This study examines the spatial and temporal patterns of the surface urban heat island (SUHI) intensity in the Phoenix metropolitan area and the relationship with land use land cover (LULC) change between 2000 and 2014. The objective is to identify specific regions in Phoenix that have been increasingly heated and cooled to further understand how LULC change influences the SUHI intensity. The data employed include MODerate-resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) 8-day composite June imagery, and classified LULC maps generated using 2000 and 2014 Landsat imagery. Results show that the regions that experienced the most significant LST changes during the study period are primarily on the outskirts of the Phoenix metropolitan area for both daytime and nighttime. The conversion to urban, residential, and impervious surfaces from all other LULC types has been identified as the primary cause of the UHI effect in Phoenix. Vegetation cover has been shown to significantly lower LST for both daytime and nighttime due to its strong cooling effect by producing more latent heat flux and less sensible heat flux. We suggest that urban planners, decision-makers, and city managers formulate new policies and regulations that encourage residential, commercial, and industrial developers to include more vegetation when planning new construction.

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During recent decades, more frequent flood-drought alternations have been seen in China as a result of global climate change and intensive human activities, which have significant implications on water and food security. To better identify the characteristics of flood-drought alternations, we proposed a modified dry-wet abrupt alternation index (DWAAI) and applied the new method in the middle and lower reaches of the Yangtze River Basin (YRB-ML) to analyze the long-term spatio-temporal characteristics of dry-wet abrupt alternation (DWAA) events based on the daily precipitation observations at 75 rainfall stations in summer from 1960 to 2015. We found that the DWAA events have been spreading in the study area with higher frequency and intensity since 1960. In particular, the DWAA events mainly occurred in May and June in the northwest of the YRB-ML, including Hanjiang River Basin, the middle reaches of the YRB, north of Dongting Lake and northwest of Poyang Lake. In addition, we also analyzed the impact of El Niño Southern Oscillation (ENSO) on DWAA events in the YRB-ML. The results showed that around 41.04% of DWAA events occurred during the declining stages of La Niña or within the subsequent 8 months after La Niña, which implies that La Niña events could be predictive signals of DWAA events. Besides, significant negative correlations have been found between the modified DWAAI values of all the rainfall stations and the sea surface temperature anomalies in the Nino3.4 region within the 6 months prior to the DWAA events, particularly for the Poyang Lake watershed and the middle reaches Keywords: dry-wet abrupt alternation; the middle and lower reaches of the Yangtze River Basin; spatio-temporal characteristics; La Niña

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Urban vegetation is an effective way in mitigating excessive heat and improving the outdoor thermal environment for residents in cities via evaporative cooling. Different urban vegetation forms (mesic or xeric) alter surface energy and water budgets in different ways, which is further complicated by interactions with buildings and anthropogenic controls. Mesic vegetation such as lawns reduces urban temperatures by evaporative cooling but requires large amounts of water for continuous irrigation. Xeric vegetation such as shade trees reduces urban temperatures mainly through radiative shading and has low water demand. The objective of this study is to investigate the impacts of different vegetation forms on microclimate in a hot desert city-Phoenix, AZ. We applied an advanced urban canopy model coupled with a single-column atmospheric model to simulate urban boundary layer dynamics over different landscaping scenarios with different combinations of mesic and xeric vegetation forms. We subsequently compared the urban land surface temperatures, near-surface air temperatures, outdoor thermal comfort in the urban canopy layer, as well as atmospheric dynamics (temperature, humidity) in the overlying boundary layer for a set of different scenarios.

Low-carbon building retrofit will contribute to delivering China's policy to reduce carbon emissions. This paper proposes viable low-carbon adaptation strategies for a recurrent building type within the Hot Summer and Cold Winter (HSCW) zone. An existing 23-storey tower in Hangzhou is investigated within the context of a representative city environment. Indoor air temperatures and energy consumption were monitored across a typical floor and simulated in EnergyPlus. Outdoor and indoor airflow patterns were modelled in an advanced computational fluid dynamics (CFD) tool, FLUIDITY. Across a typical floor, observations and modelling show marked variations. Southfacing flats overheat significantly in summer largely due to solar radiation. External sun-shading structures are proposed and evaluated to counter summer overheating. An innovative wind catcher and exhaust-stack natural ventilation system is proposed to enhance indoor thermal comfort using natural ventilation. Modelling of this integrated ventilation system indicates that the proposed retrofit system will improve indoor thermal comfort even in the lower floors. The proposed building retrofit strategy is costed using locally established construction cost estimates. Predicted energy savings suggest that the adaptation strategy proposed is potentially viable with significant implications for policy-makers, developers, constructors and designers in this challenging climate zone in China.

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