气候对森林-径流关系的影响

为了揭示气候对森林-径流关系的影响,利用已有的不同地区森林集水区试验结果分析森林-径流关系空间变化规律,然后在生物物理/动态植被模型SSi B4/TRIFFID与TOPMODEL的耦合模型对长江上游梭磨河流域不同温度下植被演替及蒸发与径流的动态变化过程的模拟结果基础上,通过分析水热条件对净光合速率、冠层湿润分数、蒸腾、冠层截留蒸发以及土壤蒸发的影响,分析水热条件对森林-径流关系的影响。主要结论有:水热条件通过控制森林的净光合速率、蒸腾、冠层截留蒸发和土壤蒸发影响森林-径流关系;随着温度增加,森林蒸散发增加幅度大于其它植被类型和裸地,使森林-径流关系发生变化,水热条件的空间变化决定了森林-径流关系和水分利用效率的空间变化;受气候垂直地带性和水平地带性影响,随着海拔高度下降或从北到南随着温度增加,水分利用效率减小,森林-径流关系存在从增加径流量到对径流量没有明显影响再到减小径流量的变化,水分胁迫或高温将抑制森林蒸腾从而减小森林对径流量减少的作用,森林集水区比较试验结果体现了森林-径流关系这种空间变化规律。

Impacts of Climate on Forest-Runoff Relationship

In order to further understand the effects of climate on forest-runoff relationship, the experimental results from different catchments are employed to detect spatial variation in forest-runoff relationship. Based on the numerical simulations of water balance of the Suomohe Basin (a tributary of the Yangtze River in the mountain region of southwestern China) which are conducted under different temperature change scenarios using the coupled model (Biophysical/Dynamic Vegetation Model SSiB4/TRIFFID coupled with TOPMODEL), the effects of water and heat factor on forest-runoff relationship are analyzed through analyzing the impacts of temperature and soil water on net canopy photosynthesis of forests, canopy wetness fraction, transpiration, canopy interception evaporation, and soil evaporation. The main conclusions are as follows: water and heat conditions affected forest-runoff relationship by controlling the net photosynthetic rate, canopy wetness fraction, transpiration, canopy interception evaporation, and soil evaporation. With the increase of temperature, the increase of forest evapotranspiration is more than that of other vegetation types and bare soil, and leading to changes in forest-runoff relationship. The spatial variation of water and heat conditions determines the spatial variation of water use efficiency and forest-runoff relationship. As temperature increases duo to the vertical and the horizontal climate zones, water use efficiency decreases and forest-runoff relationship exists from increasing runoff to no significant effect on runoff and reducing runoff. Water stress or high temperature will inhibit forest transpiration and reduce the role of forests in reducing runoff. Results from catchment experiments also indicate such spatial variation in forest-runoff relationship.