Abstract:

To investigate the spatial differentiation of the relationship between forest vegetation and runoff, the Biophysical/Dynamic Vegetation Model SSiB4/TRIFFID is coupled with TOPMODEL (hereinafter SSiB4T/TRIFFID). Long-term dynamic simulations are run of vegetation succession and carbon-water circulations for a subtropical basin (Qingyijiang Basin) and a subalpine basin (Soumo River Basin) under different climate scenarios. The impacts of forest vegetation on runoff are investigated by assessing SSiB4T/TRIFFID outputs against catchment experiments. The simulation results showed that among the three vegetation types (grass, shrub, and forest), forest transpiration, canopy interception evaporation, evapotranspiration, and forest leaf area index were the most sensitive to temperature changes in the absence of water stress. However, they were most sensitive to changes in precipitation in the presence of water stress. The simulation results of the Qingyijiang basin indicated that broadleaf trees were dominant as vegetation fractions gradually approach equilibrium. The evapotranspiration of forest, shrub, and grassland was 742.2 mm∙a^-1, 588.6 mm∙a^-1, and 546.2 mm∙a^-1, respectively. The evapotranspiration of forest was significantly greater than that of shrub and grassland. Forest reduced the runoff of the basin. The control test showed that the needleleaf trees, the dominant vegetation, gradually approach equilibrium in the Soumo River basin. The evapotranspiration of forest, tundra shrub, and grassland were 387.8 mm∙a^-1, 444.3 mm∙a^-1, and 387.5 mm∙a^-1. Forest evapotranspiration was lower than that of tundra shrub owing to low temperature in the subalpine mountain region. Forest increased the runoff of the basin. In the increase of temperature, the evapotranspiration in forest area increased the most among the vegetation types. This phenomenon could be explained by the change of forests' role from increased runoff to reduce runoff. In the humid region, as the altitude decreases or the latitude decreases from north to south, the forest could change from increasing runoff to have no significant effect on runoff, even to reduce runoff with the increase of temperature. In the semi-humid and semi-arid region, forest evapotranspiration decreases most with decreasing precipitation, which results in the impact of forest on runoff decreases with decreasing precipitation. The vertical and horizontal zonal distribution of climate controls the spatial variation of the forest-runoff relationships.

Key words: coupled model, carbon-water circulation simulation, impacts of forest vegetation on water balance

摘要：

为了揭示森林植被与流域径流量关系的空间分异规律,用生物物理/动态植被模式SSiB4/TRIFFID与流域水文模型TOPMODEL的耦合模式SSiB4T/TRIFFID进行青弋江流域和西南亚高山区的梭磨河流域各种气候情景的植被演替和碳水循环模拟。根据模拟结果并结合森林集水区试验结果,分析森林植被对流域径流量的影响。模拟结果表明,不存在水分胁迫时,在草地、灌木和森林3种植被类型中,森林蒸腾、冠层截留蒸发、蒸散和叶面积指数对温度变化最敏感;存在水分胁迫时,森林蒸腾、冠层截留蒸发、蒸散和叶面积指数对降水的变化最敏感。控制试验结果表明,青弋江流域阔叶林在植被向平衡态演替过程中取得支配地位,森林、灌木和草地蒸散分别为742.2、588.6和546.2 mm∙a^-1,森林蒸散明显大于灌木和草地,森林减小了径流量。梭磨河流域针叶林在植被向平衡态演替过程中取得支配地位,森林、苔原灌木和草地蒸散分别为387.8、444.3和387.5 mm∙a^-1,森林蒸散低于苔原灌木,森林增加了径流量。但随着温度增加,由于森林蒸散增加幅度明显大于苔原灌木和C3草地,森林蒸散逐渐大于苔原灌木,森林从增加径流量转变为减小径流量。对于湿润地区,随着温度增加,森林从增加径流量转变为对径流量没有明显影响和减小径流量。对于半湿润和半干旱地区,随着降水的减小,森林蒸散减小幅度明显大于灌木和草地,森林对径流量的影响随着降水量的减小而减小。气候的垂直地带性和水平地带性分布对森林植被与流域径流量关系的空间变化起着重要的控制作用。

关键词: 耦合模型, 碳水循环模拟, 森林植被的水文影响