In the context of the heavy spells of monsoon rain, it would be most appropriate to have two scales — one for intensity and the other for magnitude — to measure rainfall. There is no scale to classify rains above a certain intensity. The term “exceptionally heavy rainfall” is too blanket a term. For example, there was a report of 82 cm of rain on a single day in the Nilgiris district which is a record in Tamil Nadu. In Kerala, there has been rain averaging 40 cm. Therefore, the present system of classification of rains should change. The ‘intensity scale’ could be formulated to judge and predict the intensity of rain in a given area and at a given period of time. Events such as cloudbursts and a very heavy downpour may be grouped under this category. The ‘magnitude’ scale could be used to record and interpret rains for a 24-hour period in a given area. There also need to be special studies to analyse cloud patterns, with predictions of ‘intensity’ and ‘magnitude’ based on these. For the ‘magnitude scale’ , in addition to the classification of low intensity rain the revisions can be on these lines: 25 cm-50 cm: ‘Extremely heavy rain’ (Category 1); 26 cm-75 cm: ‘Extremely heavy rain’ (Category 2); 76 cm-100 cm: ‘Extremely heavy rain’ (Category 3); Above 100 cm: ‘Extremely heavy rain’ (Category 4). In the ‘intensity scale’ over a short period (less than five hours), the scale could be: 0.1 to 5 cm: ‘Moderate’; 5 to 9 cm: ‘Intense (warning); 10 cm: ‘Cloudburst’ (Take action – disaster); 10.1 to 15 cm: ‘Floods, flash floods’ (Heavily disastrous); 15.1 to 20 cm: ‘Devastation’; 20 to 30 cm: ‘Devastation on a large scale’; Above 25 cm: ‘Unimaginable consequences’.
A. Rajagopal Kamat, Malaparamba, Kozhikode, Kerala