Towards a Mediterranean GEWEX
GEWEX stands for “Global Energy and Water Cycle Experiment”(WCRP, 1990). It is a sub-programme of the World Climate Research Programme (WCRP). Its goal is to determine the hydrological cycle by global measurements. To reach this goal studies have been ini
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1 The GEWEX Strategy GEWEX stands for "Global Energy and Water Cycle Experiment"(WCRP, 1990). It is a sub-programme of the World Climate Research Programme (WCRP). Its goal is to determine the hydrological cycle by global measurements. To reach this goal studies have been initiated under the GEWEX Continental-scale International Project (GCIP) (WCRP, 1992) with the objectives as illustrated in Fig. I: • Advanced modelling of the hydrological cycle and its effects; • Prediction of the response of the hydrological cycle to environmental change; • Improvement of observing techniques and data assimilation systems. Global cycles generally can be investigated by global models or global measuring
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OBJECTIVES • Determine the hydrological cycle and energy thl.'l:e by mean of global mea. urements of ob crvable atrno ph eric and urface properties.
• Model the global bydrological cycle and its impact on the atrno phere, ocean and on the land urface. • Develop the ability to predict the variations of global and regional bydrological proce ses and water re ource , and their response to environmental cbange.
• Foster the devc\opment of ob erving teclmiques data management, and a similis.tion systems suitab le for operational application to long-range weather forecn t , hydrology, and climate prediction .
Fig. 1. The major objectives of the WCRP - GEWEX programme
H.-J. Bolle (ed.), Mediterranean Climate © Springer-Verlag Berlin Heidelberg 2003
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H.-J. Bolle, S. I. Rasool, P. Try
networks. Energy and water fluxes cannot be measured directly, they have to be computed using other measurable quantities which determine these fluxes. The global models used for this task are those which simulate the General Circulation (GCM's) of the atmosphere and the world ocean. They exist also in coupled versions and as climate models which are GCM's that can be integrated over long time periods. Global measuring networks to be considered here must be operational ones. Only this guaranties continuous operation and replacement of instruments in case of failure. Two of these systems exist, the meteorological network at the ground including aerological stations and the operational meteorological satellite system. The classical investigations of energy and water fluxes one can think of are those of Oort (1971), Vonder Haar and Suomi (1971), Oort and Vonder Haar (1976), Ellis and Vonder Haar (1978), and Peixoto and Oort (1982), and the more recently the NOAA Pathfinder Project. Both the modelling as well as the measuring approach have deficits in assessing climate variability and trends. In the models some of the important processes are only marginally represented - in other words parameterized - especially if one comes down to the smaller scales. The operational ground based and aerological measurements are not as dense as one may wish and are afflicted with instrumental errors. Only standard parameters are measured here. The observations made from space is the only data source continuous in space and
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