Exploring the properties of basin storages and their effects in the partition of precipitation under future climate conditions

Water storage is one of the main functions that define any hydrological system. It serves as a link between the input and output of the system and it regulates the magnitude and intensity of the output. Due to long term climate variability; atmospheric and hydrological variables of moisture and energy change as inputs to a hydrological system. This non-stationarity might alter the storage properties affecting its state and availability for outputs such as evapotranspiration and runoff. In this paper we use a global multi-model outputs to analyze the different relations between fluxes and stores in large river basins. We explore the hypothesis that, except for snow, the storage capacity of a river basin is finite, i.e. there is an upper limit where storage overflows. We intend to determine the maximum storage levels in the 35 largest basins in the world in the present period, how this maximum storage level is maintained in future projections, and how it affects runoff and evaporation ratios in the future. We are able to determine different storage behaviors in different climatologies around the world. Tropical humid basins are constantly reaching their maximum levels in storage and displaying a nonlinear asymptotic relation. We found that with projections showing increases in precipitation, the maximum storage level is maintained and the basins become more saturated increasing their runoff ratio. Similar behavior is observed in temperate basins not dominated by snow, although due to less humidity basins reach their maximum storage levels less frequently, showing a more linear relation. Due to the abrupt occurrence in events, and the extreme aridity, dry basins display a lot of scattering in their relations and it is not possible to determine their maximum storage. In snow dominated basins, the determination of a maximum storage level is hampered due to the inconsistent timing of high precipitation, runoff and storage, especially in basins which part of their territory is inside the arctic circle. Although further exploration is required, particularly in regions dominated by high aridity or snow, determining the maximum storage levels is possible under certain climatological conditions and it is of high importance to understand changes on the partition of precipitation and the short and long term sensitivities of runoff.