Picture (above): Clouds over a river near Esch-sur-Sûre, Diekirch, Luxembourg. Credit: Johny Goerend (Unsplash).

Despite widespread interest in hydrologic variability, there is currently no general climatology of the variability of the water cycle over land. This has limited the development of the underlying science of hydrologic extremes. This paper uses a recently published global hydrologic reanalysis (1 degree, 1984-2010) to present, for the first time, a global climatology of hydrologic variability.

The paper presents global maps and associated analysis of the inter-annual variance in evapotranspiration, runoff and soil moisture as well as precipitation.

The researchers found, – contrary to expectation – that the inter-annual variance in evapotranspiration is much smaller than that for precipitation, runoff and soil storage.

Using a theoretical framework based on the concept of source-sink variability, they show that accounting for hydrologic covariances explains why it is possible for variability in the principal sink (e.g., streamflow) to exceed variability in the source (precipitation).

The researchers concluded that a general framework for understanding hydrologic variability will require substantial scientific effort.

  • Paper: Yin, D. and Roderick, ML. 2020. Inter-annual variability of the global terrestrial water cycle. Hydrol. Earth Syst. Sci., 24(1): 381-396. doi: 10.5194/hess-24-381-2020