Suchergebnisse

Context: Walkability is an important element for assessing urban sustainability. There are increased concerns that more cities in the People's Republic of China (PRC) have become less walkable. Objectives: We aim to develop a composite walkability index. We intend to use it to evaluate the spatio-temporal evolution of the walkability of PRC cities in the context of the rapid urbanization. Methods: We developed a comprehensive walkability index that integrates five aspects of the urban built environment: dwelling density, street connectivity, land-use mix, access to public transit, and elevation variation. Using Shanghai, Hangzhou, Chongqing, and Lanzhou as cases, we evaluated the spatio-temporal patterns and changes of walkability in the context of rapid urban expansion. Results: All four cities expanded their urban land from 1990 to 2010, but that there was a higher expansion rate in 2000-2010 than in 1990-2000. For inner cities, Shanghai had the highest average walkability index, whereas Lanzhou held the lowest. In 2000-2010, however, the inner cities of Hangzhou, Chongqing, and Lanzhou and the entire cities of Shanghai and Chongqing increased their walkability index, whereas the inner city of Shanghai had decreased walkability. Furthermore, while inner cities of Shanghai and Hangzhou experienced decreased or stable walkability, inner cities of Lanzhou and Chongqing enjoyed moderate to high increases in walkability. Conclusions: The spatiotemporal changes in walkability seem to be directly associated with governmental policies at both central and local levels. The walkability index method can be widely implemented for any urban landscape because of its comprehensiveness, simplicity, and flexibility.

Abstract
The northern hemisphere has experienced regional cooling, especially during the global warming hiatus (1998–2012) due to ocean energy redistribution. However, the lack of studies about the natural cooling effects hampers our understanding of vegetation responses to climate change. Using 15,125 ground phenological time series at 3,620 sites since the 1950s and 31-year satellite greenness observations (1982–2012) covering the warming hiatus period, we show a stronger response of leaf onset date (LOD) to natural cooling than to warming, i.e. the delay of LOD caused by 1°C cooling is larger than the advance of LOD with 1°C warming. This might be because cooling leads to larger chilling accumulation and heating requirements for leaf onset, but this non-symmetric LOD response is partially offset by warming-related drying. Moreover, spring greening magnitude, in terms of satellite-based greenness and productivity, is more sensitive to LOD changes in the warming area than in the cooling. These results highlight the importance of considering non-symmetric responses of spring greening to warming and cooling when predicting vegetation-climate feedbacks.