Why cannot the advance of the southwest monsoon be measured only by calendar date?

Correct answer: Because indicators like rainfall, wind direction, humidity and cloudiness are also needed

The advance of the southwest monsoon is a weather process, not merely a date written on a calendar. Meteorologists look for a sustained change in several conditions, including rainfall over an area, the direction and strength of winds, moisture in the air, cloud development, and related atmospheric patterns. A single shower may result from a local disturbance and does not necessarily mean that the monsoon has arrived. The date of onset can also vary from year to year and from one part of India to another. Therefore, observation of weather indicators is essential.

Option C is correct because it lists the types of evidence used to identify monsoon onset. Option A is the opposite of reality, since the monsoon does not reach all India on one identical day every year. A calendar does contain seasonal dates, so option B is false. India does have weather stations, making option D incorrect. The correct approach is to combine the date with actual atmospheric observations rather than relying on the date alone.