Solar activity and extreme rainfall over Kerala, India

Abstract: This paper examines the relationship between solar activity and extreme rainfall events in Kerala, India. Kerala receives minimum and maximum rainfall during winter and monsoon seasons. Sunspot number, F10.7 Index, and cosmic ray intensity are the solar indices considered, and their variations with rainfall are studied over 57 years (1965-2021), i.e., starting from Solar Cycle 20. Correlative studies are performed for each solar cycle, and correlation coefficients are calculated. We find that rainfall in Kerala is correlated with sunspot activity but with varying degrees of significance. During Solar Cycle 21, rainfall and solar activity are correlated with high significance during both winter and monsoon seasons. The variation of different solar indices with rainfall is studied. The winter season showed a better link between the sun and rainfall than the monsoon season. The years with rainfall surplus and deficiency are calculated and compared with the solar indices. {We find that the years with rainfall excess and deficit mainly occur in the years around solar maximum or minimum (within $\pm$2 years).} We hypothesize a physical relationship between solar activity and extreme rainfall events in Kerala that contributes to their predictability.