A sensitivity analysis of the different setups of the RegCM4.5 model for the Carpathian region

Tímea Kalmár,Rita Pongrácz,Ildikó Pieczka

doi:10.1002/joc.6761

Tímea Kalmár, Rita Pongrácz + Show 1 more

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https://doi.org/10.1002/joc.6761

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Abstract

AbstractThe current study focuses on the RegCM4.5 model and specifically on a comparison of hydrostatic and non‐hydrostatic approaches as well as on different microphysical parameterisations and planetary boundary layer (PBL) schemes. The main goal of the paper is to simulate the historical regional precipitation characteristics of the Carpathian region as reliably as possible. For this purpose, seven different model experiments at a 10 km horizontal resolution were completed for a 10‐year period (1981–1990) using ERA‐Interim reanalysis data (with 0.75° resolution) as initial and boundary conditions. Our simulation matrix consists of hydrostatic and non‐hydrostatic runs together with different treatments of moisture, namely, the SUBEX and the NogTom schemes. In addition, two PBL schemes are tested, the Holtslag and the UW‐PBL scheme. In this detailed validation study, RegCM outputs (e.g., temperature, global radiation, cloud cover, precipitation) are compared to the homogenized, gridded CarpatClim data (available with 0.1° resolution) that are based on measurements at regular meteorological station sites. The validation considers seasonal and monthly means, as well as extreme climatic events. On the basis of the results we can conclude that the role of the non‐hydrostatic core can be clearly recognized for precipitation, particularly over mountains. Moreover, it was also found that the UW‐PBL scheme performs with a negative bias regarding atmospheric boundary layer thickness and temperature and it reduces the wet/dry biases of the Holtslag PBL scheme. Regarding microphysical schemes, the NogTom scheme performs better than the SUBEX scheme, but the modified SUBEX (SUB4.3) can also reduce the precipitation over mountainous areas.

Highlights

Model-based projections of climate change impacts across multiple sectors suggest that the Carpathian region will be among the hotspot regions with the highest number of severely affected areas in Europe (Ceglar et al, 2018)
The main differences between RegCM4.5 simulations can be found in winter: the use of the SUBEX scheme overestimates temperature over lowlands compared to other simulations, while the NogTom scheme produces the smallest biases over Hungary
This study aimed to evaluate RegCM4.5 simulations to determine whether they can be reliably used to further projection studies over the Carpathian region

Summary

Introduction

Model-based projections of climate change impacts across multiple sectors suggest that the Carpathian region (located in eastern-central Europe) will be among the hotspot regions with the highest number of severely affected areas in Europe (Ceglar et al, 2018). Planetary and synoptic scale processes are well represented in global climate models (GCMs) that use a horizontal resolution in the order of magnitude of 100 km in century-long simulations. Regional climate models (RCMs) are used for dynamical downscaling to increase the resolution of climate information consistently with the large-scale circulation provided by the driving GCM or reanalysis data. RCMs are widely used to provide projections on how the climate may change locally through representing land surface heterogeneity with great details and reproducing fine-scale processes more realistically (Flato et al, 2013). The analysis of any RCM projection starts with the evaluation of the model simulations of past conditions against the observations (i.e., reference data) for different regions, and the testing of the model sensitivity with respect to the parameterisations of important physical processes (e.g., cloud formation and development, radiative processes)

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