Trend analysis of long term weather parameters over Indian Sundarbans

Abstract

Sundarbans in West Bengal of India by virtue of its strategic location in the Eastern coast on the Bay of Bengal falls in the most vulnerable zones of abrupt climate change. Temporal trends of weather parameters of Canning Town (22o18'52'' N Latitude, 88o39'45'' E Longitude, elevation 10 m msl) representing Indian Sundarbans were analysed by non-parametric Mann-Kendall test and Sen’s slope approaches. Analysis of long term rainfall data (1966-2014) indicated that Canning receives a mean annual rainfall of 1818.5 mm (±344.8 mm) with a considerable variation (CV = 18.95%). Out of 49 years rainfall data, 35 years received normal (within LPA±CV), 6 years received deficit (25-43%) and 8 years received excess rainfall (35-19%) and results revealed that total annual rainfall trend decreased non-significantly at the rate of 1.00 mm/year. On an average 84 rainy days in a year was recorded in the region, where as during last ten years (2005-2014), the number of rainy days was reduced to 78.8 days/year. Contribution of monsoon months (JJAS) declined marginally at the rate of 0.60 mm, while pre (MAM) and post-monsoon (ONDJF) months increased non-significantly at an annual rate of 0.47 mm and 0.28 mm, respectively. Maximum temperature reflected marginal rising trend in eight months from May to November and February and decreasing trend during December, January, March and April, whereas minimum temperature manifested rising trend during March-November and decreasing trend during December-February. Bright sunshine hours declined significantly at an annual rate of 0.05 hours/year. Reference crop evapotranspiration (ET0) calculated using FAO Penman-Monteith method revealed that annual ET0 significantly decreased at the rate of 5.60 mm/year, which may be due to gradual decline in bright sunshine hours in the region. Pre and post-monsoon rainfall meet the 46 and 53% of crop evapotranspiration demand. There was 2.8 times surplus rainfall than crop evapotranspiration during monsoon months indicating very high scope of water harvesting to tackle water logging during the monsoon season and unavailability of fresh water for irrigation during lean season.