Investigation of flow-rainfall co-variation for catchments selected based on the two main sources of River Nile
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Date
2018
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Stochastic environmental research and risk assessment
Abstract
The co-variation of rainfall and flow was assessed in four selected catchments of the River Nile which has two
main sources including the White Nile (in the Equatorial region) and the Blue Nile (from the Ethiopian
highlands). The selected catchments included Kyoga and Kagera (from the Equatorial region), as well as Blue
Nile and Atbara (in Sudan and Ethiopia). In each catchment, the flow-rainfall co-variation was investigated at
both seasonal and annual time scales. To explain aggregated variation at larger temporal scale while
investigating the possible change in catchment behavior, which may interfere with the flow-rainfall relationship,
rainfall-runoff modeling was done at daily time scale using data (falling within the period 1949-2003) from
Kagera and Blue Nile i.e. the major catchment of each region where the River Nile emanates. Correlation
analysis was conducted to assess how well the variation of flow and that of catchment-wide rainfall resonate.
The co-occurrence of the changes in observed and simulated overland flow was examined using the Quantile
Perturbation Method (QPM). Trends in the model residuals were detected using the Mann-Kendal (MK) and
Cumulative Rank Difference (CRD) tests. The null hypothesis H0 (no correlation between rainfall and flow) was
rejected at the significance level α of 5% for all the selected catchments. The temporal changes in terms of the
QPM anomalies for both the observed and simulated flow were in a close agreement. The evidence to reject the
H0 (no trend in the model residuals) was generally statistically insufficient at α = 5% for all the models and
selected catchments considering both the MK and CRD tests. These results indicate that change in catchment
behavior due to anthropogenic influence in the Nile basin over the selected time period was minimal. Thus, the
overall rainfall-runoff generation processes of the catchments did not change in a significant way over the
selected data period. The temporal flow variation could be attributed mainly to the rainfall variation.
Description
Keywords
Rainfall-Runoff Modeling, CRD Trend Test, VHM, NAM, HBV, River Nile, QPM
Citation
Onyutha, C., & Willems, P. (2018). Investigation of flow-rainfall co-variation for catchments selected based on the two main sources of River Nile. Stochastic environmental research and risk assessment, 32(3), 623-641. http://dx.doi.org/10.1007/s00477-017-1397-9