Projected climate regime shifts in the Asi Basin, Türkiye, under SSP climate scenarios: implications of temperature and precipitation changes

Abstract

Climate change is increasingly reshaping hydroclimatic regimes in Mediterranean river basins, with significant implications for water resources, agricultural productivity, and ecosystem stability. This study evaluates projected climate regime shifts in the Asi Basin, located in southern T & uuml;rkiye, using station-based hydroclimatic observations and future climate projections under the Shared Socioeconomic Pathway (SSP) scenarios SSP2-4.5 and SSP5-8.5. Baseline climate conditions were derived from a 30-year reference period (1991-2020) using long-term observations from meteorological stations distributed across the basin. Four hydroclimatic variables were used to characterize present and future climate conditions: annual total precipitation, annual mean temperature, mean maximum temperature of the warmest month, and mean minimum temperature of the coldest month. To assess potential shifts in regional climate regimes, three empirical climate classification indices widely applied in Mediterranean environments were employed: the De Martonne aridity index, the Emberger pluviometric coefficient, and the Lang rainfall factor. Climate conditions were evaluated for four future time horizons (2040, 2060, 2080, and 2100) to capture near-, mid-, and late-century transitions. Results indicate a strong and spatially consistent warming trend across the basin under both scenarios, with substantially greater warming under SSP5-8.5. In contrast, projected precipitation changes remain comparatively moderate, but show a gradual decline under the high-emission pathway. Despite these modest precipitation changes, rising temperatures are sufficient to drive marked shifts in climate classifications. Under SSP5-8.5, semiarid areas expand to 55.03% of the basin according to the De Martonne classification, arid zones reach 14.81% under the Emberger index, and arid conditions dominate 90.30% of the basin under the Lang classification by 2100, with localized emergence of desertlike conditions. Humid and very humid climate classes decline sharply and nearly disappear in most classifications by the end of the century. These results indicate that the Asi Basin is likely to undergo substantial aridification during the twenty-first century, with important consequences for basin-scale drought risk, land use planning, and climate adaptation in southern T & uuml;rkiye.