Analysis of rainfall and streamflow trend and variability over Birr River watershed, Abbay basin, Ethiopia

Abstract

The analysis of rainfall and streamflow trends provides useful information for the effective hydrological variables, water resource planning, and management systems. Trend analysis is important to understanding the performance and features of hydrological and climatic variables over a long timescale. The goal of this study is to identify and analyze existing relationships between rainfall and streamflow trends, as well as to investigate potential drivers of streamflow variability in the Birr River watershed. The Mann Kendall test, Pettitt test, Sen's slope estimator, and an indicator of hydrological alterations were used to investigate trends, detection of change points, and the linkage of existing rainfall and streamflow at monthly, seasonal, and annual timescales. The result of this study showed that most rainfall gauging stations did not reveal statistically significant changes. On the other hand, streamflow exhibited a statistically significant increasing and decreasing pattern. In all stations, the streamflow trends and change points were found to be inconsistent. The variations in streamflow without significant changes in rainfall suggested that other variables were influencing streamflow. These could be due to the changes in watershed physical elements, such as alterations in the dynamics of Land Use Land Cover (LULC), which are most likely to be responsible for observed changes in the streamflow fluctuations. The finding of this study can be used as a platform for further studies on the effect of watershed dynamics on hydrological flow variability.