Impacts of Climate Variability on Hydrological Extremes: Droughts and Floods in a Changing Climate

Abstract

This study investigates the impacts of climate variability on hydrological extremes—droughts and floods—in the context of a changing climate. Using historical climate and hydrological data (1980–2020) alongside key climate indices, including the El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and North Atlantic Oscillation (NAO), we analyze trends in temperature, precipitation, and streamflow, and their linkages to extreme events. Results reveal a significant rise in mean temperatures (0.25°C per decade) and declining precipitation, exacerbating drought frequency and intensity, while amplifying flood magnitudes during extreme rainfall periods. El Niño phases correlate strongly with prolonged droughts, whereas La Niña phases drive flood occurrences. Hydrological modeling using the Soil and Water Assessment Tool (SWAT) demonstrates robust performance (Nash-Sutcliffe Efficiency [NSE] = 0.76 in calibration), projecting a tripling of drought and flood events by 2100 under Representative Concentration Pathway (RCP) 4.5 and RCP 8.5 scenarios. Geospatial vulnerability assessments identify regions with high exposure and low adaptive capacity, underscoring the need for integrated water management and climate-resilient infrastructure. This research highlights the critical role of climate variability in shaping hydrological risks and advocates for adaptive strategies to mitigate socio-environmental impacts in vulnerable regions.