Rainfall Pattern Analysis in the Three Major Valley Systems of Bengaluru

Abstract

Bengaluru has three major valley systems, i.e., Vrishabhavathi Valley (V-Valley), Hebbal Valley and Kormangala-Challaghatta Valley (K-C Valley) which are the repositories of many lakes. Due to the increasing population, urbanization and industrialization, the lakes and their drainage areas are being encroached. Bengaluru is facing the problem of flooding. Hence, the rainfall analysis is very important to understand the rainfall pattern, trend as well as its quantity. Rainfall analysis helps to predict urban floods. In the present study, the Taluk level station rainfall data was collected from Karnataka State Natural Disaster Monitoring Cell (KSNDMC) for the period of 50 years from 1971 to 2020 and the same was analyzed for monthly, seasonal and annual periods using the Thiessen polygon method. Based on the monthly rainfall analysis carried out in the valley systems, it is observed that the highest rainfall occurs during the month of September, i.e., nearly 20% of the total annual rainfall, whereas the January month contributes the least amount of rainfall. Based on the seasonal rainfall analysis, it is known that the South-West Monsoon contributes to the highest percentage of rainfall when compared to other two season. The South-West Monsoon contributed to nearly 54.7%, 55% and 55.4% of the total annual rainfall in the Hebbal Valley, K-C Valley and Vrishabhavathi Valley respectively. The normal average annual rainfall is observed to be 830.1mm, 890.2mm and 1002.2mm respectively for Hebbal Valley, K-C Valley and Vrishabhavathi Valley when calculated from the past 50 years data (1971 to 2020). Hebbal Valley has received a lowest rainfall of 455mm during 2012 and Vrishabhavathi Valley has recorded the highest rainfall of 1556.2mm during 2005. When analyzed annually, it was observed that the highest rainfall of 1321.2 mm (2005) and lowest rainfall of 455mm (2012) was recorded in the Hebbal Valley. In the K-C Valley, the maximum rainfall observed was 1225.3mm (2004) and the minimum rainfall of 623.9mm was observed (1985). In the Vrishabhavathi Valley, the highest rainfall of 1556.2mm (2005) was recorded and the least rainfall of 551.3mm (2012) was recorded. Since all the valleys are located spatially adjacent to each other, they experience similar kinds of monthly and seasonal rainfall pattern. The rainfall pattern in the three valleys shows an increasing trend.