Rainfall Variability and Prolonged Drying of the Menarandra Riverbed (2000–2017) in the District of Bekily (Southern Madagascar)

The Menarandra River, located in the Androy region of southern Madagascar, flows through a semi-arid environment characterized by severe water stress, a long dry season lasting seven to nine months, and a short, highly variable rainy season concentrated between December and March. Rainfall records from the Bekily meteorological station over 2000–2017 highlight pronounced interannual variability, with alternating wet years (e.g., 2001, 2005, 2011, annual totals >1,000 mm) and deficit years with totals below 700 mm (e.g., 2002, 2004, 2016, 2017). To better link raw rainfall data to effective rainfall in terms of hydrological response, the analysis incorporates the Turc formula, widely used in water balance studies to estimate potential evapotranspiration and effective rainfall. This approach allows a more precise characterization of hydrological conditions associated with rainfall variability and their potential role in riverbed drying. Rainfall analysis is complemented by qualitative interpretation of Google Earth satellite images processed in QGIS, together with field observations. Comparison of images from December 2014 and October 2018 reveals marked reduction and fragmentation of water-covered areas, indicating increasing spatial discontinuity of surface flow. While the temporal correspondence between rainfall variability and riverbed drying suggests a strong association, river intermittency likely reflects the combined influence of seasonal and interannual rainfall patterns and local hydrological controls. Overall, results indicate a progressive shift of the Menarandra toward a more intermittent flow regime, improving understanding of river drying dynamics in semi-arid southern Madagascar and informing sustainable water resource management under increasing drought conditions.