The vegetation and waterlogging dynamics as derived from spaceborne multispectral and multitemporal data

Poor water management coupled with inadequate drainage in the irrigated commands of the arid and semi-arid regions leads to waterlogging and subsequent salinization and alkalization. Space-borne multispectral data have been found to be extremely useful in deriving information on salt-affected soils and waterlogged areas. The study, reported here, aims at delineating and monitoring the extent of waterlogged areas and vegetation cover in part of the Indira Gandhi Canal command area, Rajasthan State, Western India, during the period 1975 to 1995 using Landsat Multi-Spectral Scanner (MSS) and Thematic Mapper (TM), and the Indian Remote Sensing Satellite (IRS-1A) Linear Imaging Self-scanning Sensor (LISS-I) data. Vegetation condition was assessed by generating the Normalized Difference Vegetation Index (NDVI ) from multispectral digital data whereas waterlogged areas were delineated through a systematic visual interpretation approach. An objective comparison of the temporal NDVI images has revealed two striking phenomena: (i) the areas which were non-vegetated during 1975 were found supporting more and more vegetation especially crops in successive years due to introduction of canal irrigation; and (ii) the palaeochannel (old river course) which supported very good crops during 1975 gradually became waterlogged during the 20 year period thereby resulting in the extinction of croplands therein. The detailed methodology and observations made are reported in the article.