青藏高原西北部近地表气温直减率时空分布特征

近地表气温直减率是研究山地生态系统对气候变化响应过程中的重要参数,论文基于青藏高原西北部1951—2013年的9个标准气象站以及2012—2016年的高山自设观测站的日平均气温、最低气温、最高气温（T_ave、T_min、T_max）数据,分析了青藏高原西北部近地表气温直减率（LR_Tave、LR_Tmin、LR_Tmax）的时空分布特征。结果表明：1）青藏高原西北部近地表气温随高程增大有显著下降趋势。研究区两个区域的LR_Tave、LR_Tmin、LR_Tmax均呈现出显著的空间差异性,而基于气象站的LR_Tave、LR_Tmin高于高山观测站的LR_Tave、LR_Tmin、LR_Tmax,其中LR_Tmin差异最为显著,而LR_Tmax空间差异较小。2）青藏高原西北部近地表气温直减率具有明显的季节差异,气象站的LR_Tave、LR_Tmin、LR_Tmax季节变化趋势为春季高、夏季较高、冬季低,而高山观测站的LR_Tave、LR_Tmin、LR_Tmax季节变化趋势为夏季高、冬季低。其中气象站LR_Tmax在四季中的差异最显著,而高山观测站的LR_Tmin的季节差异最大。高山观测站的气温直减率在4—9月间具有较为稳定的值。3）青藏高原西北部LR_Tave、LR_Tmin在气温突变年前后具有显著的差异,LR_Tmax无显著的变化。其中,在气温突变年之后,LR_Tave、LR_Tmin有显著的上升趋势,表明青藏高原西北部地区的LR_Tave、LR_Tmin对区域气候变化的响应显著,而LR_Tmax对区域气候变化的响应不显著。研究将有效改善青藏高原西北部气温空间分布规律研究的不足,为区域气候变化研究及生态系统对气候响应等定量研究提供理论基础。

Spatio-temporal Variation of Near-surface Temperature Lapse Rates over the Northwestern Tibetan Plateau

The lapse rate of near surface air temperature is an important parameter in hydrologic and climatic simulations, especially in the high mountainous areas without enough observations. Based on the long-term meteorological measurement data (1951-2013) and near surface air temperature (T_min, T_ave, and T_max) measured by self-established weather stations during 2012-2016, this study evaluates the spatial and temporal variations of near surface temperature lapse rate (β_local) over the northwestern Tibetan Plateau. The results show that: 1) The near surface air temperature lapse rate has a spatiotemporal distribution pattern over the northwestern Tibetan Plateau and the constant environmental temperature lapse rate (0.65 ℃/100 m) throughout the year cannot represent the variability of the temperature-elevation relationship in complex terrain areas. The temperature has a significant downward trend as the elevation increases. LR_Tave, LR_Tmin, LR_Tmax in two regions showed different spatial variations. The LR_Tave, LR_Tmin, LR_Tmax at the meteorological stations are higher than the LR_Tave, LR_Tmin, LR_Tmax at the mountain observation stations. The LR_Tmin shows significant spatial variation, while the LR_Tmax has smaller spatial variation. 2) A significant seasonal variation can be observed in this region. At the meteorological stations, the trend is that higher values are observed in spring and summer and lower values in winter. As for the mountain observation stations, the LR_Tave, LR_Tmin, LR_Tmax are higher in summer and lower in winter. The LR_Tmax at the meteorological stations and the LR_Tmin at the mountain observation stations have significant seasonal variations. 3) The variations of β_local for T_max and T_min in two regions exhibit similar monthly variation characteristics, that β_local is lower in months of winter and spring and higher in other months. Monthly β_local for T_min is higher than T_ave and T_min at the meteorological stations through the whole year. The highest β_local for T_max and T_min occurs in April, while the highest β_local for T_ave occurs in June. At the mountain observation stations, the highest β_local for T_max occurs in October, while the highest β_local for T_ave and T_min occurs in April. 4) A significant increasing trend of β_local for T_ave and T_min was observed after 1990. The difference of β_local for T_min before and after 1990 is more obvious. The differences of T_max at different elevations before and after 1990 are weak. 5) The spatial and temporal variations of β_local over the northwestern Tibetan Plateau are linked to geographic differences and climate factors. In addition, the controlling factors for the lapse rate in two regions are different. This research will provide a theoretical basis for quantitative researches of temperature distribution characteristics and mountain ecosystem’s response to climate change in mountain areas.