The Two European Hydrological Cycles:

closing of the first loop).
A "second critical threshold" can then be crossed in the second feedback loop during
intense Mediterranean cyclogenesis events, when torrential rains trigger mud flows over the
drier and vegetation-deprived mountain slopes already affected by the first feedback loop.
This can result in massive soil losses and a further reinforcement, and propagation of the
effects caused by the first feedback loop, etc. Available evidence not only indicates that
these processes and feedbacks have been operating in the Mediterranean for a long time,
but also suggests that fundamental changes, and long-term perturbations to the European
water-cycle (droughts and floods), are taking place right now.
This analysis further suggests that: up to 75% (or more) of the precipitation in southern
Europe, i.e., from Summer storms and Mediterranean Cyclogenesis, originates from water
that first evaporates and then precipitates, i.e., it is recirculated, within the major
Mediterranean drainage basin (i.e., all the areas south and east of the European Continental
Divide including the Mediterranean and Black seas, Slides 25 and 27). Moreover, on the
Mediterranean side of this divide, rain of Atlantic origin contributes less than � 20% of the
total (probably even less than that in Greece), in stark contrast with the Atlantic side of the
European Divide where � 80% or more of the precipitation is from water evaporated over the
Atlantic (Slides 28-29).
Finally, land-use appears to play a key role in the loss of summer storms, the shift to more
frequent vertical recirculation periods, and the amount of water recirculated within the basin.
These findings and the questions they raise are critical for European Union water policies in
Southern Europe because:
(a) water from precipitation tends to be treated as a given resource without duly
considering its origins,
(b) disaggregation of precipitation components is not normally performed in climatic
studies and,
(c) the feedback processes in the hydrological cycle, which govern the partitioning and
the recycling of the precipitation in each region, cannot be simulated in the Global
Models used to assess future water scenarios for Europe.
Thus, the decisions on the future of the water cycle, and particularly the timing of such
decisions, could be absolutely wrong and have catastrophic consequences for Southern
Europe. This work presents a summary of the evidence we use to support this statement
(Slide 31).