Validation of seasonal mean radiant temperature simulations in hot arid urban climates.

We validated seasonal RayMan and ENVI-met mean radiant temperature (TMRT) simulations to assess model performance in a sensitivity analysis from cold to extremely hot conditions. Human-biometeorological validation data were collected in Tempe, Arizona via transects during five field campaigns between 2014 and 2017. Transects were conducted across seven locations in two to three-hour intervals from 6:00 to 23:00 LST with a Kestrel meter and thermal camera (2014-2015) and the mobile instrument platform MaRTy (2017). Observations across diverse urban forms, sky view factors, and seasons covered a wide range of solar radiation regimes from a minimum TMRT of 8.7 °C to a maximum of 84.9 °C. Both models produced large simulation errors across regimes with RMSE ranging from 8 °C to 12 °C (RayMan) and 11.2 °C to 16.1 °C (ENVI-met), exceeding a suggested TMRT accuracy of ±5 °C for heat stress studies. RayMan model errors were largest for engineered enclosed spaces, complex urban forms, and extreme heat conditions. ENVI-met was unable to resolve intra-domain spatial variability of TMRT and exhibited large errors with RMSE up to 25.5 °C for engineered shade. Both models failed to accurately simulate TMRT for hot conditions. Errors varied seasonally with overestimated TMRT in the summer and underestimated TMRT in the winter and shoulder seasons. Results demonstrate that models should not be used under micrometeorological or morphological extremes without in-situ validation to quantify errors and assess directional bias due to model limitations.

Quantifying outdoor water consumption of urban land use/land cover: sensitivity to drought.

Outdoor water use is a key component in arid city water systems for achieving sustainable water use and ensuring water security. Using evapotranspiration (ET) calculations as a proxy for outdoor water consumption, the objectives of this research are to quantify outdoor water consumption of different land use and land cover types, and compare the spatio-temporal variation in water consumption between drought and wet years. An energy balance model was applied to Landsat 5 TM time series images to estimate daily and seasonal ET for the Central Arizona Phoenix Long-Term Ecological Research region (CAP-LTER). Modeled ET estimations were correlated with water use data in 49 parks within CAP-LTER and showed good agreement (r² = 0.77), indicating model effectiveness to capture the variations across park water consumption. Seasonally, active agriculture shows high ET (>500 mm) for both wet and dry conditions, while the desert and urban land cover types experienced lower ET during drought (<300 mm). Within urban locales of CAP-LTER, xeric neighborhoods show significant differences from year to year, while mesic neighborhoods retain their ET values (400-500 mm) during drought, implying considerable use of irrigation to sustain their greenness. Considering the potentially limiting water availability of this region in the future due to large population increases and the threat of a warming and drying climate, maintaining large water-consuming, irrigated landscapes challenges sustainable practices of water conservation and the need to provide amenities of this desert area for enhancing quality of life.

A comparative climate analysis of heat-related emergency 911 dispatches: Chicago, Illinois and Phoenix, Arizona USA 2003 to 2006.

Research into the health impacts of heat has proliferated since 2000. Temperature increases could exacerbate the increased heat already experienced by urban populations due to urbanization. Heat-related mortality studies have found that hot southern cities in North America have not experienced the summer increases in mortality found in their more northern counterparts. Heat-related morbidity studies have not assessed this possible regional difference. This comparison study uses data from emergency 911 dispatches [referred to as heat-related dispatches (HRD)] identified by responders as heat-related for two United States cities located in different regions with very different climates: Chicago, Illinois in the upper midwest and Phoenix, Arizona in the southwest. Phoenix's climate is hot and arid. Chicago's climate is more temperate, but can also experience days with unusually high temperatures combined with high humidity. This study examines the relationships between rising HRD and daily temperatures: maximum (Tmax); apparent (ATmax): minimum (Tmin) and two energy balance indices (PET and UTCI). Phoenix had more HRD cumulatively, over a longer warm weather season, but did not experience the large spikes in HRD that occurred in Chicago, even though it was routinely subjected to much hotter weather conditions. Statistical analyses showed the strongest relationships to daily ATmax for both cities. Phoenix's lack of HRD spikes, similar to the summer mortality patterns for southern cities, suggests an avenue for future research to better understand the dynamics of possible physiological or behavioral adaption that seems to reduce residents' vulnerability to heat.

Climate and heat-related emergencies in Chicago, Illinois (2003-2006).

Extreme heat events are responsible for more deaths in the United States than floods, hurricanes and tornados combined. Yet, highly publicized events, such as the 2003 heat wave in Europe which caused in excess of 35,000 deaths, and the Chicago heat wave of 1995 that produced over 500 deaths, draw attention away from the countless thousands who, each year, fall victim to nonfatal health emergencies and illnesses directly attributed to heat. The health impact of heat waves and excessive heat are well known. Cities worldwide are seeking to better understand heat-related illnesses with respect to the specifics of climate, social demographics and spatial distributions. This information can support better preparation for heat-related emergency situations with regards to planning for response capacity and placement of emergency resources and personnel. This study deals specifically with the relationship between climate and heat-related dispatches (HRD, emergency 911 calls) in Chicago, Illinois, between 2003 and 2006. It is part of a larger, more in-depth, study that includes urban morphology and social factors that impact heat-related emergency dispatch calls in Chicago. The highest occurrences of HRD are located in the central business district, but are generally scattered across the city. Though temperature can be a very good predictor of high HRD, heat index is a better indicator. We determined temperature and heat index thresholds for high HRD. We were also able to identify a lag in HRD as well as other situations that triggered higher (or lower) HRD than would typically be generated for the temperature and humidity levels, such as early afternoon rainfall and special events.

A biometeorology study of climate and heat-related morbidity in Phoenix from 2001 to 2006.

Heat waves kill more people in the United States than hurricanes, tornadoes, earthquakes, and floods combined. Recently, international attention focused on the linkages and impacts of human health vulnerability to urban climate when Western Europe experienced over 30,000 excess deaths during the heat waves of the summer of 2003-surpassing the 1995 heat wave in Chicago, Illinois, that killed 739. While Europe dealt with heat waves, in the United States, Phoenix, Arizona, established a new all-time high minimum temperature for the region on July 15, 2003. The low temperature of 35.5 degrees C (96 degrees F) was recorded, breaking the previous all-time high minimum temperature record of 33.8 degrees C (93 degrees F). While an extensive literature on heat-related mortality exists, greater understanding of influences of heat-related morbidity is required due to climate change and rapid urbanization influences. We undertook an analysis of 6 years (2001-2006) of heat-related dispatches through the Phoenix Fire Department regional dispatch center to examine temporal, climatic and other non-spatial influences contributing to high-heat-related medical dispatch events. The findings identified that there were no significant variations in day-of-week dispatch events. The greatest incidence of heat-related medical dispatches occurred between the times of peak solar irradiance and maximum diurnal temperature, and during times of elevated human comfort indices (combined temperature and relative humidity).

Neighborhood microclimates and vulnerability to heat stress.

Human exposure to excessively warm weather, especially in cities, is an increasingly important public health problem. This study examined heat-related health inequalities within one city in order to understand the relationships between the microclimates of urban neighborhoods, population characteristics, thermal environments that regulate microclimates, and the resources people possess to cope with climatic conditions. A simulation model was used to estimate an outdoor human thermal comfort index (HTCI) as a function of local climate variables collected in 8 diverse city neighborhoods during the summer of 2003 in Phoenix, USA. HTCI is an indicator of heat stress, a condition that can cause illness and death. There were statistically significant differences in temperatures and HTCI between the neighborhoods during the entire summer, which increased during a heat wave period. Lower socioeconomic and ethnic minority groups were more likely to live in warmer neighborhoods with greater exposure to heat stress. High settlement density, sparse vegetation, and having no open space in the neighborhood were significantly correlated with higher temperatures and HTCI. People in warmer neighborhoods were more vulnerable to heat exposure because they had fewer social and material resources to cope with extreme heat. Urban heat island reduction policies should specifically target vulnerable residential areas and take into account equitable distribution and preservation of environmental resources.

A case study in resort climatology of Phoenix, Arizona, USA.

Tourists often use weather data as a factor for determining vacation timing and location. Accuracy and perceptions of weather information may impact these decisions. This study: (a) examines air temperature and dew points from seven exclusive resorts in the Phoenix metropolitan area and compares them with official National Weather Service data for the same period, and (b) utilizes a comfort model called OUTCOMES-OUTdoor COMfort Expert System-in a seasonal appraisal of two resorts, one mesic and one xeric, compared with the urban Sky Harbor International Airport first-order weather station site in the central urban area of Phoenix, Arizona, USA (lat. 33.43 degrees N; long. 112.02 degrees W; elevation at 335 m). Temperature and humidity recording devices were placed within or immediately adjacent to common-use areas of the resorts, the prime recreational sites used by guests on most resort properties. Recorded data were compared with that of the official weather information from the airport station, a station most accessible to potential tourists through media and Web sites, to assess predicted weather for vacation planning. For the most part, Sky Harbor's recorded air temperatures and often dew points were higher than those recorded at the resorts. We extrapolate our findings to a year-round estimate of human outdoor comfort for weather-station sites typical of resort landscapes and the Sky Harbor location using the OUTCOMES model to refine ideas on timing of comfortable conditions at resorts on a diurnal and seasonal basis.