Deconstructing the Effects of Climate and Phenology on Hydrological Processes: A Case Study From an Inland Basin in Central Asia

The impacts of climate change on evapotranspiration (ET) and streamflow have been extensively studied. However, most research assumes static vegetation phenology, leaving uncertainty about whether phenological changes outweigh climatic factors in influencing hydrological processes. To address this gap, this study employed an eco-hydrological model with detailed physical mechanisms to quantify the contributions of temperature, precipitation and phenological shifts to ET and streamflow in the inland Kashi Basin (KSB) of Central Asia. Compared with the baseline year 2001, daytime and nighttime temperatures in the KSB were on average 0.31°C and 0.15°C higher during 2001–2020, resulting in a mean increase in ET of 1.13 mm/year and a decrease in runoff of 0.66 mm/year. An increase of 14.89 mm/year in mean annual precipitation was found to result in a 9.17 mm/year increase in ET and a 4.36 mm increase in runoff. Compared with 2001, the growing season during 2001–2020 was on average 10.24 days longer, leading to a mean increase in ET of 10.30 mm/year and a decrease in runoff of 8.65 mm/year. Notably, the effects of phenological shifts on hydrological processes were comparable to those of temperature and precipitation. Earlier spring phenology intensified ET in late spring and early summer and sustained runoff reductions throughout the summer, potentially exacerbating summer vegetation degradation. These findings underscore the critical role of dynamic phenological changes in shaping hydrological processes under warming conditions, emphasising the necessity of integrating phenology dynamics into climate-hydrology models.