CE-DYNAM (v1): a spatially explicit process-based carbon erosion scheme for use in Earth system models
Authors: Naipal Victoria , Lauerwald Ronny , Ciais Philippe , Guenet Bertrand , Wang Yilong 
Published: March 2020

Abstract. Soil erosion by rainfall and runoff is an important process behind
the redistribution of soil organic carbon (SOC) over land, thereby impacting
the exchange of carbon (C) between land, atmosphere, and rivers. However, the
net role of soil erosion in the global C cycle is still unclear as it
involves small-scale SOC removal, transport, and redeposition processes that
can only be addressed over selected small regions with complex models and
measurements. This leads to uncertainties in future projections of SOC
stocks and complicates the evaluation of strategies to mitigate climate
change through increased SOC sequestration. In this study we present the parsimonious process-based Carbon Erosion
DYNAMics model (CE-DYNAM) that links sediment dynamics resulting from water
erosion with the C cycle along a cascade of hillslopes, floodplains, and
rivers. The model simulates horizontal soil and C transfers triggered by
erosion across landscapes and the resulting changes in land–atmosphere
CO2 fluxes at a resolution of about 8 km at the catchment scale.
CE-DYNAM is the result of the coupling of a previously developed
coarse-resolution sediment budget model and the ecosystem C cycle and
erosion removal model derived from the Organising Carbon and Hydrology In Dynamic Ecosystems
(ORCHIDEE) land surface model. CE-DYNAM
is driven by spatially explicit historical land use change, climate forcing,
and global atmospheric CO2 concentrations, affecting ecosystem
productivity, erosion rates, and residence times of sediment and C in
deposition sites. The main features of CE-DYNAM are (1) the spatially
explicit simulation of sediment and C fluxes linking hillslopes and
floodplains, (2) the relatively low number of parameters that allow for running
the model at large spatial scales and over long timescales, and (3) its
compatibility with global land surface models, thereby providing
opportunities to study the effect of soil erosion under global changes. We present the model structure, concepts, limitations, and evaluation at the
scale of the Rhine catchment for the period 1850–2005 CE (Common Era). Model results are
validated against independent estimates of gross and net soil and C erosion
rates and the spatial variability of SOC stocks from high-resolution
modeling studies and observational datasets. We show that despite local
differences, the resulting soil and C erosion rates, as well as SOC stocks from
CE-DYNAM, are comparable to high-resolution estimates and observations at
subbasin level. We find that soil erosion mobilized around 66±28 Tg (1012 g) of
C under changing climate and land use over the non-Alpine region of the
Rhine catchment over the entire period, assuming that the erosion loop of
the C cycle was nearly steady state by 1850. This caused a net C sink equal
to 2.1 %–2.7 % of the net primary productivity of the non-Alpine region
over 1850–2005 CE. This sink is a result of the dynamic replacement of C on
eroding sites that increases in this period due to rising atmospheric
CO2 concentrations enhancing the litter C input to the soil from
primary production.