Abstract:
A 26-year simulation (1980–2005) was performed
with the Weather Research and Forecast (WRF) model over
the Volta Basin in West Africa. This was to investigate the
ability of a climate version of WRF to reproduce present day
temperature and precipitation over the Volta Basin. The ERAInterim
reanalysis and one realization of the ECHAM6 global
circulation model (GCM) data were dynamically downscaled
using two nested domains within the WRF model. The outer
domain had a horizontal resolution of 50 km and covered the
whole ofWest Africa while the inner domain had a horizontal
resolution of 10 km. It was observed that biases in the respective
forcing data were carried over to the RCM, but also the
RCM itself contributed to the mean bias of the model. Also,
the biases in the 50-km domain were transferred unchanged,
especially in the case of temperature, to the 10-km domain,
but, for precipitation, the higher-resolution simulations increased
the mean bias in some cases. While in general, WRF
underestimated temperature in both the outer (mean biases of
−1.6 and −2.3 K for ERA-Interim and ECHAM6, respectively)
and the inner (mean biases of −0.9 K for the reanalysis and
−1.8 K for the GCM) domains, WRF slightly underestimated precipitation in the coarser domain but overestimated precipitation
in the finer domain over the Volta Basin. The performance
of the GCM, in general, is good, particularly for temperature
with mean bias of −0.7 K over the outer domain.
However, for precipitation, the added value of the RCM cannot
be overlooked, especially over the whole West African
region on the annual time scale (mean biases of −3% for
WRF and −8% for ECHAM6). Over the whole Volta Basin
and the Soudano-Sahel for the month of April and spring
(MAM) rainfall, respectively, mean bias close to 0% was simulated.
Biases in the interannual variability in both temperature
and precipitation over the basin were smaller in the WRF
than the ECHAM6. High spatial pattern correlations between
0.7 and 0.8 were achieved for the autumn precipitation and
low spatial correlation in the range of 0.0 and 0.2 for the
winter season precipitation over the whole basin and all the
three belts over the basin.
