Browsing by Author "Koutroulis, Aristeidis"

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    Changes in climate extremes, fresh water availability and vulnerability to food insecurity projected at 1.5° C and 2° C global warming with a higher-resolution global climate model
    (The Royal Society Publishing, 2018-04-02) Betts, Richard A.; Alfieri, Lorenzo; Bradshaw, Catherine; Caesar, John; Feyen, Luc; Friedlingstein, Pierre; Gohar, Laila; Koutroulis, Aristeidis; Lewis, Kirsty; Morfopoulos, Catherine; Papadimitriou, Lamprini; Richardson, Katy J.; Tsanis, Ioannis; Wyser, Klaus
    We projected changes in weather extremes, hydrological impacts and vulnerability to food insecurity at global warming of 1.5°C and 2°C relative to pre-industrial, using a new global atmospheric general circulation model HadGEM3A-GA3.0 driven by patterns of sea-surface temperatures and sea ice from selected members of the 5th Coupled Model Intercomparison Project (CMIP5) ensemble, forced with the RCP8.5 concentration scenario. To provide more detailed representations of climate processes and impacts, the spatial resolution was N216 (approx. 60 km grid length in mid-latitudes), a higher resolution than the CMIP5 models. We used a set of impacts-relevant indices and a global land surface model to examine the projected changes in weather extremes and their implications for freshwater availability and vulnerability to food insecurity. Uncertainties in regional climate responses are assessed, examining ranges of outcomes in impacts to inform risk assessments. Despite some degree of inconsistency between components of the study due to the need to correct for systematic biases in some aspects, the outcomes from different ensemble members could be compared for several different indicators. The projections for weather extremes indices and biophysical impacts quantities support expectations that the magnitude of change is generally larger for 2°C global warming than 1.5°C. Hot extremes become even hotter, with increases being more intense than seen in CMIP5 projections. Precipitation-related extremes show more geographical variation with some increases and some decreases in both heavy precipitation and drought. There are substantial regional uncertainties in hydrological impacts at local scales due to different climate models producing different outcomes. Nevertheless, hydrological impacts generally point towards wetter conditions on average, with increased mean river flows, longer heavy rainfall events, particularly in South and East Asia with the most extreme projections suggesting more than a doubling of flows in the Ganges at 2°C global warming. Some areas are projected to experience shorter meteorological drought events and less severe low flows, although longer droughts and/or decreases in low flows are projected in many other areas, particularly southern Africa and South America. Flows in the Amazon are projected to decline by up to 25%. Increases in either heavy rainfall or drought events imply increased vulnerability to food insecurity, but if global warming is limited to 1.5°C, this vulnerability is projected to remain smaller than at 2°C global warming in approximately 76% of developing countries. At 2°C, four countries are projected to reach unprecedented levels of vulnerability to food insecurity. This article is part of the theme issue ‘The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels’.
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    Global water availability under high-end climate change : A vulnerability based assessment
    (Elsevier, 2019-01-29) Koutroulis, Aristeidis; Papadimitriou, Lamprini; Grillakis, M.G.; Tsanis, I.K.; Warren, R.; Betts, R.A.
    Global sustainability is intertwined with freshwater security. Emerging changes in global freshwater availability have been recently detected as a combined result of human interventions, natural variability and climate change. Expected future socio-economic and climatic changes will further impact freshwater resources. The quantification of the impacts is challenging due to the complexity of interdependencies between physical and socio-economic systems. This study demonstrates a vulnerability based assessment of global freshwater availability through a conceptual framework, considering transient hydro-climatic impacts of crossing specific warming levels (1.5 °C, 2 °C and 4 °C) and related socio-economic developments under high-end climate change (RCP8.5). We use high resolution climate scenarios and a global land surface model to develop indicators of exposure for 25,000 watersheds. We also exploit spatially explicit datasets to describe a range of adaptation options through sensitivity and adaptive capacity indicators according to the Shared Socioeconomic Pathways (SSPs). The combined dynamics of climate and socio-economic changes suggest that although there is important potential for adaptation to reduce freshwater vulnerability, climate change risks cannot be totally and uniformly eliminated. In many regions, socio-economic developments will have greater impact on water availability compared to climate induced changes. The number of people under increased freshwater vulnerability varies substantially depending on the level of global warming and the degree of socio-economic developments, from almost 1 billion people at 4 °C and SSP5 to almost 3 billion people at 4 °C and SSP3. Generally, it is concluded that larger adaptation efforts are required to address the risks associated with higher levels of warming of 4 °C compared to the lower levels of 1.5 °C or 2 °C. The watershed scale and country level aggregated results of this study can provide a valuable resource for decision makers to plan for climate change adaptation and mitigation actions.
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    Simulating hydrological impacts under climate change: implications from methodological differences of a pan European assessment
    (MDPI, 2018-09-26) Koutroulis, Aristeidis; Papadimitriou, Lamprini; Grillakis, Manolis G.; Tsanis, Ioannis K.; Wyser, Klaus; Caesar, John; Betts, Richard A
    The simulation of hydrological impacts in a changing climate remains one of the main challenges of the earth system sciences. Impact assessments can be, in many cases, laborious processes leading to inevitable methodological compromises that drastically affect the robustness of the conclusions. In this study we examine the implications of different CMIP5-based regional and global climate model ensembles for projections of the hydrological impacts of climate change. We compare results from three different assessments of hydrological impacts under high-end climate change (RCP8.5) across Europe, and we focus on how methodological differences affect the projections. We assess, as systematically as possible, the differences in runoff projections as simulated by a land surface model driven by three different sets of climate projections over the European continent at global warming of 1.5 °C, 2 °C and 4 °C relative to pre-industrial levels, according to the RCP8.5 concentration scenario. We find that these methodological differences lead to considerably different outputs for a number of indicators used to express different aspects of runoff. We further use a number of new global climate model experiments, with an emphasis on high resolution, to test the assumption that many of the uncertainties in regional climate and hydrological changes are driven predominantly by the prescribed sea surface temperatures (SSTs) and sea-ice concentrations (SICs) and we find that results are more sensitive to the choice of the atmosphere model compared to the driving SSTs. Finally, we combine all sources of information to identify robust patterns of hydrological changes across the European continent.