METEOROLOGICAL DROUGHT IN CHERRAPUNJEE, MEGHALAYA

INTRODUCTION More than 60% of net Indian cultivable land is rainfed; again this monsoon rainfall is not well assured at all the places during its stipulated period. Temporal and spatial variability of rainfall distribution is observed in Indian subcontinent (Dhar et al., 1979). In our country nearly 75% of the rainfall is occurring during June to September. The probability of occurrence of rainfall was various stations were estimated by various workers: Chakraborty and Mandal (2008) for Sagar Island of Sunderban; Jakhar et al. (2011) for Koraput district of Odisha; Mohanty et al. (2001) for Vidarbha region of Maharastra; Sharma et al. (1979, 1987a, 1987b) for crop planning; Sinha (1986) for Patna region; Satapathy et al. (1998, 1999) for umiam region of Meghalaya; Ray et al. (2011) for Garo Hills districts of Meghalaya; Ray et al. (2013a) for Tura region of Meghalaya; Ray et al. (2013b) for central region of Meghalaya. Extreme conditions of rainfall are also observed in certain years. Floods and droughts are the two extremes of rainfall distribution. The maximum daily rainfall analysis was done by various workers for different stations, viz., Ray et al. (2012a) for Barapani region of Meghalaya; Ray et al. (2013b) for Central region of Meghalaya; Sharda and Bhushan (1985) for Agra region. Deficiency of rainfall is the basic cause of drought. No general method is available which can be applied for the drought prediction (Salas, 1986). Depending on the climate, drought varies from place to place. Several workers have done meteorological analyses based on rainfall data (Satapathy et al., 1998, 1999; Ray et al., 2012a). Sharma et al. (1979, 1987a and 1987b) analyzed the rainfall using the definition of drought month as a month in which the actual rainfall is less than 50% of the average monthly rainfall. Drought year is the year receiving rainfall less than or equal to the average rainfall minus twice standard deviation of the series. Shrivastava et al. (2008) used this definition to assess J. Indian Water Resour. Soc., Vol 35, No. 4, October 2015 METEOROLOGICAL DROUGHT IN CHERRAPUNJEE, MEGHALAYA Lala I.P. Ray 1, P.K. Bora 1, A.K. Singh 1, Ram Singh 2, S.M. Feroze 2, N.J. Singh 1 and T.R. Das 3 ABSTRACT One of the highest rainfall regions of the world, Cherrapunjee lies in East Khasi Hills district of Meghalaya. Thirty seven years (1971-2007) daily rainfall data was used to find out the monthly, seasonal and yearly drought occurrences at this station based on India Meteorological Department (IMD) protocols. The average annual rainfall was calculated to be 10,753.61 mm. During the thirty seven years period no extreme and moderate drought years were experienced, but there were mild drought occurrences in seven years. Monthly occurrences of drought are limited to January, February, November and December months only. Key words: Rainfall analysis; meteorological drought; drought year. 1. School of Natural Resource Management, College of Postgraduate Studies, (Central Agricultural University, Imphal), Umiam, Barapani- 793103, Meghalaya; Email: lala.ray@gov.in 2. School of Social Sciences, College of Postgraduate Studies, (Central Agricultural University, Imphal), Umiam, Barapani- 793103, Meghalaya meteorological droughts in North Lakhimpur district of Assam. Sinha (1986) and Ray et al. (1987) used this definition to study the drought at Gopalpur, Odisha. Kumar and Kumar (1989), Dabral (1996) and Ray et al. (2012b) analyzed the weekly, monthly, seasonal and yearly rainfall of Pantnagar, Ranchi and Barapani respectively for drought; as per the procedure followed by Anonymous (1971), Dhar et al. (1979), Sharma et al. (1979), IMD (1979), Ray (1987), Ray et al. (2012b) and Singh et al. (2013). Tiwari et al. (2007) characterize the meteorological drought indices using the data of Hazaribagh station. Similar analysis has been done by various researchers for meteorological drought analysis at various places in India. In the present paper an attempt has been made to study the frequency of drought occurrence at Cherrapunjee in terms of rainfall deficiency. MATERIALS AND METHODS The study place, Cherrapunjee is located at 91 0 42 41 ` East Longitude and 25 0 10 to 25 0 51 North Latitude with an altitude of more than 1300 m above mean sea level sits on a plateau in the southern part of the East Khasi Hills district, facing the plains of Bangladesh with an annual mean temperature of 17.3 C. The district wise map of the Meghalaya is shown in Fig.1. The plateau rises 600 m above the surrounding valleys. Despite perennial rainfall, this place faces an acute water shortage and the inhabitants often have to trek for miles to obtain potable water. Irrigation is also 3. Scientist, IARI PUSA campus, Samastipur, Bihar Manuscript No. : 1385 Fig. 1: District map of Meghalaya showing the study area 1

hampered due to excessive rain washing away the topsoil as a result of human encroachment into the forests. The state government renamed Cherrapunjee back to its original name, "Sohra". Soils on the plateau are poor owing to deforestation and washout caused by heavy rains. Valleys around Cherrapunjee, however, are covered with lush and very diverse vegetation, containing numerous endemic species of plants, including Meghalaya subtropical forests. This place has a mild subtropical highland climate, with monsoonal influences, receives both southwest and northeast monsoonal winds. It lies on the windward side of the Khasi Hills, so the resulting orographic lift enhances precipitation. In the winter months it receives the northeast monsoon showers that travel down the Brahmaputra valley. The behavioral pattern of rainfall with reference to the amount of rainfall and number of rainy days at Cherrapunjee was analyzed using probabilistic approach from historic daily rainfall records (1973-2007). The monthly rainfall, seasonal rainfall (i.e., June to September - monsoon; October to December - post monsoon; and January to May - pre monsoon) and yearly rainfall were analyzed. The average monthly, seasonal and yearly rainfall values were worked out. The variation of rainfall for each month, season and year from the mean was determined and the mean deviation for the seasons was calculated. Total numbers of drought months, seasons and year were determined using the following definition: Drought month: if the actual rainfall is less than 50% of the average monthly rainfall (Sharma et al., 1979). Drought season: if the annual rainfall is deficient by more than twice the mean deviation of the season (Marathe et al., 2001). Drought year: if the annual rainfall is deficient by 20-60% of the average yearly rainfall and if the deficient is more than 60% of the average yearly rainfall it is known as scanty drought year (Dhar et al., 1979). The yearly intensity of drought was also determined using the criteria suggested by IMD (1971) which is based on the percentage deviation of rainfall from its long term mean and it is given by (Eq.1). Pi µ D = 100. (1) i µ Where D i is the percentage deviation from the long-term mean, P i is the annual rainfall, mm and µ is the long term mean of the annual rainfall, mm. Drought codification based on percentage departure of rainfall from normal is presented in Table-1. The percentage of deviation (D i ) is then used to categorise the drought. RESULTS AND DISCUSSION Descriptive statistical analysis of monthly rainfall was done for Cherrapunjee station. The coefficient of variation is more than 100% for the month of Jan., Feb., March, Oct, Nov. and Month Table 1: Drought codification based on percentage departure of rainfall from normal value % departure of rainfall Intensity of drought Code from normal 0.0 or above No drought M o 0.0 to -25.0 Mild drought M 1-25.0 to - 50.0 Moderate drought M 2-50.0 to -75.0 Severe drought M 3-75.0 or less Extreme drought M 4 Table 2: Monthly Normal and Extreme Rainfall (Number of Rainy Days) along with SD, CV and Percentage contribution Average rainfall (mm) Minimum (mm) Extreme Value Maximum (mm) Standard Deviation (mm) Coefficient of Variation (%) Percentage contribution (%) January 10.67 0 38.6 11.48 107.64 0.1 February 40.11 0 137.7 45.22 112.73 0.36 March 237.63 7.7 865.2 262.82 110.6 2.15 April 830.07 74 1844.6 486.9 58.66 7.5 May 1164.79 0 3976.3 857.37 73.61 10.53 June 2290.8 0 4339.9 916.66 40.01 20.71 July 3273.93 1510.5 8026.2 1463.57 44.7 29.6 August 1544.18 0 3180.9 875.45 56.69 13.96 September 1167.54 0 4988.9 1056.28 90.47 10.56 October 409.67 0 1478.4 453 110.58 3.7 November 68.62 0 380.9 119 173.41 0.62 December 22.43 0 123.4 40.37 180.01 0.2 2

Table Table 3: Weekly 5: Yearly rainfall intensity analysis of drought for drought Standard Year week Annual Mean Rainfall, Average % Half deviation of the average Category No of drought Intensity Percentage of Drought of rainfall, mm mm rainfall, mm rainfall, mm week drought week 1971 23 ( 4 th to 5967.7 10 th June) 388.13-45.68 194.06 M 2 8 Moderate Drought 5.10 1972 7492.5-31.80 M 2 Moderate Drought 1973 24 (11 th 10901.7 to 17 th June) 563.45-0.77 281.73 M 9 1 Mild Drought 5.73 1974 25 (18 th 23442.4 to 24 th June) 587.87 113.39 293.93 M 0 No 8 Drought 5.10 1975 26 (25 th to 12000 1 st July) 635.53 9.23 317.76 M 0 6 No Drought 3.82 1976 7079.6-35.56 M 2 Moderate Drought 27 (2 nd to 8 th July) 630.71 315.35 5 3.18 1977 7993.4-27.24 M 2 Moderate Drought 1978 28 (9 th to 12093 15 th July) 681.81 10.08 340.91 M 0 4 No Drought 2.55 1979 29 (16 th 7425.3 to 22 nd July) 725.26-32.41 362.63 M 2 7 Moderate Drought 4.46 1980 30 (23 rd 9418.4 to 29 th July) 874.54-14.27 437.27 M 1 10 Mild Drought 6.37 1981 10338.1-5.90 M 1 Mild Drought 1982 31(30 th to 9531.3 5 th August) 495.12-13.24 247.56 M 1 10 Mild Drought 6.37 1983 32 (6 th to12 16673.5 th August) 247.33 51.77 123.67 M 0 9 No Drought 5.73 1984 33 (13 th 11800.3 to 19 th August) 382.30 7.41 191.15 M 0 9 No Drought 5.73 1985 7970.3-27.45 M 1 Mild Drought 1986 34 (20 th 9121.9 to 26 th August) 300.47-16.97 150.23 M 11 1 Mild Drought 7.01 1987 35 (27 th 11397.5 to 2 nd September) 254.64 3.75 127.32 M 0 14 No drought 8.92 1988 36 (3 rd to 12861 9 th September) 290.53 17.07 145.27 M 0 11 No Drought 7.01 1989 8964.1-18.40 M 1 Mild Drought 37 (10 1990 th to 16 14586.1 th September) 502.43 251.21 13 8.28 32.77 M 0 No Drought 1991 38 (17 th 12503.8 to 23 rd September) 156.93 13.82 78.46 M 0 12 No Drought 7.64 1992 39 (24 th 12127.8 to 30 th September) 114.51 10.39 57.25 M 0 11 No Drought 7.01 1993 5967.6-45.68 M 1 Moderate Drought 1994 7492.5 Table 4: Analysis of monthly, -31.80 seasonal rainfall M 0 for drought Moderate Drought 1995 10901.7-0.77 M 1 Mild Drought 1996 Month/ 23442.4 Name of Average 113.39 Half of the average M 0 No. of drought, No Drought Percentage 1997 Season 12000 month/season rainfall, mm 9.23 rainfall, mm M 0 month/season/ No Drought of drought 1998 7079.6-35.56 M 1 year Moderate Drought months 1999 7993.4 Jan 10.67-27.24 5.33 M 1 10 Moderate Drought 10.31 2000 12093 Feb 40.11 10.08 20.06 M 0 11 No Drought 11.34 Mar 237.63 118.81 11 11.34 Apr 830.07 415.04 6 6.19 May 1164.79 582.39 5 5.15 Jun 2290.80 1145.40 1 1.03 Month Jul 3273.93 1636.96 1 1.03 Aug 1544.18 772.09 3 3.09 Sep 1167.54 583.77 7 7.22 Oct 409.67 204.83 11 11.34 Nov 68.62 34.31 15 15.46 Dec 22.43 11.21 16 16.49 (Twice the mean dev. value, mm) Pre monsoon 2383.27 2373.74 Season Monsoon 8276.45 6222.50 Post monsoon 500.72 862.26 (80% of total rainfall) 8848.34 6 (40% of total rainfall) 4424.17 (scanty) 0 3

Table 5: Yearly intensity of drought December. The Standard deviation varies from 11mm to 1463 mm(table-2). The weekly rainfall analysis for drought is presented in Table-3. The monthly and seasonal drought analysis of Cherrapunjee station is presented in Table-4. The highest average rainfall of 3273.93 mm was observed in the month of July and the lowest 10.67 mm occurred in the month of January. The frequency of drought was observed to be the highest at a magnitude of 16 times in 37 years in December; while it is 10, 15, 11 and 11 times in 37 years during January, November, February and March month respectively (Table-4). It indicates that, there is a need for assured irrigation in the above months. From the seasonal analysis of the rainfall, it is evident that 21.3% of rainfall was received during premonsoon, 74.4% during monsoon and 4.24% during post monsoon session. So for growing winter season crops during post monsoon season assured irrigation facilities need to be provided, simultaneously ample emphasis may be given to rainwater harvesting during the monsoon season as a high quantum of runoff is anticipated during this seasons. No drought was observed during monsoon, pre-monsoon and post monsoon period. The yearly intensity of drought for Cherrapunjee, Meghalaya is presented in Table-5. The years are codified according to IMD specification as described in the Table-1. It is found from the Table-5 that, there was no severe drought occurrence. However, for the years 1971; 1972; 1976; 1977; 1979; 1985; 1993; 1994 and 1998 there was moderate drought occurrence. The average annual rainfall of Cherrapunjee is 10,753.61 mm and average monthly rainfall of the place is 237.63, 830.07, 1164.79, 2290.80, 3273.93, 1544.18, 1167.54, 409.67 for the month of March, April, May, June, July, August, September, October, respectively. The 4

maximum average rainfall is received during the month of July to a tune of 3273.93 mm and the minimum average rainfall is received during the month of January to a tune of 10.67 mm. CONCLUSION The drought analysis of Cherapunjee made according to deficiency of rainfall shows that out of thirty seven years there was no severe drought occurrence in this region. However, mild to moderate drought was observed in the area during many years. For growing rain-fed rice during monsoon farmers of this region may depend on monsoon as there was hardly any drought occurrence. Since the post monsoon seasonal rainfall is very less, for growing winter season crops arrangement may be done for assured irrigation with proper rainwater harvesting methods. ACKNOWLEDGEMENT The financial assistance received from Central Agricultural University (CAU, Imphal) vides Code No. PG.IRP-VI/2010-11; dated, 30 th November 2010; for conducting the experiment is duly acknowledged. REFERENCES 1. Anonymous. 1971. 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