DISENTAGLING CLIMATIC AND ENVIRONMENTAL CHANGE SIGNALS ON PALEOFLOOD RECORDS: A CASE STUDY OF THE GUADALENTIN RIVER (SE SPAIN)

The Guadalentín River, located in SE Spain, is considered one of the most torrential rivers in Spain. In this paper, flood frequency and magnitude of the upper Guadalentín River was reconstructed using geomorphological evidence, combined with one dimensional hydraulic modelling and supported by records from documentary sources at Lorca in the lower Guadalentin catchment. Palaeoflood studies were conducted at a 2.5 km reach located at the confluence of the Rambla Mayor (162 km²) and Caramel River (210 km²). These tributaries join at the entrance of a narrow bedrock canyon, carved in Cretaceous limestone, which is 15-30 m wide and 40 m deep. Six stratigraphic profiles were described, the thickest and most complete corresponding to flood benches deposited upstream of the canyon constriction. The stratigraphic and documentary records identify five main phases of increased flood frequency. Phase 1, based on sedimentary palaeoflood evidence alone, occurred at ca. 950-1200 cal AD with at least ten floods with minimum discharge estimates of 15-580 m³s^-1. Phases 2-5, identified through combined sedimentary and documentary evidence occurred at: (a) AD 1648-1672, with eight documentary floods and two palaeofloods exceeding 580-680 m³s^-1; (b) AD 1769-1802, comprising seven documentary floods, of which at least two events (>250 m³s^-1) are preserved in the sedimentary record; (c) AD 1830-1840, with four documentary floods, and at least two events recorded in the stratigraphy (760-1035 m³s^-1); and finally (d) the AD 1877-1900 period that witnessed seven documentary floods, with three palaeofloods (>880 m³s^-1). The palaeoflood and historical flood information indicate an anomalous increase in the frequency of large magnitude floods between AD1830-1900, which can be attributed to climatic variability accentuated by intensive deforestation and land-use practices during the first decades of the 19^th century.