Spatio-Temporal Variability of Rainfall Indices and their Teleconnections with El Nino-Southern Oscillation for Tapi Basin, India

The long-term spatio-temporal variability in twelve rainfall indices across Tapi basin are investigated for period 1944-2013. The temporal trends in aforesaid indices, representing magnitude, intensity, frequency and duration of rainfall, are analysed using non-parametric tests. The total annual rainfall exhibit uniformly increasing trends over Lower Tapi basin (LTB), while heterogeneous trends are observed across Upper (UTB) and Middle (MTB) Tapi basins. The rainy days portrays decreasing trends at 75% stations in the basin, while rainfall intensity displays increasing trends across LTB and UTB. On other hand, LTB and Purna sub-catchment (in UTB) show coherent increasing trends in extreme rainfall, while decreasing trends are observed over Burhanpur sub-catchment (in UTB) and MTB. A considerable increase in duration of dry spells is reported at 92.5% stations in the basin, indicating a marked shift towards drier climatic regime. Further, Principal Component Analysis (PCA) is carried out to address the space-time variability of rainfall indices. The results of PCA were adopted in cluster analysis to identify the stations exhibiting similar characteristic variations in rainfall trends. The hydroclimatic teleconnections between rainfall indices and large-scale oceanic-atmospheric circulations of the tropical Pacific Ocean (viz., El Nino-Southern Oscillation) revealed the prevalence of wet conditions in the basin during moderate to strong La-Nina, while dry conditions were encountered during moderate to strong El-Nino and weak La-Nina events. The spatial estimates of rainfall indices are derived corresponding to 2-, 10- and 50-year return periods which would be helpful in hydrologic design and risk assessment of rainfall-induced disasters in near future.