Impact of Climate Change on The Heavy Rainfall Events During June to September Over Kerala (1901–2019)

Heavy rainfall (≥ 100 mm or HR) events and moderate rainfall (≥ 5 mm to 100 mm or MR) events over Kerala for June–September were analysed statistically to understand the influence of climate change in MR and HR events for the period 1901–2019 and its two different parts; 1901–1970 and 1971–2019. Most parts of coastal Kerala receive more than 50 HR events/season except the southernmost parts which receive 40–50 HR events/season. Significant negative trend was observed for MR (99%) and HR (95%) events for the entire period of 1901–2019. The total seasonal rainfall averaged over Kerala also showed significant negative trend during the entire period of 1901–2019. In dekad (10 days period) wise trend analysis for MR events during July and August, third dekad of July (21–31 July) showed significant negative trend for the entire period (99%), second dekad of August (11–20 August) showed significant negative trend (95%) for the second part of the data period. In case of HR events, first and third dekads of July (1–10 July; 21–31 July) showed significant negative trends (95% and 99.9% respectively) for the entire data period. The third dekad of July (21–31 July) showed significant negative trend (95%) for the first part of the data period (1901–1970) while the third dekad of July (21–31 July) showed significant negative trend (95%) for second part (1970–2019). First dekad of August (1–10 August) showed significant increasing trend (95%) for the second part of the data period exhibiting its peak in 2019 with 127 HR events. Both MR and HR events frequency during the entire data period was seen to be significantly decreasing (99% and 95%) over the entire Kerala. HR events frequency over few grids of eastern part of the state showed significant increase in the second part of the data period (1971–2019), where Kerala recently experienced exceptionally heavy rainfall spells of shorter durations and landslides.