Abstract
Heatwaves are often driven by subtropical persistent highs and quasi-stationary Rossby waves along with regional factors such as soil moisture. Both temperature and humidity variability play an important role in the regional heatwave patterns. Studies have differentiated the dry and moist heatwave-related extremes both in terms of their driving mechanism and in their impact on human health. With the observed increase in the intensity, frequency and duration of heatwaves in recent decades, the impact-based forecasting and monitoring (IBF) of heatwaves has assumed significance. Current operational IBF indices, especially over the Indian region are empirical and do not necessarily consider the modal dynamics or their role in the impact of dry and moist heat-related discomfort. In this study, based on two large-scale intraseasonal modes of summer temperature variability, the driving mechanisms of dry and moist heat extremes over the Indian region are identified. The regional scale impact identified based on the Heat Index is driven by these two large-scale modes. The first mode represents the conditions conducive for the formation of the dry heat extremes. The second mode represents the regional circulation pattern that supports the moisture inflow towards the coastal states. This inflow combined with the modal temperature pattern drives the moist heat extremes over India. Based on the location of the principal components of these modes in the phase space, the heat-related health risk associated with the dominant modes is assessed. Warnings for different phases of dry and moist heat extremes occurring over the Indian region are also proposed for operational use.
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Data availability
All the input datasets used for the analysis are freely available as mentioned in Section 2. Any computed data/ codes used to generate the plots will be made available on request.
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Acknowledgements
LS acknowledge the research fellowship support from MRFP Project, Ministry of Earth Sciences (MoES), Govt. of India. Authors acknowledge, Head CRS (IMD) for the support. Research support from Indian Institute of Tropical Meteorology (IITM), an autonomous institute under MoES, and India Meteorological Department (IMD) is acknowledged. All the computations and plots are carried out using the NCL-NCAR subroutines and Python packages.
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S, L., Chattopadhyay, R. & Pai, D.S. Attribution of subseasonal temperature modes as the drivers of dry and moist heat discomfort for the heat hazard monitoring over the Indian region. Clim Dyn (2024). https://doi.org/10.1007/s00382-024-07236-9
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DOI: https://doi.org/10.1007/s00382-024-07236-9