Indian summer monsoon: Extreme events, historical changes, and role of anthropogenic forcings

Abstract

The South Asian summer monsoon is a complex coupled human-natural system that poses unique challenges for understanding its evolution alongside increasing anthropogenic activities. Rapid and substantial changes in land-use, landmanagement and industrial activities over the subcontinent, and warming in the Indian Ocean, have influenced the South Asian summer monsoon. These might continue to be significant drivers in the near-term along with rising global greenhouse gas emissions. Deciphering the region's vulnerability to climate change requires an understanding of how these anthropogenic activities, acting on a range of spatial scales, have shaped the monsoon spatially and temporally. This review summarizes historical changes in monsoon rainfall characteristics, associated mechanisms, and the role of anthropogenic forcings, focusing on subseasonal variability and extreme events. Several studies have found intensified subseasonal extremes across parts of India and an increase in spatial variability of rainfall despite an overall weakening of seasonal rainfall in the monsoon core. However, understanding these changes remains challenging because of uncertainties in observations and climate models. The mechanisms and relative influences of various anthropogenic activities, particularly on subseasonal extremes, remain relatively underexplored. Large biases in the representation of relevant processes in global climate models limit the ability to attribute historical changes and make reliable projections. Nevertheless, recent advances in modeling these processes using higher-resolution modeling frameworks provide new tools to investigate the Indian summer monsoon's response to various anthropogenic forcings. There is an urgent need to understand how these forcings interact to shape climate variability and change in this vulnerable region. This article is categorized under:Paleoclimates and Current Trends > Earth System Behavioranthropogenic forcings, climate change attribution, extreme events, South Asian monsoon, subseasonal variability | INTRODUCTIONSouth Asia is one of the world's most densely populated regions, with a large fraction of people dependent on monsoonrelated activities for their livelihood. The summer monsoon season is the prime agricultural season for most of South Asia and the yields of the major cereal crops are highly sensitive to seasonal temperature and precipitation variability (DeFries et al., 2016). Recent studies have also highlighted the substantial impacts that subseasonal precipitation variability has on crop yields

Climate Change Indicators and Spatiotemporal Shift in Monsoon Patterns in Pakistan

“…us, even if the average trend in sea-surface temperature over the Indian ocean is positive, the spatial distribution of trends does not encourage spatially coherent warm sea-surface temperature (SST) or the organized dynamics necessary for the monsoon [32]. It is further complicated by the changes in land use and land cover [33] and increase or decrease in irrigated land in India which can have local as well as remote effects by altering circulations [34] and increasing concentration of greenhouse gases [2][3][4].…”

“…As large population and growing agriculture sector in South Asia depend on monsoon rainfall patterns, any disruption causes huge concerns. It is vital to explore the response of monsoon dynamics to rising temperature and varying concentrations of greenhouse gases at both scientific and societal level [1][2][3][4].…”

“…Another regional study on subseasonal scale indicates that there is a decrease in rainfall in July and August over years in the main as well as southwest monsoon regions of India [11]. Rainfall measurements taken over land depict a decreasing trend in rainfall during 1951-2000 in the subtropics and tropics and an increasing trend in the midlatitudes of the Northern Hemisphere, a consequence linked to the rising levels of greenhouse gases [2,4]. e trend of signi cant warming over the Bay of Bengal, the equatorial South Indian Ocean, and Arabian Sea signi cantly accelerated during the period of years 1971-2002 [11].…”

Implications of a Varying Observational Network for Accurately Estimating Recent Climate Trends

“…In a recent article, Lin and Huybers () explore the implications of gridded products and the underlying network inhomogeneity issues for studying mean and extreme rainfall patterns, using the case of the Indian summer monsoon. A number of studies have identified a long‐term decline in mean precipitation over the core Indian monsoon region (Turner & Annamalai, ) and significant long‐term trends in various metrics of extreme precipitation, as summarized in Singh et al (). A majority of the studies on extreme precipitation rely on the widely used daily, gridded precipitation data sets provided by the Indian Meteorological Department (IMD) at 1° × 1° (Rajeevan et al, ) and 0.25° × 0.25° (Pai et al, ) resolutions, which are derived from rain gauge station records.…”

“…Although the IMD data sets are the focus of Lin and Huybers (2018) article, such network inhomogeneity issues exist in most gridded products, which often use the largest number of suitable reporting stations to better capture the spatial variability in climate (e.g., Harris et al, 2014;Schneider et al, 2014). For the Indian domain, substantial differences exist between various precipitation data sets, as demonstrated in Singh et al (2019), for several reasons including their use of a fraction of the IMD rain gauge stations, incorporation of satellite data, different spatial resolutions, and different interpolation techniques. Similar issues and uncertainties associated with a changing observational network have been evaluated and reported for other regional (e.g., Hofstra et al, 2010, for Europe andKing et al, 2013, for Australia) gridded products.…”