How does the water cycle work and how is fresh water distributed?

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1. 1

   Intensification of the global water cycle and evidence from ocean salinity: a synthesis review

   Annals of the New York Academy of Sciences (Yu et al.)Published May 9, 2020Checked Oct 11, 2026

   “It is the center of action for global evaporation and precipitation and supplies the moisture that falls as continental precipitation. It also acts to some extent as nature's rain gauge, as it tells us about the long-term changes in the global water cycle through monitoring of the changes in ocean surface salinity. As climate warms, the global water cycle is expected to intensify as a result of the strong nonlinear dependence of water vapor pressure (moisture-holding capacity) on temperature. Such change is of great concern, as it has profound socioeconomic impacts throughout the globe. Despite the evidence of an intensified global water cycle, two important questions remain: What is the pattern of the warming-induced intensification of the water cycle? and What is the rate of intensification? Our article provides a synthesis review of recent progress in diagnosing and understanding the changes in both the global water cycle and ocean salinity in recent decades. Targeted numerical ocean model experiments are also reviewed to provide insights into the response of salinity to the changes in evaporation-minus-precipitation flux, meltwater runoff, and ocean warming.”

2. 2

   China's freshwater lake storage hotspots revealed by bathymetry and typology mapping.

   National science review (Song et al.)Published Apr 25, 2026Checked Oct 11, 2026

   “While the western interior is numerically dominated by saline lakes, our volumetric assessment reveals a counterintuitive pattern in which a few large open lakes store ∼65% of the nation's lacustrine freshwater due to their exceptional depth. The freshwater lake hotspots present a marked geographic-demographic contrast. This imbalance results in a more significant disparity in per-capita natural lake freshwater storage, with ∼20 680 m³ per person in the Tibetan Plateau lake zone versus only 65 m³ in the eastern plain lake zone, a nearly 320-fold difference. Notably, a vast network of reservoirs is concentrated in the populous eastern region, and this distribution of artificial storage helps mitigate the spatial unevenness of total surface freshwater resources. Our findings not only establish a definitive baseline for China's lake water resources but also demonstrate how lakebed geomorphologic features influence national-scale lacustrine freshwater distribution, highlighting the critical need for targeted protection strategies and the efficient utilization of these lake freshwater reserves.”

3. 3

   The Global Water Cycle Budget: A Chronological Review

   Surveys in Geophysics (Godoy et al.)Published Aug 19, 2021Checked Oct 11, 2026

   “However, these data have not been comprehensive enough due to the high spatiotemporal variability of the global water cycle. Herein, we provide a comprehensive review of the chronological evolution of global water cycle quantification, the distinct data sources and methods used, and a critical assessment of their contribution to improving the spatiotemporal monitoring of the global water cycle. The chronology of global water cycle components shows that the uncertainty of flux estimates over oceans remains higher than that over land. Comparing the standard deviation and the interquartile range of the estimates from the 2000s onward with those from all the estimates (1905-2019), we can affirm that statistical variability has diminished in recent years. Moreover, the variability of ocean precipitation and evaporation estimates from the 2000 onward was reduced by more than $$70\%$$ 70 % compared with earlier studies. These findings advocate that the consistency of global water cycle quantification has been improved.”

4. 4

   Attribution of climate change and anthropogenic activities on regional to global scale water cycle: a comprehensive review

   Environmental Research Communications (Shaw et al.)Published Jul 22, 2026Checked Oct 11, 2026

   “These studies employ various techniques ranging from process-based to semi-empirical to statistical to machine learning. This paper provides a comprehensive review of conventional and emerging attribution methods for major hydrological components, including streamflow, evapotranspiration, water levels, and groundwater storage. While each method offers unique strengths suited to a particular application, they also exhibit certain limitations creating space for potential improvement, which are further discussed in this review. Furthermore, numerous attribution studies around the globe are surveyed to highlight well-studied and overlooked basins along with their results. We found that approximately 70% of the studied basins exhibit stronger influence from human activities than from climatic factors. Finally, we propose a decision framework to guide the selection of attribution method under specific constraints. This review offers a structured guide to selecting appropriate techniques, foster advancements in methodologies, and expansion of attribution research to under-studied regions.”

5. 5

   Global water cycle and the coevolution of the Earth’s interior and surface environment

   Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences (Korenaga et al.)Published Apr 17, 2017Checked Oct 11, 2026

   “The global water cycle, which circulates surface water into the deep mantle and back to the surface again, could thus have played a critical role in the Earth’s history. In this contribution, we first review the present-day water cycle and discuss its uncertainty as well as its secular variation. If the continental freeboard has been roughly constant since the Early Proterozoic, model results suggest long-term net water influx from the surface to the mantle, which is estimated to be 3−4.5×10 14 g yr −1 on the billion years time scale. We survey geological and geochemical observations relevant to the emergence of continents above the sea level as well as the nature of Precambrian plate tectonics. The global water cycle is suggested to have been dominated by regassing, and its implications for geochemical cycles and atmospheric evolution are also discussed. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’.”

6. 6

   Transforming global water cycle observations via synergistic AI and remote sensing.

   Science advances (Yao et al.)Published Jun 17, 2026Checked Oct 11, 2026

   “Current models that rely on region-specific empirical parameters and multistage workflows fail to robustly handle complex and accelerated water cycle with high spatiotemporal resolutions. Increasing parameter complexity for fine-scale representation under various terrestrial conditions becomes prohibitive. To address these limitations, we present bidirectional encoder representations from transformers for hydrology (BERTH), an end-to-end artificial intelligence (AI) framework for global water cycle monitoring at 30-meter and daily scale, directly transforming remote sensing radiance to evapotranspiration, precipitation, soil moisture, and runoff. As a transformative paradigm for quantitative Earth science, BERTH trained on global datasets precisely captures spatiotemporal dynamics across diverse conditions, surpassing existing geophysical models in accuracy. Embodying the synergistic integration of AI and remote sensing, BERTH offers a transformative platform that supports next-generation investigations into global water resources and Earth system dynamics.”