太湖蒸发年际变化主控因子及其影响机制研究

Water loss from evaporation is about half of Lake Taihu’s volume. Studying the evaporation response to climate change is of great societal importance for drinking water supply in Lake Taihu catchment. Although many environmental factors have been shown to influence lake evaporation through complicated interactions, the decisive constraint to long-term lake evaporation variation, as well as the associated mechanism is still unclear. In this research, we will choose Lake Taihu, a large shallow subtropical lake in Yangzi River Delta as study area. Observations from the Taihu Eddy Flux Network and simulations by NCAR LISSS will be used to address the following six-fold issues: (1) to investigate the temporal and spatial variations in water evaporation and its contributing environmental factors across Lake Taihu. (2) to evaluate and improve the performance of NCAR LISSS long-term simulation by latent heat observations. (3) to simulate the historical (1979-2014) and future (2015-2100) evaporation of Lake Taihu with inputs from adjusted reanalysis and climate model products, respectively. (4) to quantify and distinguish the contributions of air temperature, solar radiation, wind speed and atmospheric humidity to interannual variations in Lake Taihu evaporation through latent heat decomposition and sensitivity analysis. (5) to uncover the linkage between energy partitioning (Bowen ratio) and climate warming. (6) to elucidate mechanisms underlying water evaporation variability caused by energy partitioning at Lake Taihu. The study aims to determine the decisive environmental factor of interannual variations in Lake Taihu evaporation, and to clarify the associated physical process. The results can advance our understanding of water evaporation variability, also provide timely data and theory support to the ongoing evaporation prediction and water recourse management at Lake Taihu.

太湖年蒸发量约占其蓄水量的50%，研究太湖蒸发对气候变化的响应关系到沿岸上千万居民的供水安全。影响湖泊蒸发的气象环境因子众多且互相反馈，至今对湖泊蒸发年际变化的主控因子及影响机制尚不明确。本研究以亚热带大型浅水湖泊—太湖为研究对象，基于太湖中尺度通量网观测数据，分析太湖蒸发时空变化特征及其影响因子；利用实测潜热，检验并优化NCAR LISSS模型对太湖年际蒸发的模拟能力；用校正后的再分析资料和气候模式产品驱动LISSS模型，模拟1979-2014年和2015-2100年的太湖蒸发年际变化特征；基于影响因子拆分和敏感性分析，量化气温、太阳辐射、风速和大气湿度对太湖蒸发年际变化的贡献；揭示太湖波文比随气温变化的规律；阐明能量分配改变对太湖蒸发的影响过程。旨在确定太湖蒸发年际变化的主控因子，明确能量分配对太湖蒸发的影响机制。本研究结果可为预测太湖蒸发未来变化提供数据支持和理论依据。

湖泊蒸发敏锐地指示着水分循环对气候变化的响应。传统观点认为，与蒸发皿蒸发相似，湖泊蒸发年际变化主要受地表太阳辐射控制。然而，蒸发皿因热容量小、无冰情变化，缺乏对大气的反馈过程，蒸发皿蒸发无法代表开阔湖面的实际蒸发。本研究以太湖为研究对象，分析了太湖实测潜热通量的时空变化特征及其影响因子，利用LISSS-NUIST模型模拟了1979-2013年和2005-2100年太湖蒸发的年际变化，拆分并量化了气象因子对太湖历史和未来蒸发年际变化的贡献。研究发现，太湖潜热通量观测所用的新一代开路式涡度相关系统—IRGASON必须进行光谱效应校正。太湖日尺度的能量闭合度为0.73，主要受动力湍流交换限制。太湖潜热蒸发的峰值和谷值分别出现在午后和凌晨，主要受水气界面湿度梯度和风速的共同影响，故质量传输模型对小时尺度太湖蒸发模拟效果最佳。太湖月平均蒸发量呈现夏高、冬低的季节变化特征，主要影响因子为可利用能量，故包含可利用能量的综合模型对太湖月和年蒸发量模拟效果最佳。在月和年尺度上，太湖水面蒸发空间差异小，对湖泊自身的生物物理属性并不敏感。在年际尺度上，LISSS-NUIST模拟的太湖水面蒸发在1979-2013年间逐步增强，速率为29.6 mm 10yr-1，向下太阳短波辐射是主要贡献因子。RCP8.5情景下耦合模拟发现，从2005年至2100年，太湖水面蒸发显著上升，速率为32.5 mm 10yr-1。大气辐射强迫和湖面长波反馈对未来太湖蒸发量上升的贡献为77%，由气温升高所引起的波文比下降对太湖蒸发年际变化的贡献为21%，水体热储量和反照率变化的贡献不足2%。本研究结果深化了对湖泊水面蒸发机理的认识，有利于改进气候模型对水分循环的模拟，可为预测太湖蒸发变化提供数据支持和理论依据。