Impacts of Climate and Land Use Change on Hydrological Response in
Gumara Watershed, Ethiopia
Abstract
Climate and land-use change affect the hydrologic cycle by altering
streamflow (SF), surface runoff (SR), base-flow (BF), and
evapotranspiration (ET). The Lake Tana basin has experienced both
land-use and climate change over the past 40 years, and this change can
continue in the future. Several studies have addressed the separate
impacts of either land-use or climate change on the watershed’s
hydrology, but few have explored the combined impacts. In this study,
the SWAT model was applied to evaluate the combined impacts of land-use
and climate change on hydrological responses in Gumara watershed. This
study examined four land-use scenarios that include the present (2015)
and projected (2050) land-use based on the business-as-usual trend
(BAU), expansion of irrigation crop (EIC), and expansion of forestland
(EFL). The climate variables were simulated using Weather Research and
Forecasting (WRF) model for the baseline (2005-2015) and projected
period (2045-2055) under RCP4.5 and RCP8.5 scenarios. The result showed
that SR increase by 5.1% under BAU scenario while BF decrease by 6.5%
without altering SF and ET noticeably. On the contrary, SF decrease by
12.5% and 5.2% respectively under EIC and EFL scenarios, while ET
increase by 4.8% and 8.9% respectively under EIC and EFL scenarios.
The simulated SF, SR, and ET under RCP8.5 may increase significantly by
34.3%, 51.8%, and 12.2%, respectively. Similarly, the simulated SF,
SR and ET may increase significantly under the combination of all three
land-use and RCP8.5 scenarios. The findings suggested that climate
change will have a greater effect on hydrologic responses than land-use
change. The expansion of agriculture and the wetter climate would
exacerbate flooding, while the expansion of irrigation and forest offset
SF increases. The results of this study can be useful to decision-makers
and planners in the design of adaptive measures to climate and land-use
change.