深圳市前海桂湾公园土壤蒸发及植被蒸腾模拟

蒸散发（ET）是连接水文循环和地表能量平衡的重要组成部分，准确的估算土壤蒸发（LE_s）和植被蒸腾（LE_v）对城市水资源分配和管理具有重要意义。针对城市林地蒸散发双源模型的缺失，本研究基于MOD16模型提出了应用于城市林地区域改进的MOD16双源模型。改进的MOD16双源模型更加准确的描述城市林地区域复杂下垫面的能量分配过程。结合高时空分辨率的Sentinel-2遥感卫星影像，对2020年深圳市前海桂湾公园20个无云日的LE_s和LE_v进行反演研究。用Shuttleworth-Wallace （S-W）模型和双作物系数法（FAO dual-K_c）验证模型性能，同时分析改进的MOD16模型对输入变量的敏感度，结果表明：改进的MOD16模型与S-W模型和FAO dual-K_c之间的均方根误差（RMSE）分别为21.39 W/m²和20.41 W/m²，平均绝对误差（MAE）分别为18.81 W/m²和19.05 W/m²，R²分别为0.801和0.634。改进的MOD16模型可以应用在城市林地LE_s和LE_v估算中。桂湾公园地区总蒸散月均值在85-165 W/m²之间。研究区域的LE_s和LE_v呈现出明显的季节变化，春夏季蒸散量升高，秋冬季蒸散量降低，LE_s的变化范围为0-50 W/m²，LE_v的变化范围为0-120 W/m²。LE_v高值在研究区呈现零散分布，多集中在前海桂湾沿岸，LE_s高值集中在研究区的西北、东北和东南部。敏感性分析结果表明，改进后的MOD16模型对植被覆盖、太阳辐射和湿度更敏感。其中，LE_v模拟结果受净辐射和植被覆盖影响最大，LE_s的模拟结果受湿度和植被覆盖的影响最大。因此，应用改进的MOD16模型时需要优先确保这些参数的准确输入。修正后的MOD16模型极大地提高了高分辨率、小尺度区域城市林地LE_s和LE_v模拟的准确性，为准确获取植被耗水量信息从而科学指导城市林地灌溉、解决城市水资源分配与管理提供有力工具。

Simulation of soil evaporation and vegetation transpiration in Qianhai Guiwan Garden of Shenzhen

Evapotranspiration (ET) is an important component of connecting hydrological cycle and surface energy balance. Accurate estimation of soil evaporation (LE_s) and vegetation transpiration (LE_v) is of great significance to urban water resources allocation and management. This study, based on the MOD16 model, proposed an improved MOD16 dual-source model, which is applied to estimate the ET of urban woodland areas. The improved MOD16 dual-source model more accurately described the energy distribution process of the complex underlying surface in the urban woodland areas. The model was applied to estimate LE_s and LE_v respectively in 20 cloudless days in Guiwan Garden area of Shenzhen City, by using Sentinel-2 remote sensing satellite images which had high spatial and temporal resolution. The Shuttleworth-Wallace (S-W) and dual crop coefficient (FAO dual-K_c) model were used to evaluate model performance. This study also analyzed the sensitivity of the input variables. The results show that the root mean square error (RMSE) between the improved MOD16 model and the S-W model is 21.39 W/m², the average absolute error (MAE) is 18.81 W/m², R²=0.801; the root mean square error (RMSE) between the improved MOD16 model and the FAO dual-K_c model is 20.41 W/m², the average absolute error (MAE) is 19.05 W/m², R²=0.634. The improved MOD16 model was successfully applied to the estimation of LE_s and LE_v of urban forest. The monthly average value of total evapotranspiration in Guiwan Garden is between 85 and 165 W/m². The LE_s and LE_v present substantially seasonal variation, with the increased evapotranspiration in spring and summer, and the decreased evapotranspiration in autumn and winter. The range of LE_s is 0-50 W/m² and the range of LE_v is 0-120 W/m². The high values of LE_v are scattered, mostly located along the coast of Guiwan Garden. The high values of LE_s are mainly located in the northwest, northeast and southeast of the study area. Sensitivity analysis showed that the improved MOD16 model was more sensitive to vegetation coverage, solar radiation and humidity. The LE_v simulation results were most affected by solar radiation and vegetation cover, meanwhile, the LE_s simulation results were most affected by humidity and vegetation cover. Therefore, it is necessary to prioritize the accurate inputs of these parameters when applying the improved MOD16 model. The improved MOD16 model greatly improved the accuracy of LE_s and LE_v simulation in high-resolution, small-scale regional urban forestland. This model provides a powerful tool for accurately obtaining vegetation water consumption information to scientifically guide urban forestland irrigation and solve urban water resource allocation and management.