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Urban ecosystems interact with surroundings via land cover changes and their subsequent impact on surface temperature. In emerging countries, large urban agglomerations often form around cities, and only a few studies have evaluated their impact. This study carries out the first ever large-scale assessment of urban heat island (UHI) and reflects on its mitigation in Morocco. The analysis reveals a well-defined UHI in urban areas built within vegetated lands and an urban heat sink (UHS) in urban areas built within arid regions. Both UHI and UHS amplitudes are higher during day than nighttime, emphasizing vegetation physiological activity. This study shows a monotonic increase in UHI amplitude with urban area size. However, unlike previous studies, this analysis shows that, as urban areas built in desert-like environments grow in size, the UHS gradually decreases to ultimately turn into an UHI. On average, cities built within vegetation are warmer than the rural fringe by 1.51 °C during daytime. This suggests that daytime urban heating may exacerbate the potential climate warming. These results also suggest that adapted trees constitute a natural cooling mechanism and should be part of urban heating mitigation in Morocco. [ABSTRACT FROM AUTHOR]

We simulate the impact of impervious surface areas (ISA) on the U.S. local and regional climate. At a local scale, we find the urban area warmer than the surrounding vegetation in most cities, except in arid climate cities where urban temperature is cooler for much of the daytime. For all 9 regions studied, simulated results show that the growing season maximum surface temperature difference between urban and the dominant vegetation occurs around mid-day and is strongest in the northern regions. Regional temperature differences of 3.0°C, 3.4°C, and 3.9°C were simulated in the Northeast, Midwest, and Northwest, respectively. In these regions evaporative cooling, during the growing season, creates a stronger urban heat island (UHI). The UHI is less pronounced during winter when vegetation is dormant. Our results suggest that the ISA temperature is set by building materials' characteristics and its departure from that of the surrounding vegetation is essentially driven by evaporative cooling. Except when rainfall is small, the highest surface runoff to precipitation ratios are simulated in most cities, especially when precipitation events occur as heavy downpours. In terms of photosynthesis, we provide a detailed distribution of maximum production in the U.S., a needed product for policy and urban planners. [ABSTRACT FROM PUBLISHER]

We combine Landsat and MODIS data in the simple biosphere model to assess the impact of urbanization on surface climate in Marrakech, circa 2010. We find the growing season surface temperature differences between urban and other cover types to vary between 1.6°C and 6.0°C at 1:00 p.m., and between 0.7°C and 1.1°C at 5:00 a.m., local time. Annually however, the built-up area warmed the city 0.3°C during daytime and 0.1°C at night compared to a simulated preurban situation in which the area was fully vegetated. A complete urbanization of the area would decrease its carbon uptake by 0.13 tons and increase its daytime surface temperature by 1.3°C, with 5.72% increase in energy consumption. However, in a “smart” urban growth scenario, we assume the build-up to cover 50% of the area, allowing it to occur first on bare lands, and then we convert all remaining bare lands to orchards; this would counterbalance 60% of daytime warming and sequester 31% more carbon, compared to the actual situation. We find irrigated golf courses to be the most water-consuming covers types, requiring 15 times the region's summer rainfall, and urban areas to distribute 43.8% of incoming precipitation as surface runoff versus only 16.74% for all other cover types combined. This can be a predictor for flash floods. [ABSTRACT FROM PUBLISHER]

We combine Landsat-and the moderate-resolution imaging spectroradiometer (MODIS)-based products in the Simple Biosphere model (SiB2) to assess the effects of urbanized land on the continental United States (CONUS) surface climate. Using National Land Cover Database (NLCD) impervious surface area (ISA), we define more than 300 urban settlements and their surrounding suburban and rural areas over the CONUS. The SiB2 modeled gross primary production (GPP) over the CONUS of 7.12 PgC (1 PgC = 1015 g of carbon) is comparable to the MODIS improved GPP of 6.29 PgC. At state level, SiB2 GPP is highly correlated with MODIS GPP, with a correlation coefficient of 0.94. An increasing horizontal GPP gradient is shown from the urban out to the rural area, with, on average, rural areas fixing 30% more GPP than urbans. Cities built in forested biomes have stronger urban heat island (UHI) magnitude than those built in short vegetation with low biomass. Mediterranean climate cities have a stronger UHI in wet season than in dry season. Our results also show that for urban areas built within forests, 39% of the precipitation is discharged as surface runoff during summer versus 23% in rural areas. [ABSTRACT FROM AUTHOR]

The National Land Cover Database (NLCD) Impervious Surface Area (ISA) and MODIS Land Surface Temperature (LST) are used in a spatial analysis to assess the surface-temperature-based urban heat island's (UHIS) signature on LST amplitude over the continental USA and to make comparisons to local air temperatures. Air-temperature-based UHIs (UHIA), calculated using the Global Historical Climatology Network (GHCN) daily air temperatures, are compared with UHIS for urban areas in different biomes during different seasons. NLCD ISA is used to define urban and rural temperatures and to stratify the sampling for LST and air temperatures. We find that the MODIS LST agrees well with observed air temperature during the nighttime, but tends to overestimate it during the daytime, especially during summer and in nonforested areas. The minimum air temperature analyses show that UHIs in forests have an average UHIA of 1°C during the summer. The UHIS, calculated from nighttime LST, has similar magnitude of 1-2°C. By contrast, the LSTs show a midday summer UHIS of 3-4°C for cities in forests, whereas the average summer UHIA calculated from maximum air temperature is close to 0°C. In addition, the LSTs and air temperatures difference between 2006 and 2011 are in agreement, albeit with different magnitude. [ABSTRACT FROM AUTHOR]

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