Department of Civil Engineering
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Item Disentangling increasing compound extremes at regional scale during Indian summer monsoon(Springer, 2021-08) Guntu, RavikumarCompound extremes exhibit greater adverse impacts than their univariate counterparts. Studies have reported changes in frequency and the spatial extent of extremes in India; however, investigation of compound extremes is in the infancy state. This study investigates the historical variation of compound dry and hot extremes (CDHE) and compound wet and cold extremes (CWCE) during the Indian summer monsoon period from 1951 to 2019 using monthly data. Results are analyzed for 10 identified homogeneous regions for India. Our results unravelled that CDHE (CWCE) frequency has increased (decreased) by 1–3 events per decade for the recent period (1977–2019) relative to the base period (1951–1976). Overall, the increasing (decreasing) pattern of CDHE (CWCE) is high across North-central India, Western India, North-eastern India and South-eastern coastlines. Our findings help in identification of the parts of the country affected by frequent and widespread CDHE during the recent period, which is alarming. More detailed assessments are required to disentangle the complex physical process of compound extremes to improve risk management options.Item Increased likelihood of compound dry and hot extremes in India(Elsevier, 2023-07) Guntu, RavikumarCompound dry and hot extremes (CDHE) are periods of prolonged dry and hot weather. Their joint occurrence typically impacts society and nature stronger compared to the occurrence of the single hazards. Understanding the likelihood, variability and drivers of CDHE is challenging due to the complexity of the climate system involving interactions and feedbacks among atmosphere-land processes. In this study, we first investigate the role of the dependence between precipitation and temperature for the likelihood of CDHEs. We demonstrate that both the dependence strength and its type, i.e. the degree of tail dependence, substantially affect the CDHE likelihood. We then analyze the space-time variation of CDHE characteristics during the Indian Summer Monsoon across India for the period 1961–2014. We find strong negative association and substantial tail dependence between precipitation and temperature in some regions. Event coincidence analysis reveals that low soil moisture preconditioned by dry extremes is responsible for 55–65% of CDHE occurrence. Our analysis of the temporal evolution of CDHE characteristics finds an increasing negative association between precipitation and temperature leading to a 2 to 3-fold rise of CDHE frequency for some regions of India.Item Compound dry and hot extremes: a review and future research pathways for India(Elsevier, 2024-05) Guntu, RavikumarCompound Dry and Hot Extremes (CDHEs) is gaining attention compared to individual dry or hot extremes, due to their amplified impacts on both the population and ecosystems in India. This underscores the importance of transitioning from studying individual extremes to adopting a compound perspective. Despite this, investigation of CDHEs during the Indian summer monsoon remain limited, and a comprehensive review of methodologies for the investigation of CDHE is absent. This review systematically synthesizes recent literature, covering concepts of CDHE with illustrative examples, including identification, characterization, drivers, and prediction. It illustrates three widely used methods for the identification of CDHEs along with their advantages and disadvantages. Furthermore, it describes concepts with illustrative examples to investigate the characteristics (frequency, spatial extent, timing, duration, severity, and likelihood), explores drivers using event coincidence analysis and a complexity-based framework, and discusses the strengths and weaknesses of a logistic regression model for predicting the occurrence of CDHE. In light of the growing significance of CDHEs, we suggest future directions for Indian CDHE research, including an improved characterization of CDHEs across multiple temporal and spatial scales, a deep understanding of the physical mechanism, a robust evaluation of climate models, attribution and projection, and a comprehensive impact assessment. CDHEs are the new normal, and there is an urgent need to advance research on CDHEs in vulnerable regions like India to combat and mitigate their effects.Item Changing spatiotemporal dependence of the precipitation-temperature during Indian Summer Monsoon using observational and CMIP6 model simulations(Elsevier, 2025-02) Guntu, RavikumarQuantifying precipitation-temperature (P-T) dependence is essential for understanding emerging patterns of compound extremes, especially in climate-vulnerable countries like India. The present study investigates the spatiotemporal variability of P-T dependence during the Indian Summer Monsoon using observational data and CMIP6 model simulations. We evaluated the performance of CMIP6 simulations and projected changes in P-T dependence under SSP1–2.6 and SSP5–8.5 scenarios. New hydrological insight for the region Observations show spatial diversity, with strong negative associations in central, western, and coastal regions, while positive associations are prominent in the Western Ghats and northeastern regions. CMIP6 models show mixed performance in capturing the spatial patterns and temporal evolution of P-T dependence. The EC-Earth model simulations effectively replicate the observed P-T dependence. In contrast, models such as ACCESS-ESM1–5, CanESM5, and ACCESS-CM2 exhibit discrepancies when compared to observations, suggesting that their future projections should be interpreted with caution. Projections under high-emission scenarios indicate a widespread increase in P-T dependence, particularly in northern and central areas, highlighting an increased likelihood of compound extremes.