Rainfall enhancement in Karnataka state cloud seeding program “Varshadhare” 2017

Abstract

Operational cloud seeding program was conducted in the Karnataka State, India during 21 August to 7 November 2017 with robust, pre-established experimental design plan following the guidelines developed under Indian national CAIPEEX program. Hygroscopic and glaciogenic seeding were carried out using areal method. A very high resolution raingauge network (spatial resolution: 5 km, temporal resolution: 15 min) was used to measure the surface rainfall. Two approaches have been used for estimating the enhancement: (i) Rainfalls within 4-h after seeding was compared at station levels with the rainfalls prior to seeding. The analysis of 618 cases showed average enhancement of 27.9% above the natural rainfall. (ii) The floating control-target area rainfall analysis was used to estimate the natural rainfall that would have occurred without seeding. For understanding maximum absolute increase in the rainfall, 7 cases in the top 5% which were well distributed within seeding period (with 4 hygroscopic and 3 glaciogenic cases) have been analyzed. The maximum increase in rainfalls in hygroscopic/glaciogenic cases were 20.8/28.1 mm which are ~5/7 times higher than the mean daily rainfall (4.3 mm) during September–October. Additional water made available due to seeding has been estimated to be 2.1 TMC. The study showed that seeding became effective in increasing rainfall under the particular dynamic and thermodynamical conditions. This is a unique study to estimate the effect of operational cloud seeding in (i) enhancement of precipitation and (ii) availability of additional water. The results of the study may find basis for the operational programs in the world.