Observing Snow Cover and Water Resource Changes in the High Mountain Asia Region in Comparison with Global Mountain Trends over 2000–2018

Abstract

The quantification of snow cover changes and of the related water resources in mountain areas has a key role for understanding the impact on several sectors such as ecosystem services, tourism and energy production. By using NASA-Moderate Resolution Imaging Spectroradiometer (MODIS) images from 2000 to 2018, this study analyzes changes in snow cover in the High Mountain Asia region and compares them with global mountain areas. Globally, snow cover extent and duration are declining with significant trends in around 78% of mountain areas, and the High Mountain Asia region follows similar trends in around 86% of the areas. As an example, Shaluli Shan area in China shows significant negative trends for both snow cover extent and duration, with −11.4% (confidence interval: −17.7%, −5.5%) and −47.3 days (confidence interval: −70.4 days, −24.4 days) at elevations >5500 m a.s.l. respectively. In spring, an earlier snowmelt of −13.5 days (confidence interval: −24.3 days, −2.0 days) in 4000–5500 m a.s.l. is detected. On the other side, Tien Shan area shows an earlier snow onset of −28.8 days (confidence interval: −44.3 days, −8.2 days) between 2500 and 4000 m a.s.l., governed by decreasing temperature and increasing snowfall. In the current analysis, the Tibetan Plateau shows no significant changes. Regarding water resources, by using Gravity Recovery and Climate Experiment (GRACE) data it was found that around 50% of areas in the High Mountain Asia region and 30% at global level are suffering from significant negative temporal trends of total water storage (including groundwater, soil moisture, surface water, snow, and ice) in the period 2002–2015. In the High Mountain Asia region, this negative trend involves around 54% of the areas during spring period, while at a global level this percentage lies between 25% and 30% for all seasons. Positive trends for water storage are detected in a maximum 10% of the areas in High Mountain Asia region and in around 20% of the areas at global level. Overall snow mass changes determine a significant contribution to the total water storage changes up to 30% of the areas in winter and spring time over 2002–2015.

Revealing four decades of snow cover dynamics in the Hindu Kush Himalaya

“…Nevertheless, we would like to stress that our findings align well with recent studies examining snow cover dynamics over continental to hemispherical scales but over much shorter timescales 29,30,[33][34][35] . In particular, the observed high interannual variability often impeding clear long-term trends is also observed by smaller-scale regional studies, and mainly linked to elevation, monsoon-influence and heterogeneously changing temperature and precipitation patterns 28,[36][37][38] .…”

Central Asia's spatiotemporal glacier response ambiguity due to data inconsistencies and regional simplifications

“…Haag et al (2019) reported a slightly positive trend in summer, winter and autumn precipitation for the Tien Shan that might influence the close-to-zero and slightly positive mass balances at the southern margin of the Tien Shan. This is in agreement with the increase of snow cover fraction reported in Notarnicola (2020). Therefore, the main driver seems to be precipitation and snow cover in spring and summer (Fig.…”

“…8, 7). This is in line with heterogeneous and sharply contrasting snow cover changes reported by Notarnicola (2020), showing a positive snow cover change matching the location of the positive mass balance anomaly in Barandun et al (2021). The neighbouring negative mass balance anomaly in the Central Tien Shan shows predominantly a spring and air temperature importance, where a sharp decrease in snow cover duration was reported (Notarnicola, 2020).…”

“…7, 8). The positive and negative mass balance clusters in Western Pamir agree well with decreasing and increasing snow cover fractions reported by Notarnicola (2020), respectively.…”

On the Relevance of Aerosols to Snow Cover Variability Over High Mountain Asia

“…Snow cover (SC) and its extent is a widely used parameter to characterize the spatiotemporal distribution of these glaciers since it serves as a conduit between surface processes and the atmosphere over it. In fact, observational studies (Notarnicola, 2020) and future projections (Lalande et al., 2021) report that approximately 86% of HMA areal extent exhibit negative trends in SC due to climate change.…”