Timothy W. Hawkins

The Role of Rural Variability in Urban Heat Island Determination for Phoenix, Arizona

Abstract The effect of rural variability in calculating the urban heat island effect for Phoenix, Arizona, was examined. A dense network of temperature and humidity sensors was deployed across different land uses on an agricultural farm southeast of Phoenix for a 10-day period in April 2002. Temperature data from these sensors were compared with data from Sky Harbor Airport in Phoenix (an urban station) to assess the urban heat island effect using different rural baselines. The smallest and largest temperature differences between locations on the farm at a given time were 0.8° and 5.4°C, respectively. A t test revealed significant temperature differences between stations on the farm over the entire study period. Depending on the choice of rural baselines, the average and maximum urban heat island effects ranged from 9.4° to 12.9°C and from 10.7° to 14.6°C, respectively. Comparison of land cover types of the agricultural farm and land cover percentages in the Phoenix urban fringe was performed with satelli...

A Case Study of the Energy Budget of a Snowpack in the Arid, Subtropical Climate of the Southwestern United States

ABSTRACT An extensive micrometeorological and numerical modeling case study was conducted at Happy Jack, Arizona, during hydrologic year 2003. The goal of the study was to provide an initial assessment of the potential difference in the energy budget of a snow covered surface between an arid subtropical climate and more popularly studied regions. Modeling the snowpack evolution using the SNTHERM snowmelt model produced snow water equivalent values that were in good agreement with measured values for three different modeled ablation periods. The importance of the net radiation flux in ablation of the snow pack was decreased compared to that in more traditionally studied regions due to the earlier timing of ablation and subsequent lower solar altitude angles at the Arizona site. Consequently, the relative importance of the sensible heat flux increased and the relative importance of the latent heat flux decreased. The ground heat flux, ignored in most studies, accounted for up to 18% of the melt energy in this study due to shallower snow depths and presumably greater heat storage during the longer warm season of the subtropical climate.

The Role of a PhD Field Exam in Preparing Graduate Students for Academic Careers

Abstract The Department of Geography at Arizona State University implemented a field exam as part of its PhD program requirements. This field exam requires students to develop an independent field-based research project based on a general question in the students specialty area. A survey of current and former PhD students and faculty members document how the field exam assists students in developing skills necessary for continuing graduate research and for preparing them for the rigors of academic employment. The outcomes of the exam include both long-term, process-related benefits and more immediate tangible rewards. For some students, the preliminary fieldwork and results redirect student interests and form the basis for their eventual dissertation. The field exam is adaptable to a diversity of geography research methods, subject areas, and graduate degree programs, while remaining grounded in the disciplines vibrant, widely respected fieldwork tradition. *The authors thank ASU faculty members, PhD students, and alumni for participating in the research, especially Anthony Brazel, Patricia Gober, and Kevin McHugh who elaborated on the history of the department and the field exam. We thank Daniel Arreola, David Stea, and two anonymous reviewers for their helpful comments and suggestions regarding an earlier draft of this article.

Parameterization of the Snowmelt Runoff Model for the Salt-Verde System, Arizona During Drought Conditions

Abstract The snowmelt season for water years 2001 to 2003 were modeled for the Salt, Tonto, and Verde basins in Arizona using the Snowmelt Runoff Model (SRM). The SRM is a degree-day-driven snowmelt model. The purpose was to assess how well the SRM could simulate the snowmelt runoff conditions in Arizona, an arid subtropical environment that was also experiencing severe drought. Arizonas snowmelt season is characterized by multiple accumulation periods and near complete melt off periods that often occur during midwinter. Successful simulation of the streamflow would necessitate defining the proper values and patterns of the SRM parameters and assessing how this parameterization differs from other basins where the SRM has been run. Correlation coefficient values for modeled and measured streamflow on the Salt, Tonto, and Verde basins were 0.89, 0.89, and 0.91, respectively. Index of agreement values were 0.93, 0.94, and 0.95, respectively. Runoff coefficients increased during the snowmelt season until the end of March and beginning of April. Coefficients had a more typical behavior for the remainder of the season as they decreased through June. The magnitude of the runoff coefficients was relatively low due to the dry atmosphere and drought conditions. Degree-day factors for all basins were constant. The x and y parameters associated with the recession coefficients had the effect of increasing the slope of the recession limb of the hydrograph.

A spatiotemporal analysis of tropical cyclone tracks in the Atlantic Basin and their relationship to El Niño-Southern Oscillation

Abstract There has been an enhanced focus on Atlantic tropical cyclone climatologies with the significant cyclones of the past decade and the associated loss of life and property. This study examines the geographic location of cyclone tracks and their relationship to El Niño-Southern Oscillation (ENSO). The average annual cyclone track latitude and longitude correlate positively with hurricane-season El Niño indices, indicating that during El Niño conditions, tropical cyclone tracks are shifted northward and eastward. June–November indices explain 11–22% and 3–11% of the variance in cyclone track latitude and longitude, respectively. Examination of the strongest and weakest El Niño years yields similar results. Higher sea level pressure over North America, a slight contraction of the Bermuda High, and a slight decrease in 500 mb heights during El Niño years helps to explain the observed northward and eastward movement of tropical cyclone tracks during El Niño years. Additionally, weaker easterly and stronger southerly winds on the western side of the North Atlantic Basin exist during El Niño years. Although future tropical cyclone track projection is beyond the scope of this research, these results may provide insight into forecast improvement and ultimately better responses for coastal communities.

Simulating the Impacts of Projected Climate Change on Streamflow Hydrology for the Chesapeake Bay Watershed

A gridded model was developed to simulate the hydrology of the Chesapeake Bay Watershed, the largest estuary in the United States. CMIP3 and CMIP5 climate projections were used to drive the model to assess changes in streamflow and watershed-wide hydrology. Index of agreement values indicated good model performance. Annual average temperature is projected to increase 1.9°C to 5.4°C by 2080 to 2099, with the greatest warming occurring in summer and fall in the northern part of the watershed. Annual total precipitation is projected to increase between 5.2 percent and 15.2 percent by 2080 to 2099, with the largest increases generally occurring in winter. Average evapotranspiration and rainfall are projected to increase while snowfall, snow water storage, and snowmelt decrease. Subsurface moisture is projected to decrease during the warmer months and the time to recharge increases and, in some cases, never actually occurs. Changes in annual runoff for all 346 climate projections averaged 0 percent (2020–2039), –1.5 percent (2050–2069), and –5.1 percent (2080–2099). There is a 48 percent, 52 percent, and 60 percent chance, respectively, for the future time periods that annual runoff will be less than baseline values (1950–1999). Extreme runoff projections are overwhelmingly associated with the negative end of the distribution. Runoff increases are confined to January through March and to higher elevations. This study is novel in its use of a large number of climate models, the gridded nature of the hydrologic model, and the simulation of several hydrologic variables, all of which allowed for the assessment of both uncertainty in the projections and variation across multiple spatial and temporal scales.

Historical and Projected Climate Trends Along the Appalachian Trail, USA, and the Implications for Trail Usage

Recent climate analyses indicate that average global temperature is rising and both global drought occurrence and precipitation intensity are increasing. The nature of climate change is unique to each location, and its impact, both positive and negative, is predicted to be widespread. One area to be potentially affected includes management and use of outdoor natural resources such as the Appalachian Trail (AT), a 3500 km continuous hiking trail in the eastern United States. Observed historical (1895-2008) and projected future (to 2099) seasonal temperature and precipitation trends were examined along the AT. The AT has generally warmed since 1895, with greater warming occurring more recently. The warming has been greatest in the northern part of the AT and during winter. Precipitation trends show wide spatial variation depending upon the season, but generally precipitation has increased more in the northern than southern AT. Temperature and precipitation are projected to increase for all regions during all seasons in the future. Implications of these changes are discussed with respect to hiker experience and trail management.

Teaching Upper-Atmospheric Meteorology Using Two- and Three-Dimensional Models

©2010 American Meteorological Society U pper-atmosphere meteorological concepts often confound introductory meteorology students. In particular, students are challenged by the threedimensional nature of constant-pressure surfaces. This struggle is likely due, in part, to the fact that nearly all representations of these three-dimensional surfaces are presented in two dimensions. Recent research argues that spatial visualization in three dimensions can be improved through instruction. However, several studies suggest that comprehension of a three-dimensional environment does not necessarily occur equally between males and females, or between individuals with different spatial abilities. The purpose of this project was to begin to assess whether threeor two-dimensional models of upperatmosphere constant-pressure surfaces were more effective as teaching and learning tools. The models were developed and tested on two groups of introductory meteorology students, and the results of the assessment were analyzed to determine which model was more effective and, secondarily, if there were differences in student performance based on sex. It was hypothesized that certain concepts would be better understood in three dimensions, while others would be better understood in two dimensions. It was also Teaching Upper-Atmospheric Meteorology Using Twoand Three-Dimensional Models a Pilot Study