Inter-annual variability of rainfall under an arid climate: case of the Gafsa region, South west of Tunisia

Abstract

Rainfall in an arid climate is limited and very irregular in time and space, and is therefore very difficult to predict. Nevertheless, examining rainfall variability in both time and space is usually required in order to establish an adequate strategy for water resources management. In this context, this work is interested in examining both spatial and temporal variation of rainfall in the region of Gafsa (South West of Tunisia) which is characterized by an arid climate. The analysis is based on annual precipitation data registered in 18 stations over a period of 56 years (1960–2015). Statistical tests showed that all observation series are independent, stationary, and homogeneous. The study of rainfall series based on principal component analysis (PCA) and the form of the curve of the cumulative rainfall index (CRI) resulted in sub-dividing the study area into five different regions, with different climatic (precipitation) and physiographic (elevation) characteristics. Moreover, this study showed that precipitation decreases, from North to South, under the influence of several factors, including the presence of a mountainous range, being an important physiographic barrier that affects rainfall downpours. The study of the temporal variation of rainfall at different steps of time (annual, monthly, and daily) showed extremely variable rainfall regime, low recurrence of rainy days, and daily rainfall anomalies, with intensities varying between 50 and 423 mm/day.