*3.3.2 Climate change impact on streamflow and sediment*

The bias-corrected rainfall and maximum/minimum temperature outputs were used as inputs to the calibrated/validated SWAT model to examine the Genale catchment streamflow and sediment yield responses in the future years. The climate-induced discharge changes are understood by assessing differences produced by the SWAT model when driven by future scenarios and present-day climates. A similar study by Negewo & Sarma (2021) for the Genale watershed revealed that the mean annual quantity of water resources is possible to increase under RCP4.5, but variations are substantial for individual sub-basins and HRUs. The study results reflected that climate change might increase the high flows in the catchment in the Autumn season (April, May, June) and Spring season (September, October & November) (**Figure 11**).

Monthly discrepancy showed that the increase in discharge is more pronounced in March, April, May, August, September under RCP4.5, and the decrease is more pronounced in the same months under RCP8.5 scenarios (**Figure 11**). The average monthly change of streamflow for the RCP4.5 and RCP8.5 was running from 16.47% to 6.58% and 3.6% to 8.27%, respectively, of 2022–2080(**Figure 12**).

#### **Figure 11.**

*Streamflow variations under historical data and two emissions scenarios.*

**Figure 12.**

*Predicted relative changes (percent of baseline levels) in monthly streamflow by RCP4.5 & RCP8.5.*

*Evaluation of Climate Change-Induced Impact on Streamflow and Sediment Yield of Genale… DOI: http://dx.doi.org/10.5772/intechopen.98515*

The change in monthly streamflow is consistent with the predicted changes in rainfall and temperature patterns in the future period.

The change patterns of sediment yield follow that of streamflow in the region. Prediction of RCM showed an increase in sediment yield for RCP4.5 and slightly decreased for the RCP8.5 scenario (**Figure 13**). Monthly variation showed that the magnitude changes in sediment yield in March, April & June was the highest with values of 21.8%, 15.0%, 15.0% and 13.7% respectively for RCP4.5 scenario, and slightly lower in January, March, November, September & December with values of 3.5%, 1.5%, 2.1%, 2.1% & 2.2% respectively for RCP8.5 scenario (**Figure 14**). It should be recognized that the maximum increase in heavy rainfall and extreme events was also predicted in the respective months. Hence, the corresponding change predicted by the model is reasonable. The monthly average changes in sediment yield for the RCP4.5 and RCP8.5 scenarios were 21.8% to 6.2% and 5.6% to 4.66%, respectively, over 2022–2080 (**Figure 14**).

The increase in change (percentage) of sediment yield is more significant than discharge, implying that the sediment concentration in the Genale catchment will likely increase in the future periods under the RCP4.5 scenario.

From the spatial distribution of the sediment yield for the baseline & two emissions scenarios periods (**Figure 15**), the high-sediment-yield regions are mainly

**Figure 13.**

*Sediment yield variations for baseline and two GHGs scenarios.*

#### **Figure 14.**

*Predicted relative monthly changes in sediment yield in future periods for two emission scenarios compared to baseline.*

**Figure 15.**

*Annual average spatial distribution of sediment yield (ton/ha/year) at sub-basin scale in historical data & future periods under baseline, RCP4.5& RCP8.5.*

#### **Figure 16.**

*Annual average spatial distribution of streamflow (mm) at sub-basin scale in historical data & future periods under baseline and two emission scenarios.*

located in the upstream regions of the catchment for all cases, in which the sediment yield varies from 0 to 31 (baseline condition), from 0 to 35 (under RCP4.5) & from 0 to 30 (under RCP8.5) over 1990–2013, 2022–2080, 2022–2080 respectively.

Irrespective of the catchment area, the spatial distribution of streamflow at the sub-basin level follows the trend of sediment yield patterns in historical data (1990– 2013) and future periods (2022–2080) under baseline conditions & two emissions scenarios (RCP4.5 & RCP8.5) (**Figure 16**).

From the results, a comparison of monthly stream discharge & sediment yield predictions for 2022–2080 indicated that the impact of climate changes induced on sediment yield is more significant than on streamflow under the two emission scenarios.
