Abstract:
The influence of soil moisture initial conditions
on the climate extreme indices over West Africa was investigated
using the fourth generation of the International
Centre for Theoretical Physics regional climate model (nonhydrostatic)
coupled with version 4.5 of the Community
Land Model (RegCM4–CLM4.5) at a 25 km spatial resolution.
We initialized the control experiments with the reanalysis
soil moisture data from the European Centre for
Medium-Range Weather Forecasts (ECMWF) reanalysis of
the 20th century (ERA-20C), while we initialized the dry and
wet experiments with the maximum and minimum soil moisture
values over the West Africa domain, respectively. For
each experiment, an ensemble of five runs was performed
for 5 years (2001–2005) with soil moisture initial conditions
for the runs prescribed on 1 June and the simulations being
performed over 4 months (122 d) from June to September.
The performance of RegCM4–CLM4.5 with respect to simulating
the 10 extreme rainfall and temperature indices used
in this study is presented. The results are then discussed for
the two idealized simulations that are most sensitive to the
dry and wet soil moisture initial conditions in order to highlight
the impacts beyond the limits of soil moisture internal
forcing in the model. Over the Central Sahel, dry (wet) experiments
lead to a decrease (increase) in precipitation extreme
indices related to the number of events, but this was
not seen for indices related to the intensity of the events. Soil
moisture initial conditions unequally affect the daily minimum
and maximum temperatures. The strongest impact is
found on the maximum temperature: wet (dry) experiments
decrease (increase) the maximum temperature over the whole region. Over the Central Sahel, wet (dry) experiments lead to
a decrease (increase) in the maximum values of the minimum
temperature.
