气候变化对西南亚高山区流域碳水平衡的影响模拟

Simulations of the Impacts of Climate Changes on Carbon and Water Balances for A Sub-alpine Basin in the Mountain Region of Southwestern China

为了揭示气候变化对西南亚高山区流域碳水平衡的影响,应用生物物理/动态植被模式SSi B4/TRIFFID与流域水文模型TOPMODEL的耦合模式SSi B4T/TRIFFID进行西南亚高山区的梭磨河流域不同气候情景下[背景条件(控制试验)、增温2℃(T+2)、增温5℃+增雨40%(T+5,(1+40%) P)]植被与碳水平衡的动态模拟。控制试验结果显示,流域蒸散在流域为苔原灌木覆盖时达到最大而径流深最小;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,由于森林、苔原灌木和C3草地3种植被类型中森林蒸散增加幅度最大,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,森林蒸散从388.1 mm·a-1增加到802.9 mm·a-1,径流深从298.0 mm·a-1减小到157.9 mm·a-1,径流系数从0.43减小到0.16;森林净初级生产力NPP从1 025.5 g·m-2·a-1增加到1 199.5 g·m-2·a-1,净生态系统生产力NEP从476.8g·m-2·a-1增加到650.8g·m-2·a-1。NPP和NEP增加幅度低于蒸散增加的幅度,表征碳水耦合关系的水分利用效率WUE随温度增加而明显减小。WUE和森林-径流关系随海拔高度变化,西南山区气候的垂直地带性分布控制了水分利用效率和森林-径流关系的空间变化。

To investigate the effects of climate changes on carbon-water balances at basin scale in the mountain region of southwestern China,the Biophysical/Dynamic Vegetation Model SSiB4/TRIFFID is coupled with TOPMODEL.Long-term dynamic simulations are run of vegetation succession and carbon-water balances under different climate scenarios for the sub-alpine.The results showed that evapotranspiration of the basin increased and reached its maximal value and runoff reached the minimum during the period of C3 grass succession into shrub.The evapotranspiration decreased,and runoff increased during the period of shrub succession into forest.A temperature increase of 5℃accompanied by an increase in precipitation of 40%[T+5,(1+40%)P]could reduce runoff from forest owing to a significant increase in water loss through canopy interception evaporation and transpiration.Among the three vegetation types forest evapotranspiration increased most,which resulted in forest-runoff relationship changed with variance in temperature.From the control test to the T+5,(1+40%)P test,the forest evapotranspiration increased from 249.7 mm·a-1 to 802.9 mm·a-1 while runoff depth decreased from 298.0 mm·a-1 to 157.9 mm·a-1 and the runoff coefficient decreased from 0.43 to 0.16.The net primary productivity increased from 1 025.5 g·m-2·a-1 to 1 199.5 g·m-2·a-1,while net ecosystem productivity NEP increased from 476.8 g·m-2·a-1 to 650.8 g·m-2·a-1.As the rate of evapotranspiration was higher than both the net primary productivity and net ecosystem productivity,the water use efficiency(WUE)which characterized the coupling relationship between carbon and water decreased with increasing temperature.WUE decreased and the role of forests to increase runoff changed to reduce runoff with altitude.The vertical zonality of climate controls the spatial variation of the forest-runoff relationship and WUE.