On the relationship between the premonsoonal rainfall climatology and urban land cover dynamics in Kolkata city, India

摘要

Empirical and modelling studies show that urbanization can have an impact on the environment. Relatively few studies have investigated urban effects on precipitation in India or other developing countries experiencing rapid urbanization. Furthermore, most precipitation-related studies for India focus on monsoonal rainfall. However, premonsoonal periods (March-May) account for 12-14% of the annual cumulative rainfall in eastern India. The majority of premonsoonal rainfall (PMR) is convective and caused by mesoscale forcing, which may include urban effects. In this study, the area under scrutiny is a large urban area in eastern India, Kolkata city. Herein, our goal was to (1) produce a comprehensive characterization of historical land cover dynamics associated with the Kolkata megalopolis, (2) provide a spatio-temporal climatology of PMR in the Kolkata region, and (3) identify possible associations between Kolkata's land cover and PMR. The analysis shows that the rate of change of urban land cover has increased by 50% compared to the period prior to India's independence in 1947. A multi-scalar time series analysis with Mann-Kendall statistics indicated statistically significant increasing trends in rainfall over the last 50 years for two Kolkata stations and a nearby downwind station. Furthermore, there was no significant trend for cumulative PMR in less urbanized stations, the country of India, or the East Gangetic region. This finding suggests that the anomaly of the three stations, showing increasing trends in PMR, could be the effect of urban land cover change.