Statistical analysis of urban regional pre-monsoon rainfall in and around Kolkata, India

Abstract

The present study aims at statistical analysis of pre-monsoon rainfall at Kolkata, India over a span of 45 yr (1970–2014) with special emphasis on the effect of urbanisation on pre-monsoon rainfall at Alipore, a core area of Kolkata (22 ∘ 34 ′ N ; 88 ∘ 24 ′ E) India, where the urbanisation is almost static during the period 1970–2014 and Dumdum (22 ∘ 65 ′ N ; 88 ∘ 45 ′ E), the outer periphery of Kolkata, where the urbanisation is still an ongoing process. As pre-monsoon rainfall is an effect of mesoscale convective development (horizontal dimensions 5–500 km), the two stations namely Dumdum and Alipore which are nearly 22 km apart from each other are taken into consideration in this study. To determine the possible changes in the pre-monsoon rainfall in both stations, a non-parametric Wilcoxon Signed Rank Sum test is conducted. This test reveals that the annual average pre-monsoon rainfall increased at Dumdum in post-urbanisation period, i.e., 1991–2014 compared to Alipore during the same period. It is important to note that the result of statistical analysis almost tallies with that of the geographical one.