气候变化下青海湖布哈河流域植被生态水文响应研究

Qinghai Lake is the biggest inland salt lake. According to the problems of water decrease flowing into the lake and water level falling, the changing process of river runoff flowing into the lake and its relevant ecohydrological mechanism are needed to be studied thoroughly. The Qinghai Lake riverbasin belongs to the alpine region, and the response to climate change is very sensitive. Discussing the riverbasin ecohydrological evolution under the climate change are the requirement of realizing the water resources and ecological protection of the Qinghai Lake riverbasin. There are many research about the ecohydrological mechanisms in alpine ecosystem and some general laws have been got. But some problems still have not been resolved such as whether the vegetation increasing will decreasing the runoff or not and why. At the same time, the ecohydrological mechanisms in Qinghai Lake riverbasin have not been studied except only the research about the soil infiltration in north-west Qinghai Lake. The ecohydrological laws in the vertical and horizontal gradients in Qinghai Lake riverbasin have not been studied up to now. Aiming at the insufficiency of the present ecohydrological mechanisms study,this research will exploring the ecohydrological laws of the Buha River, the biggest river flowing into the Qinghai Lake, based on the ecohydrological observation and experiments of vegetation, soil, runoff,evapotranspiration and so on. And according to the concrete experiments results, the vegetation ecohydrological response to the climate change will be studied. Combining the point belt and the transect, this research will study the soil water spatial distributing laws under different vegetation types and different vegetation coverage. Through the soil infiltration experiments and the evapotranspiration observation, the soil infiltration speeds, the runoff change and the runoff yield and concentration process will be studied. And then, after the interpretation and comparision of the images of different periods, the natural vegetation response under the climate change will be analyzed. Combined with the experiments ecohydrological exploration, the vegetation ecohydrological response to the climate change will be discussed in the end.

青海湖是中国最大的内陆咸水湖，面对入湖水量减少，湖水位下降等问题，需要深入研究流域入湖河流的径流变化过程及相应的植被生态水文机理。青海湖流域属高寒地区，对于气候变化的响应极为敏感，实现和维护青海湖流域生态稳定，需要探讨气候变化下流域水文演变过程及响应。项目从微观尺度，以点样和带样相结合，研究流域内不同海拔不同植被下土壤水分空间分布规律；通过土壤入渗实验和蒸散、径流过程观测，分析不同植被类型下土壤水分入渗速率以及径流变化等产汇流过程；以微观原型实验和观测为基础，总结青海湖最大入湖河流布哈河流域的植被生态水文规律。从宏观尺度，通过不同时期遥感影像解译和对比，揭示气候变化下天然地带性植被演替规律；根据原型微观实验所揭示的生态水文机理，分析由天然植被演替所产生的生态水文响应规律；运用水文模型，结合布哈河径流实测资料，模拟并验证气候变化下的植被生态水文响应规律。

气候变化与陆地生态系统之间相互影响相互作用，形成陆地植被、土壤、大气等复杂大系统。布哈河是青海湖最大的一条入湖河流，该流域的植被生态水文机理及在未来气候变化情景下的入湖径流预估可为青海湖的稳定性评价提供重要参考。以流域气象站长系列气候资料分析气候演变规律，流域气温呈明显上升趋势，降水量有增加趋势，但趋势不明显，海拔较高的气象站升温和降雨趋势增加明显（天峻站分别达到0.37℃/10a和13.4mm /10a）；过去的30a间流域土地利用类型增加量主要发生在高中低三种不同覆盖度草地，减少量主要表现在未利用地。受温度升高降水增加全球气候变化影响，流域植被转好，尤其在西北部3900m以上源头区，未利用地向低盖度草的转化明显；植被盖度及植被水源随海拔高程、坡度、坡向等地形地貌因素不同而变化，总体来说，随海拔升高、坡度变陡、坡向趋向于阳坡的地形变化，植被NDVI指数值变小。在海拔梯度影响降雨量的大格局下，坡度坡向等地形地貌因子通过影响降雨、径流、土壤水、地下水的存留状态与水资源再分配过程而为植被提供不同水源条件，从而影响植被生长；土壤水分入渗速率测定结果表明，水分入渗过程与土壤质地与结构相关，3个样点中低海拔处样点为沙质土，水分下渗速率比中高海拔快，中海拔处土壤剖面表层草根密集，下渗速率非常慢；应用SWAT模型在对现状模拟的基础上，以未来气候变化情景（气温升高0.25℃/10a，降水平均增加趋势为1.15%/10a）和土地利用变化双因子驱动，模拟未来至2030年流域径流量比现状年增加4.2%，主要是由于气温升高增加了高山冰雪融水的径流量，再加上降水量呈增加趋势，使整个流域的产流量增加。