We spoke of water-stressed and water-abundant areas in the earlier two parts. But do you know what constitutes ‘less’ rain and how much is ‘more’?

Let us have some fun with numbers today.

To start with, do you know what is the Normal Annual Rainfall that India receives? It is 1182.8 mm.

But, in general, the rainfall over India has a large spatial as well as temporal variability. In simple terms, not all areas across India receive similar rainfall, not even in same months. Let us see how.

The mean South-West Monsoon (i.e., June, July, August & September) rainfall is 877.2 mm. It contributes a whopping 74.2% of the annual rainfall (1182.8 mm). Contribution of pre-monsoon (March, April & May) rainfall and post-monsoon (October, November & December) rainfall in annual rainfall is mostly the same (11%).

During the SW monsoon months, the mean monthly rainfall during July (286.5 mm) is highest and contributes about 24.2% of annual rainfall while the mean rainfall during August is slightly lower and contributes about 21.2% of annual rainfall. June and September rainfall are almost similar and contribute 13.8% and 14.2% of annual rainfall, respectively.

Now, let us see the state wise variations. Look at the map in the above image (Sorry for the old map!!). One state i.e., Rajasthan receives annual rainfall between 250 – 500 mm (the least), seven states between 500 mm – 1000 mm, as many as 16 states receive rainfall between 1000 – 2000 mm, three states between 2000-3000 mm and six states more than 3000 mm in a year.

As is evident, the rainfall varies from state to state, place to place. The geographical diversity owes a lot to this rainfall pattern.

---- to be continued