Recent spatial aggregation tendency of rainfall extremes over India

Abstract

Significant increase in the frequency of occurrences of rainfall extremes has been reported over several parts of the world. These extreme events were defined at individual grids without considering their spatial extent. Here, using ground-based observations over India during boreal summer, we show that the average size of spatially collocated rainfall extremes has been significantly increasing since 1980. However, the frequency of occurrences of such collocated extreme events remains unchanged. Around 90% of the total number of large-sized events (area ≥ 70 × 10 3 km 2 ) of our study period (1951 to 2015) have occurred after 1980. Some of the major floods in recent decades over India are attributed to these large events. These events have distinctive precursory planetary-scale conditions, unlike their smaller counterparts. As the underlying physical mechanisms of extremes rainfall events are size-dependent, their changing spatial extent needs to be considered to understand the observed trends correctly and obtain realistic future projections.

Large‐Scale Extreme Rainfall‐Producing Synoptic Systems of the Indian Summer Monsoon

“…The LEREs occur in the southwestern sector of LPSs (Nikumbh et al, 2019). We observe that the LPS‐Lg are accompanied by SCVs on their western flank (Figure S1).…”

“…Understanding the physical processes that lead to extreme rainfall events (EREs) is a challenging multiscale problem that has received wide attention in the literature. The literature on EREs includes aspects like flash floods (Bosart & Sanders, 1981; Maddox et al, 1978, 1979), convective systems (Doswell III et al, 1996; Schumacher & Johnson, 2005), the observed trends (Goswami et al, 2006; Karmakar et al, 2017; Nikumbh et al, 2019; Rajeevan et al, 2008), and their future projections (Emori & Brown, 2005; Muller et al, 2011; O'Gorman, 2015; Trenberth, 1999). A multitude of extreme precipitation events, however, remained unpredicted (Coumou & Rahmstorf, 2012).…”

Dynamics of rainfall extremes over India: A new perspective

“…We then categorized extreme rainfall events with daily rainfall intensity exceeding 150 mm day −1 and extending over a wide region covering our area of interest (i.e., at least 10 grid cells over the MCZ must simultaneously satisfy the threshold of 150 mm day −1 ; e.g., Roxy et al, 2017). This will also ensure the defining of extreme events considering their spatial extent, following Nikumbh et al (2019).…”

“…The aforementioned studies mostly focus on wet spells, but a comprehensive process-oriented study focusing on the potential precursors leading to daily rainfall extremes has not been specifically addressed so far, except for in a few studies (Roxy et al, 2017;Nikumbh et al, 2019). Nikumbh et al (2019), while studying the observed increasing trend in the frequency of occurrences of large (i.e., spatially widespread events) rainfall extremes, noted that monsoon low pressure systems with precursory planetary scale conditions (e.g., over middle latitudes) may play a vital role for its increased occurrence. In contrast, Roxy et al (2017) suggest that precursory Indian Ocean warming may lead to more rainfall extremes over Indian landmass, with strengthened monsoon low-level westerlies transporting more moisture from Arabian Sea.…”

Integrative systems approach reveals dynamics of microbiome-metal-ion axis in mesocosms representing tropical urban freshwater canal ecosystem

“…Environment controlling factors, such as land use and rain represent chronic anthropogenic and intermittent natural disturbances, respectively [3][4][5] . The constant release of land-use-specific stressors through basal flow of water exerts a chronic anthropogenic (press) disturbance in the sedimentary ecosystems of TrUCS 1 from different land use types.…”