## 1 Introduction  
Acceleration in the rate of changes to the earth's climate system (ECS) that have been observed around the globe and its different geographical regions since the early 20 th century has become unprecedented over recent decades [1]. The evidence for rapid and dramatic climate change encompasses increasing the planet's average surface temperature, rising global sea level, reducing glacier net volumes, decreasing polar ice sheets and sea ice extent, changing heat stores in the ocean, changing rainfall patterns, and a range of other effects. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) states that \"Human influence has been detected in warming of the atmosphere and oceans, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climatic extremes\" [1]. One of the clearest indicators of climate change is the rise in global average surface temperature. According to the latest World Meteorological Organization's (WMO) report \"Statement on the State of the Global Climate in 2018\" published on March 2019 [2], \"The global mean temperature for 2018 is estimated to be \(0.99\pm 0.13\)\({}^{\circ}\)C above the preindustrial baseline (1850-1900).\" It is important that over two-third of that global mean temperature increase has occurred after 1980. This WMO's document also points out that other key climate change indicators (e.g., global mean sea level, Arctic and Antarctic sea-ice extent, greenhouse gas concentrations, extreme natural events) have become even more pronounced. The main cause of the current climate change is human activities and, above all, human-induced substantial emissions of greenhouse gases (GHG) into the atmosphere [1]. Research findings suggest that the shift to a warmer climate is accompanied by intensification of the hydrological (or water) cycle [1; 3; 4; 5; 6; 7; 8; 9; 10; 11] that describes the global circulation of water in its solid, liquid, and gas phases throughout the four geospheres (atmosphere, hydrosphere, lithosphere, and biosphere). The main physical processes that form the planetary hydrological cycle involve evaporation of water (mainly from the ocean surface to the atmosphere), condensation of atmospheric water vapor, multi-scale horizontal moisture transport (advection), precipitation that can take on different forms (e.g., rain, snow, ice crystals), runoff and snowmelt, interception, infiltration, transpiration, percolation, and storage. The hydrological cycle intensifies under global warming mainly because the amount of water that evaporates from the ocean and land to the air and the total water vapor content in the atmosphere will increase with temperature. Theoretical estimates and satellite observations suggest that as air temperature increases the saturated water vapor pressure increases as well by about 7% per Kelvin [5; 12; 13]. Indeed, let us write the approximate Clausius-Clapeyron relation assuming the latent heat of vaporization \(L_{w}\) is a constant:  
\[\frac{d\ln e_{s}}{dT}=\frac{L_{w}}{R_{w}T^{2}}.\]  
According to this equation, an infinitesimal change in temperature \(\Delta T\) is accompanied by a fractional change \(\Delta e_{s}/e_{s}\) in saturation vapor pressure of:  
\[\frac{\Delta e_{s}}{e_{s}}\approx\frac{L_{w}}{R_{w}T^{2}}\Delta T.\]  
Taking the value of \(T_{0}=273.16\) K as a reference temperature, we obtain that the fractional growth in \(e_{s}\) is \(\sim\)7% K\({}^{-1}\), meaning that to increase the temperature by 1 K results in the 7% increase in saturation vapor pressure. The observations also indicate that over the last two to three decades the precipitation has increased at about the same rate [12]. Since the hydrological cycle has a significant impact on the climate of our planet, its strengthening with rising global temperature may alter the weather patterns worldwide.