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  • Final Report Summary - CLIM-HYDROLAKE (Improving future projections of climate change induced hydrological responses by looking into the past: the Lake Prespa / Aliakmonas River case study in Greece)

Final Report Summary - CLIM-HYDROLAKE (Improving future projections of climate change induced hydrological responses by looking into the past: the Lake Prespa / Aliakmonas River case study in Greece)

CLIM-HYDROLAKE ( stimulates knowledge-exchange and long-term career integration through implementation of a multi-disciplinary research project at the National Observatory of Athens (Greece). The project advances knowledge by improving projections of hydrological responses to regional climate change, using a novel multi-proxy methodology combining hydro-climate modelling and palaeo-hydrological techniques.

Models broadly agree upon future impacts of climate change in the Mediterranean, but regional hydrological response projections are subject to a large degree of uncertainty. Improvement of such projections can be achieved through palaeo-hydrological studies, that (i) provide analogues with past (often non-linear) hydrological system responses to climate change, (ii) extend short observational records, thus enabling testing of hydrological model projections on relevant multi-decadal / centennial timescales, and (iii) provide base-line data required for evidence-based policy development and management strategies.

The study focuses on the wider Prespa catchment which is of great socio-economic importance for Greece, Albania and FYROM. The dramatic -unexplained- fall of Lake Prespa threatens the catchment’s water quantity/quality; this is particularly alarming as Prespa is a global biodiversity hotspot. Future climate scenarios predict increasing droughts and declining precipitation. Understanding lake hydrology is thus of utmost importance, as this forms the basis to providing accurate impact projections of climate change. To further this understanding, it is essential to supplement short observational records with past absolute lake level reconstructions.

The Prespa Lake Basin has an excellent beach ridge sediment archive that allows absolute lake level and quantitative palaeoclimate reconstructions. Reconstructing past climate and -hydrological changes permits also the identification of teleconnection patterns that operate on multi-decadal to centennial timescales. These patterns are highly significant for future projections of climate-induced hydrological responses throughout the wider region.

Key research goals are:
• Improving understanding of present-day lake level change;
• Providing a ~1500yr palaeohydrological record;
• Delivering new downscaled climate-model projections that drive lake responses to future climate change.

Research for CLIM-HYDROLAKE yielded novel, important findings. We prove, for the first time, that: (i) annual lake level variability is driven by wet season (Oct-Apr) precipitation, (ii) multi-annual wet season precipitation- and lake level variability are highly (negatively) correlated to the North Atlantic Oscillation (NOA), and (iii) the dramatic fall in lake level (1987-1995) was caused by multi-decadal water abstraction (amplified by climate change), while its timing was determined by a major regional hydrological drought period. These results are highly significant for water resource issues in the wider catchment, and prove for the first time the strong human impact on lake variability. The findings pave the way for new management adaptation/mitigation strategies regarding biodiversity and water resources.

Another key discovery, with regional implications, is that catchment climate changed over the past decades. Average annual rainfall shows a clear, albeit statistically non-significant, downward trend. There are statistically significant decreases in average annual snowfall, cumulative Oct-Mar rainfall, and annual runoff, while droughts are increasing. Wet season precipitation / snow cover are allied to the NAO winter index, with negative phases linked to more precipitation; this connection of the catchment area to global atmospheric circulation patterns is highly significant for both future impact projections and the interpretation of palaeo-climate records.

The lake mainly adjusts to changes in its moisture balance through increasing/decreasing the lake surface area and thus lake evaporation. Lake bathymetry is therefore of key importance in calculating water level movements in case of multi-decadal changes in the lake moisture balance. This finding is important both for future lake-hydrological impact projections and for quantifying past lake level changes.

Palaeo-hydrological analyses show that low lake levels coincided with the Medieval Warm Period (900-1430AD), while higher (fluctuating) lake levels occurred from the Little Ice Age (1450-1900AD) up to 1987. This pattern shows great similarities with lake level and flood behaviour over the past millennium in the NW Mediterranean region which has been linked to the multi-decadal NAO winter index. This link has never been proven over multi-centennial timescales in the S Balkans before. It suggests that the influence of the NAO on wet season precipitation is stable over multi-decadal to multi-centennial timescales.

Finally, climate impact projections indicate that annual- and wet season precipitation does not change for the Prespa catchment over the coming century. However, summer temperatures will rise significantly under all explored climate change scenarios and will lead to (much) higher lake surface evaporation rates. This will cause a further fall in lake level, perhaps even to 830m (14m drop to current levels) leading to a dramatic shrinkage of the lake. However, these scenarios depend to a great extent on developments in water abstraction; if it can be stabilised or decreased, the lake level fall may be limited to 2-4m.

CLIM-HYDROLAKE intensively cooperated with the Society for the protection of Prespa, Prespa Park Authorities (PPA) and the regional government. New research findings therefore directly informed innovative management adaptation / mitigation strategies, as well as agricultural adaptation plans, aimed at protecting lake water resources and biodiversity. Of particular significance is the role of our project partner, the SPP, in advising on the tri-national Prespa Basin Management Framework (based on the EU’s Water Framework Directive). Study results therefore informed directly this highly important management framework regulates future biodiversity conservation and water resource availability. Finally, and most importantly regarding the impact of CLIM-HYDROLAKE, the new collaborative LIFE project (LIFE15-NAT_GR_000936) will implement the research findings from CLIM-HYDROLAKE under the researchers direction.

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