Jeremy E. Diem

Anthropogenic Impacts on Summer Precipitation in Central Arizona, U.S.A.

Abstract This article explores the possibility of urbanization- and irrigation-induced increases in summer precipitation totals in central Arizona. Maximum precipitation impacts are hypothesized to occur downwind of the Phoenix area in the Lower Verde basin. Results from statistical tests indicate that summer precipitation totals in the Lower Verde basin are greater than totals in nearby basins. Precipitation totals in the basin also appear to be equivalent to totals at more monsoon-impacted stations in eastern Arizona. While this research is preliminary, the results do provide encouraging evidence of the existence of anthropogenically enhanced summer precipitation in central Arizona.

Comparisons of weekday–weekend ozone: importance of biogenic volatile organic compound emissions in the semi-arid southwest USA

Abstract This paper examines differences between daily maximum weekday and weekend ambient ozone concentrations in the Tucson, AZ metropolitan area. Temporal variations in the Weekend Effect (i.e. weekend ozone concentrations are larger than weekday concentrations) are not explained entirely by changes in anthropogenic emissions of ozone precursor chemicals (i.e. nitrogen oxides and volatile organic compounds). A dramatic change from the Weekend Effect in June to the Weekday Effect (i.e. weekday ozone concentrations are larger than weekend concentrations) in July is associated with the onset of the North American Monsoon. A transition from a relatively dry atmosphere during the arid foresummer months of May and June to a relatively moist atmosphere during the monsoon months of July and August seems to explain the changes in ozone concentrations. Moist conditions are associated with increases in biogenic volatile organic compound (BVOC) emissions in the urban forest and surrounding desert areas. BVOC emissions appear to be an important source of VOCs, especially during the monsoon months. Therefore, an increase in ambient BVOC concentrations from June to July presumably reverses the sensitivity of ozone production in the Tucson area from VOC- to NOx-sensitive.

Climatology and forecast modeling of ambient carbon monoxide in Phoenix, Arizona

We perform a climatology of factors influencing ambient carbon monoxide (CO), in which we examine the relationships between meteorology, traffic patterns, and CO at seasonal, weekly, and diurnal time scales in Phoenix, Arizona. From this analysis we identify a range of potentially important variables for statistical CO modeling. Using stepwise multivariate regression, we create a suite of models for hourly and 8-h ambient CO designed for daily operational forecasting purposes. The resulting models include variables and interaction terms related to anticipated nocturnal atmospheric stability as well as antecedent and climatological CO behavior. The models are evaluated using a range of error statistics and skill measures. The most successful approach employs a two-stage modeling strategy in which an initial prediction is made that may, depending on the forecast value, be followed by a second prediction that improves upon the first. The best models provide accurate daily forecasts of CO, with explained variances approaching 0.9 and errors under 1 ppm.

Interepochal Changes in Summer Precipitation in the Southeastern United States: Evidence of Possible Urban Effects near Atlanta, Georgia

Through modification of the planetary boundary layer, urbanization has the potential to have a significant impact on precipitation totals locally. Using daily summer-season precipitation data at 30 stations from 1953 to 2002, this study explores the possibility of urban effects as causes of spatial anomalies in precipitation in a zone within 180 km of Atlanta, Georgia. The time period is divided into consecutive epochs (e.g., 1953–77 and 1978–2002), and interepochal differences in precipitation totals, heavy-precipitation days, cumulative heavy precipitation, and atmospheric conditions are explored. The southern stations experienced significant decreases in precipitation, whereas significant precipitation increases occurred at central/west-central stations. The most striking increases occurred at Norcross, Georgia, which is 30 km northeast of downtown Atlanta; Norcross had the third smallest number of heavy-precipitation days during 1953–77, but, during 1978–2002, it had the most heavy-precipitation days. Not only did the amount of urban land cover upwind of Norcross increase substantially from the earlier to the later epochs, but regionwide dewpoint temperatures also increased significantly. Therefore, it is suspected that the increased precipitation at Norcross was caused by urban effects, and these effects may have been enhanced by increased atmospheric humidity.

Predictive mapping of air pollution involving sparse spatial observations

A limited number of sample points greatly reduces the availability of appropriate spatial interpolation methods. This is a common problem when one attempts to accurately predict air pollution levels across a metropolitan area. Using ground-level ozone concentrations in the Tucson, Arizona, region as an example, this paper discusses the above problem and its solution, which involves the use of linear regression. A large range of temporal variability is used to compensate for sparse spatial observations (i.e. few ozone monitors). Gridded estimates of emissions of ozone precursor chemicals, which are developed, stored, and manipulated within a geographic information system, are the core predictor variables in multiple linear regression models. Cross-validation of the pooled models reveals an overall R2 of 0.90 and approximately 7% error. Composite ozone maps predict that the highest ozone concentrations occur in a monitor-less area on the eastern edge of Tucson. The maps also reveal the need for ozone monitors in industrialized areas and in rural, forested areas.

A critical examination of ozone mapping from a spatial-scale perspective.

Following the establishment of point measurements of ground-level ozone concentrations have been attempts by many researchers to develop ozone surfaces. This paper offers a critique of ozone-mapping endeavors, while also empirically exploring the operational scale of ground-level ozone. The following issues are discussed: aspects of spatial scale; the spatial complexity of ground-level ozone concentrations; and the problems of previous attempts at ozone mapping. Most ozone-mapping studies are beset with at least one of the following core problems: spatial-scale violations; an improper evaluation of surfaces; inaccurate surfaces; and the inappropriate use of surfaces in certain analyses. The major recommendations to researchers are to acknowledge spatial scale (especially operational scale), understand the prerequisites of surface-generating techniques, and to evaluate the resultant ozone surface properly.

Synoptic-Scale Controls of Summer Precipitation in the Southeastern United States

Abstract Past climatological research has not quantitatively defined the synoptic-scale circulation deviations responsible for anomalous summer-season precipitation totals in the southeastern United States. Therefore, the objectives of this research were to determine the synoptic-scale controls of wet and dry multiday periods during the summer within a portion of the southeastern United States as well as to assess the linkages between synoptic-scale circulation and multidecadal variations in precipitation characteristics for the study domain. Daily precipitation data from 30 stations for June, July, and August from 1953 to 2002 were converted into 13-day totals. Using standardized principal components analysis (PCA), the study domain was divided into three precipitation regions (i.e., South, Northwest, and Northeast). Wet and dry periods for each region were composed of the top 56 and bottom 56 thirteen-day periods. Composite circulation maps for 500 and 850 mb revealed the following: wet periods were gen...

Validation of Satellite Rainfall Products for Western Uganda

Central equatorial Africa is deficient in long-term, ground-based measurements of rainfall; therefore, the aim of this study is to assess the accuracy of three high-resolution, satellite-based rainfall products in western Uganda for the 2001‐10 period. The three products are African Rainfall Climatology, version 2 (ARC2); African Rainfall Estimation Algorithm, version 2 (RFE2); and 3B42 from the Tropical Rainfall Measuring Mission, version 7 (i.e., 3B42v7). Daily rainfall totals from six gauges were used to assess the accuracy of satellite-based rainfall estimates of rainfall days, daily rainfall totals, 10-day rainfall totals, monthly rainfall totals, and seasonal rainfall totals. The northern stations had a mean annual rainfall total of 1390 mm, while the southern stations had a mean annual rainfall total of 900 mm. 3B42v7 was the only product that did not underestimate boreal-summer rainfall at the northern stations, which had ; 3t imes as much rainfall during boreal summer than did the southern stations. The three products tended to overestimate rainfall days at all stations and were borderline satisfactory at identifying rainfall days at the northern stations; the products did not perform satisfactorily at the southern stations. At the northern stations, 3B42v7 performed satisfactorily at estimating monthly and seasonal rainfall totals, ARC2 was only satisfactory at estimating seasonal rainfall totals, and RFE2 did not perform satisfactorily at any time step. The satellite products performed worst at the two stations located in rain shadows, and 3B42v7 had substantial overestimates at those stations.

Air Quality, Climate, and Policy: A Case Study of Ozone Pollution in Tucson, Arizona

This article addresses the need to better understand the complex interactions between climate, human activities, vegetation responses, and surface ozone so that more informed air-quality policy recommendations can be made. The impacts of intraseasonal climate variations on ozone levels in Tucson, Arizona from April through September of 1995 to 1998 are determined by relating variations in ozone levels to variations in atmospheric conditions and emissions of ozones precursor chemicals, volatile organic compounds (VOCs) and nitrogen oxides (NOx), and by determining month-specific atmospheric conditions that are conducive to elevated ozone levels. Results show that the transport of ozone and its precursor chemicals within the Tucson area causes the highest ozone levels to be measured at a downwind monitor. The highest ozone levels occur in August, due in part to the presence of the North American monsoon. Atmospheric conditions conducive to elevated ozone concentrations differ substantially between the arid foresummer (May and June) and the core monsoon months ( July and August). Transport of pollution from Phoenix may have a substantial impact on elevated ozone concentrations during April, May, and June, while El Paso/Ciudad Juarez –derived pollution may contribute significantly to elevated ozone concentrations in August and September. Two broad policy implications derive from this work. Regional pollutant transport, both within the U.S. and between the U.S. and Mexico, is a potential issue that needs to be examined more intensively in future studies. In addition, spatiotemporal variations in sensitivities of ozone production require the adoption of both NOx and VOC control measures to reduce ozone levels in the Tucson area.

Integrating remote sensing and local vegetation information for a high-resolution biogenic emissions inventory - Application to an urbanized, semiarid region

This paper presents a methodology for the development of a high-resolution (30-m), standardized biogenic volatile organic compound (BVOC) emissions inventory and a subsequent application of the methodology to Tucson, AZ. The regions heterogeneous vegetation cover cannot be modeled accurately with low-resolution (e.g., 1-km) land cover and vegetation information. Instead, local vegetation data are used in conjunction with multispectral satellite data to generate a detailed vegetation-based land-cover database of the region. A high-resolution emissions inventory is assembled by associating the vegetation data with appropriate emissions factors. The inventory reveals a substantial variation in BVOC emissions across the region, resulting from the regions diversity of both native and exotic vegetation. The importance of BVOC emissions from forest lands, desert lands, and the urban forest changes according to regional, metropolitan, and urban scales. Within the entire Tucson region, the average isoprene, monoterpene, and OVOC fluxes observed were 454, 248, and 91 micrograms/m2/hr, respectively, with forest and desert lands emitting nearly all of the BVOCs. Within the metropolitan area, which does not include the forest lands, the average fluxes were 323, 181, and 70 micrograms/m2/hr, respectively. Within the urban area, the average fluxes were 801, 100, and 100 micrograms/m2/hr, respectively, with exotic trees such as eucalyptus, pine, and palm emitting most of the urban BVOCs. The methods presented in this paper can be modified to create detailed, standardized BVOC emissions inventories for other regions, especially those with spatially complex vegetation patterns.ABSTRACT This paper presents a methodology for the development of a high-resolution (30-m), standardized biogenic volatile organic compound (BVOC) emissions inventory and a subsequent application of the methodology to Tucson, AZ. The regions heterogeneous vegetation cover cannot be modeled accurately with low-resolution (e.g., 1-km) land cover and vegetation information. Instead, local vegetation data are used in conjunction with multispectral satellite data to generate a detailed vegetation-based land-cover database of the region. A high-resolution emissions inventory is assembled by associating the vegetation data with appropriate emissions factors. The inventory reveals a substantial variation in BVOC emissions across the region, resulting from the regions diversity of both native and exotic vegetation. The importance of BVOC emissions from forest lands, desert lands, and the urban forest changes according to regional, metropolitan, and urban scales. Within the entire Tucson region, the average isoprene, monoterpene, and