摘要:正确认识气候变化对流域森林植被和水文的影响对于林业经营管理与流域生态修复具有重要意义。为了揭示气候与植被覆盖变化对西南亚高山区流域碳水循环过程的影响，用生物物理/动态植被模型SSiB4/TRIFFID（Simplified Simple Biosphere model version 4, coupled with the Top-down Representation of Interactive Foliage and Flora Including Dynamics model）与流域地形指数水文模型TOPMODEL（Topographic Index Model）的耦合模型（以下记为SSiB4T/TRIFFID）模拟了不同气候情景下西南亚高山区的梭磨河流域植被演替和碳水循环过程。结果表明，所有试验流域植被经历了从C3到苔原灌木最后到森林的变化；控制试验流域蒸散在流域植被主要为苔原灌木时达到最大而径流深最小；增温5 ℃并且增雨40%试验[记为T+5, (1+40%) P试验]流域蒸散在流域为森林覆盖时达到最大而径流深最小。随着温度增加，森林蒸腾、冠层截留蒸发和蒸散的增加幅度明显大于草和苔原灌木，导致森林从控制试验的增加径流量变为减小径流量。从控制试验到T+5, (1+40%) P试验，温度增加使森林净初级生产力有所增加，但对草和苔原灌木的净初级生产力影响很小；植被水分利用效率随温度增加明显减小。西南山区随着海拔高度降低（温度升高），森林从增加径流量转变为减少径流量，植被水分利用效率也相应明显减小。西南山区气候的垂直地带性对森林—径流关系和水分利用效率的空间变化有着重要的影响。
关键词:陆面模式/
碳水循环模拟/
气候与植被变化影响/
森林—径流关系/
水分利用效率
Abstract:Correctly understanding the hydrological impacts of forest vegetation and climate change is of considerable significance for forestry management and watershed ecological restoration. To investigate the effects of climate and vegetation cover changes on carbon-water cycles, the biophysical/dynamic vegetation model SSiB4/TRIFFID (Simplified Simple Biosphere model version 4, coupled with the Top-down Representation of Interactive Foliage and Flora Including Dynamics model) was coupled with the TOPMODEL (Topographic Index Model) based on the catchment scheme partitions between saturated and unsaturated zones. The coupled model (hereinafter SSiB4T/TRIFFID) was employed to perform long-term dynamic simulations of vegetation succession and carbon-water circulations under different climate scenarios for a subalpine basin (the Soumou River basin that is a tributary of the Yangtze River located in the mountain region of southwestern China). The results of all tests indicate that vegetation fractions initially undergo changes from C3 grass dominance to tundra shrub dominance and then gradually approach equilibrium forest dominance. The results of the control test show that evapotranspiration of the basin increases and reaches its maximum value and runoff reaches its minimum value during the succession period of C3 grasses into tundra shrubs. Additionally, evapotranspiration decreases and runoff increases during the succession period of tundra shrubs into forests. An increase in temperature by 2 ℃ enhances the rate of transpiration and canopy interception evaporation of forests more than those of grasses and tundra shrubs. As a result, the role of forests in increasing runoff is reduced. An increase in temperature by 5 ℃ accompanied by an increase in precipitation by 40% [T+5, (1+40%)P test] will cause forests to reduce runoff because of the considerable increase in water loss through canopy interception evaporation and transpiration of forests. The results indicate that sensitivity to temperature changes of canopy interception evaporation and transpiration of forests are more than those of grasses and shrubs. Such a mechanism of temperature change causes the forest-runoff relationship to change. From the control test to the T+5, (1+40%)P test, the forest net primary productivity (NPP) increases with the increase in temperature. By contrast, the increase in temperature has a slight effect on the NPP of grasses and tundra shrubs. The water use efficiency (WUE), which characterizes the coupling relationship between carbon and water, considerably decreases with the increase in temperature. As elevation decreases (temperature increases) in the mountain region of southwestern China, WUE decreases with the decrease in altitude. Moreover, the role of forests to increase runoff changes to decrease runoff. The vertical zonality of climate controls the spatial variation of the forest-runoff relationship and WUE.
Key words:Land surface model/
Carbon-water circulation simulation/
Effects of climate and vegetation changes/
Forest-runoff relationship/
Water use efficiency
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