Coupled modelling of hydrological processes and grassland production in two contrasting climates
Authors: Jarvis Nicholas , Groh Jannis , Lewan Elisabet , Meurer Katharina H. E. , Durka Walter , Baessler Cornelia , Pütz Thomas , Rufullayev Elvin , Vereecken Harry 
Published: May 2022

Abstract. Projections of global climate models suggest that ongoing human-induced
climate change will lead to an increase in the frequency of severe droughts
in many important agricultural regions of the world. Eco-hydrological models
that integrate current understanding of the interacting processes governing
soil water balance and plant growth may be useful tools to predict the
impacts of climate change on crop production. However, the validation status
of these models for making predictions under climate change is still
unclear, since few suitable datasets are available for model testing. One
promising approach is to test models using data obtained in
“space-for-time” substitution experiments, in which samples are
transferred among locations with contrasting current climates in order to
mimic future climatic conditions. An important advantage of this approach is
that the soil type is the same, so that differences in soil properties are
not confounded with the influence of climate on water balance and crop
growth. In this study, we evaluate the capability of a relatively simple
eco-hydrological model to reproduce 6 years (2013–2018) of measurements of
soil water contents, water balance components and grass production made in
weighing lysimeters located at two sites within the TERENO-SoilCan network
in Germany. Three lysimeters are located at an upland site at Rollesbroich
with a cool, wet climate, while three others had been moved from
Rollesbroich to a warmer and drier climate on the lower Rhine valley
floodplain at Selhausen. Four of the most sensitive parameters in the model
were treated as uncertain within the framework of the GLUE (generalized
likelihood uncertainty estimation) methodology, while the remaining
parameters in the model were set according to site measurements or data in
the literature. The model satisfactorily reproduced the measurements at both sites, and some
significant differences in the posterior ranges of the four uncertain
parameters were found. In particular, the results indicated greater stomatal
conductance as well an increase in dry-matter allocation below ground and a
significantly larger maximum root depth for the three lysimeters that had
been moved to Selhausen. As a consequence, the apparent water use efficiency
(above-ground harvest divided by evapotranspiration) was significantly
smaller at Selhausen than Rollesbroich. Data on species abundance on the
lysimeters provide one possible explanation for the differences in the plant
traits at the two sites derived from model calibration. These observations
showed that the plant community at Selhausen had changed significantly in
response to the drier climate, with a significant decrease in the abundance
of herbs and an increase in the proportion of grass species. The differences
in root depth and leaf conductance may also be a consequence of plasticity
or acclimation at the species level. Regardless of the reason, we may
conclude that such adaptations introduce significant additional
uncertainties into model predictions of water balance and plant growth in
response to climate change.