Rainfall variability analysis over eastern agroclimatic zone of Haryana

Monsoon rain display significant large inter-annuel variability leading to widespread drought and flood situations. Effect of drought is accentuated by the higher coefficient of variability over region of lower seasonal rainfall (Parthasarathy, 1984). In India, long-term time series of summer monsoon rainfall has no discernible trends, but decadal departures are found above and below the long time average alternatively for 3 consecutive decades and the same study employing non-parametric methods showed a decreasing trend for rainfall variables (Kothyari and Singh, 1998). Recent decades have exhibited an increase in extreme rainfall events over northwest India during the summer monsoon (Singh and Sontakke, 2004). Present investigation was carried out in the eastern agroclimatic zone of Haryana located in north-western part of India with representative locations being Karnal and Ambala for obtaining the long term trend and variability of rainfall.

Monsoon rain display significant large inter-annuel variability leading to widespread drought and flood situations. Effect of drought is accentuated by the higher coefficient of variability over region of lower seasonal rainfall (Parthasarathy, 1984). In India, long-term time series of summer monsoon rainfall has no discernible trends, but decadal departures are found above and below the long time average alternatively for 3 consecutive decades and the same study employing non-parametric methods showed a decreasing trend for rainfall variables (Kothyari and Singh, 1998). Recent decades have exhibited an increase in extreme rainfall events over northwest India during the summer monsoon (Singh and Sontakke, 2004). Present investigation was carried out in the eastern agroclimatic zone of Haryana located in north-western part of India with representative locations being Karnal and Ambala for obtaining the long term trend and variability of rainfall.
The daily rainfall data of Ambala (29°59' N, 76°81' E, 276 MSL) and Karnal (29°43' N, 76°58' E, 245 MSL) stations were collected for the period from 1977 to 2008 from Haryana state Remote Sensing Application Centre and Central Soil Salinity Research Institute, respectively. Statistical analysis was done to work out annual, seasonal and monthly variability and trend by calculating different descriptive viz., mean, standard deviation (SD), coefficient of variation (CV).

Rainfall analysis at Ambala
The monthly rainfall of Ambala varied between 9.4 to 289.7 mm. The lowest rainfall (9.4mm) is received in

Department of Agricultural Meteorology CCS Haryana Agricultural University, Hisar, Haryana-125 004, India
Email: surendersd@yahoo.com month of November with highest CV (230.6%) and highest rainfall of 289.7 mm is recived in July with lowest (52%) CV. Summer season contributed 89.9 mm rainfall with CV of 70% while monsoon season (June to September) contribtes 748.5 mm with 35.6% of CV (Table 1). Table 1 shows that summer season rainfall showed an increasing trend irrespective of period except 3 rd period. A positive trend was noted for south-west monsoon with values of 12.19 and 42.74 mm per year during 1 st and 2 nd periods, whereas a negative trend with value of 20.89 mm per year during 3 rd period. The post monsoon rainfall had also a decreasing trend during 3 rd period (3.45 mm per year) with an overall decreasing trend (0.21 mm per year). The winter rainfall had increasing trend during 1 st and 2 nd period with respective value of 0.21 and 1.00 mm but decreasing during 3 rd period by 3.10 mm per year. The seasonal trend during 1977-2008 indicated an increase in summer, and south-west monsoon season at a rate of 0.6, and 3.27 mm, respectively but decrease during post monsoon and winter by 0.21 and 1.90 mm per year, respectively. Monthly analysis indicated a significant decreasing trend in July with a value of 6.13 mm per year during 1 st period but in 2 nd period except May, November and December remaining months had increasing trend, a significant decreasing trend in July by 24.54 mm per year during 3 rd period. Overall, a decreasing rainfall trend in November to April and July was noted.

Rainfall analysis at Karnal
The monthly rainfall at Karnal ranged between 6 mm in November to 204.6 mm in July. The CV percent and inversely related to rainfall. The CV percent are less than 90 in all the months of S-W monsoon season. S-W monsoon contribute about 588.1 mm rainfall followed by 78.2 mm winter season and 75.2 mm in summer season (Table 2). Table 2 shows that there was decreasing trend during summer of the order of 5.46, 5.21 and 2.42 mm per year in 1 st , 2 nd and 3 rd  period, respectively. In south-west monsoon season there was decreasing trend of 23.58 and 23.31 mm during 1 st and 3 rd period but in 2 nd period it was increasing by 27.30 mm per year. Post monsoon trend was of decreasing during 3 rd period only but it was increasing during 1 st and 2 nd period. Rainfall trend of winter was increasing during the whole study periods with annual value of 0.76 mm. Finally there were decreasing trend of rainfall of summer, south-west and post monsoon during 1977-2008 with values of 1.12, 3.68 and 0.21 mm per year, respectively.

Seasonal trend of rainfall depicted in
Thus it is concluded that the during S-W monsoon season rainfall is increacasing at Ambala while it is decreasing at Karnal.