Revisiting the global hydrological cycle: is it intensifying?

Demetris Koutsoyiannis

Department of Water Resources and Environmental Engineering, School of Civil Engineering, National Technical University of Athens, Heroon Polytechneiou 5, GR 157 80 Zografou, Greece

Received: 11 Mar 2020 – Discussion started: 20 Mar 2020 – Revised: 31 May 2020 – Accepted: 30 Jun 2020 – Published: 07 Aug 2020

Abstract. As a result of technological advances in monitoring atmosphere, hydrosphere, cryosphere and biosphere, as well as in data management and processing, several databases have become freely available. These can be exploited in revisiting the global hydrological cycle with the aim, on the one hand, to better quantify it and, on the other hand, to test the established climatological hypotheses according to which the hydrological cycle should be intensifying because of global warming.

By processing the information from gridded ground observations, satellite data and reanalyses, it turns out that the established hypotheses are not confirmed. Instead of monotonic trends, there appear fluctuations from intensification to deintensification, and vice versa, with deintensification prevailing in the 21st century. The water balance on land and in the sea appears to be lower than the standard figures of literature, but with greater variability on climatic timescales, which is in accordance with Hurst–Kolmogorov stochastic dynamics.

The most obvious anthropogenic signal in the hydrological cycle appears to be the over-exploitation of groundwater, which has a visible effect on the rise in sea level. Melting of glaciers has an equal effect, but in this case it is not known which part is anthropogenic, as studies on polar regions attribute mass loss mostly to ice dynamics.

How to cite: Koutsoyiannis, D.: Revisiting the global hydrological cycle: is it intensifying?, Hydrol. Earth Syst. Sci., 24, 3899–3932, https://ift.tt/2PKmmpL, 2020.

From the Concluding remarks.

The most obvious anthropogenic signal in the hydrological cycle is the over exploitation of groundwater, which has a visible effect on the rise in sea level. Melting of glaciers has an equal effect, but in this case it is not known which part is anthropogenic as studies of polar regions attribute mass loss mostly to ice dynamics.

The above observations strengthen an earlier (Koutsoyian- nis et al., 2009) envisagement of the hydrological community’s role. Instead of a passive role in assessing hypothetical hydrological impacts based on doubtful climate model outputs, an active role consistent with its history is possible.

Indeed, hydrology has much more to offer to societies than prophesies of future catastrophes (cf. Koutsoyiannis, 2020a). During the 20th century, and particularly after the Second World War, hydrology, by supporting hydrotechnology, water management and risk assessment and reduction, within a strong international collaboration and a strong economy, has substantially contributed to human life as a value and to the quality and length of human life

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August 8, 2020 at 08:19AM

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