Abstract
The Mediterranean Basin, located in a transition zone between the temperate and rainy climate of central Europe and the arid climate of North Africa, is considered a major hotspot of climate change, subject to water scarcity and drought. In this work, dry and wet spells have been analyzed in the Wadi Cheliff basin (Algeria) by means of annual precipitation observed at 150 rain gauges in the period 1970–2018. In particular, the characteristics of dry and wet spells (frequency, duration, severity, and intensity) have been evaluated by means of the run theory applied to the 12-month standardized precipitation index (SPI) values. Moreover, in order to detect possible tendencies in the SPI values, a trend analysis has been performed by means of two non-parametric tests, the Theil–Sen and Mann–Kendall test. The results indicated similar values of frequency, severity, duration, and intensity between the dry and the wet spells, although wet events showed higher values in the extreme. Moreover, the results of the trend analysis evidenced a different behavior between the northern side of the basin, characterized by a negative trend in the 12-month SPI values, and the southern side, in which positive trends were detected.
Highlights
Drought, similar to floods, is a dangerous natural hazard that can affect almost every region of the world at any time
This result agrees with the results obtained by several authors e.g., [29], which evidenced that the Mediterranean rainfall regime is strongly linked to general atmospheric circulation patterns such as the El Niño Southern Oscillation (ENSO), the Mediterranean Oscillation (MO), the Western Mediterranean Oscillation (WeMO), and especially the North Atlantic Oscillation indices that are negatively correlated with precipitation in Algeria [45]
A predominant negative phase of the NAO occurred between 1940 and 1980, corresponding to a period when precipitation was above normal. This was followed by a predominant positive phase, which significantly contributed to the rainfall reduction observed from the beginning of the 1980s in the Mediterranean basin, and in Algeria [29]
Summary
Similar to floods, is a dangerous natural hazard that can affect almost every region of the world at any time. Long-term droughts affect all sectors of the economy and, as a result, society as a whole. Drought is mainly related to a rainfall deficit leading to a decrease in water supplies affecting the flora and fauna of a given region [1,2]. Meteorological drought is characterized by a deficit of precipitation, an elevated temperature, and low humidity. These anomalies propagate to impact the surface water and groundwater sources, ecosystems, and human activities. The impact of drought on society, the environment, and the economy depends on its duration and spatial extent. Water stress or water deficit caused by drought has a substantial influence on low production in major agricultural crops [3,4]
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