Review of hydro-climate variability and modeling approaches for water security under climate change in India

Climate change remains a defining challenge of the twenty-first century, with 2024 recorded as the hottest year on Earth, marking the first historical year with average global temperatures exceeding 1.5 °C above pre-industrial levels. It poses a significant threat to global water security, with India particularly at risk with its 18% share of the world's population and a mere ~ 4% of global freshwater reserves. Since the mid-twentieth century, India has experienced a rise in average temperatures (~ 0.7 °C from 1901 to 2018), a decline in monsoon precipitation (~ 6% from 1951 to 2015), and a significant increase in the frequency of extreme temperature and rainfall events (nearly tripling in some areas). The country has also faced more frequent droughts (23 recorded between 1901 and 2015), rising sea levels (~ 3.3 mm per year from 1993 to 2017), and increased intensity of severe cyclones, alongside other changes in the monsoon system. India's water security is in significant jeopardy due to its unpredictable climatic patterns, which can directly affect its food and socioeconomic security. Even though hydro-climate and its modeling have advanced scientifically, there are still questions about how climate change processes are fully understood, especially concerning the Indian monsoon. This study aims to review the influences of climate change across India, emphasizing hydro-climate, its variability, modeling, and related impacts on water security. Notably, the water sector's ability to adapt to climate change is essential to the long-term sustainable management of its resources. In this context, the review further emphasizes the integration of hydrological evaluations with finer-resolution climate projections, which has been crucial for improving our comprehension of climate-water interactions at regional scales and guiding sustainable water management plans.