On the comparison of Precipitation Gauges

Abstract

In order to assess the reliability of rainfall measurements made in India, comparisons between raingauges in routine use in the national network and raingauges adopted by WMO as International Reference Precipitation Gauges (IRPG) were organised at Poona, Bombay, New Delhi, Calcutta, N 9gpur and Madras for a period of 16-28 months spread over the three years 1963-1965. The differences between the 24-hour rainfalls recorded by the IRPG and I.M.D. gauges vary between 0.3 and 2.4 per cent. The differences between these gauges at Madras, Bombay and Calcutta are statistically insignificant, while the differences between the corresponding values at the other stations as well as for all the stations combined are statistically significant. However, the differences between the 24.hour rainfalls recorded by two I.M.D. gauges vary between 0.4 and 1 per cent while the differences between two IRPG's are smaller and insignificant. All differences are insignificant above a daily fall of 25 mm. Hence one is led to conclude that the national gauges of Indi8 need a small positive correction of 1 per cent to bring them to the IRPG value. A description of the various rain gauges and details of their installation are included for the benefit of those who are not familiar with these details.