Abstract
India faced a major heat wave during the summer of 2015. Temperature anomalies peaked in the dry period before the onset of the summer monsoon, suggesting that local land-atmosphere feedbacks involving desiccated soils and vegetation might have played a role in driving the heat extreme. Upon examination of in situ data, reanalysis, satellite observations, and land surface models, we find that the heat wave included two distinct peaks: one in late May, and a second in early June. During the first peak we find that clear skies led to a positive net radiation anomaly at the surface, but there is no significant sensible heat flux anomaly within the core of the heat wave affected region. By the time of the second peak, however, soil moisture had dropped to anomalously low levels in the core heat wave region, net surface radiation was anomalously high, and a significant positive sensible heat flux anomaly developed. This led to a substantial local forcing on air temperature that contributed to the intensity of the event. The analysis indicates that the highly agricultural landscape of North and Central India can reinforce heat extremes under dry conditions.
Highlights
High temperatures are an expected condition in India during the weeks prior to onset of the monsoon
We examined the spatial and temporal pattern of the 2015 India heat wave and quantified the potential for land surface conditions to contribute to the heat extreme
We have employed a suite of models and datasets to the analysis, including meteorological station observations, reanalysis output, South Asia LDAS, a satellite based diagnostic model (ALEXI), and standard remote sensing products (MODIS)
Summary
India faced a major heat wave during the summer of 2015. Temperature anomalies peaked in the dry period before the onset of the summer monsoon, suggesting that local land-atmosphere feedbacks involving desiccated soils and vegetation might have played a role in driving the heat extreme. The fact that extreme heat events tend to come just before the onset of monsoon rains raises an interesting question about land-atmosphere interactions This is a dry time of year in much of India, and both the approach of summer solstice and the presence of typically clear skies lead to high downwelling solar radiation at the surface. We perform a detailed investigation of HW15, that is designed to: (1) define the temporal and spatial pattern of the event, since media reports of impacts do not necessarily align with the actual climate anomaly; and (2) characterize the role that surface conditions—in particular, soil moisture anomaly and associated sensible heat flux anomalies play in the onset and evolution of the event This diagnostic analysis of land-atmosphere processes complements recent studies of the predictability of HW154 and its connection to large scale atmospheric circulations[10]
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