基于多套再分析资料的青藏高原极端降水事件变化研究

In the context of global warming, variations and trends in extreme climate events have recently received much attention because extreme climate events are more sensitive to climate change than their mean values. The Tibetan Plateau (TP), with an average elevation of over 4000 m above sea level and is the highest and most extensive highland in the world and has been called the 'Third Pole'. The TP exerts a huge influence on regional and global climate through thermal and mechanical forcing mechanisms, and it has been called 'the sensitive area' and 'the startup region' in China and is characterized as 'the driving force' and 'the amplifier' for global climate change. Climate change in the TP is becoming an academic hot in the international earth science. Due to inaccessibility and complex terrain, it is difficult to obtain direct observational stations over large portions of the TP, which limits the understanding of climate change in the TP, especially the climate extreme and climate change in the higher elevations. It is urgent and necessary to reveal the factual climate change in the TP. Reanalysis can resolve this problem, and the eight reanalyses are NCEP（National Centers for Environmental Prediction）/NCAR (National Center for Atmospheric Research), NCEP/DOE (Department of Engergy), ERA-40 (the European Center for Medium-Range Weather Forecasts (ECMWF) 40 year), ERA-Interim (ECMWF Interim), JRA-2 (Japan Meteorological Agency(JMA) 25 year), CFSR (NCEP Climate forecast System Reanalysis), MERRA (the National Aeronautics and Space Administration (NASA) Modern-Era Retrospective Analysis for Research and Application), 20CR (the National Oceanic and Atmospheric Administration -Cooperative Institute for Research in Environmental Sciences (NOAA/CIRES) 20th Century Reanalysis Version 2). The definition, statistic method and threshold of precipitation extreme in the TP have been obtained based on observations and reanalyses. Changes in indices of precipitation extremes and mechanics will be analyzed, and the comparisons with other region in the world will be studied..Based on the Mann-Kendall methods, Wavelet analysis, Empirical Orthogonal Functions (EOF) and Taylor diagram, the patterns of precipitation extreme will be discussed in the proposal. It is very useful for the monitoring and forecasting of precipitation extreme in the TP.

青藏高原由于其自身的独特性以及对周围自然环境的影响，使得其成为全球变化研究中的热点。由于环境恶劣、资料缺乏，专门针对青藏高原极端降水事件变化的研究还很少。本项目结合青藏高原地面观测台站数据，对NCEP/NCAR、NCEP/DOE、ERA-40、ERA-Interim、JRA-25、CFSR、MERRA和20CR等8套现代再分析降水数据资料开展极端降水事件的研究，确定适合青藏高原的极端降水事件的定义、统计方法以及极端阈值，采用非参数统计Mann-Kendall检验、小波分析、经验正交函数（EOF）、Taylor图等数理统计方法分析青藏高原极端降水事件的时空变化特征, 识别青藏高原极端降水事件的强度和发生频率的变化趋势。该项目对获得青藏高原极端降水事件变化机理的认识具有重要的理论意义和实际应用价值，是进一步提高极端降水事件的监测预测和评价能力的基础。

青藏高原由于其自身的独特性以及对周围自然环境的影响，使得其成为全球变化研究中的热点。由于环境恶劣、资料缺乏，专门针对青藏高原极端降水事件变化的研究还很少。本项目研究了青藏高原极端降水事件的定义与统计方法，如1日最大降水量、连续5日最大降水量、降水总量与年降水量比值等。同时，基于青藏高原地区1961～2010年高分辨率的逐日降水格点资料，对比分析了多源了降水资料（NCEP1、NCEP2、CMAP1、CMAP2、ERA-Interim、ERA-40、GPCP、20century、MERRA和CFSR）在高原地区的适用性，多源资料能刻画极端降水和年平均降水的空间分布，但高估了观测值，用来研究极端降水的年代际变化存在严重偏差。基于此，结合多源资料，分析影响高原极端降水的四条的水汽通道，这些通道与高原极端降水有较好的相关性，可做为高原极端降水的预测因子，这对预测高原极端降水具有实际意义。