Vol. 69 - special issue * Pages 1–44 * July 2024

Understanding the present and past climate, quantifying change and variability is only possible by analysing meteorological measurements and observations. The source of the climate database is the measurements from meteorological stations, which have changed significantly in recent decades thanks to automation.  Accordingly, the HungaroMet climatological database contains data that has been constantly changing in frequency and quality from the beginning of the measurements to the present day. In addition, the digitalization of measurements is still ongoing. As a consequence, data verification, homogenization and, if necessary, completion are crucial for studies on climate understanding and change. The aim of homogenization is to remove unreasonable breaks in the data series due to station relocations and changes in measurement methods while keeping the climate change signal. The application of homogenisation on an adequate mathematical statistical basis allows the data series of a given station to be examined as if the measurements had always been taken at the same location and under the same conditions. Spatially representative data can be obtained by mathematically based interpolation.

The suggested way to describe the state of the climate is in terms of 30-year averages, or climate normals. By analysing the normal values over successive 30-year periods, we can also get a comprehensive picture of climate change. In our study, we examine the mean temperature and precipitation normals since the beginning of the 20th century. Climate atlases are typically based on the most recent normal period, but nowadays they attempt to follow observed climate change also, for example by analysing changes in climate normals. HungaroMet has also undertaken to produce a new climate atlas based on data for the period 1991–2020. In addition to the current state of the climate, the atlas will present the observed and projected climate for the period 1901–2100 using measurements and climate model results.

The Hungarian meteorological service satisfies the information need on future climate change from multiple sources. The 10 km resolution climate projections based on the in-house simulations of the ALADIN-Climate and REMO regional climate models (RCM) as well as the EURO-CORDEX RCM results have been updated in the last few years. Local climate phenomena have been studied using non-hydrostatic climate models, while urban climate impacts have been explored with the SURFEX s urface model at 1 km resolution. The KLIMADAT database is established based on measurement and simulation data over Hungary and it provides climate information covering the country with 10 km resolution until 2100 with a more detailed focus on Budapest at 1 km resolution. In the framework of climate service strategy of the meteorological service, the database supports climate adaptation and related communication.

In frame of the „Drinking water: multidisciplinary assessment of secure supply from the source to the consumers” project water quality field measurement were carried out on the Danube for 12 months upstream and downstream of Budapest, and later the measurements were used for building a water quality model. The calibrated models are capable of estimating the effect of climate change. We selected two climate scenarios and projected the discharge and water temperature time series to 2100 and finally compared modelling results to the baseline results. We analysed the possibilities of long term projection of the boundary conditions and compared the changes modelled by MIKE21FM and EcoLab to the conclusions of the field measurements.

The Atlantic Meridional Overturning Circulation plays a major role in shaping the climate of our planet, especially in Europe. Because the ocean and atmosphere are in constant interaction, global climate change can also modify the ocean circulation. Investigating changes in the AMOC is a complicated task due to the insufficiency of the instrumental measurements and the uncertainty of historical reconstruction data. Based on climate model simulations AMOC is expected to slow down by the end of the century, which would result in an overall cooler climate in Europe than in present times.