[Show abstract][Hide abstract] ABSTRACT: This study presents results from regional climate model (RCM) projections for the south-west Pacific Ocean. The regional models used bias corrected sea surface temperatures. Six global climate models (GCMs) were used to drive a global variable resolution model on a quasi-uniform 60 km grid. One of these simulations was used to drive three limited area regional models. Thus a four member ensemble was produced by different RCMs downscaling the same GCM (GFDL2.1), and a six member ensemble was produced by the same RCM (Conformal Cubic Atmospheric Model—CCAM) downscaling six different GCMs. Comparison of the model results with precipitation observations shows the differences to be dominated by the choice of RCM, with all the CCAM simulations performing similarly and generally having lower error than the other RCMs. However, evaluating aspects of the model representation of the South Pacific Convergence Zone (SPCZ) does not show CCAM to perform better in this regard. In terms of the future projections of the SPCZ for the December–January–February season, the ensemble showed no consensus change in most characteristics though a majority of the ensemble members project a decrease in the SPCZ strength. Thus, similar to GCM based studies, there is large uncertainty concerning future changes in the SPCZ and there is no evidence to suggest that future changes will be outside the natural variability. These RCM simulations do not support an increase in the frequency of zonal SPCZ events.
[Show abstract][Hide abstract] ABSTRACT: The output of four regional climate models (RCMs) from the Coordinated Regional Climate Downscaling Experiment (CORDEX)-North America (NA) region was analysed for the 1990–2008 period, with particular interest on the mechanisms associated with wet and dry years over the North American Monsoon (NAM) core region. All RCMs (RCA3.5, HadGEM3-RA, REMO, and RegCM4) were forced by the ERA-Interim reanalysis. Model precipitation was compared against several observational gridded data sets at different time scales. Most RCMs capture well the annual cycle of precipitation and outperform ERA-Interim, which is drier than the observations. RCMs underestimate (overestimate) the precipitation over the coastal plains (mountains) and have some problems to reproduce the interannual variability of the monsoon. To further investigate this, two extreme summers that showed the largest consistency among observations and RCMs were chosen: one wet (1990) and one dry (2005). The impact of the passage of tropical cyclones, the size of the Western Hemisphere Warm Pool (WHWP), the Intertropical Convergence Zone (ITCZ) position, and the initial intensity of the land–sea thermal contrast (LSTC) were analysed. During the wet year, the LSTC was stronger than the 2005 dry monsoon season and there were a larger number of hurricanes near the Gulf of California, the WHWP was more extended, and the ITCZ was located in a more northerly position than in 2005. All these processes contributed to a wetter NAM season. During the dry year, the LSTC was weaker, with a later onset, probably due to a previous very wet winter. The inverse precipitation relationship between winter and summer in the monsoon region was well captured by most of the RCMs. RegCM4 showed the largest biases and HadGEM3-RA the smallest ones.
No preview · Article · Jun 2015 · International Journal of Climatology
[Show abstract][Hide abstract] ABSTRACT: The important questions about agriculture, climate, and sustainability have become increasingly complex and require a coordinated, multifaceted approach for developing new knowledge and understanding. A multistate, transdisciplinary project was begun in 2011 to study the potential for both mitigation and adaptation of corn-based cropping systems to climate variations. The team is measuring the baseline as well as change of the system's carbon (C), nitrogen (N), and water footprints, crop productivity, and pest pressure in response to existing and novel production practices. Nine states and 11 institutions are participating in the project, necessitating a well thought out approach to coordinating field data collection procedures at 35 research sites. In addition, the collected data must be brought together in a way that can be stored and used by persons not originally involved in the data collection, necessitating robust procedures for linking metadata with the data and clearly delineated rules for use and publication of data from the overall project. In order to improve the ability to compare data across sites and begin to make inferences about soil and cropping system responses to climate across the region, detailed research protocols were developed to standardize the types of measurements taken and the specific details such as depth, time, method, numbers of samples, and minimum data set required from each site. This process required significant time, debate, and commitment of all the investigators involved with field data collection and was also informed by the data needed to run the simulation models and life cycle analyses. Although individual research teams are collecting additional measurements beyond those stated in the standardized protocols, the written protocols are used by the team for the base measurements to be compared across the region. A centralized database was constructed to meet the needs of current researchers on this project as well as for future use for data synthesis and modeling for agricultural, ecosystem, and climate sciences.
Full-text · Article · Nov 2014 · Journal of Soil and Water Conservation
[Show abstract][Hide abstract] ABSTRACT: Agricultural nonpoint source pollution is the main source of nitrogen (N) and phosphorus (P) in the intensely row-cropped Upper Mississippi River Basin (UMRB) stream system and is considered the primary cause of the northern Gulf of Mexico hypoxic zone according to the US Environmental Protection Agency. A point of crucial importance in this region is therefore how intensive corn (Zed mays L.)-based cropping systems for food and fuel production can be sustainable and coexist with a healthy water environment, not only under existing climate conditions but also under a changed climate in the future. To address this issue, a UMRB integrated modeling system has been built with a greatly refined 12-digit subbasin structure based on the Soil and Water Assessment Tool (SWAT) water quality model, which is capable of estimating landscape and in-stream water and pollutant yields in response to a wide array of alternative cropping and/or management strategies and climatic conditions. The effects of the following four agricultural management scenarios on crop production and pollutant loads exported from the cropland of the UMRB to streams and rivers were evaluated: (1) expansion of continuous corn across the entire basin, (2) adoption of no-till on all corn and soybean ( Glycine max L.) fields in the region, (3) substitution of the traditional continuous corn and corn-soybean rotations with an extended five-year rotation consisting of corn, soybean, and three years of alfalfa (Medicago sativa L.), and (4) implementation of a winter cover crop within the baseline rotations. The effects of each management scenario were evaluated both for current climate and a projected midcentury (2046 to 2065) climate from a General Circulation Model (GCM). All four scenarios behaved similarly under the historical and future climate, generally resulting in reduced erosion and nutrient loadings to surface water bodies compared to the baseline agricultural management. Continuous corn was the only scenario which resulted in increased N pollution while no-till was the most environmentally effective and able to sustain production at almost the same levels. Rye (Secale cereale L.) cover crop within the fallow period was also effective in reducing erosion and both sediment-bound and soluble forms of nutrients. The results indicated that alternative management practices could reduce sediment, N, and P exports from UMRB cropland by up to 50% without significantly affecting yields. Results for the climate change scenario showed that the effectiveness of the management scenarios was strongly linked to the reduced water availability predicted under the future climate, which assisted in mitigating pollutant transport, although with a small loss of production.
Preview · Article · Nov 2014 · Journal of Soil and Water Conservation
[Show abstract][Hide abstract] ABSTRACT: We investigate major results of the NARCCAP multiple regional climate model (RCM) experiments driven by multiple global climate models (GCMs) regarding climate change for seasonal temperature and precipitation over North America. We focus on two major questions: How do the RCM simulated climate changes differ from those of the parent GCMs and thus affect our perception of climate change over North America, and how important are the relative contributions of RCMs and GCMs to the uncertainty (variance explained) for different seasons and variables? The RCMs tend to produce stronger climate changes for precipitation: larger increases in the northern part of the domain in winter and greater decreases across a swath of the central part in summer, compared to the four GCMs driving the regional models as well as to the full set of CMIP3 GCM results. We pose some possible process-level mechanisms for the difference in intensity of change, particularly for summer. Detailed process-level studies will be necessary to establish mechanisms and credibility of these results. The GCMs explain more variance for winter temperature and the RCMs for summer temperature. The same is true for precipitation patterns. Thus, we recommend that future RCM-GCM experiments over this region include a balanced number of GCMs and RCMs.
[Show abstract][Hide abstract] ABSTRACT: Adoption of genetically modified (GM) crops has raised concerns that GM
traits can accidentally cross into conventional crops or wild relatives
through the transport of wind-borne pollen. In order to evaluate this
risk it is necessary to account both for dispersion of the pollen grains
and environmental influences on pollen viability. The Lagrangian
approach is suited to this problem because it allows tracking the
environmental temperature and moisture that pollen grains experience as
they travel. Taking advantage of this capability we have combined a
high-resolution version of the WRF meteorological model with a
Lagrangian particle dispersion model to predict maize pollen dispersion
and viability. WRF is used to obtain fields of wind, turbulence kinetic
energy, temperature, and humidity which are then used as input to the
Lagrangian dispersion model. The dispersion model in turn predicts
transport of a statistical sample of a pollen cloud from source plants
to receptors. We also use the three-dimensional temperature and moisture
fields from WRF to diagnose changes in moisture content of the pollen
grains and consequent loss of viability. Results show that turbulent
motions in the convective boundary layer counteract the large terminal
velocity of maize pollen grains and lift them to heights of several
hundred meters, so that they can be transported long distances before
settling to the ground. We also found that pollen lifted into the upper
part of the boundary layer remains more viable than has been inferred
using surface observations of temperature and humidity. This is
attributed to the thermal and moisture structure that typifies the
daytime atmospheric boundary layer, producing an environment of low
vapor pressure deficit in the upper boundary layer which helps maintain
[Show abstract][Hide abstract] ABSTRACT: The potential for regional climate change arising from adoption of
policies to increase production of biofuel feedstock is explored using a
regional climate model. Two simulations are performed using the same
atmospheric forcing data for the period 1979-2004, one with present-day
land use and monthly phenology and the other with land use specified
from an agro-economic prediction of energy crop distribution and monthly
phenology consistent with this land use change. In Kansas and Oklahoma,
where the agro-economic model predicts 15-30% conversion to switchgrass,
the regional climate model simulates locally lower temperature
(especially in spring), slightly higher relative humidity in spring and
slightly lower relative humidity in summer, and summer depletion of soil
moisture. This shows the potential for climate impacts of biofuel
policies and raises the question of whether soil water depletion may
limit biomass crop productivity in agricultural areas that are
responsive to the policies. We recommend the use of agronomic models to
evaluate the possibility that soil moisture depletion could reduce
productivity of biomass crops in this region. We conclude, therefore,
that agro-economic and climate models should be used iteratively to
examine an ensemble of agricultural land use and climate scenarios,
thereby reducing the possibility of unforeseen consequences from rapid
changes in agricultural production systems.
Full-text · Article · Mar 2013 · Geophysical Research Letters
[Show abstract][Hide abstract] ABSTRACT: We combined a high-resolution atmospheric dynamical model and a Lagrangian dispersion model to assess the influence of complex terrain (e.g., mountains and valleys) on the movement of pollen from a source of genetically modified bentgrass (Agrostis stolonifera L.). We simulated 6 d (22-27 June 2003) from a reported case where gene flow in bentgrass was observed at distances greater than 20 km near Madras, OR (44 degrees 44'24 '' N, 121 degrees 9'30 '' W). Our model resolves the effects of complex terrain and local turbulence on pollen dispersion that were not considered by previous studies. We simulated pollen deposition over 20 km from its source and at locations where gene flow was previously observed. Our simulations showed that local terrain strongly affected deposition; for example, pollen grains were not deposited in large quantities within valleys or on the windward sides of mountains. Examination of the flow in these regions indicated that complex terrain creates local circulations that must be considered when predicting the potential for gene flow.
[Show abstract][Hide abstract] ABSTRACT: We analyze the ability of the NARCCAP ensemble of regional climate models to simulate extreme monthly precipitation and its supporting circulation for regions of North America, comparing 18 years of simulations driven by the NCEP-DOE reanalysis with observations. Analysis focuses the wettest 10% of months during the cold half of the year (October-March), when we assume that resolved synoptic circulation governs precipitation. For a coastal California region, the models replicate well the monthly frequency of extremes, the amount of extreme precipitation and the 500 hPa circulation anomaly associated with the extremes. For an Upper Mississippi River Basin region, the models agree with observations in both monthly frequency and magnitude, though not as closely as for coastal California. In addition, simulated circulation anomalies for extreme months are similar to those in observations. Model success appears to result in part from the substantial seasonal variation of extremes, which the models capture well.
Full-text · Article · Jan 2011 · Journal of Hydrometeorology
[Show abstract][Hide abstract] ABSTRACT: Previous studies have examined the rate of viability loss in pollen grains based on surface conditions but some pollen grains are lifted throughout the atmospheric boundary layer to heights where temperature and moisture differ markedly from near the surface. This transport may affect pollen viability in maize pollen which has been linked to its moisture content. The objective of this study was to examine how predictions of pollen viability may differ when considering the effects of boundary layer transport rather than only considering the conditions at the pollen source. We used Large-Eddy Simulation to simulate pollen dispersion and predict pollen viability upon deposition. We compared the predicted viability that was diagnosed using the atmospheric conditions at the pollen source when a pollen grain was released to viability diagnosed using the atmospheric conditions following the pollen grain's trajectory as it moved through the atmospheric boundary layer. Using surface values provided a reasonable prediction of viability for pollen grains that traveled less than a kilometer from the source field, but underpredicted pollen viability by as much as 20% for pollen that traveled several kilometers. The difference is attributed to the tendency for longer range transport to require lofting of pollen grains into the upper part of the atmospheric boundary layer, where cooler temperature and higher relative humidity are conducive to increased viability. Our results suggest that pollen grains traveling many kilometers are more likely to pollinate a receptive silk than would be expected based on the atmospheric conditions at the pollen source.
Preview · Article · Oct 2010 · Field Crops Research
[Show abstract][Hide abstract] ABSTRACT: We use Soil and Water Assessment Tool (SWAT) when driven by observations and results of climate models to evaluate hydrological quantities, including streamflow, in the Upper Mississippi River Basin (UMRB) for 1981-2003 in comparison to observed streamflow. Daily meteorological conditions used as input to SWAT are taken from (1) observations at weather stations in the basin, (2) daily meteorological conditions simulated by a collection of regional climate models (RCMs) driven by reanalysis boundary conditions, and (3) daily meteorological conditions simulated by a collection of global climate models (GCMs). Regional models used are those whose data are archived by the North American Regional Climate Change Assessment Program (NARCCAP). Results show that regional models correctly simulate the seasonal cycle of precipitation, temperature, and streamflow within the basin. Regional models also capture interannual extremes represented by the flood of 1993 and the dry conditions of 2000. The ensemble means of both the GCM-driven and RCM-driven simulations by SWAT capture both the timing and amplitude of the seasonal cycle of streamflow with neither demonstrating significant superiority at the basin level.
No preview · Article · Jul 2010 · Meteorologische Zeitschrift
[Show abstract][Hide abstract] ABSTRACT: We have developed a mathematical model to predict the diurnal pattern of maize (Zea mays L.) pollen shed on the basis of local meteorological conditions. Our goal is to improve simulations of maize pollen dispersion that have typically released pollen at a constant rate in contrast with measurements of pollen shed that show diurnal variation in the rate of shed. Measurements coupling pollen shed and local meteorological variables were made during controlled experiments and a 2004 field experiment to examine the influence of meteorological conditions on pollen shed. From these data, a model was developed to predict the diurnal pattern of pollen shed as a function of vapor pressure deficit, solar radiation, temperature, and the amount of pollen remaining to be shed. The model was validated by predicting the rate of pollen shed, normalized by the daily total of pollen shed, that occurred hourly for days during a 2003 field study ((RMSE) over bar = 0.061 h(-1)) and results from van Hout et al. (2008; (RMSE) over bar = 0.089 h(-1)). The model captured the general trend of pollen shed and predicted the time of peak shed within an hour of the measured peak on most days. The model, however, tended to underpredict the magnitude of the normalized peak rate of shed and did not account for secondary peaks in pollen shed that were occasionally observed. Thus, future model refinements will depend on identifying additional biological or environmental factors that impact the instantaneous rate of pollen shed.
[Show abstract][Hide abstract] ABSTRACT: A comprehensive intercomparison of historical wind speed trends over the
contiguous United States is presented based on two observational data
sets, four reanalysis data sets, and output from two regional climate
models (RCMs). This research thus contributes to detection,
quantification, and attribution of temporal trends in wind speeds within
the historical/contemporary climate and provides an evaluation of the
RCMs being used to develop future wind speed scenarios. Under the
assumption that changes in wind climates are partly driven by
variability and evolution of the global climate system, such changes
should be manifest in direct observations, reanalysis products, and
RCMs. However, there are substantial differences in temporal trends
derived from observational wind speed data, reanalysis products, and
RCMs. The two observational data sets both exhibit an overwhelming
dominance of trends toward declining values of the 50th and 90th
percentile and annual mean wind speeds, which is also the case for
simulations conducted using MM5 with NCEP-2 boundary conditions.
However, converse trends are seen in output from the North American
Regional Reanalysis, other global reanalyses (NCEP-1 and ERA-40), and
the Regional Spectral Model. Equally, the relationship between changing
annual mean wind speed and interannual variability is not consistent
among the different data sets. NCEP-1 and NARR exhibit some tendency
toward declining (increasing) annual mean wind speeds being associated
with decreased (increased) interannual variability, but this is not the
case for the other data sets considered. Possible causes of the
differences in temporal trends from the eight data sources analyzed are
No preview · Article · Jul 2009 · Journal of Geophysical Research Atmospheres
[Show abstract][Hide abstract] ABSTRACT: Controlling pollination of the female inbred is critical to achieve maximum kernel set and high levels of genetic purity in maize (Zea mays L.) hybrid seed production. Although kernel set associated with inbred flowering dynamics is fairly predictable, it has not been possible to predict the level of outcrossing resulting from adventitious pollen entering the seed field. Our objective was to combine our kernel set model with a new Lagrangian pollen dispersal model to determine whether outcrossing could be simulated from flowering dynamics and estimates of pollen drift. This study was conducted in a commercial seed production field in which male and female planting dates were varied to provide a range of flowering synchronies and risk for outcrossing. Kernel production varied from 13.4 x 10(6) to 24.5 x 10(6) kernels ha(-1). Outcrossing at field locations 100 to 170 m from an adventitious pollen source varied from 1.4 to 18% as determined by allelic variation at 13 loci. The kernel set model accurately simulated variation in kernel production (R-2 = 0.83; RMSE = 0.3 x 10(6)) when silk receptivity was limited to 4 d. Percentage outcrossing due to adventitious pollen also was accurately simulated (R-2 = 0.78; RMSE = 0.8) for wind conditions and plant development patterns typically encountered in maize hybrid seed production. The combined kernel set and pollen dispersal models provide a novel and robust approach for defining management strategies to optimize kernel production and genetic purity.
No preview · Article · Mar 2009 · Agronomy Journal
[Show abstract][Hide abstract] ABSTRACT: We analyze regional climate model (RCM) simulations of daily, spatially distributed extreme precipitation events, using co-operative network observations and output from 10-year RCM simulations of present and future-scenario climates. We examine an Upper Mississippi River Basin region during October–March for daily amounts that exceed the 99.95th percentile and that occur simultaneously at several observation sites or model grid points. For the observations and each simulation, nearly all such extreme regional events occur when a slow moving, cut-off-low system develops over the Rockies and Great Plains and steadily pumps moisture into the Upper Mississippi region from the Gulf of Mexico. The threshold for the extreme events increases in the future scenario by an amount similar to the increase in saturation specific humidity. The results suggest robust circulation behavior for such extremes in the face of climate change.
No preview · Article · Oct 2008 · Geophysical Research Letters
[Show abstract][Hide abstract] ABSTRACT: A simplified general circulation model (GCM), consisting of a complete dynamical core, simple specified physics. and convective momentum transport (CMT) forcing. is used to understand the effects of CMT on climate simulations with a focus on the role of convective heating in the response of circulation to the CMT forcing. It is found that the convective heating dominates the meridional circulation response and dynamical processes dominate the zonal wind response to the CMT forcing in the tropics: the simplified model reproduces sonic of the key features of CMT-induced circulation changes observed in the full GCM in the tropics. These results suggest that the CMT-induced zonal and meridional circulation changes in the tropics in the full GCM are dominated by dynamical processes and the convective heating, respectively. Inclusion of the CMT in the model induce,,, a marked change in convective heating, which negatively correlates with the change in vertical velocity. indicating the existence of CMT-induced convective heating-circulation feedback. The sensitivity experiment with the removal of mean convective heating feedback demonstrates that the convective heating affects the response of the meridional circulation to the CMT forcing through the CMT-induced convective heating-circulation feedback.