agriculture, most of the current 16 million hectares of irrigated land were developed on a step by step basis over the centuries. Many structures of these systems have aged or are deteriorating. They are, moreover, tinder various pressures to keep pace with changing needs, demands and social and economic development. Therefore the infrastructure in most irrigated areas needs to be rehabilitated, renewed or even replaced and consequently redesigned and rebuilt, in order to meet the goal of improved sustainable production. This process depends on a set of common and well-coordinated factors, such as new advanced technology, environmental protection, institutional strengthening, economic and financial assessment, research thrust and human resources development. Most of these factors are well-known and linked to uncertainties associated with climate change, world prices and international trade. These uncertainties require continued attention and suitable action on many fronts, in order to promote productivity and facilitate flexibility in agricultural systems. Therefore, water system engineers and managers should begin to systematically review existing design criteria, operating rules, contingency plans and water allocation polices. To this end, strategies need to be developed that ensure maximum productivity per unit of water and land, while reducing the use of fertilizers and pesticides to improve efficiency in order to preserve the environment. In relation to these issues and based on available information, this report gives an overview of current and future irrigation development in the Mediterranean environment. Moreover, the paper analyses the results of the most recent and advanced Global Circulation Models (GcMs) for assessing the hydrological impacts of climate change on crop water requirements, water availability and the planning and design process of irrigation systems. Finally, a five-step planning and design procedure is proposed that is able to integrate, within the development process, the hydrological consequences of climate change.