The upper Ganga basin (UGB) constituting Bhagirathi and Alakananda basins has been considered as a single hydrological unit so far with comparable climate forcing. Here, we show three distinct “topoclimatic zones” of this basin having characteristically different temperature, precipitation, and orographic processes. The orographic discontinuity forced by a mountain ridge with an average elevation of 5,200 m a.s.l. is instrumental in the development of these topoclimatic zones. The northern region of the basin is identified as high elevation and high temperature zone (HE‐HT) with monsoon moisture deficit. This monsoon deficit region is characterized by higher land surface temperature lapse rate (LSTLR) during July and August (JA) derived from MODIS‐LST (11.00°C/km) as compared to much lower LSTLR of monsoon topoclimatic zone (5.78°C/km). The nival‐glacier regimes of the monsoon dominant and monsoon deficit regions constituted the third topoclimatic zone characterized by high elevation‐low temperature zone (HE‐LT). This zone has comparatively lower temperature lapse rate (5.26°C/km) than the immediately lower elevations. The coldest points identified in the basin are mostly placed in monsoon deficit regions with higher LSTLR. The 10–12°C isotherm in the monsoon deficit zone runs at 5,300 m a.s.l. as compared to 3,200 m a.s.l. in monsoon dominant zone. It is proposed that 80% of glacier area in the UGB is in the monsoon deficit zone that is regulated by the northern region orographic processes rather than southern slopes. Glacier change in the southern and northern zones show significant difference during the period of 1994–2016/2017, with significantly higher glacier area loss in the HE‐HT zone. The study highlights the importance of these topoclimatic considerations while evaluating the climate and hydrology of UGB.
A catastrophic debris flow in the Rishiganga and Dhauli ganga river in Uttarakhand, India on 7th February 2021 left a trail of disaster. Around 200 people lost their lives, two hydro-power project were badly damaged and a bridge across the Rishiganga River was washed off in the event. Study shows that the debris flow is caused due detachment of 0.59 km2 right lobe of a hanging glacier and resultant ice-rock avalanche. This right lobe of the glacier was located over a mountain slope having an average slope of 35o at 4700–5555 m a.s.l. and travelled 12.4 km before hitting the infrastructure projects. Role of precipitation, snow cover, land surface temperature and permafrost processes were investigated for identifying causes of the event. Since 2012, monsoon precipitation and mean annual land surface temperature (LST) showed significant increasing trend. Snow cover during monsoon months showed increasing trend and September, October and November experienced decreasing trend at glacier elevations. Mean annual LST increased from − 0.3 oC in 2012 to a peak of 0.4 oC in 2016. Central lobe of the glacier advanced during this period and eventually fell off in 2016 suggesting that the LST warming forced reduction of frictional drag at the interface facilitating it advancement and eventual dislodgement. Permafrost modelling suggest warm permafrost below 50 m and conditions favorable for intense frost cracking at to 10–15 m. At ~ 40 m depth, the delayed response of 2012–2016 warming produced peak positive temperature conditions by December and probably facilitated the formation of thin film of water at the deeper layers acting as a lubricant for glacier sliding. It is also suggested that the increase in summer precipitation might have forced thickening of the accumulation area and thereby increasing the shear stress for sliding of the glacier. It is proposed that the recent change in the weather conditions in the region is primarily responsible for this event through geological, glaciological and permafrost processes. Flood modeling study suggest a flood volume of ~ 10 MCM generating 24.5 m flow depth at the bridge site with 12.7 m/s flow velocity. The event highlighted the need for improved monitoring of the cryospheric areas of the Himalaya to capture the early warning signs for better preparedness.
Uncrewed aerial systems (UASs) are becoming very popular in the domain of water resource mapping and management (WRMM). Being a cheaper and quicker option capable of providing high temporal and spatial resolution data, UAS has become a much sought-after platform for remote sensing. Still, their application in the field is in its early stage. This paper encompasses basic concepts of UAS, different payloads and sensor technologies available, various methodologies for its application in WRMM, different software available, and challenges associated with them, thus presenting a comprehensive review of multiple applications of UAS in different sub-domains of water resources. From cryosphere, rivers and lakes, and coastal areas to sub-surface water, as well as from water quality to wastewater management, the authors have discussed various applications of uncrewed aerial vehicles. At the end of the paper, the authors have identified the issues posing problems in the wider implementation of UAS in WRMM. Also, the future scope of the UAS in WRMM has been discussed.
A catastrophic debris flow in the Rishiganga and Dhauliganga rivers in Uttarakhand, India, on 7 February 2021 left a trail of disaster. Around 100-150 people lost their lives according to Uttarakhand Chief Secretary statement given to ANI news portal, two hydropower projects were badly damaged and a bridge across the Rishiganga River was washed off in the event. Study shows that the debris flow is caused due to detachment of 0.59 km 2 right lobe of a hanging glacier and resultant ice-rock avalanche. This right lobe of the glacier was located over a mountain slope having an average slope of 35° at 4700-5555 m a.s.l. and travelled 12.4 km before hitting the infrastructure projects. Role of precipitation, snow cover, land surface temperature, and permafrost processes were investigated for identifying causes of the event. Since 2012, monsoon precipitation and mean annual land surface temperature (LST) showed significant increasing trend. Snow cover during monsoon months showed increasing trend and September, October and November experienced decreasing trend at glacier elevations. Mean annual LST increased from − 0.3 °C in 2012 to a peak of 0.4 °C in 2016. Central lobe of the glacier advanced during this period and eventually fell off in 2016 suggesting that the LST warming forced reduction of frictional drag at the interface facilitating it advancement and eventual dislodgement. Permafrost modelling suggests warm permafrost below 50 m and conditions favourable for intense frost cracking up to 10-15 m. At ~ 40 m depth, the delayed response of 2012-2016 warming produced peak positive temperature conditions by December and probably facilitated the formation of thin film of water at the deeper layers acting as a lubricant for glacier sliding. It is also suggested that the increase in summer precipitation might have forced thickening of the accumulation area and thereby increasing the shear stress for sliding of the glacier. It is proposed that the recent change in the weather conditions in the region is primarily responsible for this event through geological, glaciological, and permafrost processes. Flood modelling study suggests a flood volume of ~ 10 MCM generating 24.5 m flow depth at the bridge site with 12.7 m/s flow velocity. The event highlighted the need for improved monitoring of the cryosphere areas of the Himalaya to capture the early warning signs for better preparedness.
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