Comparative Study of HBV Light and GR4J Conceptual Hydrological Models for Assessment of Impact of Climate Change on Water Availability of Awata River Watershed, Genale Dawa Basin; Southern Ethiopia

Abstract

This research was conducted to study impacts of climate change on water resource of Awata River watershed. Statistical Downscaling Model version 5.1.1 has been used to downscale the daily maximum temperature, minimum temperature, and precipitation in 30-year intervals from the second generation of the Earth System Model (CanESM2) under two Representative Concentration Pathways (RCP) Scenarios (RCP4.5 and RCP8.5). Climate change scenarios for precipitation and temperature were developed for two future periods 2018-2047 (2020s) and 2048-2077 (2050s). According to the projected climate data, the monthly minimum and maximum temperature are likely to have an increasing trend +2.94°C and 2.25°C respectively. Regarding the rainfall change, under the RCP4.5 scenario the study shows annual average increment of by 26.8% and 35.1% at near (2020) and mid-term (2050) respectively. On monthly bases rainfall shows there is incensement in some months and decrease in some months. The HBV Light and GR4J hydrological models were successfully calibrated (2003-2012) and validated (2013-2017) using current climatic inputs and observed river flows. The overall performances of both models were good, at monthly time scale; on calibration (R²=0.87 and NSE = 0.78) and validation (R²=0.85 and NSE=0.80) with HBV Light whereas, calibration (R²=0.81 and NSE=0.72) and validation (R²=0.84 and NSE= 0.75) for GR4J model. Over the two projected periods (2018-2047  and 2048-2077) under both RCP4.5 and RCP8.5 scenario HBV-Light and GR4J models simulation results showed that the mean annual discharge will significantly increase related to the baseline periods (1988-2017). HBV light indicate the percentage increment of total average annual flow volume 7.3% (2018-2047) and 7.0% (2048-2077) for RCP 4.5 scenario, and For RCP 8.5 scenario, the increment ranges between 7.7% (2018-2047) to 7.9% (2048-2077). The GR4J model indicates the percentage increment of total average annual flow volume 6.4% (2018-2047) and 6.6% (2048-2077) for RCP 4.5 scenario, and For RCP 8.5 scenario, the increment ranges between 6.2% (2018-2047) to 7.6% (2048-2077). In conclusion increase in average total annual, seasonal and monthly flow volume is observed for periods which show a corresponding increases in mean annual, seasonal and monthly precipitation during scenario developments so that, future studies must recognize the over-all implication of climate change in the Awata watershed.

Keywords: Awata, Climate change, canESM2, HBV, GR4J, SDSM, Ethiopia.

DOI: 10.7176/JNSR/9-22-01

Publication date: November 30^th 2019