Determining the quasi monsoon front in the Indian Himalayas

Isotopic analysis to quantify the role of the Indian monsoon on water resources of selected river basins in the Himalayas

“…The estimated proportion from ISM led precipitation to water resources is close to the reported range at the central and eastern Himalayas (80% of annual precipitation) (Bookhagen & Burbank, 2006; Kumari et al, 2017; Mukherjee et al, 2015; Palazzi et al, 2013; Singh & Mal, 2014). Since the interaction of ISM and WD weather systems at the regional scale (east–west Himalayan arc) is not homogeneous, there is a climatological threshold (temperature‐precipitation gradient) beyond which the intensity of ISM and WD led precipitation is reduced (Mal et al, 2021; Palazzi et al, 2013; Roderick et al, 2019). The thermal contrast between land and sea, orographic forcings, spatial extent, seasons, and large scale climatic systems (El‐Nino and La‐Nina) (Mal et al, 2021; Dimri et al, 2015, 2016; Yadav et al, 2012) are the dominant factors responsible for increasing contribution of WD over the western Himalayas and weakening influence of WDs over the central Himalayas (Cannon et al, 2015).…”

“…It is not necessary that only WDs provide precipitation in all three basins during winter. It is known from regional meteorology that the influence of the WDs decreases eastward along the Himalayas and there are some local, orographic and other types of circulations in the region, which contribute to winter and spring precipitation (Lone et al, 2019; Mal et al, 2021). The subscript (z) represents the river water at any instance and its d‐excess, d (z) , is determined by the relative percentage contribution of ISM and non‐ISM components.…”

“…The applicability of choosing representative d‐values for partitioning lies with the fact that values are nearly similar to average d‐values of July and December (e.g., TRB: 14.3‰ and 21.6‰, BRB: 12.8‰ and 19‰, IRB:11‰ and 20.5‰, respectively). These months are regarded as representative of two dominant moistures (WD and ISM) in the Himalayas, characterized with distinct d‐values (Jeelani et al, 2018; Mal et al, 2021). Furthermore, the results within the practical limit (0%–100%), also validate their applicability and made these representative d‐values reliable to characterize the end‐members.…”

“…Since the interaction of ISM and WD weather systems at the regional scale (east-west Himalayan arc) is not homogeneous, there is a climatological threshold (temperatureprecipitation gradient) beyond which the intensity of ISM and WD led precipitation is reduced (Mal et al, 2021;Palazzi et al, 2013;Roderick et al, 2019). The thermal contrast between land and sea, orographic forcings, spatial extent, seasons, and large scale climatic systems (El-Nino and La-Nina) (Mal et al, 2021;Dimri et al, 2015Dimri et al, , 2016Yadav et al, 2012) are the dominant factors responsible for increasing contribution of WD over the western Himalayas and weakening influence of WDs over the central Himalayas (Cannon et al, 2015). The lower proportion of WDs in the BRB and the TRB and lower fraction of ISM in the IRB is the resultant of above processes.…”

“…The predominant precipitation in the basin occurs during summer (>75%) when ISM are active. The remaining 25% of the rainfall could be due to non‐monsoon/WD air masses, which are also active in most parts of India (Banerjee et al, 2020; Mal et al, 2021). Monthly air temperature ranges between 6°C and 30°C with an annual average of 17°C (Lone et al, 2019; Rai et al, 2014).…”