Abstract:
Potato (Solanum tuberosum L.) is an important crop in the Gamo Highlands in Ethiopia. The region is characterised
by a complex topography with large inter-annual weather variations, where potatoes grow in a range of
altitudes between 1,600 and 3,200m above sea level (a.s.l.). Traditional large-scale crop modelling studies only
crudely represent the effect of complex topography, misrepresenting spatial variability in meteorology and
potato growth in the region. Here, we investigate how weather influenced by topography affects crop growth.
We used the Weather Research and Forecasting (WRF) model to simulate weather in relation to topography in
coarse (54 km×54 km) and fine (2 km×2 km) resolution domains. The first has a resolution similar to those
used by large-scale crop modelling studies that only crudely resolve the horizontal and vertical spatial effects of
topography. The second realistically represents the most important topographical variations. The weather
variables modelled in both the coarse and fine resolution domains are given as input to the GECROS model
(Genotype-by-Environment interaction on CROp growth Simulator) to simulate the potato growth. We modelled
potato growth from 2001 to 2010 and studied its inter-annual variability. This enabled us to determine for the
first time in Ethiopia how variations in weather are linked to crop dynamics as a function of elevation at a fine
resolution.
We found that due to its finer representation of topography, weather and crop growth spatio-temporal variations
were better represented in the fine than in the coarse resolution domain. The magnitude of crop growth
variables such as Leaf Area Index (LAI) and Length of the Growing Season (LGS) obtained with weather from the
coarse resolution domain were unrealistically low, hence unacceptable. Nevertheless, the resulting potato yields
in the coarse resolution domain were comparable with the yields from the fine resolution domain. We explain
this paradoxical finding in terms of a compensating effect, as the opposite effects of temperature and precipitation
on yield compensated for each other along the major potato growing transect in the Gamo Highlands. These
offsetting effects were also dependent on the correct estimations of the LGS, LAI. We conclude that a wellresolved
representation of complex topography is crucial to realistically model meteorology and crop physiology
in tropical mountainous areas.
