Snowmelt significantly contributes to meltwater in most parts of High Mountain Asia. The Karakoram region is one of these densely glacierized and snow-covered regions. Several studies have reported that glaciers in the Karakoram region remained stable or experience slight mass loss. This trend has called for further investigation to understand changes in other components of the cryosphere. This study estimates the comparative snow cover area (SCA) and snowline altitude (SLA) changes between 2003 and 2018 in the Karakoram region and its subbasins, including Hunza, Shigar, and Shyok. We used three different 8-day composite snow products of the Moderate Resolution Imaging Spectroradiometer (MODIS) in this study including (1) Original Aqua (MYD10A2), (2) Original Terra (MOD10A2), and (3) Improved Terra-Aqua (MOYDGL06*) snow products from 2003 to 2018. We used Mann–Kendall and Sen Slope methods to assess trends in the SCA and SLA. Our results show that the original snow products are significantly biased when investigating seasonal and annual trends. However, discarding a cloud cover of >20% in the original products improves the results and makes them more comparable to our improved snow product. The original products (without cloud removal) overestimate the SCA during summer and underestimate the SCA during winter and year-round throughout the Karakoram region. The bias in the mean annual SCA between improved and Aqua and Terra cloud threshold products for the Karakoram region is found to be −1.67% and 1.1%, respectively. The improved (MOYDGL06*) product reveals a statistically insignificant decreasing trend of the SCA on the annual scale between 2003 and 2018 in the Karakoram region and all three subbasins. The annual trends decreased at −0.13%, −0.1%, −0.08%, and −0.05% in the Karakoram, Hunza, Shigar, and Shyok, respectively. The monthly trends were slightly positive overall in December. The annual maximum SLA shows a statistically significant upward trend of 13 m above sea level (m a.s.l.) per year for the entire Karakoram region. This finding suggests a significant uncertainty in water resource planning based on the original snow data, and this study recommends the use of the improved snow product for a better understanding.

中文翻译：

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喀喇昆仑地区现代雪变化归因于 2003 年至 2018 年 MODIS 数据的改进

融雪对亚洲高山大部分地区的融水起到了重要作用。喀喇昆仑地区是这些冰川密集和积雪覆盖的地区之一。几项研究报告称，喀喇昆仑地区的冰川保持稳定或出现轻微的质量损失。这一趋势要求进一步调查以了解冰冻圈其他组成部分的变化。本研究估计了 2003 年至 2018 年喀喇昆仑地区及其子流域（包括罕萨、希加尔和绍克）的比较积雪面积 (SCA) 和雪线高度 (SLA) 变化。我们在本研究中使用了中分辨率成像光谱仪 (MODIS) 的三种不同的 8 天复合雪产品，包括 (1) Original Aqua (MYD10A2)、(2) Original Terra (MOD10A2) 和 (3) 改良 Terra-Aqua ( MOYDGL06*) 2003 年至 2018 年的雪产品。我们使用 Mann-Kendall 和 Sen Slope 方法来评估 SCA 和 SLA 的趋势。我们的结果表明，在调查季节性和年度趋势时，原始雪产品存在显着偏差。但是，在原始产品中丢弃> 20% 的云量会改善结果，并使它们与我们改进的雪产品更具可比性。原始产品（未去除云）在夏季高估了 SCA，而在整个喀喇昆仑地区的冬季和全年都低估了 SCA。发现喀喇昆仑地区的改进和 Aqua 和 Terra 云阈值产品之间的年平均 SCA 偏差分别为 -1.67% 和 1.1%。改进后的 (MOYDGL06*) 产品显示，在 2003 年至 2018 年期间，喀喇昆仑地区和所有三个子流域的 SCA 在年度尺度上呈统计上不显着的下降趋势。喀喇昆仑、罕萨、希加尔和舒克的年趋势分别下降-0.13%、-0.1%、-0.08%和-0.05%。12 月的月度趋势总体上略为正。整个喀喇昆仑地区的年最大 SLA 显示出每年海拔 13 m (m asl) 的统计显着上升趋势。这一发现表明基于原始雪数据的水资源规划存在很大的不确定性，本研究建议使用改进的雪产品以更好地理解。分别。12 月的月度趋势总体上略为正。整个喀喇昆仑地区的年最大 SLA 显示出每年海拔 13 m (m asl) 的统计显着上升趋势。这一发现表明基于原始雪数据的水资源规划存在很大的不确定性，本研究建议使用改进的雪产品以更好地理解。分别。12 月的月度趋势总体上略为正。整个喀喇昆仑地区的年最大 SLA 显示出每年海拔 13 m (m asl) 的统计显着上升趋势。这一发现表明基于原始雪数据的水资源规划存在很大的不确定性，本研究建议使用改进的雪产品以更好地理解。