Abstract:
Understanding of flood hazard response to multiple scenarios of relevant determinants in urban centers is a
precondition for proactive disaster risk management. Yet, studies on flood response to the effects of multiple
agents in Sub-Saharan Africa countries is rare. This study simulates peak runoff and water flow rate to land use
and land cover (LULC), and scenarios of rainfall intensity of different durations and return periods. An urban
flood-prone Odaw River catchment of Accra, Ghana was studied for the possible hazard responses to variations in
LULC and rainfall intensities and amounts. Landsat data for 2000, 2011 and 2020 were classified and analyzed
for changes in LULC. Rainfall intensity was estimated for different durations; and 2, 10 and 25 years of return
periods, using Intensity-Duration-Frequency (IDF) model. The rational and the successive flow routing hydrological
models were used to simulate peak runoff and flow rate, respectively. Built-up area increased in coverage
from 40% in 2000 to 65% in 2020, whereas woodland reduced from 10.5% to 4.0% for the same period. The
peak runoff was highest in the built-up areas, and directly proportional to rainfall intensities and return periods.
Replacing a given amount of woodland by equal amount of built-up area increased peak discharge by 3.5 times.
Runoff peaked 30 mins after onset of rainfall for the 10-yr and 25-yr return periods, but peaked 1 hr for the 2-yr
return period. We recommend that flood risk reduction strategies maintain substantial amount of woody vegetation
and grassland, and provide quick early warning when extremely high rainfall intensity is anticipated. Land
use planning organization should consider a range of flood hazard intensities, including rare and extreme events
in their decisions.
