Streamflow trends in the Mahanadi River basin (India): Linkages to tropical climate variability

Abstract

Mahanadi River basin is one of the recognized climatic vulnerable regions of India. Recent occurrences of the extreme climatic events in this basin underscore the importance of evaluating the trend and variability of hydroclimatic variables in order to understand the potential impact of future change. In this study, the monthly streamflow data for the period 1972–2007 and the daily rainfall data for the period 1972–2005 have been analyzed using the Mann–Kendall nonparametric test after removing serial correlation. The results reveal a substantial spatial and subseasonal difference in the monsoon season streamflow and rainfall patterns, with a predominance of the increasing trends in June and decreasing trends in August. However, a marked increase is observed in the streamflow and rainfall of the pre- and post-monsoon season. The correlation coefficients show a direct correspondence of the rainfall and streamflow series with the El Niño–Southern Oscillation (ENSO), which is contrary to the established inverse relationship over India. The noteworthy feature of this study is the observed climate uncertainty in terms of large variability in the extreme indices since the 1990s, consistent with the warming induced intensification of the hydrological cycle. Strong evidences have emerged regarding the basin-wide increases in extreme rainfall indices. In particular, the coastal sector of the basin is more vulnerable to the heavy rainfall, whereas the southern Eastern Ghats region is susceptible to the moisture stress. The discharge at the basin outlet hasdeclined at a rate of 3388x106 m3/decade, suggesting the need of environmental flow assessment. The results of this study would help the reservoir managers and policy makers in planning and management of water resources of the Mahanadi River basin.