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One of the main climatological characteristics of the region of Murcia (11,300 km2), located almost entirely in the Segura Basin (in southeast Spain), is the great temporal and spatial irregularity of its precipitation. Average annual precipitation values range between 200 and 500 mm, and coefficients of variation (CV) are high, with some values about 50%. It is a semiarid region (including a small arid area), and agriculture plays a major role in its economy. Because of this, drought is one characteristic of the region’s climate that has far-reaching consequences, from unemployment to social conflicts.
It is important to define drought and identify appropriate indicators for the region of Murcia as part of a drought watch system. This system will define the temporal and spatial limits of drought conditions. It would help policy makers and government officials establish policies for the provision of aid to farmers and cattlemen, as in Australia (White and O’Meagher, 1995).
Because of the wide range of drought impacts, there are many definitions of this phenomenon. However, one characteristic seems common to all of them: drought is caused by a deficiency in precipitation for a fairly long period of time. For simplicity, and keeping in mind that precipitation is, without doubt, the most important variable in the process, the watch system developed for the region of Murcia uses only this variable at the moment, establishing a comparison with a climatological reference (1961– 90) that we consider “normal.”