**1. Introduction**

The urban heat island (UHI) effect is a relatively well-researched surface meteorological phenomenon. It describes the difference in surface air temperature between a built-up urban area and its surrounding countryside. Said difference is usually displaying a warmer surface layer air temperature in urban areas, especially during nighttime. Several reviews of the UHI effect magnitudes, characteristics, causes and mitigation strategies can be found in the literature [1–7]. Arnfield [1] summarized the major aspects, stating that UHI intensity is highest at night, typically increases with lower wind speeds under clear sky, high pressure conditions, and is usually more pronounced during summer time and in larger, more populous cities. Recent critique and recommendations for ongoing research [7, 8] have led to

a more streamlined approach of interpreting UHI intensity on the basis of measurement techniques, locations, and urban morphological characterizations such as impervious area fractions, building heights, and canyon aspect ratios.

The causes of UHI effects are related to fundamental differences in the surface energy balance between urban and rural areas. The 3D structure of, and man-made materials in, urban areas cause albedo changes during daytime and "radiation trapping" at night [6, 9–13], causing stronger heat admission during daytime, and slower radiative heat losses at night. In addition, anthropogenic heat from the human population and its energy use in urban areas significantly enhances the UHI effect [14–22]. While rural areas convert a substantial fraction of daytime incoming net radiation into latent heat fluxes, the dominance of impervious areas and an associated lower vegetation density in urban areas compared with their rural surroundings causes a redistribution of incoming net radiation into urban heat storage and sensible heat fluxes. Increased sensible heat fluxes increase the daytime UHI intensity, while high heat storage fluxes exacerbate nighttime UHI intensities when stored heat is returned into the atmosphere [23–28]. Detailed numerical studies such as by Ryu and Baik [29] have shown that impervious surface area, a proxy for energy balance flux changes, is likely the dominant factor determining daytime UHI intensity, while anthropogenic heat releases may dominate nighttime UHI intensity. Both these factors interact with the 3D structure of the urban fabric and the prevailing meteorological conditions. This can cause daytime cool islands as man-made (impervious) surfaces store heat and can shade road "canyons"; and maximum nighttime heat islands as stored heat together with anthropogenic heat are released back into shallower nighttime surface air layers. The results also concur with higher net radiation levels under high pressure conditions in summer, and the associated lack of turbulent heat transport under low wind speeds in urban areas as summarized by Arnfield [1].

To investigate these phenomena, researchers have used both stationary and mobile air temperature measurements extensively. While early studies often used only a few weather station locations [30, 31], or limited mobile traverses [32–34], newer studies have profited from now widely available, small form factor, accurate, and cost-effective electronic temperature sensors deployed in either stationary or mobile fashion. However, the correct deployment and interpretation of such sensors and their data still requires careful consideration, such as of radiation shielding and sensor response time aspects. In comparison, a hand-operated sling psychrometer provides a highly accurate, battery-independent low-key tool that can be operated by any lay person and can be immediately ready at the required time. Sling psychrometers provide dry-bulb and wet-bulb temperatures, and thus serve to provide both air temperature and humidity. They have been used in the past for UHI "spot" measurements [35–37], supplementing weather station and mobile data, and are ideally suited as "hands-on" data collection tools in undergraduate student research projects [38].

This chapter describes a semester-long student project to determine the UHI intensity of a mid-size metropolitan area in east Texas, the Bryan/College Station (BCS) metro area, home of Texas A&M University. As part of a spring semester course on environmental atmospheric science, students were tasked to maintain regular air temperature measurements near the places they lived in town, then turn in a writing assignment at the end of the semester. During the following summer and fall semesters, the first author maintained two of the measurement sites and also carried out a mobile measurement study using her private automobile. Here, we discuss selected results from the measurements in context of past UHI studies. We also introduce an ongoing project of integrating these measurement results with remotely sensed land cover data.

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**Figure 1.**

*Low-Key Stationary and Mobile Tools for Probing the Atmospheric UHI Effect*

Sling psychrometers are traditional meteorological measurement tools to determine air temperature (dry-bulb temperature) and relative humidity (wetbulb temperature). Sling psychrometers have been used in UHI studies going back several decades [32, 35, 36, 39]. They have an educational advantage over automated measurements as they require direct student involvement in the data gathering and documentation process. The instrument used in this study was a Bacharach model 0012-7012 using two red spirit filled glass thermometers with Fahrenheit scales. The instrument is made of a robust hard plastic shell, with its outer part acting as handle when extended, while the inner part bears the two identical glass thermometers. The thermometer scales allow readings as precise as 0.5°F, and are accurate to at least 1.0°F based on intercomparisons with other sling psychrometers and a research grade meteorological sensor, comparisons that were made part of the

Here, we discuss only the dry bulb, aka air temperature data. The atmospheric UHI effect was calculated as the difference between the measured air temperature and the corresponding temperature at 2 m above ground level (agl) at the Texas A&M weather station (**Figure 1**). The weather station's combined T/RH sensor, a

*Roadmap based view of the Bryan/College Station metro area in East Texas (30.6°N, 96.32 W). The major highway traversing the area, Texas-6, is labeled alongside the two stationary measurement locations in red* 

*(T = 'trails', Q = 'quad') and the weather station location (W) in blue.*

*DOI: http://dx.doi.org/10.5772/intechopen.89514*

**2.1 Sling psychrometer measurements**

student project in this UHI study.

**2. Methods**

*Low-Key Stationary and Mobile Tools for Probing the Atmospheric UHI Effect DOI: http://dx.doi.org/10.5772/intechopen.89514*
