基于三温模型的民勤绿洲荒漠过渡带植被蒸散发与水分收支研究

Evapotranspiration (ET) strongly relates to both the energy balance and the mass balance of terrestrial ecosystems, and is of crucial importance in the disciplines of ecological construction and protection, and water resources management, especially in oasis where water deficiency is becoming a major obstacle to economic welfare and sustainable development. However, it is still a challenge to quantify ET accurately by remote sensing for most applications, which is the first step to study water budget in arid regions since water unbalance will lead to vegetation degradation, resulting in desertification. In this proposed project, an oasis-desert transitional zone (ODTZ) in Minqin county, a natural oasis between the Badain Jaran and Tengger deserts, is chosen as a typical area to study vegetation transpiration and its water budget based on three-temperature (3T) model, aiming to elaborate the impact of ET variation on vegetation water budget and degradation, and to find solutions to prevent serious vegetation degradation in the area because desert vegetation plays an alleviatory role in threatening of desertification. Therefore, objectives of this proposed project are to: (1) test and validate the performance of the 3T model; (2) retrieval and separate ET into soil evaporation and vegetation transpiration using the 3T model; and (3) quantify the impact of ET variation on water budget and vegetation degradation. To achieve the goals, this proposed project focuses on model validation and rectification, and ET retrieval and its variation impact on water budget and vegetation degradation. The 3T model is planed to be validated using observational data from Bowen ratio systems covering different land types, i.e., vegetation, soil and a mixture of both. Thereafter, ET including soil evaporation and vegetation transpiration, is estimated using the 3T model and remotely sensed images, and its decadal and interannual variability in ODTZ is elaborated. Combining the retrieved ET with other observed data, vegetation water budget and its changes will be analyzed based on the theory of water balance. Thereafter, relations between ET, water budget change and vegetation degradation can be studied and established. If this project is funded, research results, i.e., a promising method based on the 3T model can be established to estimate ET in arid regions under sparsely vegetated condition, and impact of ET variation and water budget change on vegetation degradation can be elaborated, which will provide fundamental information for vegetation restoration in Minqin oasis, preventing the two deserts (Badain Jaran and Tengger) becoming one.

"陆面蒸散发定量估算"是水热平衡研究的热点与难点问题之一，也是研究干旱区水分收支的重要环节，对绿洲生态建设与保护、水资源管理具有重要意义。近年来，干旱区石羊河流域下游的民勤绿洲荒漠过渡带植被退化加剧，严重威胁绿洲安全。本项目拟以民勤绿洲荒漠过渡带为研究区，通过地面定位观测实验和热红外与多光谱遥测，验证申请者已构建的蒸散发遥感反演方法（三温模型）；基于三温模型与卫星遥感数据反演陆面蒸散发、分离植被蒸腾与土壤蒸发，揭示不同植被蒸散发的空间分异特点与时间变化规律；根据地面观测与遥测结果和水量平衡理论，模拟不同植被的水分收支状态和变化规律，探讨蒸散发与水分收支变化对植被退化的影响，揭示水分胁迫条件下植被的适应与退化规律。通过本课题研究，可望完善三温模型，在稀疏植被覆盖下蒸散发反演方法方面实现创新，阐明干旱区蒸散发与水分收支变化对植被退化的影响机理，为恢复植被和保护绿洲提供理论依据。

陆面蒸散发定量估算”是水热平衡研究的热点与难点问题之一，也是研究干旱区水分收支的重要环节，对绿洲生态建设与保护、水资源管理具有重要意义。本项在执行期间开展了地表（不同植物冠层、土壤）温度日变化观测、气象参数（如气温、风速、相对湿度）观测、土壤蒸发观测（自制蒸渗仪）、土壤水分观测（TDR），为深入分析干旱区绿洲荒漠过渡带蒸散发日变化特征奠定了数据基础。发展了以地表温度为核心输入的蒸散发遥感模型，建立了干旱区蒸散发遥感估算的流程，以MODIS数据为主要输入，生成了石羊河流域、黑河流域2008-2012年的蒸散发产品（时间分辨率为8天、空间分辨率为1 km），且可分离为土壤蒸发与植被蒸腾产品，地面通量观测验证结果表明项目反演的蒸散发精度较高，实现了干旱气候条件下低植被覆盖与荒漠地区蒸散发定量反演。通过对比研究发现，本项目提出的蒸散发产品，与其它主流蒸散发数据相比（如MOD16），具有相同的时间与空间分辨率，但克服了MOD16的局限性（即假定荒漠地区的蒸散发为零，导致低估陆面实际蒸散发值），有利于获取干旱、半干旱地区稀疏植被覆盖条件下的蒸散发值。已发表SCI论文2篇（另有2篇SCI论文已在返修审稿中）、AGU专著章节英文论文1篇、国内核心刊物2篇。参加国内会议2人次、国际会议2人次。