Investigation on Streamflow Multi-scale temporal variability and its connection to global climate indices

Abstract

Understanding the streamflow variability and its hydroclimatic mechanism is significant, as the frequency and availability of natural resources are severely affected by changes in hydrological variables. This study first analyzes the multi-scale flow of 6 unregulated stations in India and examines the connection between flow variability and the four global climate indicators, namely, IOD, NAO, Niño 3.4, and PDO. The variability of streamflow for both gradual as well as abrupt changes has been checked. The Mann-Kendall trend test was used to find gradual fluctuation, while Changepoint analysis was carried out to detect the abrupt or step change in streamflow data. The investigation is expanded further to other stations in the chosen basin, especially in flow variability and hydroclimatic teleconnections. A total of 40 regulated stations instead of unregulated stations were selected this time. Continuous Wavelet Analysis was used to examine the multi-scale variations in streamflow data. Cross-Wavelet and Wavelet Coherence Analysis were also conducted to find coherence and links among streamflow, rainfall, and global climate indices. This study observed the distinct behavior of unregulated and regulated streamflow stations in the context of streamflow variability and hydroclimatic teleconnections. The continuous wavelet transform of unregulated streamflow revealed that all considered stations showed high variability at intra-annual, annual, and inter-annual scales in which oscillations at 0.5 and 1 year of scales are more dominant and appeared throughout the study period. In contrast, in the case of regulated stations, intra-annual variability does not appear for the majority of stations. Furthermore, streamflow observed an in-phase relationship with IOD and NAO, whereas a lag correlation with Niño 3.4 and PDO indices at intra-annual, annual and inter-annual time scales. Results obtained from regulated stations revealed that, along with a smaller scale, correlations between streamflow and climate indices at the intra-decadal scale (8 years) are also dominant and can be observed mainly from 1985-2005. So, the overall study concludes that both types of stations respond differently. Thus in any particular basin, unregulated stations cannot be considered as a proxy of regulated stations. So for better planning and management of water resources, both regulated and unregulated streamflow should be examined.