Abstract
We investigate the reasons for the opposite climate change signals in precipitation between the regional climate model REMO and its driving earth system model MPI-ESM over the greater Congo region. Three REMO simulations following three RCP scenarios (RCP 2.6, RCP 4.5 and RCP 8.5) are conducted, and it is found that the opposite signals, with REMO showing a decrease and MPI-ESM an increase in the future precipitation, diverge strongly as we move from a less extreme to a more extreme scenario. It has been shown that REMO simulates a much higher number of extreme rainfall events than MPI-ESM. This results in higher surface runoff and thus less soil infiltration, which leads to lower amounts of soil moisture in REMO. This further leads to less moisture recycling via evapotranspiration, which in turn results in less precipitation over the region. In the presence of a strong radiative forcing, the hydrological cycle becomes less intense in REMO and a downward trend in hydrological variables is observed. Contrary to this, the higher amounts of soil-moisture due to the lack of extreme rainfall events in MPI-ESM enhance the hydrological cycle. In the presence of strong radiative forcing, higher amounts of soil moisture result in increased evapotranspiration which in turn results in the higher amount of precipitation. It is concluded that the land-atmosphere coupling over the Congo region is very sensitive to the change in soil moisture amounts, which is likely to play a major role in global warming conditions. Therefore, adequate and improved representation of soil processes in climate models is essential to study the effects of climate change. However, the better representation of extreme rainfall events in REMO compared to MPI-ESM can be regarded as an added value of the model.
Highlights
The fourth Assessment Report (AR4; [1]) of the Intergovernmental Panel on Climate Change (IPCC) states that mean global temperatures will likely rise between 1.1 and 6.4 °C above 1990 levels by the end of this century
In this study we investigated the reasons for the opposite climate change signals of precipitation between the regional climate model REMO and the driving global climate model MPI-Earth System Models (ESMs)
It has been found that REMO simulates lower amounts of precipitation, evapotranspiration and integrated water vapor (IWV) as compared to MPI-ESM, even in the control period over the greater Congo region
Summary
The fourth Assessment Report (AR4; [1]) of the Intergovernmental Panel on Climate Change (IPCC) states that mean global temperatures will likely rise between 1.1 and 6.4 °C (with a best estimate of 1.8 to 4 °C) above 1990 levels by the end of this century. The robustness in the signal plays a role of utmost importance while assessing the climate change In this respect, the greater Congo region provides less clear picture as reported in AR4 [1], with some models projecting an increase in annual total precipitation while others a decrease resulting into an uncertain projection of precipitation. In the regions like Congo, soil moisture plays an important role by controlling the partitioning of the available energy into latent and sensible heat flux and conditions the amount of surface runoff. By controlling evapotranspiration, it is linking the energy, water and carbon fluxes.
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