Spatiotemporal heterogeneity of runoff in Tajikistan and its driving mechanisms under climate change

Based on monthly runoff and climate datasets spanning 2000–2024, this study employed the Theil–Sen’s slope estimation, Mann–Kendall (M–K) trend test, as well as Pearson correlation and Spearman rank correlation analyses to systematically examine the spatiotemporal patterns of runoff and its climatic driving mechanisms across Tajikistan, providing a scientific basis for sustainable water resource utilization and management in the study area. Results indicated that during 2000–2024, the annual runoff in Tajikistan exhibited statistically non-significant long-term trend ( P =0.76), while displaying pronounced seasonal variability and strong spatial heterogeneity. Spring and summer average runoff primarily exhibited slight declining tendencies, while winter average runoff exhibited pronounced reduction in localized regions, such as the Syr Darya Basin, the Vakhsh River Basin, and the lower reaches of the Zeravshan River Basin. Precipitation emerged as the dominant positive driver of runoff, exhibiting moderate to strong positive correlations across over 78.00% of the country, whereas potential evapotranspiration consistently functioned as a negative driver. Rising temperatures exerted a dual competitive effect on runoff: in high-elevation, glacier-covered regions, rising temperatures temporarily increased runoff by accelerating glacier melt; however, at the national scale, the negative impact of rising temperature on runoff has played a slightly dominant role to a certain extent by enhancing evapotranspiration. Collectively, these results indicated that the present stability of runoff in Tajikistan is strongly dependent on the short-term compensatory effects of glacier melt and the risk of future runoff decline is likely to intensify as glacier reserves continue to diminish. This study provides a critical scientific evidence to inform sustainable water resource management in Tajikistan and underscores the need for glacier conservation and integrated water resource management strategies.