气候变暖背景下羌塘自然保护区年冻融指数的变化特征

利用1971~2019年羌塘自然保护区5个气象站逐日平均气温和地表温度，通过线性回归和Mann-Kendall等方法，分析气候变暖背景下近49a自然保护区大气和地面冻融指数的时空变化特征，并预估了RCP4.5和RCP8.5两种排放情景下，未来80a（2021~2100年）大气和地面冻融指数的变化。结果表明:(1)自然保护区大气融化指数（ATI）、地面融化指数（GTI）总体上呈自西向东递减的分布，并随海拔升高而减少；大气冻结指数（AFI）和地面冻结指数（GFI）的分布规律不明显，但最大值均出现在安多站，最小值出现在不同站点。(2)近49a自然保护区AFI、GFI分别以?8.97℃·d·a?1、?10.45℃·d·a?1的速率显著减少，ATI、GTI则表现为显著增加趋势，增幅分别为7.05℃·d·a?1和11.38℃·d·a?1，地面冻融指数的变化率大于大气冻融指数的变化率。与青藏高原对比，自然保护区AFI、GFI减幅小，ATI增幅接近，GTI增幅大。(3) AFI、GFI在1970s~1990s为正距平，2000s~2010s为负距平，表现为逐年代递减的变化特征；而ATI、GTI相反，呈逐年代递增的变化特征。(4) AFI、ATI、GFI、GTI分别在2001年、1993年、1999年和1998年发生了突变，ATI突变时间最早，较AFI偏早8a。(5)自然保护区冻结指数FI减少，融化指数TI增加，与平均气温、平均最低气温显著升高、降水量增加、平均风速减小密切相关，还与积雪日数、最大积雪深度的减少有关。(6)未来80a，RCP4.5排放情景下自然保护区AFI、GFI分别将减少322.8℃·d、357.6℃·d，ATI、GTI依次增加262.2℃·d、419.7℃·d；RCP8.5排放情景下，冻融指数的变化率更大。 

Spatial and Temporal Characteristics of Freezing and Thawing Index in Changtang Nature Reserve under the Background of Climate Warming

Based on the daily ground surface and air mean temperatures of five meteorological stations in Qiangtang Nature Reserve, the spatial and temporal changes of the ground surface freezing indices (GFI), ground surface thawing indices (GTI), air freezing indices (AFI) and air thawing indices (ATI) in the nature reserve in recent 49 years under the background of climate warming were analyzed by using the trend analysis and Mann-Kendall test analysis. Moreover, changes of the FTI in the next 80 years (2021~2100) are also projected under the emission scenarios of RCP4.5 and RCP8.5. The results shows that: (1) The ATI and GTI generally showed a decreasing distribution from west to east with the increase of altitude; the distribution pattern of AFI and GFI was not obvious, but the maximum value appeared in Amdo, and the minimum value occurred at different stations. (2) In the past 49 years, AFI and GFI decreased significantly at the rates of 8.97 and 10.45℃·d·a?1, respectively, while ATI and GTI increased with the rate of 7.05 and 11.38℃·d·a?1. The change rate of the ground surface freezing and thawing indices was greater than that of atmospheric freezing-thawing index. In contrast to the Tibetan Plateau, the AFI and GFI of Nature Reserve decreased slightly, the ATI increased nearly, and the GTI increased greatly. (3) As for the decadal characteristics of AFI and GFI experienced positive anomalies in the 1970s~1990s, as compared with negative anomalies during the 2000s-2100s, showed a decreasing characteristic, while the ATI and GTI, on the contrary, presented an increasing characteristic. (4) AFI, ATI, GFI, and GTI mutated in 2001, 1993, 1999 and 1998, respectively. The mutation time of AFI was the earliest, which was 8 years earlier than that of AFI. (5) The decrease (increase) of FI (TI) in CTNRT was closely related to the significant increase of mean temperature and mean minimum temperature, increase of precipitation, decrease of mean wind speed, as well as the decrease of snow cover days and maximum snow cover depth. (6) Under the RCP4.5 emission scenario in the next 80 years, the AFI and GFI of CTNRT will decrease by 322.8·d and 357.6℃·d, respectively, and the ATI and GTI will increase at 262.2·d and 419.7℃·d, respectively. In addition, the variability of FTI becomes greater under the RCP8.5 emission scenario.