Sensitivity of the simulated regional climate to changes in the prescribed soil type distributions: Insights from Coupled Regional Climate Model EBU-POM

In previous studies, it was noticed that many high-resolution Regional Climate Models (RCMs) simulations within the state-of-the-art EURO-CORDEX multi-model ensemble tend to overestimate air temperature and underestimate precipitation in summer leading to the so-called summer drying problem. One of the possible and considerable sources of uncertainty in simulated regional climate is the choice of soil texture database and its soil parameter values. This is crucial because soil hydrophysical properties, influenced by such choices, have an impact on soil moisture and therefore affect the partitioning of surface fluxes [1]. These properties among others play a role in controlling the evolution of soil and air temperature, evapotranspiration, runoff, and precipitation. 

To better understand one of the possible reasons for this problem, we performed two simulations with the coupled regional climate model EBU-POM with two different prescribed soil type distributions. One simulation used the soil type dataset derived from the Zobler dataset and in the second simulation, we used FAO/STATSGO dataset. Two 11-year EBU-POM simulations were conducted, spanning the period from 2000 to 2010. These simulations were initiated in 1998, allowing a two-year spin-up time to reduce the impact of initial fields. The area of interest was Central Europe with a focus on Pannonian Basin because previous studies indicated pronounced dry and warm biases during summer and autumn in low-lying areas, especially in south-eastern Europe. 

The soil moisture capacity is influenced by its hydrophysical characteristics, wherein the size of soil grains plays a crucial role. In this investigation, we emphasized and analyzed the significance of soil hydrophysical properties in shaping surface fluxes. We performed the comprehensive analysis with a focus on the most common specific soil category transitions related to changes in soil parameters and bias changes in surface and near-surface variables and fluxes. The main goal of this study is not to inspect the accuracy of the soil texture map but rather to comprehend the impact on modeled surface and near-surface variables when employing one soil texture dataset versus the other. 

On the other hand, Seneviratne et al. [2] suggested that a new transitional zone characterized by strong land-atmosphere interactions shifted northwards to central and eastern Europe as a consequence of global warming. Their findings highlighted that increased temperature variability in this region is mainly due to land-atmosphere feedbacks. Hence, we analyzed bias in surface and near-surface variables and fluxes and their relation to extreme events such as the heat wave occurred in 2007 to determine their influence on heat wave formation.

[1] Dennis, E. J., and Berbery, E. H. (2021). The role of soil texture in local land surface–atmosphere coupling and regional climate. Journal of Hydrometeorology, 22(2), 313-330.

[2] Seneviratne, S. I., Lüthi, D., Litschi, M., and Schär, C. (2006). Land–atmosphere coupling and climate change in Europe. Nature, 443(7108), 205-209.

Keywords: regional climate modelling, soil moisture, soil texture, land-atmosphere interactions

Acknowledgement: This research was supported by the Science Fund of the Republic of Serbia, No. 7389, Project Extreme weather events in Serbia - analysis, modelling and impacts” - EXTREMES