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Sikkim - Climate

The climate of this state varies with the altitudes. The upper region is extremely cold but the southern part's weather is humid, similar to neighbouring state West Bengal. The climate of the state varies from cold temperate and alpine in northeast to subtropical in the south. Rainfall is heavy and well distributed during the months from May to early October. July is the wettest month in most of the places. The intensity of rainfall during south-west monsoon season decreases from south to north, while the ditribution of winter rainfall is in the opposite order. The maximum temperature is recorded usually during july and August, and the minimum during December and January.

Altitude variation across Sikkim, is the main factor controlling climate and weather conditions. Relief features such as high mountains act as barriers for the movement of the Monsoon winds. Low temperature, high rainfall on windward slopes, comparatively dry on the leeward side and heavy precipitation in the form of snow at the mountain tops are the main features of the climate.

Long term, reliable, meteorological data is available only for two stations - Gangtok and Tadong (1957 to present). For rest of the 17 stations in Sikkim, rainfall data is available measured by rain gauges, but data series are not continuous and are unreliable for assessing the changing patterns of climate for a substantial period.

Analysis of annual average maximum, minimum temperature and rainfall of the two stations indicates that though there is no change in the maximum temperature, but the minimum temperature has increased by almost by 2.5oC between the 1957 and 2009. The total rain fall has decreased by around 250 mm between the period 1983 to 2009. After the drought of 2001, the annual precipitation rose to a maximum of 3700 mm but since then it has been continuously decreasing.

However, there exists a spatial variability. Monthly, seasonal and Annual analysis of data only for Gangtok station for the period 1957 to 2005 indicates a trend towards warmer nights and cooler days, with increased rainfall except in winter. The temperature in Gangtok has been rising at the rate of 0.2-0.3C per decade and the annual rainfall is increasing at the rate of nearly 50 mm per decade. Therefore, the temperature in Gangtok has risen by 1 to 1.5oC since 1957. Comparison of long term meteorological data available for Gangtok station (1957 to 2005) with the trend over the last few years (2006-09), shows an acceleration of these patterns, with winters becoming increasingly warmer and drier. Now winter rains is increasingly becoming scarce. During the year 2008 and 2009, the state witnessed one of the driest winters in living memory.

The changes in climate over the long period of observation indicate that the weather patterns have become unreliable. Further, autumn season has extended and winters have become dry. Extreme climate events have become more frequent. Rainfall patterns have become erratic, monsoons are usually late and in general torrential rainfall has replaced the monsoon drizzle. This has increased the surface runoff and dry period during winters, resulting in a higher incidence of forest fires and drying up of springs i.e. discharge of springs has reduced and many of them have started becoming seasonal.

In 2030s, the average annual temperatures are likely to rise by 1.8 to 2.1C in 2030s with respect to 1970s. On a seasonal basis, there is a significant rise in temperatures in the monsoon period in June, July, August and September. The temperature is this season is likely to rise between 1.6 to 6.4C in 2030s with respect to 1970s. In March, April and May temperatures are also projected to increase, and the range of increase is likely to be between 1.9 to 4.1C. Similarly, the winter temperatures, starting from October are also projected to increase by 2 to 2.6C in 2030s with respect to 1970s.

Long term climate observations in Sikkim, indicate that increasingly the winters are becoming warmer and dryer. Due to increased runoff and dry winters, springs have started drying up and their lean season discharge is reducing drastically. Annual mean rainfall show high variation due to the geography, with the rain shadow areas in the lower part of South and West districts receiving only half the rainfall compared to East District. All this has resulted in a decline in the production of the winter crops and an increased incidence of forest fire which is now ascending into the temperate zone.

Ecological instability had visibly adverse effects on the economy of Sikkim. It had a negative effect on drinking water, rabi crops and cash crops like cardamom, ginger and orange. According to the Agriculture Department, the total rainfall between October 1998 to 31 March 1999 was 93.34 per cent less than the rainfall in the last 25 years in the State. Because of this prolonged drought farmers had to postpone the sowing of seeds and in many cases they had to resort to resowing of the same. Cardamom bushes, which had survived all kinds of climatic depredations for the last six to eight decades, dried up.

The crop failure had severe consequences for the farmers of North Sikkim since they are totally dependent on cardamom and vegetable crops. It is estimated that 60 per cent of the States large cardamom plantations were lost in this unprecedented dry spell. The North district alone produces more than 2,500 tonnes of large cardamom annually, valued at nearly Rs 200 million.

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