Spatio-temporal analysis of rainfall pattern in the Western Ghats region of India

Abstract

This paper investigates the rainfall pattern and its distribution, which is one of the key drivers for the water availability in the Western Ghats region of India. The daily precipitation data from 1901 to 2014 were investigated to understand the rainfall pattern and its variability. The study area has been divided as southern, coastal, central, and northern regions and rainfall amount into 0.2–10 mm, 10–20 mm, and > 50 mm classes. The trends in the annual rainfall, number of rainy days, and various classes within these regions have been investigated. The mean annual rainfall varies between 4000 mm in the coastal areas and greater than 6000 mm at the mountain crest. The Mann–Kendall test indicates significant decrease of annual rainfall, at 5% significance level in central and coastal region. On Contrary, the coastal region recorded significant decrease in the number of rainy days at 5% significance level. An increasing trend in the number of rainy days has been observed in the northern region. No significant trends have been detected in the southern region. A decreasing trend has been detected in the number of rainy days in the rainfall class with 10–20 mm in coastal region. Similarly a significant decrease of rainy days was observed in > 50 mm rainfall class both in the southern and northern regions. The change point probability and homogeneity test indicates that there is a significant increase in rainfall in few stations under the northern region and similarly decrease in the rainfall in central region during the decade of 1970 and normally the rainfall has been homogeneous in the study area. From the precipitation concentration analysis found that Mysore, Kodagu, and adjoining areas are influenced by the bi-modal rainfall, receiving the rainfall during both south–west and north–east monsoons. This analysis helps to understand the spatial variability of rainfall in the Western Ghats of India, which depict mixed trends in the quantum of rainfall and decreasing trend of rainy days across various rainfall classes. These changes detected in the historical rainfall, both in its occurrence and quantum will have significant bearing on the water availability scenario in the Western Ghats region.