青藏高原冻土区植被覆盖度时空分布及其对气象的响应

Spatial and temporal distribution of vegetation coverage and its response to meteorological factors in frozen soil region of Qinghai-Xizang Plateau

针对全球气候变暖导致青藏高原冻土不断退化,进而影响冻土区的植被生长状况的问题,该文基于2001—2020年MOD13Q1归一化植被指数,并利用像元二分法反演其对应的植被覆盖度(FVC),最后通过趋势分析和相关分析法对FVC的时空分布及其与气象因子的响应机制进行了深入研究。结果表明,20年间青藏高原冻土区FVC均值呈上升趋势,增速依次为片状多年冻土区(0.0017/a)>季节冻土区(0.0010/a)>多年冻土区(0.0008/a)>岛状多年冻土区(0.0005/a),空间上总体表现为“西北低、东南高”的分布特点。空间变化趋势上,青藏高原冻土区FVC整体以稳定为主,但呈改善趋势,显著增加面积占比大于显著减少面积之比,显著增加面积占比分别为片状多年冻土区(30.26%)>多年冻土区(24.04%)>季节冻土区(19.94%)>岛状多年冻土区(8.24%)。青藏高原冻土区FVC受气温和降水两种气象因子的影响,但是与降水的相关性更强。随气温升高,青藏高原冻土区FVC与气温的相关性从正相关转变为负相关,因此从长期来看,全球气候变暖导致的冻土退化不利于植被生长。

In view of the problem that global warming has led to the continuous degradation of frozen soil on the Qinghai-Xizang Plateau, which in turn affects the growth of vegetation on frozen soil, the pixel dichotomy was used in this paper to invert its corresponding fractional vegetation coverage(FVC) based on the MOD13Q1 normalized vegetation index from 2001 to 2020. Finally, the spatial and temporal distribution of FVC and its response mechanism to meteorological factors were studied by trend analysis and correlation analysis. The results showed that in the past 20 years, the mean value of FVC in the frozen soil region of the Qinghai-Xizang Plateau had shown an increasing trend as a whole, and the growth rate was patchy permafrost region(0.001 7/a) > seasonal frozen soil region(0.001 0/a) > permafrost region(0.000 8/a) > island permafrost region(0.000 5/a);the spatial distribution of FVC in the frozen soil area of the Qinghai-Xizang Plateau was characterized by “low in the northwest and high in the southeast”. In terms of spatial variation trend, FVC in the frozen soil area of the Qinghai-Xizang Plateau was mainly stable, but it showed an improving trend;the proportion of significantly increased area was greater than that of significantly reduced area, which was patchy permafrost area(30.26%) > permafrost area(24.04%) > seasonal frozen soil area(12.06%) > island permafrost area(8.24%). FVC in the frozen soil region of the Qinghai-Xizang Plateau was affected by two meteorological factors, temperature and precipitation, but the correlation with precipitation was stronger. With the increase of temperature, the correlation between FVC and temperature in the frozen soil region of the Qinghai-Xizang Plateau changed from positive correlation to negative correlation. Therefore, in the long run, the frozen soil degradation caused by global warming is not conducive to vegetation growth.