Projected changes in mean and extreme precipitation indices over India using PRECIS

• The projected changes depict seasonally dependent fine scale structure in response to the topographic forcing and changes in circulation, especially along the west coast and North East (NE) region of India towards the end of 21st century.
• The analysis indicates likely decrease in the frequency of rainy days and increase in the intensity of rain events towards 2080s over many parts of the India under A1B scenario.
• Changes in extreme precipitation events suggest not only the shifts, but also lengthening of the precipitation distribution with an increased probability of occurrence of the events.
• All the precipitation extreme indices excepting the CDD are projected to increase towards the end of this century.

The impact of global warming on the characteristics of mean and extremes of rainfall over India is investigated using a high resolution regional climate model PRECIS developed by Hadley Centre, UK. Five simulations of PRECIS made using the lateral boundary conditions from a suite of Perturbed Physics Ensembles (PPE) generated using Hadley Center Coupled Model (HadCM3) for Quantifying Uncertainty in Model Predictions (QUMP) project corresponding to IPCC A1B emission scenario have been analyzed here for this purpose. The projected changes depict seasonally dependent fine scale structure in response to the topographic forcing and changes in circulation, especially along the west coast and North East (NE) region of India towards the end of the 21st century i.e. 2080s (2071–2098). Analysis of the extreme precipitation indices indicates an increase in the intensity of rainfall on wet days towards 2080s under A1B scenario. Changes in extreme precipitation events and dry spells suggest not only shifts, but also a substantial increase in the spread of the precipitation distribution, with an increased probability of the occurrence of events conducive to both floods and droughts. The projected changes in various precipitation extremes show a large regional variability. Total rainfall on very heavy rainy days (R95p) is projected to increase by around 40–50% over the central parts of the country. The number of rainy days > 10 mm (R10) may increase by 10–20% over west coast, east central India and northeastern parts while over northwest and rain shadow region they may increase by 40–50%. The consecutive dry days (CDDs) may decrease by 10–20% over Indo-Gangetic plain, however over west coast there may not be any significant change. The CDDs are projected to rise by 10–20% over west central and peninsular India. The precipitation per wet day (SDII) may be more intense by 10–40% over the entire land mass, however there may not be any significant change over south peninsular India.