Investigation of trends and its magnitude by non-parameteric Mann-Kendall and Sen's slope methods

Abstract

Present study aims to determine trends and inconsistency in the magnitude of annual and seasonal rainfall using Mann-Kendall and Sen's slope non-parametric analyses. The rainfall data used in this study includes 35 years of monthly rainfall at eight rain gauge stations of Bharathapuzha catchment, Kerala. Mann Kendall analysis revealed that, out of eight stations only 25% of stations showed a positive trend in annual and south-west monsoon rainfall. And all stations showed a positive trend for pre-monsoon, while only 37.5% of stations showed a positive trend in north-east monsoon. From Sen's analysis, it was observed a decrement of 32.67 mm/yr and 23.87 mm/yr in annual and south-west monsoon in Eland. A decrement of 15.79 mm/yr was observed in Pazhaynur Seed for south-west season, while 5 mm/yr for annual monsoon. At Pokkunni an increment of 16.30 mm/yr was observed for annual and 9.33 mm/yr increment for south-west monsoon. A decrement of 6.55 mm/yr and 1.88 mm/yr was observed respectively at Walayar for annual and southwest monsoon. An overall trend analyses reflect increasing trend in the east and more decreasing trend in the south and west compared to north of the catchment.