Rainfall and temperature are vital climatic parameters, which have been frequently used to identify the alterations in global climatic conditions (Mayowa et al. 2015; Sa’adi et al. 2019). Global ocean’s and land surface temperature trend has revealed a warming of 0.85°C (ranging between 0.65°-1.06°C) during 1880–2012 (IPCC 2014). This rise in the surface temperature could result in changing rainfall patterns globally (Wang et al. 2016). For instance, Trenberth et al. (2007) have observed a rising trend in rainfall over Asia, Australia, northern Europe, North and South America, whereas decreasing trend over the Mediterranean area, southern Asia, Sahel, western and southern Africa. Likewise, Longobardi and Villani (2010) and Altava-Ortiz et al. (2011) have shown a decreasing trend in average annual precipitation over Mediterranean basin and nearby regions. More recently, Adler et al. (2017) have not detected any significant trend in the global mean precipitation, however, a rising trend over tropical oceans and a declining trend over certain mid-latitudes areas has been detected. Nicholson et al. (2018) and Caloiero et al. (2018) have detected a significant downward trend in annual rainfall over West Africa, North Africa, and eastern Mediterranean. Besides, several other attempts have been made to examine the possible influences of changing climate on spatial and temporal rainfall trends (Loo et al. 2015; Mayowa et al. 2015; Xiao et al. 2016; Hu et al. 2017; Sein et al. 2018; Biasutti 2019; Haag et al. 2019; Sa’adi et al. 2019; Gebrechorkos et al. 2019).
Additionally, it has been well-recognized that the warming environment has enhanced the intensity of extreme precipitation more rapidly than mean precipitation (Kharin et al. 2013; Boucher 2013; Berg 2013; Fischer and Knutti 2016; Myhre et al. 2019). Hartmann et al. (2013) have observed that the occurrence of extreme precipitation events has increased over larger land areas than it has decreased in the second half of 20th century. Therefore, extreme precipitation has increasingly become an illuminating subject of research during the period of changing climate (Cammarano and Tian 2018, Dahal et al 2018). Researchers have continuously made efforts to examine the extreme precipitation trends in relation to changing climate (Dore 2005; Alexander et al. 2006; Fischer and Knutti 2014; Asadieh and Krakauer 2015; Westra et al. 2013). Apart from this, increasing trends in extreme rainfall events have been detected over different parts of the world, for example, Europe (van den Besselaar et al. 2013), North America (Villarini and Vecchi 2012; Donat et al. 2013; Easterling et al. 2017), South America (Donat et al. 2013, Skansi et al. 2013), south eastern South America (Wu Y and Polvani 2017), Australia (Laz et al. 2014; Herath et al. 2017), South Asia (Sheikh et al. 2015) and south east Asia (Ge et al. 2019). Interestingly, most of the land areas have observed a rise in extreme rainfall events in summer season excluding Europe, which showed an increase during winters (Hartmann et al. 2013; Pinskwar et al. 2019).
In India, a number of efforts have been made to investigate the spatial and temporal trends in rainfall and related extremes. For instance, Guhathakurta and Rajeevan (2006) have not observed any trend in south west monsoon season rainfall over Indian region, but noticed substantial regional differences. Naidu et al. (2009) have observed a rise in summer monsoon rainfall in south India, whereas a decrease in northern India. Nonetheless, for India as a whole, the summer monsoon rainfall has not shown any trend (Kumar et al., 2010; Jain and Kumar, 2012), while Ghosh et al. (2009) have shown mixed trends in rainfall occurrence over different regions in India. Kumar et al. (2010) have shown a decline in annual and monsoon rainfall, while a rise in winter, pre- and post-monsoon seasons for India as a whole. However, these trends are statistically insignificant. Jain et al. (2013) have not detected any significant trend in annual rainfall occurrence over north east India, although seasonal trends have been detected. However, several researchers have shown a substantial rise in number and magnitude of extreme rainfall events over the Indian region (Goswami et al. 2006; Joshi and Rajeevan 2006; Krishnamurthy et al. 2009; Pattanaik and Rajeevan 2010). Conversely, Guhathakurta et al. (2011) have detected a decline in extreme rainfall events over central and north India, whereas an increase over peninsula, eastern and north eastern parts of India. Recently, Mukherjee et al. (2017) have noticed a significant rising trend in number of extreme rainfall events and ascribed it to increasing anthropogenic warming. Apart from this, numerous efforts have been done on the spatial and temporal pattern of rainfall and related extreme events for different states of India in recent times such as Kerala (Krishnakumar et al. 2009; Pal and Al-Tabbaa 2009; Pal and Al-Tabbaa 2011; Nair et al. 2014; Thomas and Prasannakumar 2016), West Bengal (Chatterjee et al. 2016; Ghosh 2018; Kundu and Mondal 2019), Andhra Pradesh (Rao et al. 2009; Patakamuri et al. 2020), Madhya Pradesh (Duhan and Pandey 2013; Jana et al. 2017); Orissa (Patra et al. 2012), Uttarakhand (Kotal et al. 2014; Nandargi et al. 2016), Jammu and Kashmir (Kumar et al. 2009), Punjab (Gill et al. 2013), Assam (Deka et al. 2013), Gujarat (Lunagaria et al. 2015; Dave and James 2017; Dave et al. 2017), and Maharashtra (Ratna 2012; Sonar 2014; Ingle 2018).
The above review exhibits that researchers have extensively examined the trends and pattern of rainfall and related extreme events for the different parts of globe, including India. However, studies on trends and pattern of rainfall and related extreme events pertaining to the dryland ecosystem of India i.e., for Rajasthan state are less in number. Climate of the Rajasthan state is of monsoon type and receives the major part of annual rainfall during the south west monsoon. The insufficient and erratic rainfall in many parts of the state constitutes a threat to agriculture. The distribution of rainfall in dryland ecosystem of Rajasthan is highly uneven and changes significantly from region to region and year to year (Pingale et al. 2014). Also, the state has been characterized by highest chances of rainfall deficiencies and drought occurrence (Rathore 2005). The region is highly dependent upon rainfall as it is an important source of groundwater recharge. The long-term climatic changes related to rainfall may affect the agriculture and water resources of the state (Yadav et al. 2018). For that reason, some investigations have been attempted to examine the rainfall and related extreme events for this state (Rao et al. 2011, 2014; Singh et al. 2012; Pingale et al. 2014; Poonia et al. 2014; Machiwal and Jha 2017; Srivastava 2018; Meena et al. 2019). However, these studies are restricted to the analyses of a particular rainfall event, district, western arid region and short period of data. No study has presented a comprehensive examination of rainfall and heavy rainfall events over entire dryland ecosystem of Rajasthan state in north western India. Therefore, a detailed analysis of recent rainfall variability for this dryland ecosystem is required. In the light of these facts, the main objective of this study is to examine recent rainfall variability over dryland ecosystem of Rajasthan state in north western India.