Orissa is fortunate to have abundant water resources both in surface and ground water, compared to its size and population. The water resource of Orissa is dependent on rainfall. Though, it is fairly adequate, it is unevenly distributed both spatially and temporarily. The distribution of rain fall is shown as Annual Isohytes in Map No-1. The term average annual rainfall is 1482 mm. The monthly average rainfall distribution is shown in the following table.

The major part of rainfall i.e. about 80% is received from southwest monsoon during June to September, while 20% of the precipitation is spread across the other eight months. After the rainfall, a part is lost by evaporation, transpiration and deep percolation. Some part is stored as ground water resource and balance flows down to sea as surface runoff. During monsoon, there are very wet days and also long dry spells. In some years both the extreme events like flood and drought occur. However, floods have become a recurring phenomenon occurring at regular intervals.

Surface water resource and River Basins:

Brahmani starts at Panposh in Orissa

Inflow of Individual Basins (Present Scenario 2001) Unit: million m3