Journal of Scientific Research and Reports

Cotton is the principal kharif cash crop of Saurashtra, yet its production is influenced by erratic rainfall and soils that differ in texture, depth, fertility and alkalinity. This study characterises the seasonal aridity of the cotton-growing period and evaluates land suitability for cotton in Amreli Taluka (83,112 ha), Gujarat, using a geographic information system. Monthly rainfall and temperature for May-January of 2000-2009 were used to compute a seasonal aridity index (SAI) using a nine-month modification of De Martonne’s formula. Land suitability was assessed with the FAO framework for land evaluation and agro-ecological zone criteria. Four thematic layers (land use, soil texture, soil fertility and soil alkalinity) were ranked, weighted using a Saaty-type pairwise scheme and combined through weighted overlay; the composite was divided into three equal-interval classes. Mean seasonal rainfall ranged from 28.8 mm (2000) to 139.0 mm (2007) per month, with about 97% of the 714.7 mm seasonal total falling from June to September. SAI ranged from 0.848 (2002) to 3.191 (2000), with a ten-year mean of 1.76, placing every year in the arid class (SAI ≤ 5). A sensitivity analysis performed here showed that this classification depends strongly on the unit of the rainfall term because using the seasonal total instead of mean monthly rainfall gave SAI values of 6.2-16.6, i.e., semi-arid in seven years and dry sub-humid in three. SAI was closely related to rainfall in the driest month (May) (r = 0.83) and not to mean seasonal rainfall (r = -0.19). Highly suitable land covered 69,341 ha (83.42%), fairly suitable land 12,424 ha (14.95%) and unsuitable land 1,347 ha (1.63%). The framework provides planners with a transparent and reproducible basis for targeting cotton and for supplemental irrigation planning in a groundwater-limited, semi-arid landscape.