**1. Introduction**

Water is a unique resource given to humankind from nature impacted by induced climate change [1]. The atmospheric scientists suggest that the Earth is warming as a global temperature increase the hydrological cycle more actively. Greenhouse gases (GHGs) increase in the surroundings is a significant concern for global warming & climate changes. These changes may influence natural water resources in the catchment [2]. The Intergovernmental Panel on Climate Change (IPCC) appraisal report stated that global mean precipitation, surface temperature, droughts, and floods had changed significantly, and the changes are expected to continue [3]. Principally, developing country like Ethiopia is now facing severe

climate change effects on water and agriculture sector. Currently, it is of great importance to evaluate the consequence of climate change on the regional and local water resources. The rise in surface earth air temperature and precipitation patterns are prominent features of change in climate that directly impact almost all other hydrological responses [4]. A temperate climate will accelerate the hydrological process, altering rainfall patterns and the magnitude & timing of streamflow. Climate changes are also expected to have remarkable impacts on the soil type since rainfall and runoff are the factors governing soil erosion and sediment yield/transport within landscapes [5].

The information derived from Global Climate Models (GCMs) is currently the most applicable in evaluating both past and possible future changes in climate scenarios. This climate data is then used as input to drive the hydrologic process. Long-term locally-observed climate data are also needed to validate climate model outputs to capture local settings [6]. However, direct implementation of GCM outputs to any hydrological model for subsequent evaluation of impact is despondent in climate studies because of coarse resolution issues. The simulation of GCMs runs on large scales to consider various grids across the globe, and GCM typically takes about 2.80 x 2.80 longitude and latitude resolution. To tackle the problems downscaling is assumed, a process of bringing down the climate information from GCM to regional & local hydrologic scales to produce outputs of the more acceptable resolution, which are more realistic with the local scale before estimating the risks associated with the future hydrologic scenarios [7, 8].

Different downscaling techniques have been advanced over the past two decades, deriving from two major blueprints; dynamic downscaling and statistical downscaling approaches. The dynamic approach is often viewed as a mini-GCM because it stimulates regional climate variables by decreasing the horizontal area covered (typically around 25 by 25 km) using the same boundary conditions as the evolving GCM. Because they produce high-resolution climate data, they have not been extensively accepted because of the complexities and costs involved in running this type of technique to capture regional-scale climate variables. Statistical downscaling approach, involving weather typing procedures, transfer functions, and stochastic weather generators, are the most known methods used in climate change studies nowadays [9]. They give future climate scenarios based on a statistical relationship between climate variables at one or more GCM grid points at a particular station. They are adopted because they are relatively economical to apply and give point climate data at a specific site of interest [5, 7].

The changes in streamflow and sediment yield characteristics resulting from climate change depend on individual watershed aspects. Decisive evaluations of the quantity and rate of runoff and sediment yield are needed to help decision-makers develop catchment management plans for better soil & water conservation measures [10, 11]. The SWAT-Soil and Water Assessment Tool model simulates the climate change-induced impacts for the San Jacinto River basin in Texas [12]. The effect of climate change on catchment hydrology is typically evaluated by characterizing climate change scenarios to a hydrological model based on the futuristic GHGs [1, 5, 4].

Streamflow modeling is essential to know sediment concentration in the stream, whereas peak streamflow rate is vital for hydraulic structure, watershed management practices, and flood protection. Different studies used empirical, statistical, and simulation methods to resolve the impacts of climate change on hydrological responses [13]. Recent studies recommended that SWAT is widely used as a capable model to evaluate environmental and hydrological changes with varying land types and climate conditions [14]. Additionally, the output components incorporated in the SWAT model are found to address various water-related systems in the

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

watershed. The study highlighted that an increase in the concentration of CO2 has a notable effect on streamflow, sediment yield, evaporation, and water yield. Carbon emission scenarios are the main driving forces in climate models. Scenarios are images or pictures of how the world is likely to emerge in the future in terms of greenhouse gasses (GHGs). In the recent study, we use the latest scenarios, called Representative Concentration Pathways (RCPs), which have rarely been applied in the study catchment. The IPCC characterizes a set of RCP scenarios (2.5, 4.5, 6.0, and 8.5) for projection of future climate based on Coupled Model Intercomparison Project (CMIP5) [15]. These four RCPs consolidate one alleviation scenario priming a low driving level (RCP2.6), two stabilization (medium) scenarios (RCP4.5 and RCP6), and one with a high GHGs emissions scenario (RCP8.5). These emissions scenarios are emerged based on the driving force such as socio-economic development, population growth, and GHGs [16]. Based on the IPCC report, by the end of the 21st century, global warming/temperature may increase by 1–5°C. Climate change scenarios for the Global Climate Model (GCM) or simple analog models are sometimes adapted to investigate climate change impacts on hydrology [17].

Nevertheless, their spatial resolutions are extremely coarse for regional climate study and need to downscale it. Therefore, either through statistical or dynamic regional climate models, the downscaling approach is required to convert GCM data into acceptable resolution before using for any hydrological study [18, 19]. Limited reports address the climate change analysis using Regional Climate Model (RCM) on streamflow and sediment concentration in the region. Nevertheless, most studies have used coarse-resolution GCM data, which are not favored for watershed hydrological modeling. The SWAT model was selected for this study because of its ability & wide range of applications, demonstrating that the model is a flexible and robust tool that can simulate various regional water flow at a watershed scale provide effective results [20].

This study contributes to investigate the effects of future climate change projection on the streamflow and sediment yield of Genale catchment using the calibrated/validated SWAT model under baseline and future two emissions and offers baseline information for adaptive soil and water resource management in a changing climate region. For the SWAT input, the future climate projection (2022–2080) statistically downscaled Regional Climate Model (RCM) Bias-corrected Coordinated Regional Climate Downscaling Experiment (CORDEX) precipitation, max/min temperature for Ethiopia, under RCP 4.5 and RCP 8.5 emissions scenario was used with historical data of (1990–2013). The climatic model data for the hydrologic modeling tool (CMhyd) is used to extract and bias-correct the climate variables obtained from RCM-CORDEX.

## **2. Materials and methodology**

#### **2.1 Description of the study area**

The surface of the Earth has three main climate zones: tropical (hot & higher humidity zones), temperate (moderate between tropical & polar), and polar (floating and pack ice). Ethiopia is placed in the tropical climate zone lying between the Equator and the Tropic of Cancer. The latitude, longitude, & altitude of Ethiopia is given as 90 <sup>8</sup><sup>0</sup> <sup>53</sup>" N, 40<sup>0</sup> <sup>29</sup><sup>0</sup> <sup>35</sup>″ E, & 1343 m respectively. Based on elevation, the country has three different climate zones: Tropical zone (Dega, Weyna Dega, and Kola), with an average annual temperature of about 27°C and annual rainfall of about 510 millimeters. The study area is located on the Genale watershed with 54,941.583 Km2 of the part of Genale Dawa River, situated in the South-Eastern part of Ethiopia and joins with Dawa River at the border with Somalia (Dolo Ado) (4° 16'N, 42° 04<sup>0</sup> E) to become the Juba River. In the Genale Basin, a total of 464 HRUs were created and scattered among 25 sub-basins. The annual mean of precipitation experienced in the area 810 mm distribution of rainfall in the watershed is 300 to 1302 mm per year. The daily max and min temperatures are 34.5 °C and 8.6 °C, respectively, with a daily average of 19 °C (**Figure 1**).
