Trend Assessment For Extrem Rainfall Indices In The Upper Mahanadi With Reference To Climate Change

Abstract

Assessment of climatic variability is an important aspect in water resources management, adaptability and reducing impact on agriculture production due to changing climate. The intergovernmental panel on climate change (IPCC) in their various reports indicated that the global temperature is increasing due to emission of greenhouse gases, industrialization, change in lifestyle and land-use/ landcover change. These and natural forces have contributed to change in earth’s climate over 20th century by warming of land and ocean surface temperature, changing in spatial and temporal pattern of precipitation, rising in sea levels and increase in frequency and intensity of Al Nino. Various studies in the past have confirmed that global temperature is rising continuously since start of industrial age that may impact surface runoff, groundwater, availability of water, water quality, crop production and livelihood of society. Precipitation being the primary input in hydrological cycle needs to be investigated for possible climate change using GCMs/RCMs or statistical analysis. In the present study, an attempt has been made to identify significant trends in monthly, seasonal rainfall and different extreme rainfall indices proposed by World Meteorological Organization (WMO) and Expert Team on Climate Change Detection and Indices (ETCCDI) considering suitability for Indian rainfall conditions in six rain gauge stations namely Ambagarh, Bhanpura, Balod, Dhamtari, Kanker and Murumsilli of upper Mahanadi catchment. The river Mahanadi is an important river for water resources development in Chhattisgarh State of India and availability of water may adversely be affected due to possible change in precipitation regime. For identification of trends, long term rainfall data from 1960 to 2012 have been used to compute extreme rainfall indices including maximum one-day rainfall (RX1D), maximum 5-days rainfall (RX5D), heavy precipitation days (R7.5cm), very heavy precipitation days (R12.5cm), moderate wet days (R75P), very wet days (R95P), precipitation friction due to moderate wet days (R75PTOT), precipitation friction due to very wet days (R95PTOT) and simple daily intensity index (SDII). The Mann Kendal’s and Spearman Rho’s test were used to identify significant trend in extreme rainfall indices at 5 % significant level. The results of analysis indicated that simple daily intensity index indicated no significant trends in any rain gauge stations while rising trend in very heavy precipitation days (R12.5cm) in most of the station. Dhamtari and Murumsilli stations showed significant rising trend in moderate wet days and very wet days related extreme indices, while extreme indices series of Bhanpura and Balod stations were found random without any significant trend.