Snow cover is particularly important in the Alps for tourism and the production of hydroelectric energy. In this study, we investigate the spatiotemporal variability in three snow cover metrics, i.e., the length of season (LOS), start of season (SOS) and end of season (EOS), obtained by gap-filling of MOD10A1 and MYD10A1, daily snow cover products of MODIS (Moderate-resolution Imaging Spectroradiometer). We analyze the period 2000–2019, evaluate snow cover patterns in the greater Alpine region (GAR) as a whole and further subdivide it into four subregions based on geographical and climate divides to investigate the drivers of local variability. We found differences both in space and time, with the northeastern region having generally the highest LOS (74 ± 4 days), compared to the southern regions, which exhibit a much shorter snow duration (48/49 ± 2 days). Spatially, the variability in LOS and the other metrics is clearly related to elevation (r² = 0.85 for the LOS), while other topographic (slope, aspect and shading) and geographic variables (latitude and longitude) play a less important role at the MODIS scale. A high interannual variability was also observed from 2000 to 2019, as the average LOS in the GAR ranged between 41 and 85 days. As a result of high variability, no significant trends in snow cover metrics were seen over the GAR when considering all grid cells. Considering 500-m elevation bands and subregions, as well as individual grid points, we observed significant negative trends above 3000 m a.s.l., with an average of −17 days per decade. While some trends appeared to be caused by glacierized areas, removing grid cells covered by glaciers leads to an even higher frequency of grid cells with significant trends above 3000 m a.s.l., reaching 100% at 4000 m a.s.l. Trends are however to be considered with caution because of the limited length of the observation period.

中文翻译：

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MODIS时代大高山地区积雪变化（2000-2019）

在阿尔卑斯山，积雪对于旅游业和水力发电的生产尤为重要。在这项研究中，我们调查了三个积雪指标的时空变异性，即季节长度 (LOS)、季节开始 (SOS) 和季节结束 (EOS)，通过每天填充 MOD10A1 和 MYD10A1 获得MODIS（中分辨率成像光谱仪）的积雪产品。我们分析了 2000-2019 年期间，评估了整个大阿尔卑斯地区 (GAR) 的积雪模式，并根据地理和气候划分将其进一步细分为四个子区域，以研究局部变化的驱动因素。我们发现了空间和时间的差异，与南部地区相比，东北地区的 LOS 通常最高（74±4 天），表现出更短的降雪持续时间（48/49 ± 2 天）。在空间上，LOS 和其他指标的变化显然与海拔（r²LOS = 0.85），而其他地形（坡度、坡向和阴影）和地理变量（纬度和经度）在 MODIS 尺度上的作用不太重要。从 2000 年到 2019 年，还观察到了很高的年际变化，因为 GAR 的平均 LOS 范围在 41 到 85 天之间。由于高度可变性，在考虑所有网格单元时，在 GAR 上没有看到积雪指标的显着趋势。考虑到 500 米高程带和子区域，以及各个网格点，我们观察到 3000 米以上的显着负趋势，平均每十年 -17 天。虽然一些趋势似乎是由冰川化区域引起的，但去除冰川覆盖的网格单元会导致更高频率的网格单元在 3000 m asl 以上具有显着趋势，在 4000 m asl 达到 100%