Urban Environment Effects

Urban environment exerts strong influence on human health through several different but partly cooperating ways. In term of direct effect of urban heat island, especially within episodes of heat waves the urban environment can cause the health risks as heart attack, especially to the specific groups of vulnerable people (elderly). Moreover, in longer term perspective it can be strengthen by the repeating abundance. In addition, the cities are significant sources of air-pollution emissions and following chemical reactions can be affected by the temperature and humidity, which are typically specific characteristics of UHI.

To assess the impact of cities and urban surfaces on weather, climate, and air-quality, the modeling approach is often used with inclusion of urban parameterization in land-surface interactions. This is especially important when going to higher resolution, which is common trend both in operational weather prediction and regional climate modelling as well as in coupled chemistry-transport modelling. Model description of urban canopy related meteorological effects can, however, differ largely given especially the underlying surface models and the urban canopy parameterizations, representing a certain uncertainty. To assess this uncertainty is important for adaptation and mitigation measures often applied in the big cities, especially in connection to climate change perspective, which is one of the main task of the new project OP-PPR Proof of Concept UK, but it is important for air-quality control as well, as studied in the project Urbi Pragensi.

In this study we contribute to the estimation of this uncertainty by performing numerous experiments to assess the urban canopy meteorological forcing over central Europe on climate for the decade 2001-2010, using two regional climate models (RegCM4 and WRF) in 10 km resolution driven by ERA-Interim reanalyses, three surface schemes (BATS and CLM4.5 for RegCM4 and Noah for WRF) and five urban canopy parameterizations available: one bulk urban scheme, three single layer and a multilayer urban scheme. Some coupled air-quality simulations are presented as well, using CAMx-RegCM, internal chemistry modul in RegCM and WRF-chem.

Effects of cities on urban and remote areas were evaluated. There are some differences in sensitivity of individual canopy model implementations to the UHI effects, depending on season and size of the city as well. Effect of reducing diurnal temperature range in cities (around 2 °C in summer mean) is noticeable in all simulations, independent to urban parameterization type and model, due to well-known warmer summer city nights. For the adaptation and mitigation purposes, rather than the average urban heat island intensity the distribution of it is more important providing the information on extreme UHI effects, e.g. during heat waves, with strong effects on human health. We demonstrate that for big central European cities this effect can approach 10°C, even for not so big ones these extreme effects can go above 5°C. The effects of air-quality on human health are well known, however, they are directly affected by the city emissions and not so much by the UHI effects on air-quality, at least on an average.