Temporal analysis of rainfall (1871-2012) and drought characteristics over a tropical monsoon-dominated State (Kerala) of India

- We analyzed rainfall for 141 years to identify rainfall trends and drought pattern.
- Decreasing trend in southwest monsoon rainfall, while increasing for other seasons.
- Irregularity in rainfall distribution at annual and seasonal scales is declining.
- Drought pattern is related with rainfall trends as well as rainfall concentration.

SummaryThe climate of Kerala is controlled by the monsoon, and the analysis of rainfall and drought scenario, for a period of 141 years (1871-72 to 2011-12), reveals a decreasing trend in southwest monsoon, and increasing trends for post-monsoon-, winter- and pre-monsoon-rainfall. The inconsistent periodicity (2-8 years) of annual- and seasonal-rainfall agrees with the periodicity of El-Nino Southern Oscillation (ENSO). The annual rainfall shows an irregular distribution, and is concentrated roughly in half of the year, which is due to the monsoon-driven climatic seasonality. The rainfall concentration at annual-, southwest monsoon-, and winter-scales exhibits significant decreasing trends, implying decline in the degree of irregularity in annual- and seasonal-rainfall. Temporal distribution as well as severity of the drought events have been analyzed using various drought indicators. The drought pattern is not only related to the rainfall trends, but also to the rainfall concentration (or monthly rainfall heterogeneity). The decreasing rainfall during southwest monsoon contributes to short-term meteorological droughts, which have serious implications on the agricultural sector and water resources of Kerala, while the increasing rainfall during other seasons helps to reduce the drought severity.