Cyclic Fluctuations in the Flood Area and Relationship with the Double (Hale) Sunspot Cycle

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  • 1 Indian Institute of Tropical Meteorology, Pune-411 005, India
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Abstract

An objective numerical index has been used to obtain, on the dryness side, the family of Drought Area Indices (DAI) and on the wetness side, the family of Flood Area Indices (FAI) for India for the period 1891–1979. Three series of the DAI family are the percentage areas of India corresponding to mean monsoon index for a given year: ≤ −1 (mild drought or worse), ≤ −2 (moderate drought or worse), and ≤ −3 (severe drought or worse). Likewise, on the wetness side, three series of the FAI family are the percentage areas of India corresponding to mean monsoon index for a given year: ≥ +1 (mild flood or worse), ≥ +2 (moderate flood or worse), and ≥ +2 (severe flood or worse). Power spectrum analysis of the DAI series shows a high-frequency peak which is probably associated with the quasi-biennial oscillation. Spectrum and cross-spectrum analysis of the FAI series and sunspot numbers of the double (Hale) sunspot cycle reveal that a highly significant ∼22-year cycle in the FAI is nearly in phase with the double sunspot cycle and that they are interrelated. Harmonic dial analysis shows that all of the large-scale flood events over India occurred consistently in the major sunspot cycle, suggesting an association of large-scale flood recurrence over India with the double sunspot cycle. The strong evidence of the relationship between areal extent of flood over India and the double sunspot cycle reported here shares in the kind of relationship reported for the western United States, but in the opposite sense of weather characteristics, i.e., for flood rather than drought.

Abstract

An objective numerical index has been used to obtain, on the dryness side, the family of Drought Area Indices (DAI) and on the wetness side, the family of Flood Area Indices (FAI) for India for the period 1891–1979. Three series of the DAI family are the percentage areas of India corresponding to mean monsoon index for a given year: ≤ −1 (mild drought or worse), ≤ −2 (moderate drought or worse), and ≤ −3 (severe drought or worse). Likewise, on the wetness side, three series of the FAI family are the percentage areas of India corresponding to mean monsoon index for a given year: ≥ +1 (mild flood or worse), ≥ +2 (moderate flood or worse), and ≥ +2 (severe flood or worse). Power spectrum analysis of the DAI series shows a high-frequency peak which is probably associated with the quasi-biennial oscillation. Spectrum and cross-spectrum analysis of the FAI series and sunspot numbers of the double (Hale) sunspot cycle reveal that a highly significant ∼22-year cycle in the FAI is nearly in phase with the double sunspot cycle and that they are interrelated. Harmonic dial analysis shows that all of the large-scale flood events over India occurred consistently in the major sunspot cycle, suggesting an association of large-scale flood recurrence over India with the double sunspot cycle. The strong evidence of the relationship between areal extent of flood over India and the double sunspot cycle reported here shares in the kind of relationship reported for the western United States, but in the opposite sense of weather characteristics, i.e., for flood rather than drought.

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