Climate change-induced aridity changes are observed globally and in India, with variable spatial and temporal distribution. Unlike droughts, aridity denotes a persistent climate condition requiring in-depth analysis utilising long-term data to identify any significant spatio-temporal shifts. Given the absence of a comprehensive assessment covering the entire Indian subcontinent, the primary objective of this study is to investigate the spatial change in aridity, its temporal trend, and the change point of its mean values across Indian mainland considering a time period of 1902-2021. Furthermore, this study also investigates the spatio-temporal variations in desertification vulnerability across the Indian mainland. Findings from the study reveal the potential for both desertification and oasification across India's diverse climate regions. Analysis over a period of 120 years (1902 to 2021), the aridity index (AI), which is calculated as a ratio of precipitation (P) and potential evapotranspiration (PET), reveals that eastern and northeast states (20% of total area) show a significant decreasing trend in the aridity index (i.e., increased aridity). In contrast, parts of north-western and southern peninsular India (21% of the total area) show a significant increasing trend (i.e., decreased aridity). This pattern shows a tendency to shift towards dryer condition in the eastern and northeast regions of India, while oasification propensity is seen in the north-western and southern regions. Wherever these changes were observed, 59% of the area experienced a sudden change in mean AI (change point at 5% significance level) between 1950 and 1980, which can be attributed to the shift in the global climate regime during the 1970s and 1980s. Furthermore, spatial extent of sub-humid regions has increased by 6.3% between pre-change point (1902-1951) and post-change point (1982-2021) time period, while semi-arid zones have been found to shrink with time. The change can be mainly attributed to changes in P and PET across India. Overall, this study emphasizes on the potential oasification and desertification trends and the vulnerability towards desertification across India. The findings enhance the understanding of impending desertification/oasification, aiding future agricultural and hydrological planning.