Cloud Aerosol Interaction and Precipitation Enhancement (CAIPEEX)

Rain Enhancement Techniques Conducted in India

A multi-year research observational campaign entitled, “Cloud Aerosol Interaction and Precipitation Enhancement (CAIPEEX)” was conducted by the Indian Institute of Tropical Meteorology (IITM), Pune during the period 2009-2011 over different parts of the country.

The objectives of the program were:

(1) to understand the role of aerosols in the rainfall processes in the clouds

(2) to carry out cloud seeding experiments in research mode for rain enhancements using modern techniques.

During the period May to September 2009, the cloud and aerosol observations were conducted over different parts of country using instrumented aircraft Total 220 hrs of flying was done. In the monsoon and post-monsoon seasons of 2010 and 2011, the cloud seeding experiments were conducted over the rain-shadow areas of peninsular India from Hyderabad base. Total 200 and 250 hours of flying was done in the years 2010 and 2011 respectively.

Modern techniques such as

(1) hired instrumented aircraft for measuring the atmospheric state parameters, aerosols and cloud microphysical parameters

(2) equipped for seeding by flares and salt powder,

3) radar for monitoring the potential clouds,

(4) pilot to ground connectivity and internet connectivity for real time transfer of data,

(5) half hourly INSAT satellite data, weather data from IMD sites

(6) high resolution weather models for the forecasting etc., were used in the program.

The Indian rainfall shows different types of trends over different regions and over different time periods. The studies carried out so far have suggested that there is increasing trend in the extreme rainfall events (>10cm/day) and decreasing trend in the moderate (2-5cm/day) and low rainfall events (<2cm/day) over central India. It is also established that there is approximately a natural 30-year cyclicity in the monsoon rainfall. Under such a decreasing phase of monsoon rainfall that is persisting for the recent three and half decades, a decreasing trend of monsoon rainfall is also persisting.

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Additionally, the factors like global warming and increasing loading of aerosols over India have established potential to modulate the natural rainfall variability to certain extent as a part of short term variability.

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