The mitigation of the heat island effect can be achieved by the use of cool materials that are characterized by high solar reflectance and infrared emittance values. Several types of cool materials have been tested and their optical and thermal properties reveal that these materials can be classified as "cool" with the ability to maintain lower surface temperatures. Cool materials can be used on buildings and other surfaces of the urban environment. Based on these results, a modeling study was undertaken to assess the urban heat island effect over Athens, Greece, a densely populated city, by trying to analyze the impacts of large-scale increases in surface albedo on ambient temperature. Numerical simulations were performed by the "urbanized" version of the nonhydrostatic fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5, version 3-6-1). Two scenarios of modified albedo were studied: a moderate and an extreme increase in albedo scenario. It was found that large-scale increases in albedo could lower ambient air temperatures by 2°C. Furthermore, the impact of high albedo measures on heat island magnitude was estimated by creating a spatial representation of the urban heat island effect over the modeled area. The results of this study can help to promote the adoption of high albedo measures in building energy codes and urban planning regulations.

Agricultural landscapes illustrate the impact of human actions on physical settings, and differential human pressures cause these landscapes to change with time. Our study explored changes in the terraced landscapes of Nisyros Island, Greece, focusing on the socioeconomic aspects during two time periods using field data, cadastral research, local documents, and published literature, as well as surveys of the islanders. Population increases during the late 19th to early 20th centuries marked a significant escalation of terrace and dry stone wall construction, which facilitated cultivation on 58.4% of the island. By the mid-20th century, the economic collapse of agricultural activities and consequent emigration caused the abandonment of cultivated land and traditional management practices, dramatically reducing farm and field numbers. Terrace abandonment continued in recent decades, with increased livestock grazing becoming the main land management tool; as a result, both farm and pasture sizes increased. Neglect and changing land use has led to deterioration and destruction of many terraces on the island. We discuss the socioeconomic and political backgrounds responsible for the land-use change before World War II (annexation of Nisyros Island by the Ottoman Empire, Italy, and Greece; overseas migration opportunities; and world transportation changes) and after the war (social changes in peasant societies; worldwide changes in agricultural production practices). The adverse landscape changes documented for Nisyros Island appear to be inevitable for modern Mediterranean rural societies, including those on other islands in this region. The island's unique terraced landscapes may qualify Nisyros to become an archive or repository of old agricultural management techniques to be used by future generations and a living resource for sustainable management.

[1] In the present study, the Penn State/NCAR Mesoscale Model (MM5) was modified by considering recent advances in the urban boundary layer. In particular, the modifications were carried out in two directions: (1) With respect to the thermal properties of an urban surface the surface energy balance was modified by taking into account the anthropogenic heat released in urban areas and the urban heat storage term to account for urban/building mass effects, including hysteresis; and (2) the surface stress and fluxes of heat and momentum were modified following recent advances in the atmospheric boundary layer over rough surfaces under unstable conditions. The whole process was supplemented by detailed information on land use cover, derived from satellite image analysis. The modifications were applied to the high-resolution nonlocal medium-range forecast planetary boundary layer parameterization scheme, based on work by Troen and Mahrt (1986). The improvements seen with the modified model, after comparison with available measurements of temperature and fluxes, refer to (1) the strengthening of the nocturnal urban heat island; (2) the changes in the temperature, which proved to be favorable through the whole diurnal cycle, resulting in decreasing the temperature amplitude wave; (3) the decrease of turbulence and fluxes during the daytime; and (4) the diffusion coefficient and potential temperature profiles that are reduced during daytime and are increased at the lower levels during the night and thus affect accordingly the mixing height.

In the present study, we examine the dynamics of a sea-breeze front and the urban heat island interacting with the heavily urbanized city of Athens. For this reason, simulations were performed with a modified version of the PSU/NCAR Mesoscale Model (MM5), whereby urban features are considered, and the model results were compared with surface routine meteorological data. An unrealistic run was also performed, where the city of Athens was replaced by dry cropland and pasture surface, as in the surrounding area. A delay in the sea-breeze front was found during daytime, together with frictional retardation concerning its penetration, as well as inland displacement of the heat island as the air moved over the city of Athens. During nighttime, the wind speed increased over the lower atmosphere in the city centre due to the enhanced urban heat island.

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