Abstract
This study investigated the impacts of climate change on the hydrology of the Upper Awash Basin, Ethiopia. A soil and water assessment tool (SWAT) model was calibrated and validated against observed streamflow using SWAT CUP. The Mann–Kendall trend test (MK) was used to assess climate trends. Meteorological drought (SPEI) and hydrological drought (SDI) were also investigated. Based on the ensemble mean of five global climate models (GCMs), projected increases in mean annual maximum temperature over the period 2015–2100 (compared with a 1983–2014 baseline) range from 1.16 to 1.73 °C, while increases in minimum temperature range between 0.79 and 2.53 °C. Increases in mean annual precipitation range from 1.8% at Addis Ababa to 45.5% over the Hombole area. High streamflow (Q5) declines at all stations except Ginchi. Low flows (Q90) also decline with Q90 equaling 0 m3 s−1 (i.e., 100% reduction) at some gauging stations (Akaki and Hombole) for individual GCMs. The SPEI confirmed a significant drought trend in the past, while the frequency and severity of drought will increase in the future. The basin experienced conditions that varied from modest dry periods to a very severe hydrological drought between 1986 and 2005. The projected SDI ranges from modestly dry to modestly wet conditions. Climate change in the basin would enhance seasonal variations in hydrological conditions. Both precipitation and streamflow will decline in the wet seasons and increase in the dry seasons. These changes are likely to have an impact on agricultural activities and other human demands for water resources throughout the basin and will require the implementation of appropriate mitigation measures.
Highlights
Scientific evidence is unequivocal that the earth’s climate is changing
The mean relative error (MRE) for GFDLE-CM3, GISS-ET-R, and MPI-ESM-LR are all less than 5% for precipitation and less than 0.55 for temperature
The magnitude of changes in percentage terms is much higher for low flows than both mean and high flows. These larger percentage changes in low flows agree with an earlier study undertaken within the Upper Awash Basin using a number of global climate models (GCMs), including some used in the current study [22]
Summary
Scientific evidence is unequivocal that the earth’s climate is changing. Due to increasing atmospheric concentrations of greenhouse gases, the average surface temperature of the earth has increased by 1 ◦C with a likely range of 0.8 to 1.2 ◦C since the preindustrial period [1,2,3]. Previous investigations of the impacts of climate change on the Awash River Basin have included hydrological modelling assessments employing earlier generation (SRES) emission scenarios as simulated by one GCM [19] and the application of one or more representative concentration pathway (RCP) scenarios provided by a number (two [20] three [21]) of climate models. Results of these studies included projected declines in annual rainfall of 9.9%, an increase in mean temperature of 0.9 ◦C, and a resultant decline in annual streamflow of 11.5% under RCP4.5 in the 2080s [20]. The linear scaling bias correction method [24], refs. [34,35,36] within an SDSM was employed to correct the GCM simulation systematic or random errors
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