## 1 Introduction
### Climate Change Indicators: Glaciers  
There has been a general trend of glacial retreat since the Little Ice Age, similar to many mountainous regions worldwide, but from the 1990s on, glacial retreat was more accelerated than during any other period in the 20 th century [32]. On a regional scale, the glacier loss in the HKH region is influenced by its distinct climate variations, as the eastern part of the region experiences monsoonal-dominated precipitation during the summer, while the western part is influenced by mid-latitude underlies bringing precipitation in the winter [33]. Individual glacier observations reveal that annual retreat rates differ from one basin to another, with some glaciers even advancing. The central Himalayan glaciers (from Uttarakhand to Bhutan) are receding at different rates than the western Himalayan glaciers [34]. The study also shows that the deglaciation rate in the Bhaga basin, western Himalayas, has drastically increased to 0.25% per year in the past two decades (2000-2020), compared to 0.12% per year in the previous decades (1971-2000). The Machoi glacier, distributed between the Greater Himalayan Mountain Range of Kashmir and Zanskar, experienced a shrinkage of 1.88 km\({}^{2}\) area, equivalent to 29%, with a frontal retreat of 500 m at a rate of 10.6 ma\({}^{-1}\) from 1972 to 2019 [35]. In the Trans-Himalayan Kang Yatze Massif, Ladakh, Northwest India, around 121 small glaciers have decreased in the area from 96.4 km\({}^{2}\) in 1969 to 82.6 km\({}^{2}\) in 2010 [36]. The loss in the glaciated area is 14% at a rate of 0.3% per year. Recent studies have reported shrinkage of glacier areas and surface elevation from 1975 to 2015 in the Kanchenjunga region of the Himalaya, which is attributed to \begin{table}
\begin{tabular}{c c c c c} \hline
**Ref.** & **Region** & **Time Period** & **Data** & **Trend (\({}^{\circ}\)K decade\({}^{-1}\))** \\ \hline
[29] & Yangtze River reaches, China & 1979–2018 & MSU (TLT) & 0.20 \\
[29] & Yangtze River reaches, China & 1979–2018 & MSU (TMT) & 0.19 \\
[13] & Western IG Plain (Annual) & 1979–2008 & MSU (TMT) & 0.18 \(\pm\) 0.05 \\
[30] & Western Himalayas (Annual) & 1979–2007 & MSU (TMT) & 0.26 \(\pm\) 0.09 \\
[13] & Western Himalayas (Annual) & 1979–2008 & MSU (TMT) & 0.16 \(\pm\) 0.05 \\
[29] & Tibetan Plateau, China & 1979–2018 & MSU (TLT) & 0.40 \\
[29] & Tibetan Plateau, China & 1979–2018 & MSU (TMT) & 0.32 \\
[31] & Tibetan Plateau (Qinghai), China & 1998–2020 & AMSU & Enhanced tropospheric \\
[13] & Tibetan Plateau & 1979–2008 & MSU (TMT) & 0.08 \(\pm\) 0.06 \\
[13] & IG plains (Annual) & 1979–2008 & MSU (TLT) & 0.32 \(\pm\) 0.27 \\
[30] & Himalayan-Hindu Kush & 1979–2007 & MSU (TMT) & 0.21 \(\pm\) 0.08 \\
[(Annual)] & 1979–2008 & MSU (TMT) & 0.13 \(\pm\) 0.04 \\
[13] & Eastern Himalayas (Annual) & 1979–2007 & MSU (TMT) & 0.182 \(\pm\) 0.08 \\ \hline \end{tabular}
\end{table} 
Table 1: Microwave Sounding Unit/Advanced Microwave Sounding Unit (MSU/AMSU) temperature trend over some of the regions in the Hindu Kush-Himalayan (HKH) region. TMT: temperature middle troposphere; TLT: temperature lower troposphere. increased air temperature [37]. The average change rates observed in the glacier area were \(-0.18\)\(\pm\) 0.07% a\({}^{-1}\) and in the surface elevation were \(-0.32\)\(\pm\) 0.02 ma\({}^{-1}\). However, in the past two decades, the Karakoram mountains have been reported to be growing and showing stable or positive glacier budgets, known as the Karakoram anomaly [38; 39; 40]. A mass balance study of 19 glaciers covering 60% of the Astore basin, north-western Himalaya, using satellite images and DEM between 1999 and 2016 shows no net mass loss in that period, exhibiting a pattern similar to the Karakoram [41]. The inhomogeneous glacier response pattern across the Himalayas is linked to the interaction between increasing temperatures and the local topography [42]. The mean snow cover peak is observed in February, and the trough is in August and September from 2000 to 2017 across the entire HKH region [43].