No abstract

Impervious surface area (ISA) from the Landsat TM-based NLCD 2001 dataset and land surface temperature (LST) from MODIS averaged over three annual cycles (2003)(2004)(2005) are used in a spatial analysis to assess the urban heat island (UHI) skin temperature amplitude and its relationship to development intensity, size, and ecological setting for 38 of the most populous cities in the continental United States. Development intensity zones based on %ISA are defined for each urban area emanating outward from the urban core to the nonurban rural areas nearby and used to stratify sampling for land surface temperatures and NDVI. Sampling is further constrained by biome and elevation to insure objective intercomparisons between zones and between cities in different biomes permitting the definition of hierarchically ordered zones that are consistent across urban areas in different ecological setting and across scales. We find that ecological context significantly influences the amplitude of summer daytime UHI (urban-rural temperature difference) the largest (8°C average) observed for cities built in biomes dominated by temperate broadleaf and mixed forest. For all cities combined, ISA is the primary driver for increase in temperature explaining 70% of the total variance in LST. On a yearly average, urban areas are substantially warmer than the non-urban fringe by 2.9°C, except for urban areas in biomes with arid and semiarid climates. The average amplitude of the UHI is remarkably asymmetric with a 4.3°C temperature difference in summer and only 1.3°C in winter. In desert environments, the LST's response to ISA presents an uncharacteristic "U-shaped" horizontal gradient decreasing from the urban core to the outskirts of the city and then increasing again in the suburban to the rural zones. UHI's calculated for these cities point to a possible heat sink effect. These observational results show that the urban heat island amplitude both increases with city size and is seasonally asymmetric for a large number of cities across most biomes. The implications are that for urban areas developed within forested ecosystems the summertime UHI can be quite high relative to the wintertime UHI suggesting that the residential energy consumption required for summer cooling is likely to increase with urban growth within those biomes.Published by Elsevier Inc.

The physiological response of terrestrial vegetation when directly exposed to an increase in atmospheric carbon dioxide (CO 2 ) concentration could result in warming over the continents in addition to that due to the conventional CO 2 “greenhouse effect.” Results from a coupled biosphere-atmosphere model (SiB2-GCM) indicate that, for doubled CO 2 conditions, evapotranspiration will drop and air temperature will increase over the tropical continents, amplifying the changes resulting from atmospheric radiative effects. The range of responses in surface air temperature and terrestrial carbon uptake due to increased CO 2 are projected to be inversely related in the tropics year-round and inversely related during the growing season elsewhere.

among islands and regions using nested, mixed-model ANOVA. We screened several potential estimators to find that the Chao 1 procedure provided the most stable values for local species richness. This estimator is the sum of the observed number of species and the quotient a 2 /2b, where a and b equal the number of species represented by one and two colonies, respectively.To analyse the local-regional species richness relationship in each habitat, we used a simple linear regression of the mean local richness per site in a region against habitatspecific regional richness. Linearity is supported by these and supplemental regressions using: (1) log-transformed richness data; (2) local richness standardized to 100 or more colonies per sample 18 ; and (3) the two alternative measures of local species diversity, Fisher's alpha and the Chao 1 estimator of local richness.