Hydrological change trends of the Surkhob and Khingov river basins in the Vakhsh River of Tajikistan under climate change

The hydrological system in Central Asia is highly sensitive to global climate change, significantly affecting water supply and energy production. In Tajikistan, the Vakhsh River—one of the main tributaries of the Amu Darya—plays a key role in the region’s hydropower and irrigation. However, research on long-term hydrological changes in its two top large basins—the Surkhob and Khingov river basins—remains limited. Therefore, this study analyzed long-term climate and hydrological changes in the Vakhsh River, including its main tributaries—the Surkhob and Khingov rivers—which are vital for the water resource management in Tajikistan and even in Central Asia. Using long-term hydrometeorological observations, the change trends of temperature (1933–2020), precipitation (1970–2020), and runoff (1940–2018) were examined to assess the impact of climate change on the regional water resources. The analysis revealed the occurrence of significant warming and a spatially uneven increase in precipitation. The temperature changes across three climatic periods (1933–1960, 1960–1990, and 1990–2020) indicated that there was a transition from baseline level to accelerated warming. The precipitation showed a 2.99 mm/a increase in the Khingov River Basin and a 2.80 mm/a increase in the Surkhob River Basin during 1970–2020. Moreover, there was a gradual shift toward wetter conditions in recent decades. Despite the relatively stable annual mean runoff, seasonal redistribution occurred, with increased runoff in spring and reduced runoff in summer, due to the compensation of glacier melting. Moreover, this study forecasted runoff change during 2019–2040 using the exponential triple smoothing (ETS) method and revealed the occurrence of alternating wet and dry phases, emphasizing the sensitivity of the Vakhsh River Basin’s hydrological system to climate change and the necessity of adaptive water resource management in mountainous regions of Central Asia. Therefore, this study can provide evidence-based insights that are critical for future water resources planning, climate-resilient hydropower development, and regional adaptation strategies in climate-vulnerable basins in Central Asia.