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Observed changes in extreme wet and dry spells during the South Asian summer monsoon season


The South Asian summer monsoon directly affects the lives of more than 1/6th of the world’s population. There is substantial variability within the monsoon season, including fluctuations between periods of heavy rainfall (wet spells) and low rainfall (dry spells)1. These fluctuations can cause extreme wet and dry regional conditions that adversely impact agricultural yields, water resources, infrastructure and human systems2,3. Through a comprehensive statistical analysis of precipitation observations (1951–2011), we show that statistically significant decreases in peak-season precipitation over the core-monsoon region have co-occurred with statistically significant increases in daily-scale precipitation variability. Further, we find statistically significant increases in the frequency of dry spells and intensity of wet spells, and statistically significant decreases in the intensity of dry spells. These changes in extreme wet and dry spell characteristics are supported by increases in convective available potential energy and low-level moisture convergence, along with changes to the large-scale circulation aloft in the atmosphere. The observed changes in wet and dry extremes during the monsoon season are relevant for managing climate-related risks, with particular relevance for water resources, agriculture, disaster preparedness and infrastructure planning.

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Figure 1: July–August precipitation characteristics.
Figure 2: Extreme wet and dry spell characteristics.
Figure 3: Dynamics of extreme wet and dry spells.
Figure 4: Sensitivity of statistical results to spatial domain.

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We thank the Indian Meteorological Department (IMD) and the APHRODITE (Asian Precipitation-Highly Resolved Observational Data Integration towards the Evaluation of Water Resources) project members for making the daily rainfall gridded data sets available. This work was supported in part by National Science Foundation Grant 0955283 to N.S.D. B.R. was supported in part by the National Science Foundation under Grant Nos DMS-CMG 1025465, AGS-1003823 and DMS-1106642, AFOSR Grant FA9550-13-1-0043, and the UPS Foundation Fund.

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D.S., B.R. and N.S.D. conceived and designed the study; D.S. and M.T. implemented the analytical tools; B.R. developed and supervised the statistical analyses; and D.S., M.T. and N.S.D. analysed the data and co-wrote the manuscript. All authors discussed the results and commented on the draft.

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Correspondence to Deepti Singh.

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Singh, D., Tsiang, M., Rajaratnam, B. et al. Observed changes in extreme wet and dry spells during the South Asian summer monsoon season. Nature Clim Change 4, 456–461 (2014).

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