Topoclimatic zones and characteristics of the upper Ganga basin, Uttarakhand, India

Abstract

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.

Hanging glacier avalanche (Raunthigad–Rishiganga) and debris flow disaster on 7 February 2021, Uttarakhand, India: a preliminary assessment

“…Small glaciers are more susceptible to climate fluctuations and respond faster to the changes. This has been illustrated by recent studies in the region, which suggested small glaciers are losing more mass than big glaciers in recent times (Bhambri et al 2012;Mir et al 2017;Yadav et al 2020). This event highlighted the need for improved monitoring of Himalayan cryospheric systems as complex interlinking snow, glacier, permafrost, geology, and climate cause such catastrophic events.…”

“…This is a critical factor as monsoon-dominated areas of Uttarakhand Himalaya have less than 20% glaciers compared to the monsoon deficit zone in the north of the TC, suggesting less favourable conditions of southern slopes for glaciers. This also demonstrated by shallower temperature lapse rates at the monsoon-dominated glacier areas suggesting a high energy system through latent heat release of precipitating monsoon (Thayyen et al 2005;Thayyen and Dimri 2018;Yadav et al 2020). Nearest high elevation precipitation station located at Chamoli (2640 m a.s.l.)…”

“…(2) Glaciers < 2km 2 , V = 0.024 A 1.36 (3) Glaciers > 2km 2 , V = 0.027 A 1.36 1985; 2003; 2005; 2012; 2015; 2017; 2019 15 cm-30 cm (error ≤ 1 K, ≤ 2 K, ≤ 3 K , and > 3 K) have been generated and built a continuous data series by incorporating the less accurate data in a hierarchical way (Yadav et al 2020) n . The remaining gap is filled by interpolation.…”

“…The Raunthigad catchment, where the glacier is situated, forms the northern boundary of the monsoon influence zone of the southern slopes (Fig. 5), and the topographic control (TC) (Yadav et al 2020) runs through the northern ridges of Raunthigad reaching up to 7120 m a.s.l. (Trishul peak).…”

Hanging glacier avalanche (Raunthigad - Rishiganga) and Debris flow disaster of 7th February 2021, Uttarakhand, India, A Preliminary assessment

“…Where volume, V in km 3 and area, A in km 2 has been generated and built a continuous data series by incorporating the less accurate data in a hierarchical way (Yadav et al, 2020) . The remaining gap is filled by interpolation.…”