On the impact of corn and soybeans to the local moisture budget in Iowa.Abstract 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 dew point: see dew. can be the difference between thunderstorms thunderstorms a storm characterized by thunder and lightning caused by strong rising air currents; identified as agents of animal disease because of their involvement causing (1) spasmodic colic; (2) lightning strike; (3) injuries of cattle acquired in stampedes initiated by storms. occurring or not. Corn and soybean soybean, soya bean, or soy pea, leguminous plant (Glycine max, G. soja, or Soja max) of the family Leguminosae (pulse family), native to tropical and warm temperate regions of Asia, where it has been acreage each comprise one-third of the total land area in Iowa during the growing season growing season, period during which plant growth takes place. In temperate climates the growing season is limited by seasonal changes in temperature and is defined as the period between the last killing frost of spring and the first killing frost of autumn, at which . In July and August, atmospheric demand (i.e., the combination of atmospheric elements such as temperature, wind, relative humidity relative humidity n. The ratio of the amount of water vapor in the air at a specific temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage. , etc. which determine the amount of water a crop uses) for crop evapotranspiration evapotranspiration Loss of water from the soil both by evaporation from the soil surface and by transpiration from the leaves of the plants growing on it. Factors that affect the rate of evapotranspiration include the amount of solar radiation, atmospheric vapor pressure, 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 boundary layer In fluid mechanics, a thin layer of flowing gas or liquid in contact with a surface (e.g., of an airplane wing or the inside of a pipe). The fluid in the boundary layer is subjected to shear forces. and the amount of evapotranspiration. 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 a·gron·o·my n. Application of the various soil and plant sciences to soil management and crop production; scientific agriculture. ag practices (e.g., irrigation irrigation, in agriculture, artificial watering of the land. Although used chiefly in regions with annual rainfall of less than 20 in. (51 cm), it is also used in wetter areas to grow certain crops, e.g., rice. usage). 1. Introduction It is not uncommon for operational meteorologists Atmospheric scientists
Golfo de Mexico Atlantic, Atlantic Ocean - the 2nd largest ocean; separates North and South America on the west from Europe and Africa on the east as a factor in the severe weather episode of 11 June 2001 in southern Minnesota. Numerous modeling studies (e.g., Pielke et al. 1999; Rozoff et al. 2003, etc.) have shown that land use can impact convective development. The impact of land use is becoming a more important consideration in the forecast process for NOAA/National Weather Service (NWS NWS National Weather Service NWS Naval Weapons Station NWS New World Symphony NWS Nuclear Weapon State NWS Not Work Safe NWS National Watercolor Society NWS North Warning System NWS Nose Wheel Steering NWS National Waste Strategy (UK) ) meteorologists producing high time and space resolution forecast grids for a variety of parameters, and can certainly be a factor for any forecaster providing site-specific, high detail forecasts. For areas where land use is dominated by agriculture, it follows that an understanding of crop water use and seasonal crop growth changes could be important, at times, in the forecast process. While scientists in the agricultural community have conducted extensive research to quantify crop water use, little of this work has translated into understanding and practical application in the operational meteorological me·te·or·ol·o·gy n. The science that deals with the phenomena of the atmosphere, especially weather and weather conditions. [French météorologie, from Greek community, exclusive of some operational numerical models where proxy estimates of land use can be incorporated based on satellite-observed greenness values (Kurkowski et al. 2003). In Iowa, agriculture dominates land use across the state. The main crops are corn and soybeans, each comprising approximately one-third of the total land area in the state (National Agricultural Statistics Service 2005). Pastures comprise another 10% of the land area, while woodlands, farm lots, and developed areas comprise most of the remainder. Crop water use can be evaluated using a general form of the surface energy budget (Rosenberg et al. 1983) [R.sub.n] = S + LE + H (1) where the total net radiation at the earth's surface Noun 1. Earth's surface - the outermost level of the land or sea; "earthquakes originate far below the surface"; "three quarters of the Earth's surface is covered by water" surface ([R.sub.n]) is partitioned into the sensible heat Sensible heat is potential energy in the form of thermal energy or heat. The thermal body must have a temperature higher than its surroundings, (also see: latent heat). The thermal energy can be transported via conduction, convection, radiation or by a combination thereof. term (S), the latent heat latent heat, heat change associated with a change of state or phase (see states of matter). Latent heat, also called heat of transformation, is the heat given up or absorbed by a unit mass of a substance as it changes from a solid to a liquid, from a liquid to a gas, term (LE), and the soil heat flux term (H). The latent heat term represents the energy used in the process of ET. ET is defined as evaporation of free surface water and soil water, plus transpiration transpiration, in botany, the loss of water by evaporation in terrestrial plants. Some evaporation occurs directly through the exposed walls of surface cells, but the greatest amount takes place through the stomates, or intercellular spaces (see leaf). from vegetation. Transpiration is the evaporation of water which has already passed through the plant (Rosenberg et al. 1983). Several factors influence ET including the availability of both free and soil water, soil type, solar radiation solar radiation, n the emission and diffusion of actinic rays from the sun. Overexposure may result in sunburn, keratosis, skin cancer, or lesions associated with photosensitivity. ([R.sub.n]), temperature, wind, relative humidity, and vegetation type and stage of growth. This paper will focus on how the last two factors, vegetation type and stage of growth, are a variable part of the local moisture budget in Iowa. The approach presented here can be applied to other agricultural and non-agricultural regions of the country to estimate the impact of local vegetation in the water budget under non-advective conditions. [FIGURE 1 OMITTED] [FIGURE 2 OMITTED] 2. Crop Water Use Crop type and stage of growth are the two agronomic factors that have the greatest impact on crop water use. In subsequent discussions, the assumption is made that soil moisture is NOT a limiting factor A factor or condition that, either temporarily or permanently, impedes mission accomplishment. Illustrative examples are transportation network deficiencies, lack of in-place facilities, malpositioned forces or materiel, extreme climatic conditions, distance, transit or overflight rights, in crop water use, i.e., that evaporation and transpiration are not limited by a lack of soil moisture. a. Corn In Iowa, corn planting typically begins in late April and continues through May (Fig. 2). Crop emergence depends on soil and air temperatures plus soil moisture, and usually occurs in a 1-2 week period following planting. ET use during this period and the subsequent few weeks is small and mostly results from soil water evaporation, since the crop has either not yet emerged or is small in leaf area available for transpiration. [FIGURE 3 OMITTED] During July, the crop reaches the silk stage during which water use is at its peak (Fig. 3). The crop canopy has filled in at this point (i.e., covers all bare soil) resulting in more leaf area to facilitate ET. In Fig. 3, crop water use is expressed as a proportion of open pan evaporation Pan evaporation is a measurement that combines or integrates the effects of several climate elements: temperature, humidity, solar radiation, and wind. Evaporation is greatest on hot, windy, dry days; and is greatly reduced when air is cool, calm, and humid[1]. . Note the rapid increase in water use rate from late June to early July. At its peak, crop water use averages about 0.30 in. per day or 80% of open pan evaporation in Iowa (Denmead and Shaw 1959; Shaw 1976). This value can vary depending on climatic factors. For example, water use during this period would be higher in the westernmost portions of the Corn Belt since atmospheric demand (higher solar radiation/less cloudiness and lower humidity levels) is higher (Neild and Newman 1986). By late August as the crop matures, water use begins to decline rapidly. Thus, ET in corn is at a maximum for only a fraction of the total growing season, and in Iowa, that period is July through mid-August. b. Soybeans Soybean water use parallels corn except that the peak is displaced a few weeks later in the growing season. In Iowa, soybean planting occurs after corn in May through early June (Fig. 4). Soybean water use begins to increase rapidly in mid-July as the plant enters the bloom or flowering stage and the canopy has filled in (Fig. 5) (Shaw and Laing 1966; Van Doren Van Dor·en , Carl Clinton 1885-1950. American literary critic, editor, and writer whose biography of Benjamin Franklin (1938) won a Pulitzer Prize. and Reicosky 1987). Water use continues at a high rate through September when the crop begins to mature and drop its leaves. Peak water use is slightly higher than corn, roughly 0.33 in per day or about 85% of open pan evaporation. [FIGURE 4 OMITTED] c. Pasture Pasture water use is complicated by the fact that the hay is typically cut twice or more per season, and the loss in leaf area from the cutting limits water use (Fig. 6). Note that water use increases to the maximum rate much earlier in the season than either corn or soybeans. This occurs because pastures start the growing season with a well-developed root system, and above ground growth begins before corn and soybeans. Similar to corn, peak water use values average about 80% of open pan evaporation, but a significant decrease in water use occurs after the hay is cut. Subsequently, water use begins to increase again as the crop grows toward full ground cover before the next cutting. d. Native prairie The growing season of the native tallgrass prairie The tallgrass prairie is an ecosystem native to central North America, with fire as its primary periodic disturbance. In the past, tallgrass prairies covered a large portion of the American Midwest, just east of the Great Plains, and portions of the Canadian Prairies. in Iowa is longer than the growing season for corn and soybeans and more similar to pasture since, like pasture, in general root systems are already established as soon as growth can begin in the spring. Studies by Knapp et al. (2001) and Hutchinson et al. (2001) noted that water use totaled over the entire growing season for a well-irrigated tall grass prairie is roughly equal to that of corn and soybeans. Since both prairie and corn and soybeans use about the same amount of water in an entire growing season, but corn and soybeans concentrate that use in a shorter period of time, one can logically conclude that the local contribution to the moisture budget has changed due to human factors. 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 and Changnon et al., 2003), and even fog development. [FIGURE 5 OMITTED] [FIGURE 6 OMITTED] [FIGURE 7 OMITTED] 3. Operational Considerations In an effort to understand the impact of evapotranspiration (ET) on local dew point trends, simple calculations were made of changes in the mixing ratio (r) (see Appendix for details). In each calculation, several assumptions were made: 1) horizontal advection ad·vec·tion n. 1. The transfer of a property of the atmosphere, such as heat, cold, or humidity, by the horizontal movement of an air mass: is negligible; 2) the ET rate is distributed evenly over 12 (daylight) hours; and, 3) vertical mixing of moisture occurs rapidly throughout the depth (h) of the planetary boundary layer The planetary boundary layer (PBL), also known as the atmospheric boundary layer (ABL) or peplosphere, is the lowest part of the atmosphere and its behavior is directly influenced by its contact with a planetary surface. (PBL PBL Problem-Based Learning PBL Phi Beta Lambda PBL Performance Based Logistics PBL Planetary Boundary Layer PBL Publishing and Broadcasting Limited (Australia) PBL Philippine Basketball League PBL Peripheral Blood Leukocyte ). The total contribution of ET to r is shown in Table 1. Notice the reduced impact of ET on dew points as h increases. This dependence of mixing ratio tendency on ET and h may be visualized in Fig. 7. Following these examples, 0.10 in. (0.25 cm) of ET from 1 [m.sup.2] of surface results in 2.5 kg of liberated moisture. Distributed linearly (using an air parcel density of 1 kg [m.sup.-3]) over h of 1000 m results in an increase of 2.5 g [kg.sup.-1] in the r of a typical parcel over the span of 12 hours. This results in a mean hourly increase of 0.2 g [kg.sup.-1] [hr.sup.-1]. At 1000 mb and a dew point of 70[degrees]F (21.1[degrees]C), this change amounts to an increase of 4[degrees]F (2.2[degrees]C) in the dew point temperature over 12 hours. Of the assumptions stated previously, the most noticeably violated of these is that of even ET distribution over 12 hours. While the 12 sunlit sun·lit adj. Illuminated by the sun. Adj. 1. sunlit - lighted by sunlight; "the sunlit slopes of the canyon"; "violet valleys and the sunstruck ridges"- Wallace Stegner sunstruck hours allow transpiration, evaporation can occur anytime. Yet, with relative humidity typically highest overnight, evaporation is effectively limited during the 12 nighttime hours. Moreover, ET is a function of temperature, humidity, and solar radiation (implying impact from cloud cover as well as the diurnal diurnal /di·ur·nal/ (di-er´nal) pertaining to or occurring during the daytime, or period of light. di·ur·nal adj. 1. Having a 24-hour period or cycle; daily. 2. cycle), among others (Rosenberg et al. 1983). The assumption of negligible horizontal advection presumes that the ET is occurring uniformly over a large homogenous homogenous - homogeneous area (e.g., similar vegetation type), which may or may not be valid depending on local growing patterns, crop rotations, land use, and the like. Lastly, the assumption of a well-mixed PBL suggests wind profile with significant wind speed changes with height. On days with weak mixing and or low h, the distribution will not occur over as deep a layer and will confine moisture to a smaller, near-surface volume. Should such processes occur over several days, it should be noted that some of the moisture would be recycled as dew-fall during the night then re-evaporated during the day. 4. Summary Land surface effects are known to, at times, have a pronounced impact on local sensible weather. In particular, agricultural crops whether irrigated or not, can be an important component of the local moisture budget. We have explored the impact that com and soybeans can have on local dew points in Iowa when the crop is well watered during non-advective conditions, and have developed an approach for assessing crop effects on the local moisture budget that can be applied to other regions given those two key assumptions. First, one needs knowledge of the land use patterns in the area of interest (e.g., how much of the area is native vegetation, urban, agricultural, etc). Second, one must understand soil types and be able to monitor soil moisture status to determine if water is available for ET. Third, one must understand patterns of seasonal water use of crops, forests and/or native vegetation, and whether and when irrigation is used (e.g., Pennington and Wolf 1989). Finally, combine the knowledge of those elements to evaluate the impact on dew point temperature, paying particular attention to the assumptions of well-watered crops/vegetation and non-advective conditions. Acknowledgments The authors gratefully acknowledge the suggestions of the two reviewers which resulted in an improved manuscript. Authors Ray Wolf is the Science and Operations Officer at the NWS Weather Forecast Office (WFO WFO Weather Forecast Office WFO Wirtschaftsförderung Osnabrück Gmbh WFO Western Field Ornithologists WFO Washington Field Office WFO Work for Others (USACE) WFO World Federation of Orthodontists WFO Wide Full Open ) in Davenport, Iowa (Quad Cities). Previously he served as a forecaster at the WFO in Denver, Colorado and as an agricultural forecaster at the NWS office in Stoneville, Mississippi. His interests include the study of meso and stormscale processes associated with severe convective storms. He received a B.S. in Meteorology meteorology, branch of science that deals with the atmosphere of a planet, particularly that of the earth, the most important application of which is the analysis and prediction of weather. in 1982 and an M.S. in Agricultural Climatology climatology Branch of atmospheric science concerned with describing climate and analyzing the causes and practical consequences of climatic differences and changes. Climatology treats the same atmospheric processes as meteorology, but it also seeks to identify slower-acting in 1985, both from Iowa State University Academics ISU is best known for its degree programs in science, engineering, and agriculture. ISU is also home of the world's first electronic digital computing device, the Atanasoff–Berry Computer. . Pat Market is an associate professor of atmospheric science at the University of Missouri-Columbia. He received a B.S. in meteorology from Millersville University of Pennsylvania History Millersville University was established in 1855 as the Lancaster County Normal School, the first state normal school in Pennsylvania. It subsequently changed its name to the Millersville State Normal School in 1859 and Millersville later became a state teacher’s in 1994 as well as M.S.(R) and Ph.D. degrees in meteorology from Saint Louis University Saint Louis University, mainly at St. Louis, Mo.; Jesuit; coeducational; opened 1818 as an academy, became a college 1820, chartered as a university 1832. Parks College (est. 1927 as Parks College of Aeronautical Technology) in Cahokia, Ill. in 1996 and 1999, respectively. Dr. Market has held positions as a forecaster and as a certified weather observer. Presently, he serves as a councilor coun·cil·or also coun·cil·lor n. A member of a council, as one convened to advise a governor. See Usage Note at council. coun for the NWA NWA Northwest Airlines (ICAO code) NWA Northwest Arkansas NWA National Wrestling Alliance NWA National Weather Association NWA National Works Agency (Jamaica) NWA Network Analyzer . References Changnon, D., M. Sandstrom, and C. Schaffer, 2003: Relating changes in agricultural practices to increasing dew points in extreme Chicago heat waves. Clim. Res., 24, 243-254. Cheresnick, D.R., and J.B. Basara, 2005: The impact of land-atmosphere interactions on the Benson, Minnesota, tornado of 11 June 2001. Bull. Amer. Meteor. Soc., 86, 637-642. Denmead, O.T., and R.H. Shaw, 1959: Evapotranspiration in relationship to the development of the corn crop. Agron. J., 51, 725-726. Hutchinson, S.L., J.K. Koelliker, A.K. Knapp, and G.A. Clark, 2001: Development of water-usage coefficients for the tallgrass prairie. 2001 Annual Meeting, Sacramento, CA, Amer. Soc. Agric. Biol. Eng. [Available online at http://asae.frymulti/techpapers.asp?=sca2001] Knapp, A.K., J.M. Briggs, and J.K. Kohler, 2001: Frequency and extent of water limitation to primary production in a mesic mes·ic adj. Ecology Of, characterized by, or adapted to a moderately moist habitat. mesic Relating or adapted to a moderately moist habitat. temperate grassland. Ecosystems, 4, 19-28. Kurkowski, N.P., D.J. Stensrud, and M.E. Baldwin, 2003: Assessment of implementing satellite-derived land cover data in the Eta model. Wea. Forecasting, 18, 404-416. National Agricultural Statistics Service, Iowa Field Office, 2005: U.S. Dept. of Agriculture. [Available online at http://www.nass.usda.gov/ia/] Neild, R.E., and J.E. Newman, 1986: Growing season characteristics and requirements in the Corn Belt. National Corn Handbook NCH-40, Purdue University, West Lafeyette, IN, 13 pp. [Available online at http://www.ces.purdue.edu/extmedia/NCH/NCH-40.html] Pielke, R.A., Sr., R.L. Walko, L.T. Steyaert, P.L. Vidale, G.E. Liston, and W.L. Lyons, 1999: The influence of anthropogenic an·thro·po·gen·ic adj. 1. Of or relating to anthropogenesis. 2. Caused by humans: anthropogenic degradation of the environment. landscape changes on weather in south Florida. Mon. Wea. Rev., 127, 1663-1673. Pennington, D.A., and R.A. Wolf, 1989: Variability of seasonal water use of rice during flood. Mississippi Agricultural and Forestry Experimental Station Research Report, Vol.14, No.12, 6 pp. Rosenberg, N.J., B.L. Blad, and S.B. Verma, 1983: Microclimate microclimate Climatic condition in a relatively small area, within a few feet above and below the Earth's surface and within canopies of vegetation. Microclimates are affected by such factors as temperature, humidity, wind and turbulence, dew, frost, heat balance, : The Biological Environment. 2nd ed., John Wiley and Sons, New York New York, state, United States New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of , 495 pp. Rozoff, C.R., WR. Cotton, and J.O. Adegoke, 2003: Simulation of St. Louis, Missouri, land use impacts on thunderstorms. J. Appl. Meteor., 42, 716-738. Shaw, R.H., 1964: Prediction of soil moisture under meadow. Agron. J., 43, 9-15. ______, 1976: Water use and requirements of maize--a review. Proceedings of the Symposium on the Agrometeorology of the Maize (Corn) Crop, Ames, LA, USA. World Meteorological Organization World Meteorological Organization (WMO), specialized agency of the United Nations; established in 1951 with headquarters at Geneva. It replaced the International Meteorological Organization, which was established in 1878. , Geneva Geneva, canton and city, Switzerland Geneva (jənē`və), Fr. Genève, canton (1990 pop. 373,019), 109 sq mi (282 sq km), SW Switzerland, surrounding the southwest tip of the Lake of Geneva. , Switzerland, 119-134. ______, and D.R. Laing, 1966: Moisture stress and plant response. Plant Environment and Efficient Water Use. W.H. Pieree Ed. Amer. Soc. Agron., 73-94. Sparks, J., D. Changnon, and J. Stark, 2002: Changes in the frequency of extreme warm-season surface dewpoints in northeastern Illinois: Implications for cooling-system design and operation. J. Appl. Meteor., 41, 890-898. Van Doren, Jr., D.M., and D.C. Reicosky, 1987: Tillage and irrigation. Soybeans: Improvement, Production and Uses. Amer. Soc.Agron. J. R. Wilcox Ed., 391-428. Appendix Simple calculations are made that attempt to translate a measured value of evapotranspiration (ET) into a change in the mixing ratio (r) and thus a change in the local dew point temperature ([T.sub.d]). In each calculation, several assumptions were made: 1) horizontal advection is negligible; 2) the ET rate is distributed evenly over 12 (daylight) hours; 3) vertical mixing of moisture occurs rapidly throughout the depth (h) of the planetary boundary layer (PBL), and; 4) density variation over the depth of the PBL is negligible. Note that condition (1) above does not preclude the presence of a wind, merely that horizontal advection of moisture is negligible. Consider the case of 0.33 in. (0.84 cm) of ET yielded from 1 [m.sup.2] of surface area. Using the well-known physical relationship whereby 1 [cm.sup.3] [H.sub.2]O = 1 g [H.sub.2]O (A1) we may multiply the ET (often posed as a depth) by the area from which the moisture is assumed to come 0.84 cm x 100 cm x 100 cm (A2) and arrive at a volume of moisture of 8400 [cm.sup.3] or simply 8.4 kg of liberated moisture. Recall from assumption (2) above that this moisture is distributed evenly in time over 12 hours. Not all of the moisture is liberated at once. If we assume a PBL of depth h = 1000 m with constant density throughout and use an initial parcel density of 1 kg [m.sup.-3], then we may think of this scenario as a tower of 1000 1-[m.sup.-3] cubes stacked one on top of the other, yielding a total volume of 1000 [m.sup.-3]. With a uniform, linear distribution of the moisture, 8.4 kg, over the total volume, 1000 [m.sup.-3], each of the 1000 "cubes" having an initial mass of 1 kg will receive 8.4 kg / 1000 [m.sup.3] = 8.4 kg / 1000 kg = 8400 g / 1000 kg = 8.4 g / kg(A3) (A3) or an added 8.4 g of moisture in each of the 1 kg parcels by the end of the 12 hour period. One may then calculate the corresponding increase in the [T.sub.d], or simply consult a thermodynamic ther·mo·dy·nam·ic adj. 1. Characteristic of or resulting from the conversion of heat into other forms of energy. 2. Of or relating to thermodynamics. diagram to assess the corresponding change in [T.sub.d]. For a pressure of 1000 mb and an initial [T.sub.d] of 70[degrees]F (and thus a mixing ratio of 16.0 g [kg.sup.-1]), a change in mixing ratio of 8.4 g [kg.sup.-1] corresponds to a [T.sub.d] change of ~12[degrees]F, or a final dew point of ~82[degrees]F. While this may seem to be an extreme result, one must recognize that, in addition to the preliminary assumptions, this example deals with a high ET rate and a relatively shallow PBL. Raymond A. Wolf NOAA/National Weather Service Weather Forecast Office Davenport, Iowa Patrick S. Market Department of Soil, Environmental and Atmospheric Sciences University of Missouri-Columbia Columbia, Missouri
Table 1. Daily liberated moisture (g [kg.sup.-1] [day.sup.-1]) as a
function of evapotranspiration (ET) and the depth of the planetary
boundary layer (h).
ET 0.10" 0.25" 0.33" 0.50
h
300 m 8.5 21.2 27.9 42.3
500 m 5.1 12.7 16.8 25.4
1000 m 2.5 6.4 8.4 12.7
1500 m 1.7 4.2 5.6 8.5
2000 m 1.3 3.2 4.2 6.4
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