Increasing 2020‐Like Boreal Summer Rainfall Extremes Over Northeast Indian Subcontinent Under Greenhouse Warming

Abstract

Extreme persistent rainfall poses serious impacts on human and natural systems, predominately through its related hydrogeological disasters. Due to sustained heavy downpours, the summer of 2020 was the second wettest on record over Northeast Indian subcontinent since 1901. Here, we find that this orographically anchored extreme rainfall event was largely associated with the anomalous anticyclone (AAC) over the Indo‐Northwest Pacific region and La Niña‐induced Walker circulation intensification. The overall effect of anthropogenic forcings contributed little to the occurrence probability of this event, because the warming and wetting effects of greenhouse gases were almost negated by anthropogenic aerosols. Climate models project a prominent increasing trend of such extreme event under future greenhouse‐induced warming due to increase in atmospheric water vapor and 2020‐like AAC frequency. Our findings thus call for scaling up climate change adaptation efforts for increasingly extreme persistent rainfall in highly populated but low‐resilience South Asian developing countries.

Delayed Onset of Indian Summer Monsoon in Response to CO2 Removal

“…Particularly, the land where human beings live is extensively warmed by 1.6°C. Continuous warming leads to more frequent and intense weather and climate extremes across the globe, such as heatwaves, rainstorms, and droughts, which pose colossal threats to natural ecosystems and human societies (Tang et al., 2022; X. Zhang et al., 2023). To reduce the risks posed by global warming and ensure sustainable development, several ambitious and feasible efforts, including “The Paris Agreement,” are now being considered.…”

Climate change quadruples flood‐causing extreme monsoon rainfall events in Bangladesh and northeast India

“…As a result, three distinct rainfall maxima occur over the SEB (Chittagong), NEBI (Sylhet division of Bangladesh & Meghalaya Plateau of India), and northwest Bangladesh (NWB; Rangpur). Among these three maxima regions, the NEBI receives the largest mean monsoon rainfall and frequent extreme rainfall events (Rimi et al, 2019;Shahid, 2011;Tang et al, 2022) (Figure 1c,d).…”

“…The influence of tropical SST on the flooding events due to extreme rainfall events on the interannual time‐scale over the NEBI is well known (Chowdhury & Ward, 2007; Rimi et al, 2019; Tang et al, 2022; Wahiduzzaman & Luo, 2021). SST anomalies related to the tropical Pacific (El Niño–Southern Oscillation, ENSO) and Indian Ocean (Indian Ocean Dipole, IOD) can influence the extreme rainfall events individually or all at once (Chowdhury & Ward, 2007) during the summer monsoon.…”

“…The annual mean extreme daily precipitation events increased over the past decades (1958–2018) and are projected to keep increasing over the north Indian monsoon region significantly (Seneviratne et al, 2021). Very few studies have analyzed the monsoon‐related daily extreme rainfall over Bangladesh and northeast India and explored the physical mechanisms behind it for the observed trends and future projections (Rimi et al, 2019; Shahid, 2011; Tang et al, 2022). Analyzing observed station data of Bangladesh, Shahid (2011) found that the heavy rainfall days over Bangladesh increased during the pre‐monsoon season (April–May) from 1958 to 2007.…”

Diversity of Northwest Pacific atmospheric circulation anomalies during post-ENSO summer

“…While the moisture transport from tropics to East Asia is strengthened, rainfall over the mountainous central China is significantly enhanced due to orographic lifting (Wu et al, 2003;Hu et al, 2017;Hu et al, 2020). Moreover, a tripole pattern of precipitation anomalies over the South Asian region can be observed when the anomalous anticyclone extends westward to the North Indian Ocean (Mishra et al, 2012;Chowdary et al, 2016a;Srinivas et al, 2018;Chowdary et al, 2019;Liu and Huang 2019;Tang et al, 2022b), characterizing a prolonged hot pre-monsoon period and a delay of the South Asian summer monsoon onset (Zhou et al, 2019). These climate responses are nearly reversed during La Niña, although the asymmetry exists between El Niño and La Niña (e.g., Hoerling et al, 1997;Hoerling et al, 2001;Zhang et al, 2014;Tao et al, 2017;Wang et al, 2021b;Wang et al, 2022).…”