Knowledge Resource Center for Ecological Environment in Arid Area
| 青藏高原不同类型下垫面水热交换特征及其对气候变化的响应 | |
| 其他题名 | Surface Water and Heat exchange and its responses to climate change over different surface types of the Tibetan Plateau |
| 解晋 | |
| 出版年 | 2018 |
| 学位类型 | 博士 |
| 导师 | 余晔 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 地表能量和水分交换对理解区域天气过程和气候演变极为重要，一直是陆面过程研究的核心问题之一。青藏高原地表能量和水分交换过程不仅影响着区域和全球的大气环流形势，也影响着亚洲地区季风的发展和降水的分布，因此在过去的几十年受到了广泛的关注。由于气候变化和人类活动的共同影响，近年来高原地区的植被状况发生了显著变化，而植被状况的变化又会显著改变地气间能量和水分的交换，最终对全球和区域气候和环境变化产生影响。本论文以气候变化背景下青藏高原地区不同类型下垫面的水热交换时空变化特征及其影响因素为研究目标，首先对比分析了高原3种典型下垫面，即玛曲高寒草甸、那曲高寒草原和北麓河稀疏短草地，的地表辐射和能量平衡特征及影响其能量分配的气候因子。其次，利用高原地区85个常规气象观测站点数据计算分析了高原地区1981年—2014年地表感热的时空变化特征及其对气候要素的响应。并分析了再分析资料地表热通量在高原地区的时空变化特征及其在高原地区的适用性。最后结合植被类型和归一化植被指数（NDVI）数据，探讨了不同类型下垫面感热通量的变化特征及其对气候变化的响应。得到如下结论：（1） 地表干湿程度对辐射通量中的长波辐射影响较大，对感热和潜热通量的分配也有较为显著的影响。在玛曲，感热对地表干湿程度的响应较为敏感，在那曲和北麓河，潜热对地表干湿程度的响应较为敏感。通过对比三个站点的地表能量分配与净辐射、地气温差、水汽压差以及地表干湿程度的相关关系发现，在玛曲和那曲，净辐射为影响地表能量分配的主导因子，在北麓河，地表能量与各气候要素之间的相关程度受地表干湿状况的显著影响，表层土壤含水量对北麓河地表能量分配有重要作用。（2） 利用85个常规气象站点的观测资料计算分析了高原地区感热通量的年际变化特征，发现高原地区感热通量无论在全年还是各季节，自1981年以来均呈现先减少后增加的变化趋势，转折点大概为2003年。前期感热通量的减少（-1.02 W/m2/decade）主要与平均风速的减小有关，而后期感热通量的增加（3.02 W/m2/decade）主要受地气温差增加的影响，但在空间上，各站点的变化趋势并不同步，感热通量增加较为显著的站点主要位于青海省。高原地区的感热通量与各气候要素的相关性存在明显的时空差异，整体上地气温差和风速是主要影响因素，在高原的南部，降水起显著的作用。在季节尺度上，感热通量与各气候因子的相关性在夏季最为显著，在秋季和冬季较差。（3） 1981-2013年间，3套再分析资料（ERA-Interim、JRA-55和MERRA）在高原地区的年均感热和潜热通量在时空变化特征上存在明显的差异，这些差异与各套再分析资料间气候因素、地表状况和热交换参数化方案选取的差异有密切的联系。与观测数据对比后发现，ERA-Interim的感热通量空间分布及其在1981-2003年间的下降趋势与基于观测计算的感热通量最为接近，但只有MERRA能再现感热通量在2004-2013年间的上升趋势。此外，在年际变化尺度上，3套再分析资料的感热通量在高原西部的适用性要好于在高原东部，但在逐月变化尺度上，ERA-Interim在植被状况较好的玛曲站点模拟效果要好于JRA-55和MERRA，而在植被状况较差的那曲站和阿里站，其模拟效果则不如JRA-55和MERRA。（4） 结合下垫面类型和归一化植被指数（NDVI）将高原分为六种下垫面，分析了不同下垫面地表感热通量的变化特征，发现1981-2014年前期感热通量的下降趋势在荒漠和高寒草原下垫面不明显，后期感热通量变化趋势发生转折的时间最早发生在1998年位于荒漠地区，最晚发生在2003年位于高寒草原地区。年均感热通量的变化趋势在植被茂盛的地区（NDVI>0.4）主要受降水和日照时数的影响，在植被稀疏的高寒草原和荒漠地区（NDVI<0.25）主要受风速的影响。 |
| 英文摘要 | As a very important aspect of land surface process, the land surface energy and water exchange is crucial for understanding land-atmosphere interactions and regional climate change. The surface energy and water exchange over the Tibetan Plateau has received extensive attention in the past decades because of its remarkable effects on the shaping of Asian and global climate, especially the Asian monsoon and precipitation. It is also closely related with the occurrence of extreme temperature and precipitation events which affect people's living. However, due to the combined effects of climate change and human activities, the vegetation over Tibetan Plateau has undergone significant changes which can significantly change the characteristics of surface energy and water exchange, which will eventually contribute to the change of global climate and environment.In the present work, we focus on the spatiotemporal characteristics of energy and water exchange as well as their influencing factors over different types of surfaces over the Tibetan Plateau in the context of global climate change. Firstly, three typical underlying surfaces of the Tibetan plateau were chosen which are Maqu (alpine meadow), Naqu (alpine grassland) and Beiluhe (sparse vegetation). The characteristics of surface radiation and energy balance and the climate factors which affected the surface energy partitioning over the three underlying surfaces are compared and analyzed. Secondly, the spatial and temporal changes of surface sensible heat flux from 1981 to 2014 over the Tibetan Plateau and their responses to climate factors were analyzed using surface sensible heat fluxes deduced from conventional meteorological observations from 85 CMA stations. Then, the temporal and spatial changes of surface heat fluxes from three reanalysis datasets, and their applicability over the Tibetan Plateau were analyzed. Finally, the changes of vegetation and sensible heat fluxes over different surface types were discussed using combined information on vegetation types and NDVI data, and the temporal trends of water and heat exchange in regions with significant vegetation changes were compared and analyzed. The conclusions are as follows:(1) Surface soil water content have relatively greater impact on the long wave radiation as well as the partition of surface sensible heat and latent heat fluxes over different surface types. Sensible heat flux in Maqu tend to be more affected by surface soil water content while in Naqu and Beilue latent heat fluxes is more susceptible to surface soil water content. Furtherly, the correlations of surface energy partitioning with the net radiation, the land-air temperature difference and the vapor pressure deficit under drier and wetter surface at the three sites are compared. At Maqu and Naqu, surface energy partitioning is most sensitive to net radiation.At Beiluhe, the energy partitioning is mainly affected by the soil water content with the correlations between surface heat fluxes and climate factors being more significant when surface was wetter.(2) The interannual variation of sensible heat flux over the Tibetan Plateau are analyzed using the sensible heat fluxes deduced from conventional meteorological observation data from 85 stations. It is found that both the seasonal and the annual averaged sensible heat flux first rose then fell during the past more than 30 years since 1981. The decline of sensible heat flux between 1981 and 2003 (-1.02 W/m2/decade) was mainly caused by the decrease of the average wind speed, while the raise between 2004 and 2014 (-1.02 W/m2/decade) was mostly related to the significant increase of land-air temperature difference. It was also found that not all the stations decrease or increase at the same pace. Stations with increased sensible heat flux are mostly located in Qinghai province. The correlations between sensible heat flux and climate factors have obvious temporal and spatial differences. Surface-air temperature difference and wind speed are the main factors affecting sensible heat fluxes at most of the stations, while other climate factors, such as precipitation, sunshine hours, are tend to be also important in some regions. The correlations between sensible heat flux and climate factors are more significant in summer than in autumn and winter.(3) The three reanalysis datasets (ERA-Interim, MERRA and JRA-55) give different spatiotemporal changes for the annual average SH and LE for the period of 1981-2013 which are closely related to their differences in meteorological and vegetation conditions as well as the different parameterizations used for surface transfer coefficients calculation. Compared with the calculated sensible heat flux，ERA-Interim can capture the decresing trend between 1981 and 2003, while MERRA shows a similar increasing trend between 2004 and 2013. the In general, the heat fluxes from the three reanalysis have a better representation in the western TP than that in the eastern TP on inter-annual scale. In terms of monthly variation, ERA-Interim is more applicable at Maqu with dense vegetation, while SH of JRA-55 and LE of MERRA are more representative for Naqu and Ali with poor vegetation.(4) Based on classifying observation sites of different vegetation types and Normalized Difference Vegetation Index (NDVI) data, it is found that that barren and steppe areas did not decrease at the early period during 1981-2014 which are different from other surface types. Surface sensible heat fluxes of barren areas began increasing in 1998 which is earlier than that over other surface types while that of steppe is later than that over other surface types in 2003. Surface sensible heat flux is mainly affected by precipitation and sunshine duration in shrub (NDVI>0.4) and forest regions, while it is mainly affected by wind speed in steppe and barren areas (NDVI<0.25). |
| 中文关键词 | 青藏高原 ; 下垫面类型 ; 感热和潜热 ; 气候变化 ; 植被变化 |
| 英文关键词 | Tibetan Plateau Surface types Sensible and latent heat fluxes Climate change Vegetation change |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 气象学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288138 |
| 推荐引用方式 GB/T 7714 | 解晋. 青藏高原不同类型下垫面水热交换特征及其对气候变化的响应[D]. 中国科学院大学,2018. |
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