青藏高原作为我国重要的生态屏障，被称为“亚洲水塔”，拥有大量的冻土与冰雪，对气候变化极为敏感。蒸散发是生态系统水热平衡的关键过程，是水流在SPAC（土壤-植被-大气连续体）系统传输的途径，是植被水分利用率评价及水资源预测与管理的重要内容。近年来青藏高原气候暖湿化显著，研究蒸散发和其组分时空格局变化，对生态系统服务功能评估和水资源管理具有重要的科学与现实意义。由于青藏高原区域气候变化和人类活动复杂交互作用，以往的研究在蒸散发主导因素研究方面尚未形成统一的认知，对其组分的研究相对较少。本研究在原有点尺度蒸散发双源模型基础上，发展构建了青藏高原区域蒸散发模型，结合青藏高原地区的气象、植被、土壤水热和土地覆盖等数据，模拟重建了青藏高原区域2003-2018年逐日1km蒸散发和其组分时空格局；基于地面站点观测、同类蒸散发产品数据比较的方式评估率定了模型模拟结果，确定植被蒸腾及土壤蒸发对蒸散发的贡献比例；量化分析气候变化和植被变化对蒸散发的影响；基于情景诊断分析，区分量化土地利用/覆盖变化和气候变化对区域蒸散发的贡献。
（1）模型校验与率定
地面站点观测的校验与率定结果显示：总体上模型模拟值和观测值在时间序列上呈现出较好的一致性（IOA=0.93），R2为0.76、NSE为0.71，表明模型能较好地重现蒸散发的月动态。与同类产品数据集对比结果表明：模型在青藏高原区域蒸散发模拟较为合理。青藏高原蒸散发呈现出东南多西北少的空间格局，区域多年平均蒸散发量为366.01±14.27毫米，蒸散发量在季节尺度由大到小依次为夏季（158.39±9.41毫米）、春季（91.86±3.68毫米）、秋季（77.46±3.18毫米）、冬季（38.30±2.55毫米），具有明显的季节变化特征；青藏高原蒸散发和其组分在逐年增加，蒸散发每年以2.27毫米的速度增加，土壤蒸发和植被蒸腾分别以每年0.93毫米、1.34毫米的速度增加。蒸散发拆分结果表明：土壤蒸发多年平均值为212.84±6.33毫米，植被蒸腾为153.16±8.34毫米，在季节和年际上，土壤蒸发对总量的贡献均高于植被蒸腾对总量的贡献，土壤蒸发在青藏高原蒸散发中占主导地位，蒸发比为68.75%。该模型优势总结如下：首先，能够有效地重现植被冠层和地表的辐射传输和能量分配过程，估算蒸散发及组分（蒸发和蒸腾）；其次，通过应用Newton-Raphson迭代方案，准确解决冠层和地面的能量平衡方程，不需要地表辐射温度的输入；最后，模型明确包含了气孔导度对蒸腾的控制，以及土壤阻抗对水分运移的影响。
（2）气候变化与植被变化对蒸散发影响
青藏高原区域蒸散发时空格局是多种环境因素综合作用的结果。去趋势相关性分析结果表明：气温和短波辐射的增加促进了蒸散发的增加，而相对湿度的增加对蒸散发具有抑制作用，风速和气压的变化对蒸散发的影响较为复杂，具体影响因地区而异；土壤水热的时空变化对蒸散发有着显著的影响，土壤水分在西北部部分区域与蒸散发呈现显著正相关，而土壤温度的提高普遍促进了蒸散发；叶面积指数的增加也显著提高了蒸散发量。在区域上使用偏最小二乘回归模型量化了各环境因素对蒸散发的影响，结果表明叶面积指数对蒸散发的解释作用最强（0.52），青藏高原植被变绿是促进区域蒸散发的主导因素。
（3）土地利用/覆盖变化对青藏高原蒸散发影响
2003-2018年，青藏高原土地利用/覆盖格局较为稳定，但在局部地区存在植被类型间的转换，各个区域都出现了不同程度的土地覆盖变化，有10.67万平方千米的土地覆盖发生了变化，其中草原、灌木和森林的面积经过转移后出现了增长，而农田和其他植被类型面积出现了减少。青藏高原2003-2018年不同植被覆盖类型年均蒸散发总量差异显著，其中森林最大，随后是农田、草原、灌木及其他植被类型。情景诊断分析表明：土地利用/覆盖变化总体上促进植被蒸腾，一定程度减少土壤蒸发，最终导致蒸散发总量的增加。较气候变化而言，土地利用/覆盖变化对蒸散发变化的贡献相对较小，多年平均贡献度13.20%（对土壤蒸发和植被蒸腾变化的贡献度分别为-13.42%、33.10%），气候变化对蒸散发变化起主导作用，多年平均贡献度86.80%（土壤蒸发113.42%、植被蒸腾66.90%）。
本研究为青藏高原地区蒸散发和其组分的模型模拟及驱动机制分析提供了可行的方法，并对未来该地区的水资源管理和生态保护具有一定的参考价值。

The Qinghai Tibetan Plateau, serving as a crucial ecological barrier for China and dubbed the "Water Tower of Asia", possesses extensive permafrost and ice, making it highly sensitive to climate change. Evapotranspiration is a critical process in the hydrothermal balance of ecosystems, facilitating water movement within the Soil-Plant-Atmosphere Continuum (SPAC), and is essential for assessing vegetation water use efficiency and for predicting and managing water resources. The recent warming and humidification of the climate on the Qinghai Tibetan Plateau underscore the significance of studying the spatiotemporal patterns of evapotranspiration and its components for ecosystem service assessment and water resource management. Due to the complex interplay between regional climate change and human activities, there has been no unified understanding of the dominant factors influencing evapotranspiration, and research on its components has been relatively limited. This study builds on existing point-scale dual-source evapotranspiration models to develop a regional model for the Qinghai Tibetan Plateau, integrating meteorological, vegetation, soil water-thermal, and land cover data to simulate daily 1 km resolution evapotranspiration and its components from 2003-2018. The model simulation results were evaluated and calibrated using ground station observations and similar remote sensing product data, establishing the contributions of vegetation transpiration and soil evaporation; the impacts of climate change and vegetation changes on evapotranspiration were quantitatively analyzed; and scenario diagnostic analysis was used to differentiate and quantify the contributions of land use/cover changes and climate changes to regional evapotranspiration.
(1) Model validation and calibration
Validation and calibration based on ground station observations demonstrated good temporal consistency between model simulations and observed values (IOA = 0.93), with an R2 of 0.76 and an NSE of 0.71, indicating that the model accurately reproduces the monthly dynamics of evapotranspiration. Comparisons with similar product datasets indicate that the model provides reasonable simulations of evapotranspiration in the Qinghai-Tibet Plateau region. The spatial pattern of evapotranspiration shows higher values in the southeast and lower in the northwest, with a regional average annual evapotranspiration of 366.01 ± 14.27 mm; seasonal variations are pronounced, with the highest in summer (158.39 ± 9.41 mm), followed by spring (91.86 ± 3.68 mm), autumn (77.46 ± 3.18 mm), and winter (38.30 ± 2.55 mm); the Qinghai Tibetan Plateau's evapotranspiration and its components are increasing annually by 2.27 mm, with soil evaporation and vegetation transpiration increasing by 0.93 mm and 1.34 mm per year, respectively. The breakdown shows that soil evaporation, averaging 212.84 ± 6.33 mm annually, dominates over vegetation transpiration, which averages 153.16 ± 8.34 mm, contributing more both seasonally and annually, with an evaporation ratio of 68.75%. The advantages of this model are summarized as follows: Firstly, it effectively reproduces the processes of radiation transmission and energy distribution in vegetation canopies and the ground, estimating evapotranspiration and its components (evaporation and transpiration). Secondly, by applying the Newton-Raphson iteration scheme, it accurately solves the energy balance equations for canopies and the ground without requiring input of surface radiation temperature. Lastly, the model clearly includes the control of stomatal conductance on transpiration and the impact of soil resistance on water movement.
(2) Impact of climate and vegetation changes on evapotranspiration
The spatiotemporal patterns of evapotranspiration in the Qinghai Tibetan Plateau are the result of the combined effects of various environmental factors. Detrended correlation analysis shows that increases in temperature and shortwave radiation promote evapotranspiration, while increases in relative humidity suppress it; changes in wind speed and air pressure have complex impacts varying by region; spatiotemporal variations in soil water-thermal conditions significantly affect evapotranspiration, with soil moisture in some northwestern areas showing a significant positive correlation with evapotranspiration, while increases in soil temperature generally promote it; increases in leaf area index also significantly raise evapotranspiration. Regional analysis using Partial Least Squares Regression (PLS regression) quantified the impacts of environmental factors on evapotranspiration, showing that leaf area index has the strongest explanatory power (0.52), indicating that greening of vegetation is the primary driver of increased evapotranspiration on the Qinghai Tibetan Plateau.
(3) Impact of land use/cover change on evapotranspiration in the Qinghai Tibetan Plateau
From 2003 to 2018, the land use/cover pattern on the Qinghai Tibetan Plateau was relatively stable, though transitions between vegetation types occurred in some areas, resulting in land cover changes over 106.7 thousand square kilometers, including increases in grasslands, shrubs, and forests, and decreases in farmlands and other vegetation types. Annual evapotranspiration varied significantly among different vegetation cover types, with forests being the highest, followed by farmlands, grasslands, shrubs, and other types. Scenario diagnosis analysis indicates that land use/cover changes generally promote vegetation transpiration and moderately reduce soil evaporation, ultimately leading to an increase in total evapotranspiration. Compared to climate change, land use/cover changes contribute relatively less to changes in total evapotranspiration, with an average annual contribution of 13.20% (soil evaporation -13.42%, vegetation transpiration 33.10%), while climate change plays a leading role, contributing 86.80% on average (soil evaporation 113.42%, vegetation transpiration 66.90%).
This research provides a feasible method for modeling and analyzing the driving mechanisms of evapotranspiration and its components in the Qinghai Tibetan Plateau area and offers valuable insights for future water resource management and ecological protection in the region.