Centennial rainfall variation in semi arid and tropical humid environments in the cardamom hill slopes, southern Western Ghats, India


1 National Institute of Advanced Studies, IISc Campus, Bangalore-560012, India.

2 Department of Atmospheric Sciences, Jawaharlal Nehru Center of Advanced Scientific Research, Jakkur, Bangalore-560 064, India

3 Physical Research Laboratory, Navrangpura Road, Ahmedabad-380 009, India.

4 Cardamom Research Station, Pampadumpara- 685556, India.

5 Dept. of Urology, KLES Kidney Foundation, KLES Prabhakar Kore Hospital & Medical Research Centre, Nehru Nagar, Belgaum. 590 010 India.


Studies of rainfall variation generally focus on large areas. For example, in India, the area average monsoon rainfall series of the whole country or meteorological subdivisions are used. This would be of no use for local agriculture, particularly in places where rainfall is very high or very low, especially for crops like small cardamom and vanilla which are very sensitive to soil moisture and atmospheric air relative humidity. With this view, we present the data and analysis of the long term rainfall variations in semi arid as well as tropical humid environments in cardamom hill slopes in south-WesternGhats in India. In our analysis, the semi-arid cardamom hill slopes showed decreasing trend in rainfall over the recent past three decades ranging from 2.7 to 3.4 mm/yr with R2 values ranging from 0.42 to 0.85 (P= 0.05). Year-to-year variation in rainfall was considerable. No alternating pattern of increase and decrease in rainfall was seen in decads, epochal trends as accounted by ISM for the rest of the country were absent. If the present trend continues, agricultural production in this semi-arid, poor rain fed system will suffer, unless conservation and mitigation efforts are undertaken. In case of windward side humid tropics, the year- to- year variations in the monthly rainfall values were very large. For example, January and February rainfall values changed by a factor as high as two or more from one year to another. The lowest rainfall during a period was reported in 1987 which was one of the intense El-Nino years. There was a strong association of El-Nino phenomenon with below average rainfall (67% of the El-Nino years), indicating a good ENSO relationship. In case of La-Nina years, fifty per cent of the years had enjoyed excess rainfall. However, the impact of El-Nino phenomenon was not severe during the first pentad of this century (2000-2005) in this mountain range. This indicates that the relationship seems to have weakened. The coefficient of variation of rainfall for the entire data series ranged from 9 to 27%. The decadal averages for the first three decades (1896-1925) and the last three decades (1976-2005) studied, reported less than the annual mean (5000 mm) for the whole period (1896-2005). Only during the middle period (1926-1975) the decadal average rainfall exceeded the series annual mean.
Arkin, P.A. and Ardanuy, D. (1989) Estimating climatic scale-precipitation from space. A review. Journal of Climate 2, 1229-1238.
Barrett, E.C. and Martin, D.W. (1981) The use of Satellite data in rainfall monitoring. Academic press, pp 340.
Cubasch, U. (2001) Projections of future climate change. Climate change 2001. The scientific basis, J.T. Houghton et al., eds. Cambridge University Press. pp. 525-582.
International Tea Committee (2007) Commodity situation – A stock taking. Planters’ Chronicle-August: pp.15-32.
Kane, R.P. (2006) Unstable ENSO relationship with Indian regional rainfall. International Journal of Climatology 26, 771-783.
Khole M., De U.S. (2003) A study on northeast monsoon rainfall over India. Mausam, 54(2), 419-426.
Mooley, D.A., Parthasarathy, B. (1979) Poisson distribution and years of bad monsoon over India. Archives of Meteorological Geophyics 27, 381-332.
Murugan, M., Miniraj, N., Josephrajkumar, A., Pradeep, K.P. and Yosuf, L. (2003) Analysis and forecast of winter monsoon based on Pre-vedic literature and simuated model. Journal of Asian Agri-History. 7, 219-231.
Kummerow, C. (2000) The status of the Tropical Rainfall Measuring Mission (TRMM) after two years in orbit. Journal of Applied Meteorology. 39, 1965-1982.
Parthasarathy, B. and Mooley, D.A. (1978) Some features of homogeneous series of Indian summer monsoon rainfall. Monthly weather review. pp. 771-781.
Parthasarathy, B. and Dhar, O.N. (1976) A study of trend and periodicities in the seasonal and annual rainfall of India. Indian Journal of meteorology, hydrology and Geophysics. 27, 23-28.
Murugan et al. 39 Ropelwski, C.F. and Halpet, M.S. (1987) Global and regional scale precipitation patterns associated with the El-Nino /Southern Oscillation. Monthly Weather Review 115, 1606-1626.
Reyes, T. Luukkanen, O. and Quiroz, R. (2006) Small cardamom-precious for people, harmful for mountain forests Mountain Research and Development, 26, 131-137.
Singh, N. and Sontakke, N.A. (1990) On the variability and prediction of rainfall in the post monsoon season over India. International Journal of Climatology. 19, 309- 339.
Sridharan, S. and Muthusamy, A. (1990) North east monsoon rainfall in relation to El- Nino, QBO and Atlantic hurricane frequency. Vayu Mandal. 20, 105-111.
Sulochana, G. Abrol, Y.P. and Rao, P.R.S. (2005) On the growth and fluctuation of Indian food grain production available at (ww.ias.ac.in/currsci/feb25/artiles21. html).
Thapiliyal, V. and Kulshrestha, S. (1992) Recent models for long range forecasting of south west monsoon rainfall over India. Mausam. 43, 239-248.
Werth, D. and Avissar, R. (2006) The local and global effect of South Asian deforestation. Geophysical Research Letters. 32, L 20702.
Wentz, F.J. (1999) A well calibrated ocean algorithm for special sensor microwave /imager. Journal of Geophysical Research. 102, 8703-8718.
Xie, P. and Arkin, P.A. (1996) Analysis of global monthly precipitation using gauge observations, satellite estimates, and numerical model predictions. Journal of Climate. 9, 840-858.
Xie, S.P. Xu, H. Saji, N.H. and Wang, Y. (2006) Role of narrow mountains in largescale organization of Asian monsoon convection. Journal of climate. 19, 3420- 3429.