Climate-driven acceleration in forest evapotranspiration fuelling extreme rainfall events in the Himalaya

Abstract

Warming-induced expansion in vegetation coverage and activity can accelerate the montane hydrological regimes. However, the climate impacts on ecohydrology of forested valleys of the Himalaya are uncertain. In this study, utilizing results of about three centuries of cellulose isotope chronologies (δ 13C and δ 18O) of dominant tree species, geo-chronological proxies, bio-geophysical dataset and simulations including satellite observations, we show an activation in the ecophysiological processes including evapotranspiration (ET) since the 1950s. Observation suggests rapid greening, while isotopic records indicate enhanced assimilation and transpiration in deciduous species vis-à-vis conifers post 1950s. Given strong vegetation-precipitation feedback and superimposed on the increasing trends of conducive atmospheric factors affecting valley-scale convective processes, intensification in forest ET is manifesting in a progressive enhancement in extreme rainfall events (EREs) since the last few decades. Results suggest that representation of ecophysiological processes and dynamics of seasonal moisture loading in observational and modelling framework is critical for understanding EREs under climate change.

Adaptation potential of Neotropical montane oaks to drought events: Wood anatomy sensitivity in Quercus delgadoana and Quercus meavei

“…Increasing temperatures result in high evapotranspiration levels (Singh et al, 2021); this well‐established relationship led to previous suggestions that TMCF oaks are among the most vulnerable and sensitive trees to climate change (Jiménez‐García & Peterson, 2019; Poorter et al, 2017). Likewise, annual growth in both study species was clearly drought stressed ( r s ≥ 0.5), during the high temperature of midsummer period from June to August, and the EvT from May to July appears to have a negative effect on radial growth.…”

“…Increasing temperatures result in high evapotranspiration levels (Singh et al, 2021) water entering the system as drizzle, fog and mist) likely compensates for this low precipitation, modulating the growth sensitivity of both oaks to drought periods (Fang & Lechowicz, 2006;Long et al, 2022).…”

Satellite Imagery reveals an accelerating rate of increase in land evapotranspiration

“…In various regions of Asia, positive ET trends are linked to land use changes and vegetation greening (e.g., Turkey, India, and China). We have identi ed region-speci c drivers, such as the expansion of croplands and irrigated areas 49 in Turkey, the increase in deciduous and evergreen vegetation coverage in the Himalayas 50 , and the intensi cation of agriculture and afforestation in China and India 51 . In contrast, the declining ET trends in northern Asia are associated with soil moisture de cits, mainly due to earlier vegetation greening 52 and intensi cation of dry season 53 .…”

Tree-Ring Isotopic Records Suggest Seasonal Importance of Moisture Dynamics Over Glacial Valleys of the Central Himalaya

“…Moreover, it is interesting to note that despite a further and strong decline in ISM precipitation since the mid-20th century (Figure 2), the stability of the correlations is remarkable (Figure 6B). Therefore, it is highly possible that decadal-scale greening (Shen et al, 2015;Silva et al, 2016;Parida et al, 2020;Sigdel et al, 2020) with consequent increase in evapotranspiration (Singh et al, 2021b) and pre-monsoon precipitation in the region since the mid-20th century (Singh et al, 2006) might have compensated for the ISM precipitation deficit that helped to lower down and maintain the correlation (Figure 6B).…”