Assessment of the Impact of Climate Change on Hydrological Drought in Lake Tana Catchment, Blue Nile Basin, Ethiopia

Enyew Bd Van Lanen Haj

doi:10.4172/2329-6755.1000174

Abstract

Droughts are common natural phenomenon in Ethiopia which has been affecting food insecurity and imposing other complex problems. Severe droughts happened once every 10 years in the north and north east Ethiopia, now becoming more frequent and covering areas that never experience drought before, in the southern parts of the country. According to IPCC droughts will become more intense, frequent and severe in the future due to the impact of climate change. This thesis presents the assessment of projected impact of climate change on hydrological drought in the Lake Tana basin in Ethiopia, which is the headwater for the Blue Nile River. The rainfall-runoff HBV model was calibrated and validated against historical data to obtain a reference situation to the possible impact of climate change on hydrological drought in four sub-basins and the Lake Tana basin. Datasets obtained from the EU- ATCH project for three General Circulation Models (CNCM3, IPSL and ECHAM) were used as an input to the HBV model, which was recalibrated for the same historic period to obtain an assessment to what local downscaled, bias-corrected GCM can be used as a forcing data for hydrological drought assessment. Next the GCM outputs with the recalibrated HBV model were used to simulate future streamflow for two future time windows (2021-2050 and 2071-2100) and for one future emission scenario A2. The variable threshold level method combined with a 10-day moving average streamflow was used to detect hydrological drought characteristics.

Highlights

In the rainy season (JJAS) at which the basin gets more than 70 to 90% of the total rain, the precipitation is projected to increase by about 2.6% and 5.7% for ECHAM and IPSL, respectively, while CNCM3 predicts a reduction in precipitation by about 5.8% for the intermediate future
The minimum increase in mean temperature for this period is projected by CNCM3 and the maximum is projected by ISPL
The average drought duration and average deficit volume are higher in simulated streamflow in all sub-basins except Lake Tana basin.Intercomparison of drought characteristics simulated with HBV using local forcing’s data with that from general circulation models (GCMs) outputs for historical period revealed that all GCMs underestimated the number of droughts in the range -38 to 68% in the Lake Tana basin (Figure 7)

Summary

Introduction

In the rainy season (JJAS) at which the basin gets more than 70 to 90% of the total rain, the precipitation is projected to increase by about 2.6% and 5.7% for ECHAM and IPSL, respectively, while CNCM3 predicts a reduction in precipitation by about 5.8% for the intermediate future. Comparison of drought characteristics derived from observed data with that derived from GCMs for the reference situation revealed that, the number of drought derived from all GCMs is smaller than the number of droughts simulated using observed data for the historical period, in the Lake Tana basin Both ECHAM and CNCM3 underestimated the number of droughts by 38%, and IPSL by about 68%. The climate change impact assessment revealed that, according to CNCM3, the number of droughts in the Lake Tana basin is expected to increase by 100% and 68.8% in the intermediate and far future, respectively. In case of the Lake Tana basin, IPSL projected an increase in the average drought duration by 80 and 95% for the intermediate and far future respectively.

Objectives

Results

Discussion

Conclusion