- In India, the regional and seasonal distribution of rainfall is uneven. On the one hand, Jaislamer receives less than 9 cm of annual rainfall and on the other hand, Mawsynram, near Cherapunji, receives more than 1140 cm of annual rainfall. Similarly, most of the rainfall in India is received in the months of June, July, August and September.
- Generally, variations in the amount of rainfall are found more in the regions where the rainfall is uneven and less and these regions are more affected by droughts.
- Drought is an abnormally long dry season, which creates a clear imbalance in the availability of water. both, the vagaries of monsoon and dominant factor, which cause drought and drought like conditions.
- The irrigation commission, on the basis of the amount of rainfall and its variability, has divided the drought affected areas into two types:
- Drought Areas: Drought areas have annual rainfall less than 50 cm and variability is more than 25%. Under these areas are included the western Rajasthan, Saurashtra and Katchchar regions.
- Drought-prone areas: Drought-prone areas are the regions where average annual rainfall is less than 75 cm and its negative variability is more than 25%. It includes Gujarat, Rajasthan, Punjab, Haryana, Western Uttar Pradesh, Western Madhya Pradesh, Central Maharastra, internal Karnataka, Rayalsima, Southern Telangana, certain parts of Tamil Nadu, Palamau in Jharkhand, etc.
- When the streams spread their waters in the adjacent areas after cutting their banks, the conditions is called flood. Its main causing factor is excessive rainfall in the water catchment area of the rivers.
- Flood conditions are observed in the coastal areas due to cyclonic rainfall. Flood like situations called ‘flash floods’ are observed sometimes even in dry regions like Rajasthan due to cloudburst. Through, the main reason for floods is monsoon, but situations of river basins, changing of river courses, excessive cutting of trees in the hill slopes, etc. are other factors responsible for floods.
- Areas of Maximum Frequency: The areas where floods occur every year. It includes the Brahmaputra valley, lower Ganga valley, delta regions of Godavari, Krishna, Mahandi and Kaveri and the basins of rivers like Gandak, Kosi, etc.
- Areas of Medium Frequency: These areas are affected by floods in five or less years. Most of the flood-affected areas of India are included in it.
- Areas of Minimum Frequency: These are the areas receiving less rainfall. But, in these areas flood conditions are observed due to sudden cloud burst or improper water drainage system in five or more years.