Impact of climate change on water resources status: A case study for Crete Island, Greece
Highlights
► Analysis and assessment of water resources availability, during the 21st century. ► 24 Scenarios of projected hydro-climatological regime, demand and supply potential. ► A robust signal of water scarcity is projected for all scenarios. ► Climate change plays an equally important role to water use and management. ► Necessity of improving and updating local strategic water management planning.
Introduction
Climate change is expected to affect precipitation and evapotranspiration patterns (Tsanis et al., 2011), and consequently variables such as local water availability, river discharge, and the seasonal availability of water supply (Arnell et al., 2011). As demand for freshwater on a global scale rises due to a variety of factors including population growth, water pollution and economic progress, land use and climate change render its availability into the future uncertain (Davies and Simonovic, 2011). Social and environmental aspects such as agriculture, tourism and biodiversity conservation are connected to water resources quality and availability, and therefore adaptation measures for water will be strongly bound with policies in a wide spectrum of disciplines (Iglesias et al., 2011).
The latest review on the current state of the art on climate change research for the Mediterranean region by Ludwig et al. (2011) shows that recently observed trends and projections from climate model ensembles indicate a strong susceptibility to change in hydrological regimes, an increasing general shortage of water resources and consequent threats to water availability and management. These projections enhance the necessity for more robust water management, pricing and recycling policies, in order to secure adequate future water supply and prevent tensions among users (García-Ruiz et al., 2011).
Despite the increasing research efforts, there are still considerable uncertainties in the future climate drivers and in how global hydrological systems will respond to their behaviour (Harding et al., 2011). A number of studies (e.g. Akhtar et al., 2008, Alcamo et al., 2007, Barnett and Pierce, 2009, Charlton and Arnell, 2011, Christensen and Lettenmaier, 2007, Fujihara et al., 2008, Georgakakos et al., 2012) have described the impacts of the expected climate change on global and regional water resources with respect to the various inherent uncertainties. The increasing availability of climatic outputs from general and regional circulation models provide the potential of exploring model uncertainties in predicting future climate through the use of ensembles, at global (Manning et al., 2009) but more importantly at regional scales where forcing data is often less accessible but more accurate.
Indicative of the instability in the Mediterranean is the island of Crete, where analysis of climate models data depicts that precipitation on average is likely to be less frequent but more intense and droughts are likely to become more frequent and severe in some regions (Koutroulis et al., 2010, Koutroulis et al., 2011, Tsanis et al., 2011). Shorter rainy periods and seasonality shifts could seriously affect water resources by significant reduction of water availability with wide ranging consequences for local societies and ecosystems. It is indicative that, during the last decade, the island of Crete has faced an increased number of droughts (Koutroulis et al., 2011). Moreover, the rapid development of Crete in the last 30 years has exerted strong pressures on many natural resources. Urbanization and growth of agriculture and tourism industry have strong impact on the water resources of the Island by substantially increasing water demand. Water use in Crete increased following the expansion of irrigated land by over than 55% during the period 1985–2000 (Donta et al., 2005). Regarding future water demands of the island, recent estimates forecast total uses for the year 2015 in the order of 550 Mm3/year, which represents 7% of the mean annual precipitation. This highlights that any arising water stress issue will be due to poor extraction or retention technology rather than actual availability. It is therefore considered essential to tackle the increasingly severe water problems that the island will face via strategic policies adopting to climate change by using integrated water management systems.
This paper assesses the implications of global climate change on the water resources status for the island of Crete for a range of 24 different scenarios from a combination of projected hydro-climatological regimes, demand and supply potentials. For this purpose, “state of the art” climate model results within WATCH FP6 (Harding et al., 2011) modelling framework under A2 and B1 emission scenarios and FP6 ENSEMBLES (van der Linden and Mitchell, 2009) regional climate model results under A1B emission scenario are compared, to explore the water resources availability during the 21st century. A two-step bias correction procedure is adopted to adjust precipitation on the observed long-term frequency and intensity distribution based on the period 1970–2000 (Ines and Hansen, 2006, Law and Kelton, 1982, Wood et al., 2002). The correction involves truncating the RCM rainfall distribution and then mapping it onto a gamma distribution fitted to the observed intensity distribution. The SAC-SMA hydrological model (Burnash, 1995) is used to estimate the evolution of hydrological variables and water availability on the island of Crete. The outcome of the analysis is useful for the comprehension of the role and consequently the priority of certain water resources related infrastructure development.
Section snippets
Framing the problem
The present water resources assessment includes various water management issues regarding actions up to present as well as future perspectives for policy, management and hydrological (climate) regime, resulting in the modelling framework presented in Fig. 1. These future scenarios include the augmentation of agricultural practices, improvement and extension of the already established irrigation network as well as tourism, permanent population and demand trends. For the purposes of this study,
Case study
The island of Crete occupies the southern part of the country of Greece (Fig. 2). With an area of 8265 km2, Crete covers almost 6.3% of the area of Greece. The mean elevation is 482 m ranging from sea level to 2450 m and the average slope 228 m/km with the topography fracturing into small catchments with ephemeral streams and karst geology. Crete has a typical Mediterranean island environment with about 53% of the annual precipitation occurring in the winter, 23% during autumn and 20% during spring
Historic hydrologic regime (1970–1999)
Continuous hydrological modelling for the 1970–1999 period resulted to the hydrologic regime of the reference period. Standardizing the balances with the respective basin areas, runoff is 10–15% of the approximately 934 mm or 7697 Mm3 of long term annual precipitation that falls on the island of Crete, almost equal with the fraction of water that infiltrates towards slow runoff (14–17%), whereas 68–76% of precipitation goes toward evapotranspiration (Table 2). The monthly estimated actual
Conclusions
Despite limitations and uncertainties, this study presents a wide range of draft estimates and results, providing water resources management community with a glimpse into a very plausible future where the quantitative impact of climate change on water availability can be substantial, especially in a Mediterranean island like Crete. RCM model results (Ensembles) project increased precipitation reduction and consequently show increased water insufficiency compared to GCM projections (WATCH).
Acknowledgments
The financial support of this work has been provided by the European Commission through the WATCH FP6, COMBINE FP7, IMPACT2C FP7 and ECLISE FP7 projects. The ENSEMBLES data used in this work was funded by the EU FP6 Integrated Project ENSEMBLES (Contract Number 505539) whose support is gratefully acknowledged. We also thank the three anonymous reviewers whose comments have improved the paper.
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