Modifications in energy demand in urban areas as a result of climate changes: an assessment for the southeast Mediterranean region

Abstract

The impact of climate changes on the urban environment may be assessed by calculating the modifications in energy production and consumption for such daily operations as heating and cooling. In this study climate changes in the southeastern Mediterranean (the area of Greece) were simulated for the year 2030 on the basis of specially constructed climatic scenarios which describe potential reductions in the emissions of greenhouse gases, and were, thereafter, used to calculate the heating and cooling degree days for the same year. The results show that the cumulative amount of heating and cooling degree days will decrease and increase, respectively, as compared to the respective amounts for the year 1990. In terms of the cooling degree days, it was found that the areas most affected were the Attica and central Macedonia regions, the Aegean islands and Crete, whereas in terms of the heating degree days, it was found that a large part of the country will require less energy for heating.

Introduction

Use of natural resources, especially solid fuels, results in the annual release of billions of tons of carbon dioxide in the earth’s atmosphere. In addition, methane, nitric oxides and chlorofluorocarbons are also released due to human activities. As a result the atmospheric concentrations of such gases, termed greenhouse gases, have increased with considerable impacts on global climate and on surface temperature. In particular, since the end of the 19th century, a global warming of 0.5°C is observed, whereas since the middle of the 1970s, the increasing trend exhibits a faster rate [18], [8], [9].

The area of Europe and especially the Mediterranean have been the subject of several research studies in terms of the climatic variations [1], [4], [6], [10], [11], [13], [14], [15], [16], [17].

According to the European Climate Assessment [5], the variation of annual and seasonal mean temperatures during the last century for a number of European stations indicates a warming trend for almost all parts of Europe. It should be mentioned, however, that a relative cooling is observed for the eastern Mediterranean for the period 1981–1990. According to the same report, the annual mean precipitation fluctuations during this century for a number of Mediterranean stations indicate decreasing precipitation in southern Europe.

In 1996, Paluticof and Wigley [14] estimated the temperature changes for the Mediterranean on the assumption that carbon dioxide is abruptly doubled to find increases from 0.7°C to 1.6°C for every degree of the mean global temperature increase. Cubasch et al. [4] found that by the year 2100, the temperature increases will be 2.5°C for the Mediterranean sea, 3–4°C for the coastal zones of the Mediterranean and 5.5°C for Morocco. Finally Rosenzweig and Tubiello [16] reported that a temperature increase from 1.4° to 2.6°C may occur in the Mediterranean due to the increased emissions of greenhouse gases as early as 2020. It should be mentioned that the results of these studies disregard the role of aerosols, which may compensate partially the warming trend. According to Mitchell et al. [12], the temperature in the Mediterranean may decrease by 1–2°C between 1975 and 2030–2050, whereas according to Hasselmann et al. [7], a possible decrease in temperature in the central Mediterranean is possible, especially during summer.

It is expected that climate changes will affect energy production and consumption in an immediate manner. A complete analysis of the relationship between energy and climate would require a thorough assessment of the role of several parameters which result in the production of greenhouse gases, influence the energy budget, act as control factors regarding potential changes, and enhance or limit the impacts of the resulting climate changes. For the purposes of this study, it is considered satisfactory to use the energy demand for heating and cooling of buildings as an indicator of the impact of climate on the energy sector. In particular, this is achieved through estimation of the heating and cooling degree days (hereinafter referred to as HDD and CDD, respectively).

HDDs, calculated with the sine method, are the annual cumulative amount of daily mean temperatures below a specified threshold temperature. This threshold is selected in order to represent a reference outdoor temperature. If the actual outdoor temperatures do not exceed the reference one, heating is activated to sustain the indoor temperatures. The smaller the outdoor temperature, the higher is the sum of the HDDs and the higher is the energy demand for heating.

CDDs are the annual cumulative amount of daily mean temperatures over a specified threshold temperature. This threshold is selected in order to represent a reference outdoor temperature. If the actual outdoor temperature exceeds the reference one, cooling of the buildings is required.

For HDDs, the reference outdoor temperature is selected to be slightly lower than the minimum temperature which is required in the buildings to compensate for the “occupancy” and “activity” corrections. The former relates to the fact that in addition to the heat provided by the domestic heating device, heat is being also offered by electrical lights, operating machines, and even the employees and the residents. The latter takes into account the activities of the people which live or work in the building.

For the purposes of this study, the reference threshold values are 15.5°C and 18.0°C for HDD and CDD, respectively.