The Effect of Climate Change on Loss of Lake Volume: Case of Sedimentation in Central Rift Valley Basin, Ethiopia

Abstract

Evaluating the impact of climate change on sediment yield has become one of the major topics in climate research. The purpose of this study was to investigate sediment yield contribution to lake volume change under changing climatic conditions in the Central Rift Valley Basin. The ensemble mean of five regional climate models (RCMs) in the coordinated regional climate downscaling experiment (CORDEX)-Africa was considered for the purpose of this study. The climate variables (precipitation, minimum and maximum temperatures) in RCMs were bias corrected against observed data using linear scaling (LS), power transformation (PT), variance of scaling (VS), and quantile mapping (QM). Two emission scenarios, the Representative Concentration Pathways, RCP4.5 and RCP8.5, were considered for the future scenario period . Better results were obtained when the ensemble values of the bias correction methods were used. Hence, the projected values of climate variables after bias correction were used in the Soil and Water Assessment Tool (SWAT) hydrological model to estimate the sediment yield contribution to lake volume change due to climate change. The results show that the average projected precipitation will decrease by 7.97% and 2.55% under RCP4.5 and RCP8.5, respectively. On average, the maximum temperature will increase by 1.73 • C and 2.36 • C under RCP4.5 and RCP8.5, respectively, while the minimum temperature will increase by 2.16 • C and 3.07 • C under RCP4.5 and RCP8.5, respectively. The average annual sediment yield contributions to Lake Ziway were 431.05 ton/km 2 and 322.82 ton/km 2 for the Meki and Ketar rivers, respectively, in the historical period . The study also reveals that the annual sediment yield that was estimated for the Meki River was 323 ton/km 2 and 382 ton/km 2 under RCP4.5 and under RCP8.5, respectively. The sediment estimations for the Ketar River were 157 ton/km 2 and 211 ton/km 2 under RCP4.5 under RCP8.5, respectively. This will decrease the rate of volume change in Lake Ziway by 38% under RCP4.5 and by 23% under RCP8.5. The results show that the life expectancy of the lake is likely to increase under climate change scenarios. This will help water resources managers make informed decisions regarding the planning, management, and mitigation of the river basins.Hydrology 2018, 5, 67 2 of 18 reservoirs, ponds, and rivers. The sedimentation of the water bodies reduces their capacity and the useful lifespan of the reservoir. Sediment yield can be described as the amount of sediment that would enter into a reservoir located at the outlet of the basin [1]. It is the net result of soil erosion and processes of sediment accumulation, so it depends on variables that control water and sediment discharge to reservoirs [2]. Sediment yield is influenced by many factors, which include topography, soil, climate, land use, and drainage characteristics [3][4][5][6]. The problem of sedimentation is aggravated by human activities and climate change. A study conducted by Belete [7] on Lake Hawasa showed that sediment...

Effect of Land Use and Land Cover Change on Soil Erosion in Erer Sub-Basin, Northeast Wabi Shebelle Basin, Ethiopia

“…The model was run to estimate the actual annual rates of soil loss in the study landscape for the years 2000 and 2018. The soil erosion risk within the study area was classified into eight categories, based on previous work by Uddin et al [5], and the estimated mean soil loss rates (t ha −1 y −1 ): very low (< 5), low (5-10), low medium (10)(11)(12)(13)(14)(15), medium (15)(16)(17)(18)(19)(20), high medium (20)(21)(22)(23)(24)(25), high (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35), very high (35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50), and extremely high (>50). Areas with a mean annual soil loss rates lower than low were rated as tolerable soil loss limit [52].…”

“…Agriculture sector, which accounts for about 50% of the Gross Domestic Product (GDP), 85% of the total export revenue, and over 80% of the total employment, is the main source of the country's economy [21][22][23][24][25]. The great majority of the population is dependent on subsistence agriculture that is an overwhelming vulnerable to the recurrent droughts and land degradation [21][22][23][24][25][26][27][28]. Rapid population increase and growing demand posed a greater pressure on land resources, leading to severe soil erosion and land degradation in various parts of the country.…”

“…It was estimated that the land degradation cost to an annual agricultural GDP range from 2% to 6.75% [21]. The loss of topsoil by water erosion in Ethiopia was estimated at 1.5 billion tons per annum with a mean erosion rate of 42 t ha −1 y −1 [27,28]. However, the magnitude of soil erosion rates varies across the physiographical regions in the country.…”

Effect of Land Use and Land Cover Change on Soil Erosion in Erer Sub-Basin, Northeast Wabi Shebelle Basin, Ethiopia

“…It was estimated that land degradation cost to an annual agricultural GDP range from 2% to 6.75% [21]. The loss of topsoil by water erosion in Ethiopia was estimated at 1.5 billion tons per annum with a mean erosion rate of 42 t ha -1 y -1 [27,28]. However, the magnitude of soil erosion rates varies across the physiographical regions in the country.…”

“…The model was run to estimate the actual annual rates of soil loss in the study landscape for the years 2000 and 2018. The soil erosion risk within the study area was classified into eight categories, based on previous work by Uddin et al[5], and the estimated mean soil loss rates (t ha -1 y -1 ): very low (< 5), low (5-10), low medium(10)(11)(12)(13)(14)(15), medium(15)(16)(17)(18)(19)(20), high medium (20-25), high(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35), very high (35-50), and extremely high (>50). Areas with a mean annual soil loss rates lower than low were rated as tolerable soil loss limit[52].…”