天山高寒山区降水形态转变驱动因子研究

Precipitation mainly has two types, snowfall and rainfall. There is a trend from snowfall to rainfall for the precipitation in mid-latitude regions of the northern hemisphere recently. However, key factors of precipitation formation and transformation are unknown. And it is not clear that in what types the precipitation will fall in the future. Located in the northwest of China, a mid-latitude and alpine region with reputation of “water tower of central Asia” and “solid reservoir”, Tianshan Mountainous Area (TMA) is particularly sensitive to global warming. Selecting TMA as the study area, the following points will be investigated in this project: (1) According to knowledge from higher atmospheric dynamics, meteorology and physical geography of TMA, key factors of precipitation formation and transformation in TMA will be clarified. (2) Based on the observed data from meteorological gaging stations and determination methods of precipitation types, spatial and temporal distribution of precipitation in different types and pattern of transformation from one form to another one will be analyzed. (3)It will reveal scenarios of precipitation transformation from one type to another one in the future under different scenarios of concentration emission (especially the air temperature rise by 2°C or higher) from IPCC 5th report. This work aims to study pattern of precipitation transformation and its future scenarios in the alpine region under the background of global warming. It could provide decision support to prevent and respond to flooding in early spring and water shortage in summer in TMA. And furthermore, it will be beneficial to allocation of water resources and sustainable development in this region.

降水主要有降雪（固态）和降雨（液态）两种形态。当前北半球中高纬度地区冬季降水形态有从降雪向降雨转变之势。然而各形态降水形成和转变的关键驱动因子尚未明确，未来转变态势亦未明朗。因此，本项目拟选取位于西北中纬度高寒地带具有“中亚水塔”和“固体水库”之称的天山山区作为研究区，进行如下研究：（1）结合高等大气动力学、气象学、天山自然地理学等相关理论知识，辨析该区域不同形态降水形成和相互转变的关键驱动因子；（2）基于实测站点资料和降水形态识别判据等研究方法，分析该区域各形态降水时空分布特征和转变态势；（3）以IPCC AR5 气候模式集CMIP5为背景资料，预估不同排放情景下（尤其是温升≥2°C时）未来降水形态转变情景并提出适应对策。本项目旨在研究全球变暖背景下高寒山区降水形态转变态势和未来转变情景，从而为该区域提早预防春季洪涝灾害和夏季水资源短缺等问题以及区域可持续发展提供相关理论决策和支持。

本项目以中国天山为研究区，针对降水形态转变的驱动因子、现状和未来变化情景问题，广泛搜集资料，开展了大量的分析和研究，取得主要结论如下：.（1）气温是影响中国天山降水形态转变的关键驱动因子，地表温度、海拔、纬度和气压为次要驱动因子。.（2）1980-2017年，中国天山降水形态从固态向液态转化趋势显著。降水日数变化范围为50-78d，线性倾向率为0.2 d·(10a)-1，表现为缓慢增长趋势，降雨日数显著增加增长率为2.4 d·(10a)-1，降雪日数显著减少，雨夹雪日数无显著变化趋势。.（3）三种情景（RCP2.6、RCP4.5和RCP8.5）下，中国天山2011-2100年秋末与初春时段降雨降水比（RPR）较基准期（1981-2010）均有升高。排放情景越高，RPR越大，同一排放情景下，时间越往后，RPR越大，表明随着时间的推移，未来在高排放情景下秋末与初春时段中国天山将有更多的降雪转变为降雨。.（4）相对湿度、气温和经度是影响中国天山降雪量的最主要的因子，海拔、坡向和纬度对降雪的影响次之，而坡度和平均风速的影响最小。.（5）中国天山在总体变暖的背景下，存在局部变冷的现象，其增温幅度从−0.57°C至3.64°C，平均增幅为1.19°C，超过全球平均增幅。中国天山的增温幅度存在较大的时空异质性，主要表现在春季、秋季和冬季的增温速率高于夏季，另外本来比较热的地方增温幅度更大，如东天山的吐哈地区。.本项目的成功实施厘清了中国天山降水形态转变的关键驱动因子、转变现状和未来趋势，为区域气候变化影响提供了新的思路，也为提早预防春季洪涝灾害和夏季水资源短缺等问题以及区域可持续发展提供相关理论决策和支持。