Contemporary Snow Changes in the Karakoram Region Attributed to Improved MODIS Data between 2003 and 2018

Abstract

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.

Climate change decisive for Asia’s snow meltwater supply

“…In contrast, past and future relevance of snow to the region's hydrology has been marginally addressed at the scale of HMA, since research has predominantly focused on smaller subregions 3,5,12,13 or on snow properties that provide limited hydrological context such as snow cover 14 or depth 15 . Accurate and detailed information about the amount of water stored in HMA's snowpacks (that is, their snow water equivalent (SWE)) is largely absent or inaccurate at large scale because SWE is notoriously difficult to monitor using remote sensing [16][17][18][19][20] . Nonetheless, to unravel many of the societal and environmental processes that occur in HMA, an improved understanding of the influence of snow on the region's (future) water balance is essential [21][22][23] .…”

Development of Global Snow Cover—Trends from 23 Years of Global SnowPack

“…The next point is to discuss whether the chosen approach, which combines the MK test and Theil-Sen slope, is suitable. The combination of these has often been used for snow surface dynamics [17,64,65], but it also means that some developments remain undetected. Larger interannual SCD variations and fluctuations lead to a lower significance and are therefore not noticeable in such a large data set.…”

Snow Persistence and Snow Line Elevation Trends in a Snowmelt-Driven Basin in the Central Andes and Their Correlations with Hydroclimatic Variables

“…For instance, Nepal (0.15 Mkm 2 ) exhibited a positive trend of 33, 33, and 67 m • year −1 in Western, Central, and Eastern parts of the country, respectively, between 2003 and 2018 [28]. In the Karakoram Region (7050 km 2 ), remote sensing identified a significant upward trend of 13 m • year −1 between 2003 and 2018 [29].…”