Climate Change, Ecosystems and Hydrology;
How Ecosystems Adjust Their Root Zone Storage Capacity.
Hubert Savenije1
1

Delft University of Technology, The Netherlands
Email: H.H.G.Savenije@tudelft.nl

Climate, Ecosystems and Hydrology are closely connected and have co-evolved overtime. Understanding the mechanisms of co-evolution is key to understanding (and predictionof) how climate, ecosystems and hydrology change over time. Ecosystems, like climate andhydrology are not in steady state. They change over time, but do so in conjunction. The factthat a certain ecosystems exists in a particular setting is prove that it survived the conditionsof the past and evolved in interaction which its climatic and hydrological drivers. In turn,ecosystems influence hydrology and even climate, implying that these three system elementsco-evolve over time. In the Anthropocene, societies are part of this complex system, whereby
societies not only depend on climate, ecosystems and hydrology, but also influence them.
This fact is the motivation for the IAHS decade on Panta-Rhei, which uses socio-hydrology as
the science to enhance our understanding of this complex interaction (Sivapalan et al., 2012).
This mutual interaction is not only a complication for hydrological modelling, it is also
the way to help us understand the interdependency between climate and importanthydrological variables, such as the root zone storage capacity of ecosystems. Recent research
has shown that it is possible to derive a key hydrological model parameter, such as the rootzone storage capacity, from climate information (Gao et al., 2014). This knowledge can help
us to predict how the structure of hydrological models will change over time, in response toclimatic change. In this presentation, an example is given of a scale-independent hydrologicalmodel, parameterized on the basis of climatic time series, which can predict evaporation andrunoff both at local and global scale (Wang et al., 2016). The Figure shows how the root zone
storage capacity (mm) varies over the world. We can see that this capacity is largest in thesubtropics, or in the tropics where evergreen forests have to overcome extended periods ofdrought. In places where rainfall occurs throughout the year, the storage capacity is smaller,even if the evaporative demand is large (e.g. on the equator). In the colder parts of the world,
where the evaporative demand is low and rainfall is high, the storage capacity is small. In the(semi-)deserts the storage capacity is also small because there is no vegetation, or thevegetation that is present has other coping mechanisms to overcome a drought.

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So in conclusion we can see that the root zone storage capacity is the result ofcoevolution between ecosystem and climate, whereby the ecosystem has created sufficientbuffer to overcome the variability of the local climate.
REFERENCES
Gao, H., M. Hrachowitz, S.J. Schymanski, F. Fenicia, N. Sriwongsitanon, H.H.G. Savenije(2014), Climate controls how ecosystems size the root zone storage capacity at catchment
scale, Geophysical Research Letters, 41, 7916-7923, doi: 10.1002/2014GL061668.
Sivapalan, M., H.H.G. Savenije, and Guenter Bloeschl (2012), Socio-hydrology: A newscience of people and water, Hydrological Processes, 26, 1270-1276 doi: 10.1002/hyp.8426
Wang-Erlandsson, L., W. G. M. Bastiaanssen, H. Gao, J. Jägermeyr, G. B. Senay, A. I. J. M.
van Dijk, J. P. Guerschman, P. W. Keys, L. J. Gordon, and H. H. G. Savenije (2016),
Global root zone storage capacity from satellite-based evaporation. Hydrol. Earth Syst.
Sci., 20, 1459–1481, doi:10.5194/hess-20-1459-2016-6-