Long-term Rainfall Analysis towards Detection of Meteorological Drought over Kozhikode District of Kerala

摘要

This study was carried out with the objective of identifying the trends in season, annual rainfall and occurrence of drought events using different statistical methods for the period of 110 years for Kozhikode district of Kerala, India. The results showed that the average annual rainfall of Kozhikode is 3177 mm with the standard deviation of 551.7 mm. The coefficient of variation confirmed that annual rainfall has very low inter annual variability, but the seasonal variability is high. Trend analysis results revealed that the rainfall is decreasing in Southwest Monsoon, Northeast Monsoon and Winter Season while increasing trend was observed in Summer Season. To understand the variation due to climate change, the time scales were divided into two (viz., 1902-1956 and 1957-2012), and trend analysis were carried out. The results showed that the Southwest Monsoon indicated a decreasing trend in both time scales; however substantial decreasing trend was observed for the recent decade i.e. 1957-2012 indicating the climatic variability. Precipitation Concentration Index (PCI) analysis showed that, among the 110 years, 57 years are coming under the classification of strong irregularity in the rainfall (PCI > 20) and the remaining years falls under the class of irregular precipitation with the PCI value 15-20. Drought indices were characterized using Rainfall Anomaly Index, Departure Analysis of Rainfall, Deciles, and Standardized Precipitation Index and the occurrence of drought events were identified. The wavelet analysis clearly showed noticeable change in the rainfall pattern after 1950 and indicating the impact of climate change. Findings from such studies are useful tools for policy makers to devise strategic management plans to overcome droughts and mitigate their effects on the activities in different sectors of the Kerala State.