Examining Spatio-Temporal Intensity-Frequency Variations in Extreme Monsoon Rainfall using High Resolution Data

Abstract:

The study of extreme events has gained the attention of hydrologists in recent times. Though these events are rare, the effects are catastrophic. It is reported that the frequency of the occurrence of these events has increased in recent decades, and is attributed to the recent revelation of climate change. Numerous studies have pointed out significant changes in extremely heavy precipitation over India, using coarse resolution data. Though there are disagreements in the results and its spatial uniformity, all these studies emphasize the need of fine resolution analysis. Fine resolution analysis is necessary mainly due to the highly heterogeneous characteristics of Indian monsoon, and for the proper employment in flood hazard preparedness and water resources management. The present study aims to analyse the spatio‑temporal variation and trends in the intensity and frequency of heavy precipitation during Indian monsoon using 0.25°×0.25° resolution gridded data for a period of 113 years (1901-2013). The exceedance threshold is fixed at 90^th percentile of rainfall over 113 years and parameters are defined accordingly. The maximum intensity of each extreme rainfall episode of 30 year moving window has been modelled using Peak Over Threshold based Extreme Value Theory to compute return level (considered for intensity). In addition, the number of such episodes in a particular year has been termed as frequency. Non-parametric Mann-Kendall test has been carried out for both intensity and frequency, to compute the statistical trend. In addition, moving block bootstrap approach has been used to incorporate the serial correlation. The significance of the trend has been evaluated at different significance levels and finally, change in trend over last century has been examined.