Trend of Annual One-Day Maximum Rainfall Series over South India

Transcription

1 Trend of Annual One-Day Maximum Rainfall Series over South India Dr. Ashoke Basistha Hydrologist Dam Rehabilitation & Improvement Project 1 st National Dam Safety Conference, Chennai

2 2 Organization Introduction Objective & Methodology Data Results Conclusion

3 3 Introduction Design flood calculated using UH increases linearly with design rainfall Out of the 5 States currently under DRIP, 3 are in South India A lot of the dams in these states date back to pre-independent era of empirical hydrology Earlier research reported significant increasing trend in one-day extreme rainfall over the south peninsular region (Guhathakurta et al. (2010, 2011) It has been projected by that the end of this century, extreme precipitation events over wet tropical regions will very likely be more intense (IPCC, 2013)

4 4 Objective & Methodology This study explores the presence of long-term trend in annual maximum rainfall series over South India Pre-whitened Mann-Kendall test has been used to detect presence of trend Theil and Sen s Median Slope has been used to assess the practical significance of trend as a change that is statistically significant may not have practical significance (Yue and Hashino 2003)

5 5 Data This study used gridded Indian daily rainfall data set over prepared by the Indian Institute of Tropical Meteorology, Pune Annual one-day maximum rainfall series for the South Indian land region (Kanyakumari to 19 north, 69 grid points) was derived therefrom

6 6

7 7

8 8 Results: Pre-whitened Mann-Kendall Test At 10% level of significance Out of 69 grid points over South India, significant rising trends shown at 20 points None of the grid points showed significant falling trend Out of the 29 grid points over the DRIP states, only 5 points show rising trend

9 9

10 10 Results: Pre-whitened Mann-Kendall Test At 5% level of significance Out of 69 grid points over South India, significant rising trends shown at 14 points Out of the 29 grid points over the DRIP states, only 2 points show rising trend

11 11

12 12 Results: Pre-whitened Mann-Kendall Test At 1% level of significance Out of 69 grid points over South India, significant rising trends shown at 4 points Out of the 29 grid points over the DRIP states, none show rising trend

13 13

14 14 Practical Significance of Change Assessed as percentage change over the data period Obtained by multiplying Theil and Sen s median slope with data period and calculating percentage over highest one-day rainfall at the point A change of 10% or more considered to be of practical significance

15 15 Results: Practical Significance of Change At 23 grid points (out of 69) the increase over 58 year period exceeded 10% At 33 points the increase was of magnitude less than 10% At 12 points the absolute magnitude of decrease was less than 10% At 1 point the absolute magnitude of decrease was greater than 10% The maximum estimated increase was 19.55% The maximum decrease was % The average change over the region is 6.69%, increasing

16 16 Results: Practical Significance of Change At 2 grid points within the DRIP states (out of 29) the increase over 58 year period exceeded 10% At 18 points the increase was of magnitude less than 10% At 8 points the absolute magnitude of decrease was less than 10% At 1 point the absolute magnitude of decrease was greater than 10% The maximum increase in the DRIP states is 16.94% The maximum decrease was % The average change in the DRIP states is 3.04%, increasing

17 17

18 18 Results: Combined At 14 grid points (out of 69) the rising trend is significant both statistically and practically Within the DRIP states rising trend is significant statistically and practically at 1 point only

19 19

20 20 Conclusion One-day maximum rainfall over South India shows increasing trend, reaffirming results of earlier studies Though the increase at individual points warrants attention, average increase over the region does not appear to be alarming The effect is less pronounced over the DRIP states Further studies are required for attribution

21 21 References Guhathakurta, P., Menon, P., Mazumdar, A.B., and. Sreejith, O. P, Changes in Extreme Rainfall Events and Flood Risk in India During the Last Century, National Climate Centre Research Report No: 3/2010. Guhathakurta, P., Sreejith, O.P. and Menon, P.A., 2011, Impact of Climate Change on Extreme Rainfall Events and Flood Risk in India, J. Earth Syst. Sci.120, No. 3, pp IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., Qin, D., Plattner, G.-K., Tignor, M., Allen, S.K., Boschung, J., Nauels, A., Xia, Y., Bex V., and Midgley P.M. (eds.)], Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Yue, S. and Hashino, M., 2003, Long Term Trends of Annual and Monthly Precipitation in Japan, Journal of the American Water Resources Association,

22 22