流域水热条件和植被状况对青海湖水位的影响

Influence of watershed hydrothermal conditions and vegetation status on lake level of Qinghai Lake

湖泊是陆地水资源的重要组成部分,也是局地气候和全球环境变化的敏感指示器之一。湖泊面积增加和水位的变化直接反映了流域内水量平衡变化过程,对区域和全球的气候变化的反映较为敏感。利用线性趋势法对青海湖流域长时间序列气象、水文资料以及流域水热条件和植被生长状况进行分析研究,利用皮尔逊相关系数法计算了各因素与湖水位的相关关系,旨在定量评估区域气象、水文、植被等要素的变化对和湖泊水位变化过程的贡献,开展细致的青海湖水位变化特征的影响因子探讨与分析。结果表明:该流域气候呈现显著的暖湿化趋势,其中流域年降水量总体上呈现弱的增加态势,气候倾向率为10.8 mm·(10 a)-1;流域年平均气温呈显著的升高趋势(P<0.01)。流域年可能蒸散率和年实际蒸散波动较大,年实际蒸散虽有波动但增加趋势非常明显(P<0.01)。流域净第一性生产力(NPP)平均值为2.86 t DM·hm^-2·a^-1,呈现显著的增加趋势(P<0.01)。从1961年开始湖水位呈现逐年波动下降的趋势,到2004年水位最低(P<0.01);2004-2015年的近10 a连续上升,上升速率达14.4 m·(10 a)^-1(P<0.01)。流域气温升高、降水量增加,流域气候呈显著的暖湿化特征,入湖河流径流量也呈现出弱的增加态势;气候暖湿化特征导致流域生物温度增加,植被生长状况得到改善,NPP显著增加。年降水量增多,河流径流量增大,湖水位抬升;前一年的降水量、≥0℃积温、温度、径流量、NPP和蒸发量对湖水位的影响更大;NDVI和NPP的增加反映流域植被生长状况得到好转,从而增加了流域植被水土保持和水源涵养能力,对湖水位产生间接的影响。降水量、≥0℃积温、温度、径流量和NPP对青海湖水位起到正反馈效应,而蒸发量对湖水位主要起负反馈效应,年降水量和年径流量是湖水位变化的最直接的影响因子。

As an important part of land water resource,lake is an important indicator of local climate and global environment change.The increase of lake area and change in the lake’s water level directly reflect the process of water balance change in its basin,which is sensitive to regional and global climate change.Qinghai Lake is the largest saline lake in China,with 3 190 m asl in the arid-semiarid area of the Qinghai-Tibet Plateau.The lake has experienced decline in water level and lake area over the past 50 years,but it has rebounded over the latest 10 years.This study investigated lake hydrology,climate change and hydrothermal and vegetation growth conditions in the basin,focusing on the causes for water level variation.To reveal hydrology,meteorology and vegetation change,linear trend method was used to analyze long-term data in this study.The Pearson correlation coefficient method was used to calculate relationship between various factors and the lake water level to quantitatively evaluate the lake water level change effected by regional meteorological,hydrological,and vegetation factors.The results showed that the basin climate had a significant warming and wetting trend,and the total precipitation had a weak increase trend with a climatic tendency rate of 10.8 mm·(10 a)^-1.The annual evapotranspiration rate and annual actual evapotranspiration fluctuated greatly in the basin.Average net primary productivity(NPP) of the basin was 2.86 t DM·hm^-2·a^-1,showing a significant increase trend(P<0.01).The water level was dropped during the period from 1961 to 2003,and was significantly increased from 2004 to 2015 with an increasing rate of 14.4 m·(10 a)^-1(P<0.01).The trend of warming and wetting of the climate was intensified and the runoff into the lake got increased,resulting in a significant rise in water level.The vegetation growth is improved and NPP is significantly increased.The amount of precipitation,the accumulated temperature(above 0 degree Celsius),annual air temperature,run-off,NPP and evaporation in the year before had even bigger impact on the lake’s water level in current year.The increase of the NDVI and NPP reflected the improvement of the vegetation growth in the basin which in return enhanced the capability of the basin in the conservation of water and soil,indirectly impacting the lake’s water level.The precipitation,the accumulated temperature(above 0 degree Celsius),air temperature,runoff and NPP had a positive feedback effect on the lake’s water level,while evaporation has a negative feedback effect on the lake’s water level.The annual precipitation and runoff were the most direct factors of the water level changes.