Hydrological Cycle in the Danube basin in present-day and XXII century simulations by IPCCAR4 global climate models

TL;DR

This study evaluates 20 global climate models' ability to simulate the hydrological cycle in the Danube basin for historical and future scenarios, highlighting model discrepancies and challenges in predicting climate change impacts.

Contribution

It provides a comprehensive intercomparison of GCMs' performance in simulating the Danube hydrological cycle and assesses future changes under climate scenarios.

Findings

Model simulations encompass observed water balances.

Reanalyses are unreliable as verification benchmarks.

Future scenarios show decreased water balance and increased variability.

Abstract

We present an intercomparison and verification analysis of 20 GCMs included in the 4th IPCC assessment report regarding their representation of the hydrological cycle on the Danube river basin for 1961-2000 and for the 2161-2200 SRESA1B scenario runs. The basin-scale properties of the hydrological cycle are computed by spatially integrating the precipitation, evaporation, and runoff fields using the Voronoi-Thiessen tessellation formalism. The span of the model simulated mean annual water balances is of the same order of magnitude of the observed Danube discharge of the Delta; the true value is within the range simulated by the models. Some land components seem to have deficiencies since there are cases of violation of water conservation when annual means are considered. The overall performance and the degree of agreement of the GCMs are comparable to those of the RCMs analyzed in a previous work, in spite of the much higher resolution and common nesting of the RCMs. The reanalyses are shown to feature several inconsistencies and cannot be used as a verification benchmark for the hydrological cycle in the Danubian region. In the scenario runs, for basically all models the water balance decreases, whereas its interannual variability increases. Changes in the strength of the hydrological cycle are not consistent among models: it is confirmed that capturing the impact of climate change on the hydrological cycle is not an easy task over land areas. Moreover, in several cases we find that qualitatively different behaviours emerge among the models: the ensemble mean does not represent any sort of average model, and often it falls between the models' clusters.