This article provides an inventory based on Intergovernmental Panel on Climate Change (IPCC) reports that suggest that changes in the Earth’s system, and primarily atmospheric changes, can be attributed to global warming. The majority of the changes are connected with the phase change of the Earth’s water, changes in glaciers, and the decrease of ice cover. A further indication of this global change can be seen in the change of the annual course of precipitation in many places. In some regions droughts occur more frequently, while in other regions more intense precipitation has been recorded. The effects of global warming in agriculture and forestry are detected in the higher latitudes. The vegetation period starts earlier and the growing season has become longer and longer. Besides the evident rise in temperature that has been detected in meteorological data, significant changes were demonstrated in the observed marine and freshwater biological systems. The detected changes could be consequences of rising water temperature and of decreasing ice cover, of changes of salinity modification, and of change in oxygen content and circulation. After summarising the general signals of climate change, the impact of the warming that has started and that very probably will continue is assessed using the results of climate models and impact studies based on these models. We deal with climate change influences in the hydrosphere separately. Finally, we summarise the possible weather changes in Hungary and in its closest neighbors in the Carpathian Basin. The regional climate models show significant increases in temperature in every season. In the case of precipitation the future is more complicated. The only clear prognosis is that significant decreases could be forecasted in summer. The warming from 1980 to the present in accordance with the global tendency is not only evident in Hungary, but also more severe. The rate of warming is higher in Hungary than the global mean. The average increase for the period 2021–2050 in Hungary is expected to be 1–2°C, for 2071–2100 3–4°C. The average rainfall is expected to decline. However, with respect to the number of rainy days exceeding 20 mm of precipitation, the rain fall intensity shows a slight increase.

Összefoglalás. Jelen dolgozatban áttekintjük a víz körforgásának legfontosabb összetevőit, áramlási irányait. Bemutatjuk a párolgás és kondenzáció jelentőségét a légkör dinamikai folyamataiban. A jelenkori éghajlatváltozás hatásai meghatározó módon befolyásolják a globális vízkörforgalom valamennyi elemét: emelkedik a tengerek szintje, a légkörben tárolható vízgőz mennyisége, szélsőségesebbé válik a csapadék és az aszály területi és időbeli eloszlása. A csapadékintenzitásra vonatkozóan a hazai megfigyelések és számítások eredményeit is bemutatjuk. Felhívjuk a figyelmet a globális hidrometeorológiai monitoring rendszerek fontosságára, valamint a vízrajzi és meteorológiai közszolgáltatások összehangolt szemléletű kezelésének szükségességére. Ez vonatkozik az egyes fizikai változók megfigyelésére, ezek várható tér- és időbeli változásainak előrejelzésére, a klímapolitikák kialakítására – beleértve a kármérséklés és az alkalmazkodás problémaköreit. Summary. In this paper, we review the most important components and flow directions of the water cycle. Water is one of the special compounds of the Earth system: it can exist in solid, liquid and gaseous states under the prevailing temperature and pressure conditions on Earth, so it can be found in all terrestrial spheres. It plays a fundamental role in maintaining life, thermodynamic processes on a global scale, and regulating the climate. In the Earth’s atmosphere, on average, only every ten-thousandth molecule is water, yet it plays a decisive role in shaping atmospheric energetic and dynamic processes and, in regulating the climate. Through evaporation, condensation, cloud and precipitation formation, and air movements, the atmosphere plays the most important role in the continuous cycle of water between natural water reservoirs. It is typical of the dynamics of atmospheric processes that the average residence time of water molecules in the atmosphere is approx. 10 days, compared to the durations estimated for the ice sheet (12 thousand years) and the oceans and seas (3 thousand years). Water vapor is the most important greenhouse compound in the atmosphere, responsible for approximately 60% of the total atmospheric greenhouse effect. The movement of water vapor is mainly determined by atmospheric circulation processes. The effects of present climate change have a decisive influence on all elements of the global water cycle: the sea level rises, the amount of water vapor that can be stored in the atmosphere increases, the spatial and temporal distribution of precipitation becomes more extreme. The global environmental changes attributable to natural and anthropogenic causes are largely linked to water and the variability of the global water cycle. Natural phenomena on a regional and local scale, which can also be associated with global changes, pose a serious risk to life and property protection in certain situations, can adversely affect the conditions of agricultural management and damage natural ecosystems. Results of relevant Hungarian measurements are also presented. Floods, droughts and atmospheric storms, which are often accompanied by intense rainfall events, are collectively responsible for a very significant part of natural damage events. We draw attention to the importance of global hydrometeorological monitoring systems, as well as the need for coordinated management of hydrographic and meteorological public services. This applies to the observation of individual physical variables, the prediction of their expected changes in space and time, the development of climate policies - including the issues of mitigation and adaptation.