Abstract:

Evapotranspiration acts as an intermediate link in the terrestrial water and energy cycles while also serving as a crucial nexus connecting soil, vegetation, and atmospheric processes. Investigating changes in evapotranspiration holds significant scientific importance for the scientific management of water resources, addressing challenges posed by climate change, and ensuring regional eco-hydrological security. This study utilizes observational data from representative sites in the Yellow River Basin, namely the source region, the Hetao region, and the downstream region, which correspond to Haibei Station, the Semi-Arid Climate and Environment Observatory of Lanzhou University, and Yucheng Station. The purpose is to evaluate the performance of the 6th Phase of the Coupled Model Intercomparison Project (CMIP6) in simulating evapotranspiration across different regions of the Yellow River Basin. Based on this, the spatiotemporal variations of evapotranspiration across different regions of the Yellow River Basin under historical (1980-2014) and future (2026-2100) scenarios are analyzed using the multi-model ensemble mean results. The results show that the evapotranspiration derived from the CMIP6 multi-model ensemble mean exhibits good correlation and high Taylor skill scores in the source region, the Hetao region, and the downstream region of the Yellow River. Therefore, it is considered a suitable tool for investigating the spatiotemporal distribution of evapotranspiration. Furthermore, the annual evapotranspiration derived from the CMIP6 multi-model ensemble mean shows an increasing trend, with the highest change rate of 3.45 mm·(10 a)^-1 identified in the source region of the Yellow River, while the increasing rates in the Hetao and downstream regions are relatively slower. Evapotranspiration shows increasing trends in spring and winter across the Yellow River Basin. However, the trends in summer and autumn exhibit spatial heterogeneity, with evapotranspiration rising in the source region but decreasing in the Hetao and downstream regions. Notably, the downstream region shows pronounced decreasing trends, with rates of 1.13 mm·(10 a)?1 and 0.73 mm·(10 a)?1 in summer and autumn, respectively. Under all future scenarios, evapotranspiration is projected to continue increasing throughout the 21^st century in the source region, Hetao, and the downstream regions of the Yellow River Basin, peaking around the year 2100. As anthropogenic emissions increase, the rate of evapotranspiration increase is expected to accelerate further, with the most significant acceleration projected for the downstream region.

Key words: the Yellow River Basin, evapotranspiration, CMIP6, spatiotemporal variation, future projection

摘要：

蒸散是陆地水循环和能量循环过程的关键环节，同时也是连接土壤、植被、大气过程的纽带。开展蒸散变化研究，对科学管理水资源、应对气候变化挑战、保障区域生态水文安全具有重要科学意义。本文分别在黄河源区、河套和下游地区选取一个代表性站点（分别为海北、兰州大学半干旱气候与环境观测站及禹城站），利用站点观测资料评估第六次国际耦合模式比较计划（Coupled Model Intercomparison Project Phase 6，CMIP6）对黄河流域不同区域蒸散的模拟能力。在此基础上，基于多模式集合平均结果，分析黄河流域不同区域历史（1980—2014年）和未来（2026—2100年）不同排放情景下蒸散的时空变化。结果表明，CMIP6多模式集合平均蒸散在黄河源区、河套和下游地区的相关性较好，泰勒评分较高，模拟得到的蒸散更为合理，适用于蒸散时空分布研究。CMIP6多模式集合平均年蒸散呈增加趋势，其中黄河源区变化速率最大[3.45 mm·（10 a）^-1]，河套和下游地区增加速率相对较缓。春季和冬季蒸散呈增加趋势，但夏季和秋季蒸散变化趋势存在差异，其中黄河源区蒸散呈增加趋势，而河套和下游区域蒸散呈减少趋势，下游减小趋势明显[夏季和秋季减少速率分别为1.13、0.73 mm·（10 a）^-1]。在所有未来情景下，黄河源区、河套和下游地区蒸散均呈持续上升趋势，并预计于2100年达到峰值。随着人为排放量的增加，蒸散上升速率也将进一步加快，其中下游区域蒸散增加趋势最显著。

关键词: 黄河流域, 蒸散, CMIP6, 时空变化特征, 未来预估