亚洲中部春夏季大气环流持续性异常与我国东部夏季旱涝的关系

通过对北半球(20oN以北)1958~2002年 500 hPa月平均高度场各格点的点对点月际相关系数的分析,探讨了环流的持续性。结果表明,亚洲中部上空存在着北半球中高纬度唯一的显著的高度场持续区,它的中心区位于(30oN~50oN, 70oE~110oE),这里正是广袤的青藏高原北坡、蒙古高原及黄土高原地区,一年中各月的持续性有明显的季节变化,冬末春初的2月对3月和3月对4月基本上没有持续性可言;4~5月出现了明显的持续性,相关系数突然增长到0.6;5月对6月的持续性继续增加,相关系数达到0.8。夏季至初秋(6~9月)各个月际稳定地保持着0.8的高相关系数。秋、冬各月持续性逐渐减弱,直至春季降到了最低。将1958~2002年中5~9月的月平均高度距平正、负持续最明显的两个7年的逐月环流和季环流作对比分析,得知在正持续年夏季东亚中纬度大气环流呈“西高东低”型;而负持续年的夏季则是“东高西低”型。它们都具有气候意义的稳定性。相应的,在明显正持续年夏季中国东部降水分布呈“北少南多”;而在明显负持续年则是“北多南少”。在这45年间,夏季亚洲中纬度500 hPa的月高度距平由负持续转为正持续,与中国东部降水由“北多南少”转为“南多北少”是对应的。分区逐日识别500 hPa天气系统的结果表明,正持续年亚洲中纬地区盛行高脊,长江中下游地区多低槽和辐合流型;负持续年则盛行低槽,长江中下游多副高控制和西南流型。揭示了中国夏季发生区域旱涝灾害的两种不同的气候进程和盛行天气过程。这样在5、6月份即可预测东亚夏季或盛夏环流形势与中国的降水趋势。     

Landscape persistence and stakeholder perspectives: The case of Romania's Carpathians

The traditional use of land for food, fuel and wood created cultural landscapes, which are threatened across Europe. The factors which contributed to their endangerment need to be identified to achieve effective preservation of such landscapes. The aim of our study was to identify landscapes with historical persistence in a GIS-based comparative analysis of historical and contemporary maps and the most prominent causes of the past landscape changes, based on stakeholders' perspective. We considered a case study in Romania's Carpathians. Three major land cover types were extracted from maps dating from 1912, 1980 and 2009: built-up, pastures and forests. The historical persistence of all land cover types was poor (<20%) and profound changes were quantitatively confirmed. Large, compact patches of unchanged forests were located in the neighbourhood of a national park. The persistent pastures were situated close to human settlements, and their preservation can be related to local traditional agro-silvo-pastoral management. Although the built-up area has increased over time, the corresponding surfaces are small and consist of scattered patches located around historical monuments. Semi-structured interviews were conducted to investigate stakeholders' perspective. Using cluster analysis five prominent causes of past landscape changes are identified: 'increasing tourism', 'land tenure and social changes', 'land-use intensification', 'post-communist transition', and 'foreign investments'. We join the results of the GIS analysis with those from stakeholders' perspective to gain more insights into the landscape changes. This research offers important information that could be used for the further planning of these valuable cultural landscapes in order to avoid potential conflicts and degradation.