Improving water-carbon coupling under seasonal hydroclimatic variability: Exploring water use efficiency and its seasonal aridity resilience in the Tana River Basin, Kenya

Tana River Basin in Kenya. Water use efficiency (WUE) is a pivotal variable to understand the balance of ecosystem carbon gain and water loss. However, the periodic seasonal aridity chronically affects the ecosystem water and carbon cycling processes. Therefore, for improving the water-carbon coupling in regions with seasonal hydroclimatic variability, it is pivotal to conducting a comprehensive understanding of both WUE and its seasonal aridity resilience (SAR). Based on the quantifying evaluation of WUE and its SAR, this study analyzed their spatiotemporal variation and influencing factors with Theil-Sen ' s slope, Mann-Kendall test, and interpretable machine learning models. (1) Around 73.46 % areas of the basin presented a decreasing trend of SAR, indicating the negative impact of seasonal aridity on water-carbon coupling is intensifying; (2) The sub-humid/humid zone and farmland presented the highest WUE (2.00 and 2.09 g C kg −1 H 2 O) but the lowest SAR (0.92 and 1.01) among climate zones and biomes, respectively; (3) At the basin scale, WUE was mainly influenced by vegetation composition, leaf area index, and temperature, while solar radiation, aridity index and leaf area index were the dominant factors for SAR. Moreover, the dominant factors in different climate zone and biome were varying. These insights provide scientific supports for the management of ecosystem water-carbon coupling in regions with seasonal hydroclimatic variability. • Negative impact of seasonal aridity on water-carbon coupling is intensifying. • Sub-humid/humid zone and farmland had the highest WUE but the lowest SAR. • Identified the key factors influencing WUE and SAR among basin and ecosystem types. • Targeted management strategies considering both the WUE and SAR were provided.