Trend analysis for rainfall in Delhi and Mumbai, India Arun Rana • Cintia Bertacchi Uvo • Lars Bengtsson • P. Parth Sarthi Received: 15 June 2010 / Accepted: 19 April 2011 / Published online: 4 May 2011 Ó Springer-Verlag 2011 Abstract Urbanisation has burdened cities with many problems associated with growth and the physical envi- ronment. Some of the urban locations in India are becoming increasingly vulnerable to natural hazards rela- ted to precipitation and flooding. Thus it becomes increasingly important to study the characteristics of these events and their physical explanation. This work studies rainfall trends in Delhi and Mumbai, the two biggest Metropolitan cities of Republic of India, during the period from 1951 to 2004. Precipitation data was studied on basis of months, seasons and years, and the total period divided in the two different time periods of 1951–1980 and 1981–2004 for detailed analysis. Long-term trends in rainfall were determined by Man-Kendall rank statistics and linear regression. Further this study seeks for an explanation for precipitation trends during monsoon period by different global climate phenomena. Principal compo- nent analysis and Singular value decomposition were used to find relation between southwest monsoon precipitation and global climatic phenomena using climatic indices. Most of the rainfall at both the stations was found out to be taking place in Southwest monsoon season. The analysis revealed great degree of variability in precipitation at both stations. There is insignificant decrease in long term southwest monsoon rainfall over Delhi and slight signifi- cant decreasing trends for long term southwest monsoon rainfall in Mumbai. Decrease in average maximum rainfall in a day was also indicated by statistical analysis for both stations. Southwest monsoon precipitation in Delhi was found directly related to Scandinavian Pattern and East Atlantic/West Russia and inversely related to Pacific Decadal Oscillation, whereas precipitation in Mumbai was found inversely related to Indian ocean dipole, El Nin ˜o- Southern Oscillation and East Atlantic Pattern. Keywords Urbanization  India  Statistical analysis  Man-Kendall  Climate indices  Principal component analysis  Singular value decomposition 1 Introduction Urbanization has established a network of competitive urban centres that set the physical reference points for today’s globalization. Some of the urban locations in India are becoming increasingly vulnerable to natural hazards related to weather and climate (De and Dandekar 2001). Global averaged precipitation is projected to increase, but both increases and decreases are expected at the regional and continental scales (IPCC 2001). Information about the trends of rainfall are important as it is closely related to the practical water relates issues in the region especially flood related problems. Thus it becomes increasingly important to study the trends in precipitation and their physical explanation. Several studies have addressed the important issue of trends in rainfall in India since last century. For example, Guhathakurta and Rajeevan (2006) have shown that there is no long term trend in the southwest monsoon seasonal rainfall over the country, when about 60–90% of the annual rainfall over India is received (Joshi and Rajeevan 2006), A. Rana (&)  C. B. Uvo  L. Bengtsson Department of Water Resources Engineering, LTH, Lund University, Box No. 118, 22100 Lund, Sweden e-mail: Arun.Rana@tvrl.lth.se; arunranain@gmail.com P. Parth Sarthi Center for Environmental Sciences, Central University of Bihar, Camp Office: BIT Campus-Patna, P.O-B.V. College, Patna, Bihar 800014, India 123 Clim Dyn (2012) 38:45–56 DOI 10.1007/s00382-011-1083-4