Assessment of chill units accumulation and apple productivity under changing climatic conditions in high hill temperate wet zone of North-Western Himalayas

Investigations were carried out during 2014–15 in high hill temperate wet zone of Himachal Pradesh to assess chilling trends and its effect on apple productivity using UTAH model for the period of 1986 to 2015. Results indicated a decreasing trend of the order of 11.40 chill units per year. Chill units (CU) for the last three decades i.e. 1986–1995, 1996–2005 and 2006–2015 also revealed a decreasing trend of the order of 119.30 CU decrease per decades as per the regression equation y =-119.30 x + 1249. Monthly accumulation of chill unit hours during the period for each winter month (November, December, January and February) revealed maximum decrease of 6.24 chill unit (CU) per year was observed for the month of November. Trend analysis of last five years 2011–2015 showed there was a decrease of 2.92 chill units per year as per regression equation y =-2.92x + 1058. Data on apple productivity in Shimla district during last twenty five years (1988–2014) revealed an increasing trend as per the regression equation y = 0.146x + 5.565. Overall there was a decreasing trend of chill units accumulation during the scenario in the Shimla district which indicates that climatic conditions might become unfavorable in coming years for cultivation of apple. This may leads to shift in apple belt to higher altitude in the region so as to accumulate required chill units