[Paper Review] Time-scale characteristics of Kasai river hydrological regime variability for 1940-1999

Jean-Marie Tshitenge Mbuebue, Albert Mbata Muliwavyo+4 more|arXiv (Cornell University)|Aug 27, 2016

Hydrological Forecasting Using AI4 citations

TL;DR

This study analyzes the time-scale variability of the Kasai River's hydrological regime (1940–1999) using wavelet analysis to detect multi-scale fluctuations in rainfall and discharge. It identifies strong annual cycles and intermittent 2–8-year and 8–16-year oscillations, with weak coherence between hydrological variables and major climate indices (coherence < 0.55).

ABSTRACT

The present study was undertaken with the aim of contributing to the characterization of the nonstationary variability of the hydrological regime of the Kasai River using the wavelet analysis for 1940-1999. The rainfalls and discharge over Kasai Basin have marked fluctuations with a perceptible downward trend and some shift around 1950, 1960, 1970, 1983 and 1994. The results show that rainfalls over Kasai basin and the discharge at Ilebo station patterns exhibit a strong annual oscillation and some intermittent oscillations in 2-8 years (1950-1975, 1983-1995) and 8-16 years (1970-1999) time scales. The wavelet coherence analysis reveals a weak possible connection between hydrological variables (rainfalls, discharge) and climate indices relative to sea surface temperature and atmospheric circulation over Atlantic tropical, Indian and Pacific Oceans (coherence less than 0.55).

Motivation & Objective

• To characterize nonstationary variability in the hydrological regime of the Kasai River basin over the 20th century.
• To identify dominant time-scale patterns in rainfall and river discharge using advanced signal processing.
• To assess the influence of large-scale climate indices on Kasai River hydrology through coherence analysis.
• To detect structural shifts and trends in hydrological time series during the study period.
• To improve understanding of hydrological dynamics for better water resource management in Central Africa.

Proposed method

• Applied continuous wavelet transform (CWT) to analyze temporal variability in rainfall and discharge data from 1940 to 1999.
• Used wavelet power spectra to identify significant oscillations at different time scales (e.g., annual, 2–8 years, 8–16 years).
• Conducted wavelet coherence analysis to examine relationships between hydrological variables and climate indices (SST, atmospheric circulation).
• Evaluated statistical significance of wavelet features using Monte Carlo testing with red noise background.
• Analyzed shift points in hydrological patterns around 1950, 1960, 1970, 1983, and 1994 using time-series decomposition.
• Validated results against observed trends and known climatic events in the region.

Experimental results

Research questions

• RQ1 What are the dominant time-scale oscillations in rainfall and discharge within the Kasai River basin from 1940 to 1999?
• RQ2 How do structural shifts in hydrological patterns correlate with climatic transitions around 1950, 1960, 1970, 1983, and 1994?
• RQ3 To what extent are Kasai River discharge and rainfall linked to large-scale climate indices such as SST and atmospheric circulation?
• RQ4 Are there persistent multi-year oscillations in the hydrological regime, and how do they vary over time?
• RQ5 How strong is the coherence between hydrological variables and climate indices across different time scales?

Key findings

• Rainfall and discharge in the Kasai Basin exhibit a strong annual oscillation, indicating seasonal control over hydrological dynamics.
• Intermittent 2–8-year oscillations were detected in rainfall and discharge between 1950–1975 and 1983–1995, suggesting decadal variability.
• A persistent 8–16-year oscillation was observed in rainfall and discharge from 1970 to 1999, indicating longer-term climatic modulation.
• Wavelet coherence analysis revealed weak connections between hydrological variables and climate indices, with coherence values consistently below 0.55.
• The study identified perceptible downward trends in both rainfall and discharge, with notable shifts around 1950, 1960, 1970, 1983, and 1994.
• The nonstationary nature of the hydrological regime is confirmed by time-varying spectral features, especially in the 2–8-year and 8–16-year bands.