Karnataka, located mainly on the Deccan Plateau, is the less irrigated state in South India, with the most arid climate (rainfall is lower than 800 mm per annum), except for the coast and the Ghats which are well watered (2 500 mm/year).

The densely irrigated zones (green spots on the map) result all, in Karnataka, from large dams, built for the majority since 1950, and from long perennial canals that distribute water to wide areas. Thus, close to Belgaum, in the South of Bijapur and close to Hospet, one can see the influence of, respectively, the dams called Hidkal (see for example the site [waterresources.kar.nic.in/belgaum.htm] presenting the various dams of Belgaum district), Narayampur and Tungabhadra. The canals on left and right bank of Tungabhadra, built in 1963, are among the longest of South India, measuring 226 and 349 km (it is surprising besides that the percentage of irrigated lands does not form a continuous zone along these canals). Close to Shimoga, several dams were built, explaining the scattering of irrigated lands. In the South, along Cauvery, the irrigated zones mainly depend on the dam Krishna Raja Sagar built at the time of the maharaja of Mysore (1932).

A clear difference is observed between the drier North of Karnataka which depends essentially on a rainfed agriculture and the South where the famous Indian "tanks" are very numerous. A tank (kere in Kannada, eri in Tamil, gantu in Telugu) is a technique, many centuries old, which consists in a storage-reservoir dammed up on three sides, supplied either by run-off and rainwater, or by the surplus of tanks located upstream, or by a canal which derives water from a river. A tank stores water only during 4 to 6 months of the year, which limits the irrigation to this period. However, it has the advantage of recharging the aquifers. The size of the tanks is variable - from a few hectares to 40 sq km - but the majority can be managed on a village scale. In Karnataka, most of the 40 000 tanks are small, of a surface lower than 20 hectares.

O.A.