Regional impacts of climate change on water resources quantity and quality indicators

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Abstract

The aim of this paper is to assess the impacts of climate change on water resources (surface runoff) and on water quality. Two GCM-based climate change scenarios are considered: transient (HadCM2) and equilibrium (UKHI). A conceptual, physically based hydrological model (WBUDG) is applied on a catchment in central Greece, simulating the effect of the two climate scenarios on average monthly runoff. A newly developed in the stream model (R-Qual) is applied in order to simulate water quality downstream of a point source under current and climatically changed conditions. Simulated parameters include monthly concentrations of BOD, DO and NH4+.

Both scenarios suggest increase of temperature and decrease of precipitation in the study region. Those changes result in a significant decrease of mean monthly runoff for almost all months with a considerable negative impact on summer drought. Moreover, quality simulations under future climatic conditions entail significant water quality impairments because of decreased stream flows.

Introduction

The research work presented herein originates from two EU funded research programmes (EUROTAS and CHESS, both funded under the fourth FP—DGXII) that address the impacts of ‘greenhouse’ warming on water resources quantity and quality on a catchment, regional and European scale.

The study area is the Pinios river basin, situated in the central part of Greece. Because of an intensive cultivation, water needs are considerable. Additionally, the large application of pesticides and fertilisers can cause serious degradation of the quality of the surface and groundwater of the basin. Because of physical, chemical and biological processes occurring within the river, the river's role is far from that of a conduit for the transport of inputs. These processes have a strong purifying effect leading to an improvement of water quality downstream from a source of pollution. A quality parameter of primary importance that accelerates these processes is the dissolved oxygen concentration. Hence purification is largely dependent on the continued oxygenation of the river water, which is enhanced under high flow conditions that encourage surface aeration. On the contrary the aggregated contribution of pollutants under low flow conditions can cause serious downstream problems regarding water quality. Eutrophication, which is caused by excessive levels of nutrients, is the most notable example.

The climate change scenarios are constructed by the Climatic Research Unit (CRU) of the University of East Anglia (UK) and are the results of two climate change experiments based on the General Circulation Models (GCM) (Hulme et al., 1994). More specifically, one equilibrium experiment, UKHI and one transient experiment, HADCM2 are applied. Changes refer to rainfall, temperature and potential evapotranspiration.

In order to estimate the hydrological effects of climate changes, a conceptual, physically based water balance model (WBUDG), developed for this purpose, is applied. It allows the calculation of surface runoff, soil moisture and actual evapotranspiration. Water quality parameters are estimated by using an in stream model (R-Qual), which in combination with the WBUDG model allows a complete simulation of flows and water quality, under current and changed climatic conditions up to the terminal year 2050.

Section snippets

Study region and data used

The Pinios river is located in the Thessaly district (central part of Greece) The total drainage area of the river is 9.450 km2, with a varied topography from narrow gorges to wide flood plains.

The Pinios catchment area consists of 15 sub basins drained by the main river and its five most important tributaries. Owing to lack of sufficient data for most sub basins, the study focuses on the Ali Efenti sub basin (Fig. 1), for which reliable hydrometeorological time series of adequate length are

Climate change scenarios

The climate scenarios used have been constructed by the Climatic Research Unit (CRU) of the University of East Anglia, England.

The methodology adopted used the CRU 1961–1990 baseline climatologies for Europe, the results from two GCM (General Circulation Models) climate change experiments (UKHI and HadCM2) and a range of projections of global warming calculated by MAGICC (Model for the Assessment of Greenhouse gas Induced Climate Change), a simple upwelling-diffusion energy balance climate

Water quantity

The assessment of climate change impacts on several water resources quantity indicators was based on the use of a monthly water balance model (WBUDG), developed for this purpose. The flow chart of the model structure is shown in Fig. 2. The main input parameters are precipitation, temperature, relative humidity, sunshine duration and wind speed. The main output parameters are evapotranspiration, soil moisture and stream runoff. Details on the model operation can be found in a series of previous

Results

Table 6 presents the mean monthly runoff for the terminal year 2050, regarding the base run, UKHI change and HadCM2 change. Additionally and for comparison, the percent increase or decrease of the climatically changed runoff from the base run is also given.

It has been estimated that there will be a significant decrease of the mean monthly runoff for all months by taking into account climate change from the transient experiment. A significant decrease of the mean monthly runoff for almost all

Conclusions

Basic conclusions drawn from this research are the following:

  • Both scenarios seem to give reasonable and quite consistent results. The transient scenarios (HadCM2) give more significant changes than the equilibrium (UKHI).

  • Mean annual runoff values are reduced.

  • Mean winter runoff values (November–April) are reduced.

  • The most significant reduction is expected in mean summer runoff values (May–October).

  • The results on runoff change are in accordance with results drawn from previous relevant research

Acknowledgements

This research was supported by the Environment and Climate Programme of the EU, DGXII, in the framework of the contracts ENV4-CT97-0535 (EUROTAS: European River Flood Occurrence and Total Risk Assessment) and ENV4-CT97-0440 (CHESS: Climate, Hydrochemistry and Economics of Surface—Water Systems).

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