Hydrological Extremes in Western Himalayas-Trends and Their Physical Factors

Abstract

Recent exacerbation of extreme precipitation events (EPEs) and related massive disasters in western Himalayas (WH) underpins the influence of climate change. Such events introduce significant losses to life, infrastructure, agriculture, in turn the country’s economy. This chapter provides an assessment of long-term (1979–2020) as well as recent changes (2000–2020) in precipitation extremes over WH for summer (JJAS) and winter (DJF) seasons. Different high-resolution multi-source climate datasets have been utilized to compute the spatiotemporal trends in intensity and frequency of EPEs. The hotspots of rising extremes over the region have been quantified using the percentile approach where daily precipitation exceeds the 95th percentile threshold at a given grid. The findings reveal geographically heterogeneous trends among different datasets; however, precipitation intensity and frequency show enhancement both spatially and temporally (though insignificant). For both seasons, dynamic and thermodynamic parameters highlight the role of increased air temperatures and, as a result, available moisture in the atmosphere, signifying the consequences of global warming. Rising precipitation extremes in summer are sustained by enhanced moisture supply combined with increased instability and updraft, due to orography, in the atmosphere whereas winter atmosphere is observing an increase in baroclinicity, available kinetic energy, vertical shear and instability, contributing to a rise in precipitation extremes.

Underlying physical mechanisms of winter precipitation extremes over India's high mountain region

“…Recent studies suggest a rise in the frequency and intensity of winter EPEs in the WHR (Krishnan et al ., 2019; Madhura et al ., 2015; Narasimha Rao et al ., 2021; Nischal et al ., 2023). Some attributable factors include warming climate (Ballesteros‐Cánovas et al ., 2018), growing prevalence of atmospheric rivers (Nayak et al ., 2021), and increased WD variability through enhanced upper level baroclinicity (Madhura et al ., 2015).…”

“…However, empirical evidence is insufficient to firmly establish a trend in WD frequency, suggesting potential changes in intensity. The disastrous impacts of EPEs extend to both natural and anthropogenic ecosystems, resulting in damage to life, infrastructure, crops, and power networks, sparking serious concerns about their impacts on human lives (Dimri et al ., 2021; Nischal et al, 2023). For instance, Figure 1c (Disastrous Weather Events catalogue by India Meteorological Department) illustrates the human mortality rate linked to winter extreme snowfall events over the WHR since the 1980s.…”

Delving into Recent Changes in Precipitation Patterns in the Western Himalayas under Global Warming

“…During summer monsoon, a substantial amount of precipitation (approximately 65-76%) [6] occurs over the WH, which is primarily attributed to orographic-induced mechanisms, as explained in various research studies [13,[19][20][21][22][23][24][25]. Moisture-laden winds from the Arabian Sea (AS) and the Bay of Bengal (BoB) converge along the WH foothills resulting in widespread precipitation throughout the region [26][27][28]. On the other hand, winter precipitation in the WH is characterized by the influence of western disturbances (WDs), which are extra-tropical cyclonic systems embedded in the subtropical westerly jet [5,29].…”

“…On the other hand, winter precipitation in the WH is characterized by the influence of western disturbances (WDs), which are extra-tropical cyclonic systems embedded in the subtropical westerly jet [5,29]. This precipitation plays a critical role in meeting the ecological and socioeconomic needs of the region, sustaining regional glaciers and supporting agricultural activities, and also influences the glacial mass balance and river runoff [5,28,29]. The spatiotemporal distribution of precipitation in the WH exhibits high variability influenced by atmosphere-land surface exchange processes, diverse land surface characteristics, and orography [5,30,31].…”

“…Regional-scale forcings influenced by local topographical features and land-use characteristics can influence climate change patterns, including weather and climate extremes, notably over complex terrains with distinctive geographical attributes such as WH [34]. Given the dense population in the WH and surrounding areas, they are highly susceptible to climate extremes [5,28,35,36]. Moreover, elevation-dependent warming in the Himalayan region is a major concern, causing shifts in precipitation patterns, including a reduced snow season and increased liquid precipitation [37].…”