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Relating changes in agricultural practices to increasing dew points in extreme Chicago heat waves

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Abstract

The temporal distribution of surface atmospheric water vapor levels during short-duration extreme heat events at Chicago was assessed. Heat events were characterized by at least 3 consecutive days with a minimum temperature greater than 24degreesC (75degreesF) and a maximum temperature greater than 35degreesC (95degreesF). Thirteen such heat events were identified during the 75 yr (1928-2002) record at Chicago Midway Airport located inside the city. Average dew points in events fluctuated considerably over time, but generally increased. Event average hourly dew-point values before the mid 1980s were generally below 21degreesC, rising to an average of 24degreesC during the mid 1990s. The temporal changes in dew-point values were related to 2 factors: (1) the existence of average to above-average regional precipitation anomalies occurring in May and during the 20 d period prior to the heat event, and (2) changes in agricultural practices that have led to enhanced evapotranspiration rates in the Midwest.

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... Record electrical usage levels, related to cooling campus buildings, were established during the 1995 and 1999 Midwestern heat waves (Saari, pers. comm., August 20, 2002 Previous research identified that the frequency of extreme summer dew points has increased not only in northern Illinois (Sparks et al., 2002;Changnon et al., 2003), but also at weather stations across much of the Midwest (Gaffen and Ross, 1999;Robinson, 2000;Sandstrom et al., 2004), suggesting that as new systems are developed, they should be designed to adequately handle unusually high dew point levels. In their examination of diurnal temperature and dew point cycles, Knappenberger et al. (1996) suggested that, on average, hourly summer dew points were highest in the late afternoon and reached a minimum in the early morning. ...
... Other researchers such as Kunkel et al. (1996) and Palecki et al. (2001) have noted the high levels of dew point during two of these recent events (July 12-16, 1995, andJuly 19-31, 1999). Furthermore, five of these high dew point events-1986, 1987, 1995 (2), and July 19-31, 1999-occurred simultaneously with five of 13 short-term Chicago Midway heat waves during the 1928-2002 period (Changnon et al., 2003). No trend is apparent when examining the length of event or number of stations involved in the event. ...
... This region coincides with some of the most productive corn and soybean growing areas in the United States. Previous studies (Changnon et al., 2003;Sandstrom et al., 2004) speculate that changing agricultural practices have (Schwartzman et al., 1998) have suggested that land use and/ or cover changes such as those related to urbanization could influence diurnal dew point cycles and trends. ...
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Daily average dew points (DADPs) computed for 46 Midwestern first-order stations (FOS) were examined from 1960 to 2000 to identify and characterize extreme warm-season high dew point events. To be classified as an extreme event, more than 50% of the FOS had to experience a DADP of 22°C (72°F) or higher for two or more consecutive days within the event. Nine events were found to have occurred during the 41-year period. The length of the events varied from 5 to 13 days, while the number of stations involved in each event ranged from 24 to 40. Two summers, 1995 and 1999, each experienced two events. Event intensity, based on the percentage of all station hours during each event with dew points ≥ 22°C, was greatest in the events that occurred in the 1990s. An examination of the event diurnal cycle identified that: (1) the minimum number of stations experiencing an hourly dew point value ≥ 22°C occurred at 0300 and 0600 local time, while the maximum number of stations meeting this dew point threshold generally occurred at 0900 and 1200; (2) the biggest dew point increases in terms of spatial coverage of values ≥ 22° occurred between 0600 and 0900; and (3) in 10 of 73 (14%) event days dew points remained ≥ 22°C at ≥ 50% of the stations for 24 consecutive hours. Developing a greater understanding of the spatial and temporal evolution of widespread and intense high dew point events should assist those involved in the design and operation of air conditioning systems that rely on evaporative processes to cool air.
... Because Wisconsin is adjacent to two of the Great Lakes , located in the vicinity of the Corn Belt where a high density of land area planted in corn and soybeans efficiently move water from the soil back to the atmosphere during July and August ( Changnon et al . , 2003 ) , and impacted by the interaction of multiple air masses through the changing seasons ( Bryson , 1966 ) , it is possible that patterns of future climate change may be quite difficult to predict by Global Circulation Models ( GCMs ) based on the historical record of climate varia - tion . Some of the spatial variability in the results ...
... he frequency of very hot days—or at least an unexpected absence of increases as observed in this study as well as across larger regions of the Midwest and Great Plains—could be attributed to increasing daytime cloudiness ( Dai et al . , 1997 ; Pan et al . , 2004 ; Zhou et al . , 2008 ) , more surface evapotranspiration from expanding agriculture ( Changnon et al . , 2003 ) , and altered atmospheric circulation patterns , including those associated with the development of the nocturnal low - level jet in the Great Plains ( Pan et al . , 2009 ) . Schwartz ( 1995 ) took an even closer look at the change in frequency of dif - ferent air - mass types across the North Central U . S . from 1958 to 1992 to bett ...
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Trends in meteorological and ecological variables were calculated across the state of Wisconsin from 1950 to 2006 to quantify recent patterns of climate change. In summary, annual average nighttime low temperatures have increased by 0.6 to 2.2 degrees C, whereas the annual average daytime high temperatures have warmed by 0.3 to 0.6 degrees C. Annual average precipitation has increased by 50-100 mm in the central and southern portions of the state, about a 10-15% increase, while precipitation across the far northern portion of the state appears to have declined by 20-60 mm since 1950, with the most pronounced decrease occurring during summer. On a seasonal basis, warming temperatures are more pronounced during winter and springtime, and nighttime temperatures are warming faster than daytime high temperatures. Some cooling trends in daytime high temperatures were observed during late summer and fall, particularly in the northeast and far southwest portions of the state. We calculated that the length of the growing season has increased by 5 to 20 days, with the greatest change in the central and northern part of Wisconsin. The annual number of days each year with low temperatures less than 0 degrees F (-17.8 degrees C) has diminished substantially, while the number of days each year with highs greater than 90 degrees F (32.2 degrees C) has remained relatively constant. A slight shift northward of the ecological "Tension Zone" was also documented.
... Investigations of factors leading to these conditions concluded that evapotranspiration from crops and recently wetted soils assisted in providing a large supply of low-level moisture in the region (Kunkel et al., 1996;Karl and Knight, 1997). In a study that examined dew point levels in extreme Chicago heat waves over a 75-year period, Changnon et al. (2003) noted that changes in a number of agricultural practices (e.g. acres planted with corn and soybean, planting densities, improved hybrids and no till-farming techniques) have likely enhanced evapotranspiration and increased surface dew points. ...
... These land-use types are also dynamic with major shifts currently ongoing throughout the region (e.g. rural to urban, pasture to row crops; Changnon et al., 2003;Kalnay and Cai, 2003). Modelling studies further suggest that land-atmosphere interactions in mid-continental locations are important factors in determining the magnitude of global warminginduced climate changes (Menzel et al., 1992;Wetherald and Manabe, 1995). ...
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Eight Midwestern extremely high dew point events were examined with respect to their synoptic characteristics and evolution. Individual and composite analyses of events suggest that there exists three predominant features associated with extreme dew point events. In nearly all cases, the evolution of the synoptic environment includes the development and propagation of low pressure from the high plains through the upper Great Lakes. The low pressure increases and backs the surface winds acting to advect low-level moisture from eastern Nebraska, Iowa, Missouri eastward into Illinois and Indiana. The progression of the low pressure and attendant frontal boundaries also acts to modulate the length of the extreme low-level dew point event. Healthy crops and sufficient soil moisture content throughout this large agricultural region were also evident during the periods of extreme low-level moisture. Finally, the vertical thermal profile of the atmosphere during extreme dew point events supports previous findings and highlights the importance of restricted low-level mixing as instrumental in allowing near-surface moisture to become trapped and increased. Copyright © 2007 Royal Meteorological Society
... Similarly, the relative humidity (RH) which refers to the amount of water vapour in the air, expressed as a percentage of the maximum amount that the air could hold at the given temperature, is also changing. The RH range of about 30-70% is healthy for humans while very high or low RH may cause health problems [3] and also affect plants' transpiration. Similarly, heat wave from high surface temperature might cause discomfort or heat stroke with the severe cases occurring above 40 °C [4]. ...
... In the case of RH, the annual mean intensity is 83.01% while the monthly mean values are low between January and March with magnitude above 70% (Fig. 4b); a limit already considered to be unhealthy for human [3]. For instance, the monthly intensity rises from the least magnitude of 78.06% in February to the peak (87.29%) in July after which it shows an overall reduction that reaches 82.13% in December (Fig. 4b). ...
Article
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The variability in the temperature and Relative Humidity (RH) observed within Lagos State, a coastal region in Nigeria, is investigated using data from Nigeria Meteorological Agency (NIMET) for 1980 to 2010. The results reveal an annual mean value of 27.20°C and 83.01% for the temperature and RH respectively and an increasing trend in RH over the study period while such rising trend in the mean temperature is reversed from 2005 to 2010. The findings show an inverse relationship between the temperature and RH while it further indicates that low temperature is associated with increased rainfall under the accompanying cloudy condition and vice versa. These observations are supported by the strong correlation coefficients between the RH and the rainfall (0.72) and that between the RH and the temperature (-0.95) while-0.59 is obtained between the rainfall and the corresponding temperature. The correlations show that the impacts of the precipitation on RH are stronger than the effects it has on the temperature while both temperature and RH strongly depends on each other. Hence, under a future global warming, extremely warm atmospheric condition characterized by high RH in the coastal region could cause heat stroke, discomfort and health problems among the inhabitants. However, the area becomes conducive and attractive to tourists under moderate RH and good temperature.
... This suggests that RH can affect ecosystems in a manner that is independent from P. The important role of increased summer RH raises an interesting question regarding the source of influential climate change in the Midwest region. If, as some studies suggest, intense agricultural production of the Midwest Corn Belt is responsible for the observed increase in summertime humidity [Changnon et al., 2003], this implies that human land use practices can have a significant effect on local climate as well as surrounding ecosystems. Another implication is that local-scale forcings have the potential to alter regional-or global-scale forcings, perhaps confounding future climate change projections. ...
Article
[1] We investigated the impacts of recent climate change on potential vegetation distributions and carbon and water cycling across the Upper Midwest from 1948 to 2007. We used the Agro-IBIS dynamic vegetation model driven by a newly developed gridded daily climate data set at 5 min × 5 min spatial resolution. Trends in climate variables were spatially heterogeneous over the study period and were associated with an overall increase in net primary productivity (NPP). We observed an average regional change in total NPP of 41 ± 30 g C m−2 (8%). Increased summer relative humidity and increased annual precipitation were key variables contributing to the positive trends. Mechanisms for increased productivity included a reduction in soil moisture stress as well as increased stomatal conductance resulting from an increase in summertime humidity. Model simulations also showed an average total increase in annual groundwater recharge throughout the region of 39 ± 35 mm (45%) driven by increases in annual precipitation. Evapotranspiration had a highly variable spatial trend over the 60 year period, with an average total change of 5 ± 21 mm (1%) across all grid cells. The location of the Tension Zone, a broad ecotone dividing northern mixed forests and southern hardwood forests and prairies, was not observed to migrate using analysis of meteorological variables.
... While the differences in the datasets used could explain these disparities, further research is needed to solidify the associated temporal patterns. Rising dew points in the growing season in Midwestern United States were linked to high precipitation anomalies and rapid rates of evapotranspiration with increased corn and soybean planting densities, expansion of irrigation, and other changes in agricultural practices (Changnon et al., 2003). As discussed later, we similarly found increasing mean precipitation within both warm (sβ = 0.001 -0.012 mm⋅year − 1 ) and cold (October-March, sβ = − 0.003 -0.010 mm⋅year − 1 ) seasons, which could collectively provide more moisture to the atmosphere. ...
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Forecasts of increased frequency of meteorological extremes have received considerable attention due to their potential impact on the integrity of biotic communities, stability of terrestrial and aquatic environments, availability of ecosystem services, and broader societal prosperity. Canada is projected to experience greater warming rates than many other regions of the world and changes in meteorological extremes are predicted to be variable across the country. In this context, our goal is to evaluate the long-term trends of extreme meteorological variables (air and dew point temperature, relative humidity, wind speed, and precipitation) in southern and central Ontario (from 42°N to 50°N), while considering the role dynamics of large-scale atmospheric oscillations (El Niño–Southern Oscillation, North Atlantic Oscillation, Arctic Oscillation, and Pacific Decadal Oscillation). Air temperature minima increased year-round, while temperature maxima mainly increased during the cooler months of the year. Consistent with recent evidence from the literature, our study identified an increase in the amount of atmospheric water since the 1950s, as shown by the rising trends in dew point temperature maxima and minima during winter and mid-summer/early-autumn, respectively. Likewise, we found a weak decline in the relative humidity during the warm season, and a more discernible declining trend during the cooler part of the year, which could be in turn reflective of the moderate change of temperature maxima and rising minima, respectively. Consistent with the broader evidence of a global terrestrial stilling, our analysis showed a declining occurrence of high wind-speed events across the entire study domain, and frequent slow-wind speeds during both warm and cold periods of the year. Interestingly, a closer examination of temporal trends in calm wind frequency provides evidence of a recent reversal in the latter trend with diminishing prevalence of very calm wind conditions. We generally found a weakly increasing temporal trend with maximum total daily precipitation, but without a coherent spatial pattern within the broader study area. Our analysis showed that large-scale phenomena have a discernible signature mostly on air temperature and humidity variables, but had little impact on low relative humidity, high and low wind-speed, and precipitation variability. Given the modest impact of teleconnections on long-term temporal trends, our study concludes that the meteorological extremes are more directly influenced by regional and local heat and humidity balance processes rather than global-scale atmospheric mechanisms. The observed trends of air temperature, humidity, and wind speed extremes suggest a profound impact on the phenology of aquatic and terrestrial ecosystems and human experience of weather.
... This introduction of water at the surface has the ability to change the near-surface moisture content (Ferguson & Maxwell, 2011). Changnon, Sandstrom, and Schaffer (2003) stated that recent short duration heat events in the Chicago region have experienced higher dew points than those that occurred earlier in the period of record. Their research attributed these changes to changes in agricultural practices that increased evapotranspiration (ET) rates in the region. ...
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Recent upward trends in acres irrigated have been linked to increasing near-surface moisture. Unfortunately, stations with dew point data for monitoring near-surface moisture are sparse. Thus, models that estimate dew points from more readily observed data sources are useful. Daily average dew temperatures were estimated and evaluated at 14 stations in Southwest Georgia using linear regression models and artificial neural networks (ANN). Estimation methods were drawn from simple and readily available meteorological observations, therefore only temperature and precipitation were considered as input variables. In total, three linear regression models and 27 ANN were analyzed. The two methods were evaluated using root mean square error (RMSE), mean absolute error (MAE), and other model evaluation techniques to assess the skill of the estimation methods. Both methods produced adequate estimates of daily averaged dew point temperatures, with the ANN displaying the best overall skill. The optimal performance of both models was during the warm season. Both methods had higher error associated with colder dew points, potentially due to the lack of observed values at those ranges. On average, the ANN reduced RMSE by 6.86% and MAE by 8.30% when compared to the best performing linear regression model.
... According to Robinson (2001), currently there is ly, this extreme phenomenon is not only associated with the values of meteorological variables -especially temperature-but also with the effects on ecosystems (Changnon et al., 2003;Khalio et al., 2005;Nogueira and Paixao, 2008). Lopez-Díaz (2004) studied the behavior of heat waves using only long temperature series obtained at several observatories in peninsular Spain, and highlighted including the need to use the threshold variable. ...
Article
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The temporal behavior of the annual frequency of heat and cold waves observed between 1961 and 2010 is established for the Spanish Central Plateau and for the two sub-areas in it. The series of daily maximum and minimum temperature anomalies for the working areas were calculated from the daily data concerning temperature anomalies. The thresholds of these series of anomalies, determined by the P10 and P90 percentiles values, were obtained. Heat waves occur when there are two or more consecutive days on which the maximum and minimum temperature anomalies are simultaneously greater than the values of the thresholds obtained for the P90 percentile. The heat waves that affected the Spanish Central Plateau and the two sub-areas during the period of time considered were identified and their monthly and annual frequencies were obtained. Likewise, a cold wave is considered to have occurred when there are two or more consecutive days on which the maximum and minimum temperature anomalies are simultaneously lower than the thresholds established by the corresponding P10 percentiles. The cold waves occurring in the study area were identified and their monthly and annual frequencies in the study period were established. According to the results, the months with highest number of heat waves between 1961 and 2010 were May (25 waves) and June (23 waves). Trend analysis of the series of annual frequencies indicates that there was an increasing trend towards the occurrence of heat waves, with a confidence level greater than 99%. The linear model established indicates that an increase had occurred in the frequency of heat waves in the Spanish plateau of the order of 0.6 waves every 10 years. Regarding cold waves, these were detected in each month of the year and their frequency ranged between eight and 16 events per year. The months with lowest number of cold waves were April (nine), July (eight) and August (nine), and the months with the highest number were March, May, June and October, with 16 cold waves. The years with the highest number of cold waves were 1969, 1971 and 1977, with seven cases. In the other years the annual rate was between one and six. Trend analysis of the series of annual frequencies indicated that there was a decreasing frequency of cold waves, at the confidence level of 99%. When a linear model was considered for the Spanish Central Plateau a decreasing frequency of the cold waves of the order of 0.54 waves in every 10 years was observed from 1961 to 2010.
... In a very recent study, Schoof (2012) found increases in maximum dew point temperatures during the summer season across the Midwest which partially offset flat or decreasing maximum air temperatures and a wide variance in trends of resulting apparent temperatures. A likely cause of higher dew point temperatures during the growing season is the significant increase in plant density from earlier decades, which greatly enhances the transpiration of water from the soil to the atmosphere (Changnon et al. 2003). ...
Article
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The usefulness of climate information for agricultural risk management hinges on its availability and relevance to the producer when climate-sensitive decisions are being made. Climate information providers are challenged with the task of balancing forecast availability and lead time with acceptable forecast skill, which requires an improved understanding of the timing of agricultural decision making. Achieving a useful balance may also require an expansion of inquiry to include use of non-forecast climate information (i.e. historical climate information) in agricultural decision making. Decision calendars have proven valuable for identifying opportunities for using different types of climate information. The extent to which decision-making time periods are localized versus generalized across major commodity-producing regions is yet unknown, though, which has limited their use in climate product development. Based on a 2012 survey of more than 4,770 agricultural producers across the U.S. Corn Belt region, we found variation in the timing of decision-making points in the crop year based on geographic variation as well as crop management differences. Many key decisions in the cropping year take place during the preceding fall and winter, months before planting, raising questions about types of climate information that might be best inserted into risk management decisions at that time. We found that historical climate information and long term climate outlooks are less influential in agricultural risk management than current weather, short term forecasts, or monthly climate projections, even though they may, in fact, be more useful to certain types of decision making.
... Al respecto de estos episodios temporales de condiciones climáticas más extremas, hay que decir que no existe una definición precisa ni universalmente aceptada. Su definición se establece más por la incidencia que tienen sobre el hombre y sus diversas actividades (CHANGNON et al., 2003; ROBINSON, 2001; NOGUEIRA y PAIXÃO, 2008), que no por los valores de las variables meteorológicas, principalmente las temperaturas. Las definiciones manejadas, líneas atrás justificadas, no se ajustan estrictamente con la percepción habitual que al respecto tiene el ser humano (larga prolongación de días muy fríos o muy calurosos). ...
Article
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The growing interest in studies of Climate Change to identify and assess their entity in different parts of the world and its evolution over the last decades and in the future, led since 1997 to develop a line of research on Climate Change within the Climate Analysis Recognized Research Group in the Universities of Salamanca (Department of General Physics and Atmosphere) and Valladolid (Department of Geography), currently active. We present the results of scientific research and production carried out since, coinciding now with the change of principal investigator, D. José Luis Salazar Labajo. The aim is to show the methodological proposals followed over these years in the study of meteorological variables to characterize climate change in Castilla y León and throughout the Iberian central platform. The research has focused on the analysis and modeling of time series of temperature, precipitation and atmospheric pressure at the surface level, using statistical techniques and artificial neural networks. The contributions made in the analysis of trends, frequency of extreme values and behaviors of cold and heat waves, are summarized in this paper.
... A factor in the negative trends in the eastern United States may be downstream effects of increasing irrigation further west (DeAngelis et al., 2010) from the 1950s onwards, coinciding with a positive precipitation trend (Kirtman et al., 2013;Portmann et al., 2009). Changes in agricultural practices leading to higher evaporation have also been implicated (Changnon et al., 2003). It has been speculated that revegetation after the decline of agriculture might also have been a factor (Portmann et al., 2009). ...
Article
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It sounds straightforward. As the Earth warms due to the increased concentration of greenhouse gases in the atmosphere, global temperatures rise and so heatwaves become warmer as well. This means that a fixed temperature threshold is passed more often: the probability of extreme heat increases. However, land use changes, vegetation change, irrigation, air pollution, and other changes also drive local and regional trends in heatwaves. Sometimes they enhance heatwave intensity, but they can also counteract the effects of climate change, and in some regions, the mechanisms that impact on trends in heatwaves have not yet been fully identified. Climate models simulate heatwaves and the increased intensity and probability of extreme heat reasonably well on large scales. However, changes in annual daily maximum temperatures do not follow global warming over some regions, including the Eastern United States and parts of Asia, reflecting the influence of local drivers as well as natural variability. Also, temperature variability is unrealistic in many models, and can fail standard quality checks. Therefore, reliable attribution and projection of change in heatwaves remain a major scientific challenge in many regions, particularly where the moisture budget is not well simulated, and where land surface changes, changes in short‐lived forcers, and soil moisture interactions are important.
... At the surface, water vapor (or humidity) is an important meteorological and climate variable that affects human comfort (Changnon et al. 2003), surface evaporation and plants' transpiration. Surface specific (q) and relative humidity (RH) is conventionally measured using wet and dry bulb thermometers or RH sensors exposed in thermometer screens at a large number of weather and climate stations and on many marine platforms. ...
Article
In situ observations of surface air and dewpoint temperatures and air pressure from over 15 000 weather stations and from ships are used to calculate surface specific (q) and relative (RH) humidity over the globe (60°S-75°N) from December 1975 to spring 2005. Seasonal and interannual variations and linear trends are analyzed in relation to observed surface temperature (T) changes and simulated changes by a coupled climate model (namely the Parallel Climate Model (PCM)) with realistic forcing. It is found that spatial patterns of long-term mean q are largely controlled by climatological surface temperature, with the largest q of 17-19 g kg1 in the Tropics and large seasonal variations over northern mid- and high-latitude land. Surface RH has relatively small spatial and interannual variations, with a mean value of 75%-80% over most oceans in all seasons and 70%-80% over most land areas except for deserts and high terrain, where RH is 30%-60%. Nighttime mean RH is 2%-15% higher than daytime RH over most land areas because of large diurnal temperature variations. The leading EOFs in both q and RH depict long-term trends, while the second EOF of q is related to the El Niño-Southern Oscillation (ENSO). During 1976-2004, global changes in surface RH are small (within 0.6% for absolute values), although decreasing trends of 0.11% 0.22% decade1 for global oceans are statistically significant. Large RH increases (0.5%-2.0% decade1) occurred over the central and eastern United States, India, and western China, resulting from large q increases coupled with moderate warming and increases in low clouds over these regions during 1976-2004. Statistically very significant increasing trends are found in global and Northern Hemispheric q and T. From 1976 to 2004, annual q (T ) increased by 0.06 g kg1 (0.16°C) decade1 globally and 0.08 g kg1 (0.20°C) decade1 in the Northern Hemisphere, while the Southern Hemispheric q trend is positive but statistically insignificant. Over land, the q and T trends are larger at night than during the day. The largest percentage increases in surface q (1.5% to 6.0% decade1) occurred over Eurasia where large warming (0.2° to 0.7°C decade1) was observed. The q and T trends are found in all seasons over much of Eurasia (largest in boreal winter) and the Atlantic Ocean. Significant correlation between annual q and T is found over most oceans (r 0.6-0.9) and most of Eurasia (r 0.4-0.8), whereas it is insignificant over subtropical land areas. RH-T correlation is weak over most of the globe but is negative over many arid areas. The q-T anomaly relationship is approximately linear so that surface q over the globe, global land, and ocean increases by 4.9%, 4.3%, and 5.7% per 1°C warming, respectively, values that are close to those suggested by the Clausius-Clapeyron equation with a constant RH. The recent q and T trends and the q-T relation- ship are broadly captured by the PCM; however, the model overestimates volcanic cooling and the trends in the Southern Hemisphere.
... Ishii et al. (2005) reported that globally averaged dew points over the ocean have risen by about 0.25°C between 1950 and 2000. Increasing extremes in summer dew points, and increased humidity during summer heat waves, were found at three stations in northeastern Illinois (Sparks et al., 2002;Changnon et al., 2003) and attributed in part to changes in agricultural practices in the region. Dai (2006) analysed near-global (60°S-75°N) synoptic data for 1976 to 2005 from ships and buoys and more than 15,000 land stations for specifi c humidity, temperature and relative humidity. ...
... Recent summer heat waves in northern Illinois (July 1995 and July 1999) have been associated with higher dew point levels (Kunkel et al. 1996;Palecki et al. 2001;Sparks et al. 2002;Changnon et al. 2003). These higher levels of atmospheric water vapour have impacted not only on air conditioning systems, but also created big demands for electricity and caused health-related problems. ...
Article
In an effort to save money during the summer of 2003, Northern Illinois University (NIU) administrators instituted a four-day working week and stopped air conditioning buildings for the three-day weekends (Friday through Sunday). Shutting down the air conditioning systems caused a noticeable drop in electricity usage for that part of the campus that features in our study, with estimated total electricity savings of 1,268,492 kilowatt-hours or 17% of the average usage during that eight-week period. NIU's air conditioning systems, which relied on evaporative cooling to function, were sensitive to dew point levels. Greatest savings during the shutdown period occurred on days with higher dew points. An examination of the regional dew point climatology (1959–2003) indicated that the average summer daily dew point for 2003 was 14.9°C (58.8°F), which fell in the lowest 20% of the distribution. Based on the relationship between daily average dew points and electrical usage, a predictive model that could estimate electrical daily savings was created. This model suggests that electrical savings related to any future three-day shutdowns over summer could be much greater in more humid summers. Studies like this demonstrate the potential value of applying climatological information and of integrating this information into practical decision-making.
... In the central USA, the relative humidity has increased by 0.5–2.0% decade -1 from 1976 to 2004 (Dai 2006), and this may be partially attributable to increased agricultural productivity and crop density delivering more water to the atmosphere (Changnon, Sandstrom & Schaffer 2003). Transpiration is regulated by complicated interactions of plant physiology and environmental conditions; therefore, it is important to understand what controls leaf transpiration in the present climate, and also how these environmental factors and feedbacks may change in the future. ...
Article
Stable isotopes in water have the potential to diagnose changes in the earth's hydrological budget in response to climate change and land use change. However, there have been few measurements in the vapour phase. Here, we present high-frequency measurements of oxygen isotopic compositions of water vapour (δv) and evapotranspiration (δET) above a soybean canopy using the tunable diode laser (TDL) technique for the entire 2006 growing season in Minnesota, USA. We observed a large variability in surface δv from the daily to the seasonal timescales, largely explained by Rayleigh processes, but also influenced by vertical atmospheric mixing, local evapotranspiration (ET) and dew formation. We used δET measurements to calculate the isotopic composition at the sites of evaporative enrichment in leaves (δL,e) and compared that with the commonly used steady-state prediction (δL,s). There was generally a good agreement averaged over the season, but larger differences on individual days. We also found that vertical variability in relative humidity and temperature associated with canopy structure must be addressed in canopy-scale leaf water models. Finally, we explored this data set for direct evidence of the Péclet effect.
... Furthermore, understanding heat vulnerability is much more complex than a maximum temperature. Humidity, for example, has been shown to have a compounding impact -heat stress increased with very high dew points in Chicago in 1995 (Sparks et al., 2002;Changnon et al., 2003), but also increased with low humidity in Seville, Spain (Diaz et al., 2002a). Recent work, by Gaffen and Ross (1999) and Robinson (2001), has focused on developing long-term quality-controlled humidity datasets to facilitate longer-term climatological analyses of heat stress. ...
... Furthermore, understanding heat vulnerability is much more complex than a maximum temperature. Humidity, for example, has been shown to have a compounding impact -heat stress increased with very high dew points in Chicago in 1995 (Sparks et al., 2002;Changnon et al., 2003), but also increased with low humidity in Seville, Spain (Diaz et al., 2002a). Recent work, by Gaffen and Ross (1999) and Robinson (2001), has focused on developing long-term quality-controlled humidity datasets to facilitate longer-term climatological analyses of heat stress. ...
... Al respecto de estos episodios temporales de condiciones climáticas más extremas, hay que decir que no existe una definición precisa ni universalmente aceptada. Su definición se establece más por la incidencia que tienen sobre el hombre y sus diversas actividades (CHANGNON et al., 2003;ROBINSON, 2001;NOGUEIRA y PAIXÃO, 2008), que no por los valores de las variables meteorológicas, principalmente las temperaturas. ...
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El interés creciente por los estudios acerca del Cambio Climático para delimitar y valorar su entidad en diferentes lugares del planeta, así como su evolución a lo largo de las últimas décadas y en un futuro, llevó desde 1997 al desarrollo de una línea de investigación sobre Cambio Climático, dentro del Grupo de Investigación Reconocido de Análisis del Clima de las Universidades de Salamanca (Departamento de Física General y de la Atmósfera) y de Valladolid (Departamento de Geografía), activo en la actualidad. Se presentan los resultados obtenidos de la investigación y producción científica llevada a cabo desde entonces, coincidiendo ahora con el cambio de su investigador principal, D. José Luis Labajo Salazar. El objetivo es mostrar las propuestas metodológicas seguidas a lo largo de estos años en el estudio de variables meteorológicas a partir de las cuales se pueda caracterizar el Cambio Climático en Castilla y León y en toda la meseta central española. Las investigaciones se han centrado en el análisis y modelado de las series temporales de temperaturas, precipitaciones y presión atmosférica a nivel de superficie, empleando técnicas estadísticas y de redes neuronales artificiales. Las aportaciones realizadas en el análisis de sus tendencias, frecuencias, comportamientos de valores extremos y olas de frío y calor, se sintetizan en el presente trabajo.
... Many studies have shown that industrial greenhouse gas emissions increase both global mean temperature and heat index (HI) of heat waves (Tett et al 1999, Karoly et al 2003, Stott et al 2004, Stott et al 2011, Christidis et al 2012, yet land use and land use change can also alter heat waves at the regional scale. Urban heat islands exacerbated the impact of heat waves in the Midwest in 1995 (Kunkel et al 1996) and historical meteorological data indicate that agricultural irrigation raised the dew point temperature during heat waves in Chicago (Changnon et al 2003). With the same air temperature, higher dew point temperature can increase the apparent temperature (Steadman 1984) resulting in greater mortality and severe human health effects (Smoyer 1998, Naughton et al 2002, Conti et al 2005. ...
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A potential decline in irrigation due to groundwater depletion or insufficient surface water would not only directly affect agriculture, but also could alter surface climate. In this study we investigated how loss of irrigation affects heat wave frequency, duration, and intensity across fifteen heat wave indices (HINs) using a regional climate model that incorporated dynamic crop growth. Averaged across all indices, loss of irrigation increased heat wave frequency, duration, and intensity. In the United States, irrigation effects on heat waves were statistically significant over irrigated cropland for the majority of HINs, but in non-irrigated regions, the effects were significant only for a few HINs. The heat index temperature metrics that include humidity were less sensitive to loss of irrigation due to the trade-off between increased temperature and decreased humidity. Using the same temperature metric but different temperature thresholds resulted in qualitatively similar effects on heat waves. Regions experiencing strong groundwater depletion, such as the southern high plains, may suffer more and longer heat waves with reduced irrigation.
... The ubiquitous higher dewpoint temperatures occur during the hottest conditions, in agreement with findings for individual heat waves such as the July 1995 event in Chicago (Kunkel et al. 1996;Livezey and Tinker 1996), indicating that higher humidity may particularly exacerbate heat stress during heat waves. This pattern in Chicago during the heat waves in a recent decade was found highly correlated to the anomalies of regional precipitation prior to the heat event as well as the change of agricultural practices (Changnon et al. 2003). Interestingly, within each class a strong urban moisture deficit (relative to rural areas) occurs for the afternoon (Aqua-day) overpass, when strong afternoon convective activity is often present. ...
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Extreme heat is a leading cause of weather-related human mortality. The urban heat island (UHI) can magnify heat exposure in metropolitan areas. This study investigates the ability of a new MODIS-retrieved near-surface air temperature and humidity dataset to depict urban heat patterns over metropolitan Chicago, Illinois, during June-August 2003-13 under clear-sky conditions. A self-organizing mapping (SOM) technique is used to cluster air temperature data into six predominant patterns. The hottest heat patterns from the SOM analysis are compared with the 11-summer median conditions using the urban heat island curve (UHIC). The UHIC shows the relationship between air temperature (and dewpoint temperature) and urban land-use fraction. It is found that during these hottest events 1) the air temperature and dewpoint temperature over the study area increase most during nighttime, by at least 4K relative to the median conditions; 2) the urban-rural temperature/humidity gradient is decreased as a result of larger temperature and humidity increases over the areas with greater vegetation fraction than over those with greater urban fraction; and 3) heat patterns grow more rapidly leading up to the events, followed by a slower return to normal conditions afterward. This research provides an alternate way to investigate the spatiotemporal characteristics of the UHI, using a satellite remote sensing perspective on air temperature and humidity. The technique has potential to be applied to cities globally and provides a climatological perspective on extreme heat that complements the many case studies of individual events.
... Further, DPT also influences crop yields by the spread of many pathogens through free moisture [2]. Nevertheless, a slow rate of drop in the dew point temperature results in evaporative cooling [3] and, conversely, a rise in DPT intensifies the impacts of heat waves on the environment [4]. ...
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Dew point temperature (DPT) is known to fluctuate in space and time regardless of the climatic zone considered. The accurate estimation of the DPT is highly significant for various applications of hydro and agro-climatological researches. The current research investigated the hybridization of a multilayer perceptron (MLP) neural network with nature-inspired optimization algorithms (i.e., gravitational search (GSA) and firefly (FFA)) to model the DPT of two climatically contrasted (humid and semi-arid) regions in India. Daily time scale measured weather information, such as wet bulb temperature (WBT), vapor pressure (VP), relative humidity (RH), and dew point temperature, was used to build the proposed predictive models. The efficiencies of the proposed hybrid MLP networks (MLP-FFA and MLP-GSA) were authenticated against standard MLP tuned by a Levenberg-Marquardt back-propagation algorithm, extreme learning machine (ELM), and support vector machine (SVM) models. Statistical evaluation metrics such as Nash Sutcliffe efficiency (NSE), root mean square error (RMSE), and mean absolute error (MAE) were used to validate the model efficiency. The proposed hybrid MLP models exhibited excellent estimation accuracy. The hybridization of MLP with nature-inspired optimization algorithms boosted the estimation accuracy that is clearly owing to the tuning robustness. In general, the applied methodology showed very convincing results for both inspected climate zones.
... Human physical comfort is dependent not only on air temperature, but also on the interaction of a number of weather variables. For example the human response to outdoor conditions is worse on sultry days than at the same air temperature in a dry air mass (Baranowska et al. 1968, Thompson et al. 1996, Changnon et al. 2003. ...
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Heat waves have not been defined officially, however there are many non-official definitions in use. This paper reviews some of the most frequently used definitions of heat wave and its measures. It also reveals different numbers of heat periods that result from an analysis employing different definitions of a heat wave. This has been exemplified on the basis of data from Poland and confirmed the need for regionally accepted guidelines by which to define heat waves.
... Human physical comfort is dependent not only on air temperature, but also on the interaction of a number of weather variables. For example the human response to outdoor conditions is worse on sultry days than at the same air temperature in a dry air mass (Baranowska et al. 1968, Thompson et al. 1996, Changnon et al. 2003. ...
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Based on the case of the military-industrial city of Ust'-Kamenogorsk, Kazakhstan, this paper explores (a) Soviet and post-Soviet era migration into former closed cities, and (b) the present housing situation of migrant groups living in them, paying particular attention to their ethnic background. The study is based on a survey carried out by the author and the regional statistical authority in January 2001. The principal findings suggest that there has been a clear increase in migrants from the oblast's rural areas to the regional capital, which is attributable to the regional urbanisation pressure which had been created during the city's period of 'closure', and that the origin of these migrants has shifted in favour of areas with larger Kazakh populations. Also, contradicting the Soviet goals, and resulting from structural factors re-enforced by the closed city regime, the ethnic housing gap is greatest among those who arrived during the Soviet period.
... Although other approaches have been used to infer the impact of the US Corn Belt (Changnon et al., 2003) on regional humidity, the combined data, analytical, and modeling approaches used here offer a unique and more direct quantification. The higher amplitude of crop transpiration rates during the mid growing season indicate that summertime humidity can be significantly amplified by crops and may, therefore, enhance convective precipitation. ...
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Increasing atmospheric humidity and convective precipitation over land provide evidence of intensification of the hydrologic cycle – an expected response to surface warming. The extent to which terrestrial ecosystems modulate these hydrologic factors is important to understanding feedbacks in the climate system. We measured the oxygen and hydrogen isotope composition of water vapor from a very tall tower (185 m) in the Upper Midwest, United States to help diagnose the sources, transport, and fractionation of water vapor in the planetary boundary layer (PBL) over a 3-year period (2010 to 2012). These measurements represent the first set of annual water vapor isotope observations for the region. Models and cross wavelet analyses were used to assess the importance of Rayleigh, evapotranspiration (ET), and PBL entrainment processes on the isotope composition of water vapor. The vapor isotope composition at this tall tower site showed a very large seasonal amplitude (mean monthly δ18Ov ranged from −40.1 to −15.5 ‰ and δ2Hv ranged from −278.7 to −109.1 ‰) and followed the familiar Rayleigh distillation relation with water vapor mixing ratio at the annual time-scale. However, this relation was strongly modulated by ET and PBL entrainment processes at time-scales ranging from hours to several days. The wavelet coherence spectra indicate that the oxygen isotope ratio and the deuterium excess (dx) of water vapor are sensitive to synoptic and PBL processes. According to the phase of the coherence analyses, we show that ET often leads changes in dx, confirming that it is a potential tracer of regional ET. Isotope mixing models indicate that on average about 31 % of the growing season PBL water vapor is derived from regional ET. However, isoforcing calculations and mixing model analyses for high PBL water vapor mixing ratios events (> 25 mmol mol−1) indicate that regional ET can account for 40 % to 60 % of the PBL water vapor. These estimates are in relatively good agreement with that derived from numerical weather model simulations. This relatively large fraction of ET-derived water vapor implies that ET has an important impact on the precipitation recycling ratio within the region. Based on multiple constraints, we estimate that the summer season recycling fraction is about 30 %, indicating a potentially important link with convective precipitation.
... Although other approaches have been used to infer the impact of the US Corn Belt (Changnon et al., 2003) on regional humidity, the combined data, and the analytical and modeling approaches used here offer a unique and more direct quantification. The higher amplitude of crop transpiration rates during the middle of the growing season (Fig. S4) indicate that summertime humidity can be significantly amplified by crops and may, therefore, enhance convective precipitation. ...
Article
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Increasing atmospheric humidity and convective precipitation over land provide evidence of intensification of the hydrologic cycle - an expected response to surface warming. The extent to which terrestrial ecosystems modulate these hydrologic factors is important to understand feedbacks in the climate system. We measured the oxygen and hydrogen isotope composition of water vapor at a very tall tower (185 m) in the upper Midwest, United States, to diagnose the sources, transport, and fractionation of water vapor in the planetary boundary layer (PBL) over a 3-year period (2010 to 2012). These measurements represent the first set of annual water vapor isotope observations for this region. Several simple isotope models and cross-wavelet analyses were used to assess the importance of the Rayleigh distillation process, evaporation, and PBL entrainment processes on the isotope composition of water vapor. The vapor isotope composition at this tall tower site showed a large seasonal amplitude (mean monthly δ18Ov ranged from -40.2 to -15.9‰ and δ2Hv ranged from -278.7 to -113.0‰) and followed the familiar Rayleigh distillation relation with water vapor mixing ratio when considering the entire hourly data set. However, this relation was strongly modulated by evaporation and PBL entrainment processes at timescales ranging from hours to several days. The wavelet coherence spectra indicate that the oxygen isotope ratio and the deuterium excess (dv) of water vapor are sensitive to synoptic and PBL processes. According to the phase of the coherence analyses, we show that evaporation often leads changes in dv, confirming that it is a potential tracer of regional evaporation. Isotope mixing models indicate that on average about 31% of the growing season PBL water vapor is derived from regional evaporation. However, isoforcing calculations and mixing model analyses for high PBL water vapor mixing ratio events (>25 mmol mol1) indicate that regional evaporation can account for 40 to 60% of the PBL water vapor. These estimates are in relatively good agreement with that derived from numerical weather model simulations. This relatively large fraction of evaporation-derived water vapor implies that evaporation has an important impact on the precipitation recycling ratio within the region. Based on multiple constraints, we estimate that the summer season recycling fraction is about 30%, indicating a potentially important link with convective precipitation.
... Croplands have a detectable influence on the surface exchanges of heat and water vapor. These surface exchanges, in turn, can impact boundary layer growth and mesoscale convergence/convection (Changnon et al., 2003;Freedman et al., 2001;Levis et al., 2012;McPherson et al., 2004;Raddatz, 1998). To study the impacts of land use/land change on hydroclimatic systems, a better understanding of the interactions between soil-crops-atmosphere is necessary. ...
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Abstract The study postulates that crop rooting depth representation plays a vital role in simulating soil‐crop‐atmospheric interactions. Rooting depth determines the water access for plants and alters the surface energy participation and soil moisture profile. The aboveground crop growth representation in land surface models continues to evolve and improve, but the root processes are still poorly represented. This limitation likely contributes to the bias in simulating soil‐crop‐related variables such as soil moisture and associated water and energy exchanges between the surface and the atmosphere. In Noah‐MP‐Crop, the rooting depth of crops is assumed as 1 m regardless of crop types and the length of growing seasons. In this study, a simple dynamic rooting depth formulation was integrated into Noah‐MP‐Crop. On comparing with soil moisture observations from the in situ Ameriflux, USDA Soil Climate Analysis Network, and the remote‐sensed Soil Moisture Active Passive data set, the results highlight the improved performance of Noah‐MP‐Crop due to modified rooting depth. The improvements were noted in terms of soil moisture and more prominently in terms of the energy flux simulations at both field scale and regional scale. The enhancements in soil moisture profiles reduce the biases in surface heat flux simulations. The impact of rooting depth representation appears to be particularly significant for improving model performance under drought‐like situations. Although it was not possible to validate the simulated rooting depth due to lack of observations, the overall performance of the model helps emphasize the importance of enhancing the representation of crop rooting depth in Noah‐MP‐Crop.
... The efficiency with which crops transfer water vapor from the crop root zones to the atmosphere heavily depends on seasonal variations of crop phenology. Crops have a detectable influence on regional distributions of atmospheric water vapor and temperature and can affect convective triggering by modifying mesoscale boundaries [Raddatz, 1998;Changnon et al., 2003;Levis et al., 2012]. Therefore, croplands can significantly influence land-atmosphere coupling, surface exchanges of heat, water vapor, and momentum, which in turn can impact boundary layer growth and mesoscale convergence/convection [Freedman et al., 2001;McPherson et al., 2004]. ...
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Croplands are important in land-atmosphere interactions and in the modification of local and regional weather and climate; however, they are poorly represented in the current version of the coupled Weather Research and Forecasting/Noah with multiparameterization (Noah-MP) land surface modeling system. This study introduced dynamic corn (Zea mays) and soybean (Glycine max) growth simulations and field management (e.g., planting date) into Noah-MP and evaluated the enhanced model (Noah-MP-Crop) at field scales using crop biomass data sets, surface heat fluxes, and soil moisture observations. Compared to the generic dynamic vegetation and prescribed-leaf area index (LAI)-driven methods in Noah-MP, the Noah-MP-Crop showed improved performance in simulating leaf area index (LAI) and crop biomass. This model is able to capture the seasonal and annual variability of LAI and to differentiate corn and soybean in peak values of LAI as well as the length of growing seasons. Improved simulations of crop phenology in Noah-MP-Crop led to better surface heat flux simulations, especially in the early period of growing season where current Noah-MP significantly overestimated LAI. The addition of crop yields as model outputs expand the application of Noah-MP-Crop to regional agriculture studies. There are limitations in the use of current growing degree days (GDD) criteria to predict growth stages, and it is necessary to develop a new method that combines GDD with other environmental factors, to more accurately define crop growth stages. The capability introduced in Noah-MP allows further crop-related studies and development.
... Thus during the months of July and August, corn and soybeans add more moisture to the local environment when well watered than native tallgrass prairie growing under similar conditions. Since this would result in locally increased dew points, there is potential for these effects to also impact convective development, human comfort during periods of hot temperatures Sparks et al., 2002 andChangnon et al., 2003), and even fog development. ...
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Land use in general, and agricultural crops in Iowa specifically, can under certain circumstances account for a significant component of the local moisture budget. Numerical modeling studies have shown that land use can impact the development of convection, and that subtle changes in dew point can be the difference between thunderstorms occurring or not. Corn and soybean acreage each comprise one-third of the total land area in Iowa during the growing season. In July and August, atmospheric demand (i.e., the combination of atmospheric elements such as temperature, wind, relative humidity, etc. which determine the amount of water a crop uses) for crop evapotranspiration is maximized and the crops are at their peak water-using stage. Assuming non-advective conditions and a well-watered crop, it is shown that corn and soybeans can increase local dew points up to several degrees, depending on the height of the boundary layer and the amount of evapotranspira-tion. The approach developed in this study can be applied to other locations given a local knowledge of land use, crop/vegetation water use, and agronomic practices (e.g., irrigation usage).
... Several studies have examined the influence of agriculture on surface dew point temperature ( ). For example, Changnon et al. [5] showed that agriculture enhanced daily evapotranspiration (ET) and increased the mean daily dew point temperature ( -mean ) during Chicago heat waves. Raddatz and Hanesiak [6] reported that about 80% of summer precipitation events on the Canadian Prairies include convective rainfall whose probability-of-occurrence is enhanced by the impact of ET from annual field crops on and subsequently on convective available potential energy (CAPE). ...
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It is important to increase our knowledge of the role of land use in changing the regional climate. This study asked, "Has the increase in continuous cropping over the past 50 years on the Canadian Prairies influenced the daily mean and range of morning dew point temperatures (Td) during the foliar expansion period (from mid-June to mid-July) of annual field crops?" We found that there has been a general increase in the decadal average of mean daily Td and in the range of morning Td from the 1960s to the 2000s. The increase in the observed range of Td between the daily minimum value, which typically occurs near sunrise, and the late morning peak was found to be related to the increase in annual crop acreage and consequent decrease in summerfallow area. The relationship was more significant in the subhumid climatic zone than in the semiarid climatic zone, and it was influenced by whether the region was experiencing either wet, normal, or dry conditions.
... In another urban climate study, Roy and Yuan (2009) found elevated nocturnal minimum temperatures and a decrease in overall daily temperature range associated with urban development in the Twin Cities metropolitan area. Closely relating to the study reported here, Changnon, Sandstrom, and Schaffer (2003) examined the occurrence of elevated dewpoints during Midwest heat-wave events and speculated on the influence of contributions from agricultural evapotranspiration, although this study was driven purely by climatic variables backed by spatial data on crop production. In a later follow-up study, Changnon, Sandstrom, and Bentley (2006) found greater occurrences of high dewpoint events in more recent years focused within the Midwest region. ...
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Agricultural land use changes have likely played an important role in modifying local and regional climate factors. According to a recent study, summers in the Midwest were significantly cooler and wetter due to the dramatic increases in production of corn and soybeans caused by an intensification of agricultural practices (Alter et al. 2018). In this context, this study examines regional changes manifested in multiple climate variables and directly quantifies the magnitude of potential moisture contributions from Midwest corn and soybean agriculture. Meteorological data were collected for daily minimum, maximum, and dewpoint temperatures over a sixty-one-year study period from fifty-nine National Weather Service first-order stations and cooperative network stations. Regional growing season climatology for two study regions that focused on the rain-fed Midwest Corn Belt and the southern United States extending to the Gulf Coast was analyzed. Further, vapor pressure deficit was calculated to ascertain any regional changes. Field surveys of corn and soybean crop transpiration were used in a multivariate model to estimate lower atmospheric moisture contributions at midday during peak season directly from intensified rain-fed agriculture. Findings indicate an increase in regional dewpoint, associated with elevated nocturnal minimums and suppression of both daily maximum and vapor pressure deficit, concentrated in the Midwest Corn Belt, which was not evident within the South. The estimation results of the atmospheric moisture contributions from the Corn Belt confirm the intensification of Midwestern agriculture as a regional climate modifier. Key Words: agriculture, dewpoint, energy balance, humidity, regional climate.
... Freshly applied fertilizer P is much more susceptible to runoff loss than P that has reacted with soil for several months (Franklin et al., 2007). Furthermore, in Illinois and much of the US Midwest, the potential for surface water runoff may be greater in the spring than in fall due to two reasons: (i) precipitation patterns show that spring is normally wetter than fall (Changnon et al., 2003), and (ii) soils are typically drier in the fall (after crops have removed large amounts of water), leaving them with a greater capacity to retain precipitation than in spring (when they tend to be near field capacity). According to the combination of these factors, when P fertilizer is applied in fall, deep placement of P should be recommended to reduce P losses. ...
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Phosphorus fertilization can increase P losses in surface runoff, but limited information is available for fields with <2% slopes in the US Midwest. Our objectives were to determine the effects of tillage-fertilizer placement (no-till-broadcast, strip till-broadcast; or strip till-deep placement, -15-cm subsurface band) and fertilizer rate applied in the fall (0, 52, or 90 kg P2O5 ha⁻¹ yr⁻¹) on runoff P concentrations and loads in fields with <2% slopes near Pesotum, IL, during fall and spring simulation runoff events, and to measure corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] grain yield. Across four simulated runoff events, deep placement reduced dissolved reactive P (DRP) loads by 69 to 72% compared with the broadcast treatments. A tillage-fertilizer placement × P rate interaction showed that DRP and total P (TP) concentrations remained low when P was deep placed, regardless of P rate, whereas concentrations increased with increasing P rate for the broadcast treatments, but no differences existed for bioavailable P (BAP) (α = 0.05). At one site, rainfall simulation in the spring versus fall increased runoff volumes but sharply decreased BAP concentrations. During fall runoff simulations, deep placement reduced TP loads, and greater TP loads occurred with the 90- than the 52-kg P2O5 ha⁻¹ yr⁻¹ rate. Similarly, when P was broadcast in the fall, DRP and TP concentrations were greater than deep-placed P, but no treatment differences occurred in the spring. Deep banding P and K did not reduce crop yield but reduced runoff losses of P from flat fields compared with broadcast P applications, particularly at high rates of P application. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.
... Crop growth modifies the seasonal evolution of land surface characteristics such as albedo and emissivity, available water for evaporation, plant phenology (e.g., vegetation coverage and LAI), and the land-atmospheric exchange of heat, moisture, and greenhouse gases (GHG). These in turn affect surface heat and moisture fluxes, air temperature and humidity, precipitation, soil moisture and runoff, and heatwaves as evidenced in observations (e.g., Eddy et al. 1975;Barnston andSchickedanz 1984, Changnon 2001;Changnon et al. 2003;Haugland and Crawford 2005;Mahmood et al. 2008;DeAngelis et al. 2010;Alter et al. 2015aAlter et al. , 2018Chen et al. 2018). Therefore, it is imperative to represent the agriculture in Earth system models (ESMs). ...
Article
Applied meteorology is an important and rapidly growing field. This chapter concludes the three-chapter series of this monograph describing how meteorological information can be used to serve society’s needs while at the same time advancing our understanding of the basics of the science. This chapter continues along the lines of Part II of this series by discussing ways that meteorological and climate information can help to improve the output of the agriculture and food-security sector. It also discusses how agriculture alters climate and its long-term implications. It finally pulls together several of the applications discussed by treating the food–energy–water nexus. The remaining topics of this chapter are those that are advancing rapidly with more opportunities for observation and needs for prediction. The study of space weather is advancing our understanding of how the barrage of particles from other planetary bodies in the solar system impacts Earth’s atmosphere. Our ability to predict wildland fires by coupling atmospheric and fire-behavior models is beginning to impact decision-support systems for firefighters. Last, we examine how artificial intelligence is changing the way we predict, emulate, and optimize our meteorological variables and its potential to amplify our capabilities. Many of these advances are directly due to the rapid increase in observational data and computer power. The applications reviewed in this series of chapters are not comprehensive, but they will whet the reader’s appetite for learning more about how meteorology can make a concrete impact on the world’s population by enhancing access to resources, preserving the environment, and feeding back into a better understanding how the pieces of the environmental system interact.
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This paper lists selected observational and modeling studies which provide evidence that agriculture, through the transformation and management of vegetation, has had, and continues to have, an impact upon the weather and climate on the local, regional and global scales. The influence of agriculture on weather and climate, through the alteration of the physiological properties of the land cover, is illustrated by examples from the cropped grassland of the Canadian Prairies.The physiological and physical properties of the vegetation, along with the land cover's impact upon the level of available soil moisture, affect the weather and climate by influencing the transfer of heat, moisture and momentum from the land surface to the overlying air. The principle physiological properties are leaf area, stomatal resistance, and rooting depth; the main physical properties are albedo and surface roughness. By land clearing, cultivation and the grazing of domesticated animals, man has transformed and now manages the vegetation over vast areas of the globe. Agriculture influences the availability of energy and water vapour mass for moist deep convection on the local and regional scales. By creating latent heat flux discontinuities, it may induce mesoscale circulations that initiate moist deep convection. Agriculture, by affecting the level of stored soil moisture, moisture that is available to the vegetation during a later period, may influence the level of convective activity within a region during a subsequent season. Thus agriculture, through the physiological and physical properties of the land cover, has had, and continues to have, an impact upon near surface weather elements and, more significantly, upon the regional hydrologic cycle.Spatially coherent and persistent patterns of thunderstorms play a role in the export of heat and moisture from lower to higher latitudes—this may effect the general circulation. Thus agriculture, by influencing the occurrence, location and intensity of moist deep convection, particularly in the tropics, may also influence global weather and climate.
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Much of our current risk assessment, especially for extreme events and natural disasters, comes from the assumption that the likelihood of future extreme events can be predicted based on the past. However, as global temperatures rise, established climate ranges may no longer be applicable, as historic records for extremes such as heat waves and floods may no longer accurately predict the changing future climate. To assess extremes (present‐day and future) over the contiguous United States, we used NOAA's Climate Extremes Index (CEI), which evaluates extremes in maximum and minimum temperature, extreme one‐day precipitation, days without precipitation, and the Palmer Drought Severity Index (PDSI). The CEI is a spatially sensitive index that uses percentile‐based thresholds rather than absolute values to determine climate “extremeness,” and is thus well‐suited to compare extreme climate across regions. We used regional climate model data from the North American Regional Climate Change Assessment Program (NARCCAP) to compare a late 20th century reference period to a mid‐21st century “business as usual” (SRES A2) greenhouse gas‐forcing scenario. Results show a universal increase in extreme hot temperatures across all models, with annual average maximum and minimum temperatures exceeding 90th percentile thresholds consistently across the continental U.S. Results for precipitation indicators have greater spatial variability from model to model, but indicate an overall movement towards less frequent but more extreme precipitation days in the future. Due to this difference in response between temperature and precipitation, the mid‐21st century CEI is primarily an index of temperature extremes, with 90th percentile temperatures contributing disproportionately to the overall increase in climate extremeness. We also examine the efficacy of the PDSI in this context in comparison to other drought indices. This article is protected by copyright. All rights reserved.
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Land use and land cover interact with atmospheric conditions to determine current climate conditions, as well, as the impact of climate change and environmental variability on ecological systems. Such interactions are ubiquitous, yet changes in LULC are generally made without regard to their biophysical implications. This review considers the potential for LULC to compound, confound, or even contradict changes expected from climate change alone. These properties give LULC the potential to be used as powerful tools capable of modifying local climate and contributing significantly to the net impact of climate change. Management practices based modifications of LULC patterns and processes could be applied strategically to increase the resilience of vulnerable ecological systems and facilitate climate adaptation. These interventions build on the traditional competencies of land management and land protection organizations and suggest that these institutions have a central role in determining the ecological impact of climate change and the development of strategies for adaptation. The practical limits to the use of LULC-based tools also suggest important inflection points between manageable and dangerous levels of climate change.
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Daily average dew points (DADPs) were examined at 68 central-U.S. weather stations from 1949 to 2000 to identify temporal trends in the occurrence of summer (June—August) extreme surface dew-point days (DADP ≥22°C). Data homogeneity testing revealed that changes in equipment, station location, and instrument height, in addition to calculated DADPs based on available hourly data caused very few statistically significant changes in the data. Temporal patterns based on four 13-yr. periods indicated that much of the Midwest experienced a consistent increase in extreme DADPs through time while those along the Gulf Coast remained generally unchanged. Using accumulated DADP departure from the median graphs, the 52-yr. record was separated into two periods. A comparison of the mean frequency from an earlier (1949-1976) to later (1977-2000) period indicated that the greatest percent increases also occurred in the Midwest. Smaller increases to the south of this area suggest that these increases are not primarily linked to advection from the Gulf of Mexico, rather they are related to changes in a regional moisture source. This moisture source appears to be related to enhanced levels of evapotranspiration from corn and soybean crops, which have experienced a near doubling in total acreage from 1950 to 2000.
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The physiological response of vegetation to increasing atmospheric carbon dioxide concentration ([CO2 ]) modifies productivity and surface energy and water fluxes. Quantifying this response is required for assessments of future climate change. Many global climate models account for this response; however, significant uncertainty remains in model simulations of this vegetation response and its impacts. Data from in situ field experiments provide evidence that previous modeling studies may have overestimated the increase in productivity at elevated [CO2 ], and the impact on large-scale water cycling is largely unknown. We parameterized the Agro-IBIS dynamic global vegetation model with observations from the SoyFACE experiment to simulate the response of soybean and maize to an increase in [CO2 ] from 375 ppm to 550 ppm. The two key model parameters that were found to vary with [CO2 ] were the maximum carboxylation rate of photosynthesis and specific leaf area. Tests of the model that used SoyFACE parameter values showed a good fit to site-level data for all variables except latent heat flux over soybean and sensible heat flux over both crops. Simulations driven with historic climate data over the central U.S. showed that increased [CO2 ] resulted in decreased latent heat flux and increased sensible heat flux from both crops when averaged over 30 years. Thirty-year average soybean yield increased everywhere (~10%); however, there was no increase in maize yield except during dry years. Without accounting for CO2 effects on the maximum carboxylation rate of photosynthesis and specific leaf area, soybean simulations at 550 ppm overestimated leaf area and yield. Our results highlight important model parameter values that, if not modified in other models, could result in biases when projecting future crop-climate-water relationships. This article is protected by copyright. All rights reserved.
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Hourly archived rainfall records are separated into individual rainfall events with an Inter-Event Time Denition. Individual storms are characterized by their depth, duration, and peak intensity. Severe events are selected from among the events for a given station. A lower limit, or threshold depth is used to make this selection, and an upper duration limit is established. A small number of events per year are left, which have relatively high depth and average intensity appropriate to small to medium catchment responses. The Generalized Pareto Distributions are tted to the storm depth data, and a bounded probability distribution is tted to storm duration. Peak storm intensity is bounded by continuity imposed by storm depth and duration. These physical limits are used to develop an index measure of peak storm intensity, called intensity peak factor, bounded on (0; 1), and tted to the Beta distribution. The joint probability relationship among storm variables is established, combining increasing storm depth, increasing intensity peak factor, with decreasing storm duration as being the best description of increasing rainstorm severity. The joint probability of all three variables can be modelled with a bivariate copula of the marginal distributions of duration and intensity peak factor, combined simply with the marginal distribution of storm depth. The parameters of the marginal distributions of storm variables, and the frequency of occurrence of threshold-excess events are used to assess possible shifts in their values as a function of time and temperature, in order to evaluate potential climate change eects for several stations. Example applications of the joint probability of storm variables are provided that illustrate the need to apply the methods developed. The overall contributions of this research combine applications of existing probabilistic tools, with unique characterizations of rainstorm variables. Relationships between these variables are examined to produce a new description of storm severity, and to begin the assessment of the eects of climate change upon severe rainstorm events. i
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Extreme heat has negative impacts on human health, labor productivity, and many other aspects of life. Both historical trends and future projections suggest that the extreme heat hazard will increase, but measures to reduce risk are being studied and implemented to lessen the impacts of extreme heat. Heat health early warning systems and longer-term planning and preparedness require skillful, seamless predictions of the heat hazard from weeks to months and from years to decades into the future. They allow for shorter-term interventions and longer-term policy and infrastructural investments which can reduce risk. Investments in observing systems, science to understand the physical mechanisms driving heat extremes, and model improvements are essential to developing these predictions and a critical part of addressing the human health risks of extreme heat in a changing climate.
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Heat waves are characteristic features of summertime climate in the Midwest United States, and can have significant agricultural, hydrological, and societal impacts. Historically, heat waves in the Midwest state of Illinois have been either extreme (high temperature, low humidity) or oppressive (high temperature, high humidity) in nature, but our knowledge of the factors determining which heat wave type occurs is limited. We use self-organizing maps to classify synoptic-scale atmospheric circulation patterns associated with oppressive and extreme heat events, and analysis of variance to evaluate the atmospheric and land surface features responsible for differences in humidity that characterize the two. We find the majority of extreme and oppressive heat events are associated with similar synoptic-scale atmospheric conditions. Additionally, both locally-evaporated moisture and advected moisture sources were important for determining which of the two heat wave types occurred. Specifically, oppressive heat waves were characterized by abundant antecedent precipitation, surplus soil moisture, and elevated evapotranspiration and related atmospheric humidity. Lower humidity levels during extreme heat wave events were driven by relative reductions in evapotranspiration due to limited soil water content. Overall, our results suggest that the onset of heat waves in Illinois is primarily driven by circulation features in the upper atmosphere; however, the distinction of extreme or oppressive heat wave is due to differences in boundary layer humidity, driven in part by land surface moisture availability for evapotranspiration.
Article
In this research, the mean relative humidity (RH) trend was investigated in the monthly, seasonal and annual timescales during 1960–2005 in 32 synoptic meteorological stations. The Mann–Kendall test after the removal of the significant lag-1 serial correlation effect from the RH time series by pre-whitening was used to determine significant trends. Sen’s slope estimator was used to determine the median slope of positive or negative RH trends in seasonal and annual timescales. Also, in order to facilitate trend analysis and exploring in datasets, 10-year moving average low-pass filter was applied on mean annual normalized RH. Furthermore, smoothed time series by the mentioned filter were classified in four clusters and then they were mapped to show the spatial distribution of trend patterns in Iran. Results showed both significant downward and upward trends, but the number of negative trends was more than positive ones. In general, the stations located in arid central and eastern parts of country had more negative trends. Results of the Sen’s slope estimator showed that in annual timescale, Gorgan synoptic station had the most increasing slope by (+) 2 % per decade, while the most negative slope was detected in Bam by (−) 2.79 % per decade. Also, the analysis of smoothed time series of RH and their relationship with smoothed temperatures showed a strong inverse relationship particularly after 1995. It can be concluded that alongside the increasing of temperature in many parts of Iran, lack of sufficient water vapor has led to decreasing trend of RH in the country.
Article
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Twentieth century trends of precipitation are examined by a variety of methods to more fully describe how precipitation has changed or varied. Since 1910, precipitation has increased by about 10% across the contiguous United States. The increase in precipitation is reflected primarily in the heavy and extreme daily precipitation events. For example, over half (53%) of the total increase of precipitation is due to positive trends in the upper 10 percentiles of the precipitation distribution. These trends are highly significant, both practically and statistically. The increase has arisen for two reasons. First, an increase in the frequency of days with precipitation ]6 days (100 yr)1[ has occurred for all categories of precipitation amount. Second, for the extremely heavy precipitation events, an increase in the intensity of the events is also significantly contributing (about half) to the precipitation increase. As a result, there is a significant trend in much of the United States of the highest daily year-month precipitation amount, but with no systematic national trend of the median precipitation amount.These data suggest that the precipitation regimes in the United States are changing disproportionately across the precipitation distribution. The proportion of total precipitation derived from extreme and heavy events is increasing relative to more moderate events. These changes have an impact on the area of the United States affected by a much above-normal (upper 10 percentile) proportion of precipitation derived from very heavy precipitation events, for example, daily precipitation events exceeding 50.8 mm (2 in.).
Article
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The July 1999 heat wave in the Midwest was an event of relatively long duration punctuated by extreme conditions during its last 2 days. The intensity of the heat wave on 29 and 30 July rivaled that of the 1995 heat wave that killed more than 1000 people in the central United States. In 1999, however, the death toll was about one-fourth of this amount in the same region. The 1999 heat wave 2-day maximum apparent temperature was slightly less than during the 1995 heat wave at most Midwestern first-order stations. In addition, the 2-day peak was preceded by several hot days that allowed some short-term acclimatization to occur prior to the intense final days. In Chicago, conditions during the peak of the 1999 heat wave were very similar to those during the 1995 heat wave peak, especially the extreme nocturnal conditions of temperatures and humidity. Therefore, it seems unlikely that the reduction in the heat wave death toll in Chicago from about 700 in 1995 to 114 in 1999 is due solely to meteorological differences between the two heat waves. In St. Louis, the 1999 heat wave was intense for a much longer duration than the 1995 heat wave, thus partially explaining the increase in heat-related deaths there from the 1995 event to the 1999 event. An examination of heat wave response efforts in both Chicago and St. Louis leads to the conclusion that both cities were quite effective at mitigating their respective heat wave mortality rates, which in the 1999 event were almost exactly the same in both metropolitan areas. This represents a great improvement for the city of Chicago compared to the 1995 heat wave. Suggestions are made for further improving municipal heat wave response efforts based on the 1999 experience.
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In 1888, Iowa weather researcher Gustavus Hinrichs gave widespread convectively induced windstorms the name "derecho". Refinements to this definition have evolved after numerous investigations of these systems; however, to date, a derecho climatology has not been conducted.This investigation examines spatial and temporal aspects of derechos and their associated mesoscale convective systems that occurred from 1986 to 1995. The spatial distribution of derechos revealed four activity corridors during the summer, five during the spring, and two during the cool season. Evidence suggests that the primary warm season derecho corridor is located in the southern Great Plains. During the cool season, derecho activity was found to occur in the southeast states and along the Atlantic seaboard. Temporally, derechos are primarily late evening or overnight events during the warm season and are more evenly distributed throughout the day during the cool season.
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Daily observations of precipitation and maximum and minimum temperature from the National Weather Service's cooperative observer network collected prior to 1948 were keyed into a digital database. This database includes stations in the nine midwestern states of Illinois, Indiana, Iowa, Kentucky, Michigan, Minnesota, Missouri, Ohio, and Wisconsin. The primary source used in this project was the publication Climatological Data, which began in 1896. This database provides a substantial enhancement to the National Climatic Data Center's TD-3200 Summary of the Day database, which includes little data prior to 1948. Approximately 2 × 107 data values were keyed, increasing the amount of pre-1948 digital data by about a factor of 3 and substantially improving its spatial uniformity. The data were subjected to an extensive set of quality control procedures. It is expected that these data will find their greatest value in applications requiring very long historical records, such as assessments of the risks of extreme events.
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This study describes the impact of weather on human mortality at numerous locations around the United States. We evaluate forty-eight cities and determine the differential impact of weather on mortality on an intercity and interregional level. The mortality data are analyzed separately for different age, race, and cause of death categories. The possible impact of geographical and within-season acclimatization is also analyzed. Thresh-old temperatures, which represent the temperature beyond which mortality increases, are identified for all the categories and all cities in summer and winter. We correlate numerous weather variables with mortality for days with temperatures beyond the threshold. In summer, warm, humid, calm conditions (especially at night) relate to the highest mortality. The strongest relationships occur in regions where hot weather is uncommon and the weakest relationships in the hottest locales. Regional acclimatization appears to be especially important in summer. A strong intra-seasonal acclimatization factor is also apparent, and hot weather early in the season produces a more pronounced response than similar weather late in the season. Winter relationships are generally weaker, and cloudy, damp, snowy conditions are associated with the greatest mortality. In both seasons, the elderly appear to be disproportionately stressed when compared to other age groups. Racial responses appear similar on a national and seasonal level, but there are differential responses on a regional level. Non-whites appear more sensitive than whites in the South during both seasons.
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Climatological annual and seasonal dewpoint, specific humidity, and relative humidity maps for the United States are presented using hourly data from 188 first-order weather stations for the period 1961-90. Separate climatologies were calculated for daytime (three observations per day between 0800 and 1600 LST), nighttime (three observations per day between 2000 and 0400 LST), and the full day (eight observations per day, every 3 h). With extended datasets for the period 1961-95, trends in these same variables and temperature are calculated for each of 170 stations and for eight regions of the country. The data show increases in specific humidity of several percent per decade, and increases in dewpoint of several tenths of a degree per decade, over most of the country in winter, spring, and summer. Nighttime humidity trends are larger than daytime trends. The specific humidity increases are consistent with upward temperature trends. The upward temperature and humidity trends are also consistent with upward trends in apparent temperature, a measure of human comfort based on temperature and humidity. Relative humidity trends are weaker than the specific humidity trends, but they do show evidence of increases, especially in winter and spring. The possibility that the detected trends may be artifacts of changes in instrumentation was examined, but several lines of reasoning suggest that they are not. Anthropogenic water vapor produced from fossil fuel consumption, both locally and globally, is too small a source to explain the observed trends.
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Our paper documents that land-use change impacts regional and global climate through the surface-energy budget, as well as through the carbon cycle. The surface-energy budget effects may be more important than the carbon-cycle effects. However, land-use impacts on climate cannot be adequately quantified with the usual metric of 'global warming potential'. A new metric is needed to quantify the human disturbance of the Earth's surface-energy budget. This 'regional climate change potential' could offer a new metric for developing a more inclusive climate protocol. This concept would also implicitly provide a mechanism to monitor potential local-scale environmental changes that could influence biodiversity.
Article
Forty-one years of data from 13 first-order National Weather Service stations in the southeastern United States were analyzed to determine the spatial variability in the frequency and duration of hours and days when temperatures were ≥32° C (high-heat). Spatial analysis indicated that extreme high temperature characteristics from individual stations should not be combined into a regional or statewide average. For determining high-heat scenarios, May through September (summer) average maximum temperature (Tmax) was found to be a more appropriate indicator of high-heat conditions than the average temperature (Tmean). Comparing conditions in average warm and cool summer seasons indicated that: (1) increases in the frequency and duration of high-heat hours and days from cool to warm summer seasons range from 70 to 997%; (2) the number of high-heat hours per day increases significantly (27 to 118%) from cool to warm summer seasons; (3) increases in Tmax from cool to warm summer seasons are greater than increases for Tmean; (4) Tmean values underestimate the number and duration of high-heat events; and (5) the diurnal temperature range increases during warm summer seasons. These results show that great variability already exists in today's climate characteristics, and that any potential shift in average temperature will cause even greater changes in the frequency and duration of extreme high temperatures in this region.
Article
A study was conducted on how to achieve a compact but representative data set regarding humidity issues in bin energy analysis. It is demonstrated that conventional bin data using one parameter with a mean-coincident value of another parameter will lead to significant load errors, while joint-frequency bins, which constitute a more compact weather representation than do hourly data, allow for an accurate representation of sensible, latent, and total building loads. A method of using joint frequency for simplified analyses of full building loads is discussed.
Article
Heat waves are a major cause of weather-related deaths. With the current concern for global warming it is reasonable to suppose that they may increase in frequency, severity, duration, or areal extent in the future. However, in the absence of an adequate definition of a heat wave, it is impossible to assess either changes in the past or possible consequences for the future. A set of definitions is proposed here, based on the criteria for Heat stress forecasts developed by the National Weather Service (NWS). Watches or warnings are issued when taresholds of daytime high and nighttime low heat index (H 1) values are exceeded for at least two consecutive days. The heat index is a combination of ambient temperature and humidity that approximates the environmental aspect of the thermal regime of a human body, with the NWS thresholds representing a generalized estimate of the onset of physiological stress. These thresholds cannot be applied directly nationwide. In hot and humid regions, physical, social, and cultural adaptations will require that the thresholds be set higher to ensure that only those events perceived as stressful are identified. In other, cooler, areas the NWS criteria may never be reached even though unusually hot events may be perceived as heat waves. Thus, it is likely that a similar number of perceived heat events will occur in all regions, with the thresholds varying regionally. Hourly H 1 for 178 stations in the coterminous United States was analyzed for the 1951-90 period to determine appropriate threshold criteria. Use of the NWS criteria alone indicated that much of the nation had less than three heat waves per decade, and this value was adopted as the baseline against which to establish suitable thresholds. For all areas, a percentile thresholds approach was tested. Using all available data, daytime high and nighttime low thresholds were established separately for each specific percentile. Heat waves were treated as occuring when conditions exceeded both the daytime high and the nighttime low thresholds of the same percentile for two consecutive days. Several thresholds were tested. For much of the South, 1% thresholds produced appropriate values. Consequently, a heat wave was defined as a period of at least 48 h during which neither the overnight low nor the daytime high H 1 falls below the NWS heat stress thresholds (80° and 105°F, respectively), except at stations for which more than 1% of both the annual high and low H 1 observations exceed these thresholds, in which case the 1% values are used as the heat wave thresholds. As an extension, "hot spells" were similarly defined, but for events falling between the 1% values and NWS thresholds, with "warm spells" occuring between the 2% and 1% values. Again, stations for which the 1% or 2% H 1 values exceed the NWS thresholds were given modified definitions. The preliminary investigation of the timing and location of heat waves resulting from these definitions indicated that they correctly identified major epidemiological events. A tentative climatic comparison also suggests that heat waves are becoming less frequent in the southern and more frequent in the midwestern and eastern parts of the nation.
Article
During the 19th and 20th centuries, the landscape of the North American Great Plains was rapidly modified from natural grasslands to agricultural farmlands. These changes affected much of the continent with potential impacts in grasslands equal to deforestation elsewhere. Therefore, the resulting impacts on weather and climate should be studied. In this study, a soil water balance model is applied for 3 land uses at 3 locations, These locations are representative of the east to west declining precipitation gradient of the Great Plains. It was found, in McCook, Nebraska, for example, that annual total evapotranspiration for irrigated maize is 36% higher compared to natural grass. This accounts for an additional 50 million m(3) of water evapotranspired into the atmosphere from an area of 19 000 ha during the growing season, In some instances, Clay Center, Nebraska, and the vicinity evapotranspired nearly 100 million m(3) additional water (compared to a grass covered surface) from irrigated maize during the growing season. Compared to grass, irrigated maize farming elevated soil water in the soil profile, while rainfed maize lowered soil water. This study shows that intensity of the response of soil water distribution in the root zone is a function of vegetation cover and soil physical properties.
Article
Water vapor variables were calculated from radiosonde stations in each of six U.S. regions for which cloudiness observations were available. Associations among variations of cloudiness, precipitable water and relative humidity during the 1973-93 period over the U.S. as a whole and in the six regions were determined. Trends in the quantities as well as relations among seasonal variations have been examined. There was a general increase in precipitable water in each season and in each region and a suggestion of increases in relative humidity. These were not accompanied by a general increase in cloudiness that was significant. However, there were significant correlations between seasonal anomalies of cloudiness and both relative humidity and precipitable water.
Article
A brief but intense heat wave developed in the central and eastern United States in mid-July 1995, causing hundreds of fatalities. The most notable feature of this event was the development of very high dewpoint temperature (Td) over the southern Great Lakes region and the Upper Mississippi River Basin. At many locations, hourly values of Td set new records. The combination of high air and dewpoint temperatures resulted in daily average apparent temperatures exceeding 36°C over a large area on some days. A comparison with past heat waves shows that this was the most intense short-duration heat wave in at least the last 48 years at some locations in the southern Great Lakes region and Upper Mississippi River Basin. An analysis of historical data for Chicago, where the majority of fatalities occurred, indicates the intensity of this heat wave was exceeded only by a few periods in the 1910s and 1930s. Impacts in the Chicago urban center were exacerbated by an urban heat island that raised nocturnal temperatures by more than 2°C. An analysis of radiosonde data indicates that maximum daytime boundary layer mixing depths were only a few hundred meters in the core region of the heat wave. Simulations using a single-column version of a three-dimensional mesoscale model strongly suggest that this contributed to the very high values of Td since soil moisture in the central United States was near to above average and evapotransporation was likely high, causing a rapid moistening of the shallow boundary layer.
Article
The short but intense heat wave in mid-July 1995 caused 830 deaths nationally, with 525 of these deaths in Chicago. Many of the dead were elderly. and the event raised great concern over why it happened. Assessment of causes for the heat wave-related deaths in Chicago revealed many factors were at fault, including an inadequate local heat wave warning system, power failures, questionable death assessments, inadequate ambulance service and hospital facilities, the heat island, an aging population, and the inability of many persons to properly ventilate their residences due to fear of crime or a lack of resources for fans or air conditioning. Heat-related deaths appear to be on the increase in the United States. Heat-related deaths greatly exceed those caused by other life-threatening weather conditions. Analysis of the impacts and responses to this heat wave reveals a need to 1) define the heat island conditions during heat waves for all major cities is a means to improve forecasts of threatening conditions, 2) develop a nationally uniform means for classifying heat-related deaths, 3) improve warning systems that are designed around local conditions of large cities, and 4) increase research on the meteorological and climatological aspects of heat stress and heat waves.
Article
Warm-season (1 May-30 September) hourly dewpoint data were examined for temporal changes at two weather stations in northeastern Illinois during a 42-yr period (1959-2000). This area has dense population (greater than 8 million), and shifts to more or less atmospheric moisture have major implications on cooling demands. The 42-yr period was analyzed as two separate arbitrarily chosen equally sized periods, the early (1959-79) and the later (1980-2000) periods. Analyses of data from Chicago's O'Hare International Airport and the Greater Rockford Airport showed a statistically significant increase in the number of hours with dewpoints greater than or equal to 24°C (an important cooling-plant threshold) in the latter period. Examination of heat-wave periods indicated that later (especially 1995 and after) heat waves contained many more extreme dewpoint values. These increases in extreme dewpoint characteristics in northeastern Illinois affect the operation of, and suggest shifts in design criteria for, air-conditioning systems and affect summer peak electrical loads.
Article
Spatial patterns in trends of four monthly variables: average temperature, precipitation, streamflow, and average of the daily temperature range were examined for the continental United States for the period 1948-88. The data used are a subset of the Historical Climatology Network (1036 stations) and a stream gage network of 1009 stations. Trend significance was determined using the nonparametric seasonal Kendall's test on a monthly and annual basis, and a robust slope estimator was used for determination of trend magnitudes. A bivariate test was used for evaluation of relative changes in the variables, specifically, streamflow relative to precipitation, streamflow relative to temperature, and precipitation relative to temperature.Strong trends were found in all of the variables at many more stations than would be expected due to chance. There is a strong spatial and seasonal structure in the trend results. For instance, although annual temperature increases were found at many stations, mostly in the North and West, there were almost as many downtrends, especially in the South and East. Among the most important trend patterns are (a) increases in March temperature at almost half of the stations; (b) increases in precipitation from September through December at as many as 25 percent of the stations, mostly in the central part of the country; (c) strong increases in streamflow in the period November-April at a maximum of almost half of the stations, with the largest trend magnitudes in the north-central states; (d) changes in the temperature range (mostly downward) at a large number of stations beginning in late spring and continuing through winter, affecting as many as over half of the stations. The observed trends in streamflow are not entirely consistent with the changes in the climatic variables and may be due to a combination of climatic and water management effects.
Article
A unique rainstorm in northern Illinois produced 43 cm of precipitation in mid-July 1996, the highest 24-h precipitation amount ever recorded officially in the upper Midwest. Rains exceeding 20 cm fell over an area of 4400 km2, creating extremely damaging flash floods in portions of Chicago and its suburbs. Measurements from 496 rain gauges, including 80 recording gauges in the heavy rain area, made it possible to accurately define this storm.The heavy rains were the result of two massive mesoscale convective systems, one in the afternoon and one at night. These systems formed to the north of a nearby stationary warm front. Several factors contributed to the excessive rainfall. Excessive moisture was present to the southwest of the warm front over Iowa and western Illinois; atmospheric moisture content was enhanced by surface evaporation from a very wet surface created by heavy rains the previous day, creating a conditionally unstable atmosphere. A cool air mass transported by easterly winds off Lake Michigan strengthened and slowed the movement of the warm front. A low-level jet oriented perpendicular to the warm front resulted in rising motion north of the warm front. These factors (instability, moisture availability, lifting mechanism) combined to form intense storms. This paper, the first of a three-part series, describes the storm in detail, including its morphology and causes, and the resulting rainfall distributions.
Article
Secular trends in streamflow are evaluated for 395 climate-sensitive streamgaging stations in the conterminous United States using the non-parametric Mann-Kendall test. Trends are calculated for selected quantiles of discharge, from the 0th to the 100th percentile, to evaluate differences between low-, medium-, and high-flow regimes during the twentieth century. Two general patterns emerge; trends are most prevalent in the annual minimum (Q0) to median (Q50) flow categories and least prevalent in the annual maximum (Q100) category; and, at all but the highest quantiles, streamflow has increased across broad sections of the United States. Decreases appear only in parts of the Pacific Northwest and the Southeast. Systematic patterns are less apparent in the Q100 flow. Hydrologically, these results indicate that the conterminous U.S. is getting wetter, but less extreme.
Article
Spatial patterns in trends of four monthly variables: average temperature, precipitation, streamflow, and average of the daily temperature range were examined for the continental United States for the period 1948-88. The data used are a subset of the Historical Climatology Network (1036 stations) and a stream gage network of 1009 stations. Trend significance was determined using the nonparametric seasonal Kendall's test on a monthly and annual basis, and a robust slope estimator was used for determination of trend magnitudes. A bivariate test was used for evaluation of relative changes in the variables, specifically, streamflow relative to precipitation, streamflow relative to temperature, and precipitation relative to temperature. Strong trends were found in all of the variables at many more stations than would be expected due to chance. There is a strong spatial and seasonal structure in the trend results. For instance, although annual temperature increases were found at many stations, mostly in the North and West, there were almost as many downtrends, especially in the South and East. Among the most important trend patterns are (a) increases in March temperature at almost half of the stations; (b) increases in precipitation from September through December at as many as 25 percent of the stations; (c) strong increase in streamflow in the period November-April at a maximum of almost half of the stations, with the largest trend magnitudes in the north-central states; (d) changes in the temperature range (mostly downward) at a large number of stations beginning in late spring and continuing through winter, affecting as many as over half of the stations. The observed trends in streamflow are not entirely consistent with the changes in the climatic variables and may be due to combination of climatic and water management effects. 34 refs., 16 figs, 7 tabs.
Article
In this study, hourly data for the 1951–1990 period for 178 stations in the coterminous United States were used to establish temporal trends in dew point temperature. Although the data had been quality controlled previously (Robinson, 1998. Monthly variations of dew point temperatures in the coterminous United States. International Journal of Climatology18: 1539–1556), comparisons of values between nearby stations suggested that instrumental changes, combined with locational changes, may have modified the results by as much as 1°C during the 40-year period. Nevertheless, seasonally averaged results indicated an increase over much of the area, of slightly over 1°C/100 years in spring and autumn, slightly less than this in summer. Winter displayed a drying of over 1°C/100 years. When only the 1961–1990 period was considered, the patterns were similar and trends increased by approximately 1–2°C/100 years, except in autumn, which displayed a slight drying. Analyses for specific stations indicated periods of both increasing and decreasing Td, the change between them varying with observation hour. No single change point was common over a wide area, although January commonly indicated maximum values early in the period in the east and west, and much later in the north-central portion. Rates of increase were generally higher in daytime than at night, especially in summer. Investigation of the inter-decadal differences in dew point, as a function of wind conditions, indicated that changes during calm conditions were commonly similar in magnitude to that of the overall average changes, suggesting an important role for the local hydrologic cycle in driving changes. Other inter-decadal changes could be attributed to the changes in the frequency and moisture content of invading air-streams. This was particularly clear for the changes in north–south flow in the interior. Copyright © 2000 Royal Meteorological Society
Article
Data from the 1997 National Resources Inventory (NRI) are used in this study to examine recent trends in the conversion of cropland to urban land with special attention paid to the spatial distribution of these conversions relative to rangeland to cropland conversions. Our findings are that the approximately 11 million acres of cropland converted to urban land between 1982 and 1997 was coincident with an equal amount of rangeland converting to cropland. The rangeland to cropland conversions equate to replacement lands for cropland lost to urban encroachment. Approximately one third of the cropland lost to urban development occurs on prime farmland while the new cropland converted from rangeland is more likely to be irrigated as it resides principally in the arid western United States. The findings are discussed in light of a sustainable land use system perspective.
Article
Long-term temperature changes are expected to give rise to changes in the water vapor content of the atmosphere, which in turn would accentuate the temperature change. It is thus important to monitor water vapor in the troposphere and lower stratosphere. This paper reviews existing data for such an endeavor and the prospects for improvement in monitoring. In general, radiosondes provide the longest record but the data are fraught with problems, some arising from the distribution of stations and some from data continuity questions arising from the use of different measuring devices over both time at one place and over space at any one time. Satellite records are now of limited duration but they will soon be useful in detecting changes. Satellite water vapor observations have their own limitations; there is no one system capable of measuring water vapor over all surfaces in all varieties of weather. Among the needs are careful analysis of existing records, the collection of metadata about the measuring systems, the development of a transfer standard radiosonde system, and the commitment to maintaining an observing system dedicated to describing any climate changes worldwide.
Article
Corn (Zea mays L.) has one of the highest evapotranspiration (ET) rates (both daily and seasonally) of all the irrigated crops in the Southern High Plains. ET of fully irrigated corn was measured with precise weighing lysimeters during the 1989, 1990, and 1994 growing seasons at Bushland, TX. In 1994, ET was measured for two different maturity corn hybrids also. Fully irrigated corn achieved a maximum leaf area index (LAI) of 4.5 to 5.5 m2 m-2 at tassel emergence for the full-season hybrids in each season. LAI was lower for the short-season hybrid in the 1994 season. Crop growth and yields were similar on the lysimeters and the fields and were representative of normal regional corn production. Seasonal ET varied from 744 mm to 901 mm in the three seasons. Daily ET rates often exceeded 10 mm d-1. Peak daily ET rate was not appreciably lower for the short-season hybrid; however, it did have a much smaller seasonal ET but similar water use efficiency as a full-season hybrid. Percolation volumes averaged less than 2% of the total water input (rainfall + irrigation) under the sprinkler irrigation regimes.
Article
To examine the effects of spatial variations of soil moisture and vegetation coverage on the evolution of a prestorm environment, the Goddard mesoscale model is modified to incorporate a simple evapotranspiration model that requires these two parameters. The case study of 3-4 June 1980 is of special interest due to the development of a tornado producing convective complex near Grand Island, Nebraska during a period of comparatively weak synoptic-scale forcing. It is shown that the observed stationary front was strongly enhanced by differential heating created by observed gradients of soil moisture, as acted upon by the vegetation cover.
Central Iowa dew point comparison-DEWPEX. Central Region Applied Research Papers
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  • J Stark
Schafer K, Stark J (1997) Central Iowa dew point comparison-DEWPEX. Central Region Applied Research Papers, 18-05, National Weather Service, Washington, DC
Conceptual model showing the influence of agricultural changes and growing-season precipitation anomalies on the magnitude of annual extreme dew points
  • Fig
Fig. 11. Conceptual model showing the influence of agricultural changes and growing-season precipitation anomalies on the magnitude of annual extreme dew points Clim Res 24: 243–254, 2003
Using rainfall simulators for water quality education
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Ross BB, Dillaha TA, Mostaghimi S, Heatwole CD (1991) Using rainfall simulators for water quality education. J Extension 29(1):1–2. Available at http://www.joe.org/ joe/1991spring/iw3.html
Planting corn in rows narrower than 30-Inches
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Lauer J (1996) Planting corn in rows narrower than 30-Inches. Field Crops 28:423-428
Corn hybrid response to plant population. Pioneer Hi-Bred International
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Paszkiewicz S, Butzen S (2001) Corn hybrid response to plant population. Pioneer Hi-Bred International, Des Moines, Crop Insights 11(6):1-9
Illinois Agricultural Statistics Service Available at http://www.agstats.state.il.us Kalkstein LS Weather and human mortality: an evaluation of demographic and interregional responses in the United States
Illinois Agricultural Statistics Service (2002) Illinois Agricultural Statistics Service. USDA, Washington, DC. Available at http://www.agstats.state.il.us Kalkstein LS, Davis RE (1989) Weather and human mortality: an evaluation of demographic and interregional responses in the United States. Ann Assoc Am Geogr 79:44–64
Streamflow trends in the United States
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Lins HF, Slack JR (1999) Streamflow trends in the United States. Geophys Res Lett 26:227–230
Crop water use or evapotranspiration. Department of Agronomy
  • M Al-Kaisi
Al-Kaisi M (2000) Crop water use or evapotranspiration. Department of Agronomy, Cooperative Extension Service, Iowa State University. Ames. Available at http://www. ent.iastate.edu/ipm/icm/2000/5-29-2000/wateruse.html
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