scholarly journals Divergent responses of maize yield to precipitation in the United States

2021 ◽  
Author(s):  
Ru Xu ◽  
Yan Li ◽  
Kaiyu Guan ◽  
Lei Zhao ◽  
Bin Peng ◽  
...  
Keyword(s):  
United States ◽  
Spatial Heterogeneity ◽  
Temperature Response ◽  
Maize Yield ◽  
The United States ◽  
Security Assessment ◽  
Crop Modeling ◽  
Crop Models ◽  
Precipitation Response ◽  
Precipitation Threshold

Abstract How maize yield responds to precipitation variability in space and time over broader scales is largely unknown compared with the well-understood temperature response, even though precipitation change is more erratic with greater spatial heterogeneity. Here, we develop a method to quantify the spatially explicit precipitation response of maize yield using statistical data and crop models in the contiguous United States. We find the precipitation responses are highly heterogeneous with inverted-U (40.3%) being the leading response type, followed by unresponsive (30.39 %), and linear increase (28.6%). The optimal precipitation threshold derived from inverted-U response exhibits considerable spatial variations, which is higher under wetter, hotter, and well-drainage conditions but lower under drier and poor-drainage conditions. Irrigation alters precipitation response by making yield either unresponsive to precipitation or having lower optimal thresholds than rainfed conditions. We further find that the observed precipitation responses of maize yield are misrepresented in crop models, with a too high percentage of increase type (59.0% versus 29.6%) and an overestimation in optimal precipitation threshold by ~90 mm. These two factors explain about 30% and 85% of the inter-model yield overestimation biases under extreme rainfall conditions. Our study highlights the large spatial heterogeneity and the key role of human management in the precipitation responses of maize yield, which need to be better characterized in crop modeling and food security assessment under climate change.

scholarly journals Fulfilling U.S. Commitment to Refugee Resettlement

2017 ◽  
Vol 5 (1) ◽  
pp. 155-236
Author(s):  
Keyword(s):  
United States ◽  
Foreign Policy ◽  
National Security ◽  
International Law ◽  
The United States ◽  
Government Agencies ◽  
Refugee Resettlement ◽  
Security Assessment ◽  
The U.S ◽  
Policy Solutions

At a time when the U.S. refugee admissions program is under serious threat and the world’s displaced population is at its highest, this Report sets forth extensive recommendations regarding the United States’ role in protecting vulnerable refugees and compliance with its commitments under domestic and international law that together safeguard people fleeing persecution and fearing return to torture. The Report also identifies key national security reasons for supporting and enhancing the refugee program in keeping with U.S. foreign policy priorities. Additionally, the Report provides an in-depth discussion of the robust, multistep security-assessment mechanisms already in place for screening refugees; offers viable policy solutions to improve the integration of resettled refugees through enhanced collaboration among government agencies, private resettlement agencies, and sponsors involved in domestic resettlement; and demonstrates the positive economic impact of refugee resettlement in the United States. Drawing on the perspectives of longtime domestic refugee resettlement experts, the Report also provides fresh insights into how publicprivate partnerships function in refugee resettlement and the ways in which they can be strengthened.

scholarly journals Decomposing the sources of SARS-CoV-2 fitness variation in the United States

2020 ◽  
Author(s):  
Lenora Kepler ◽  
Marco Hamins-Puertolas ◽  
David A. Rasmussen
Keyword(s):  
United States ◽  
Spatial Heterogeneity ◽  
Genetic Factors ◽  
Population Level ◽  
The United States ◽  
Host Population ◽  
Extrinsic Factors ◽  
Transmission Potential ◽  
Transmission Rates ◽  
Fitness Effects

AbstractThe fitness of a pathogen is composite phenotype determined by many different factors influencing growth rates both within and between hosts. Determining what factors shape fitness at the host population-level is especially challenging because both intrinsic factors like pathogen genetics and extrinsic factors such as host behaviour influence between-host transmission potential. These challenges have been highlighted by controversy surrounding the population-level fitness effects of mutations in the SARS-CoV-2 genome and their relative importance when compared against non-genetic factors shaping transmission dynamics. Building upon phylodynamic birth-death models, we develop a new framework to learn how hundreds of genetic and non-genetic factors have shaped the fitness of SARS-CoV-2. We estimate the fitness effects of all amino acid variants and several structural variants that have circulated in the United States between February and September 2020 from viral phylogenies. We also estimate how much fitness variation among pathogen lineages is attributable to genetic versus non-genetic factors such as spatial heterogeneity in transmission rates. Up to September 2020, most fitness variation between lineages can be explained by background spatial heterogeneity in transmission rates across geographic regions. Furthermore, no genetic variant including the Spike D614G mutation has had a significant effect on population-level fitness. Instead, the rapid increase in the frequency of the Spike D614G can be explained by the variant having a spatial transmission advantage due to first establishing in regions with higher transmission rates during the earliest stages of the pandemic.

scholarly journals A U.S. CLIVAR Project to Assess and Compare the Responses of Global Climate Models to Drought-Related SST Forcing Patterns: Overview and Results

2009 ◽  
Vol 22 (19) ◽  
pp. 5251-5272 ◽  
Author(s):  
Siegfried Schubert ◽  
David Gutzler ◽  
Hailan Wang ◽  
Aiguo Dai ◽  
Tom Delworth ◽  
...  
Keyword(s):  
United States ◽  
Southern Oscillation ◽  
Global Climate ◽  
Global Climate Model ◽  
The United States ◽  
Signal To Noise ◽  
The Pacific ◽  
Precipitation Response ◽  
Sst Forcing ◽  
The Impact

Abstract The U.S. Climate Variability and Predictability (CLIVAR) working group on drought recently initiated a series of global climate model simulations forced with idealized SST anomaly patterns, designed to address a number of uncertainties regarding the impact of SST forcing and the role of land–atmosphere feedbacks on regional drought. The runs were carried out with five different atmospheric general circulation models (AGCMs) and one coupled atmosphere–ocean model in which the model was continuously nudged to the imposed SST forcing. This paper provides an overview of the experiments and some initial results focusing on the responses to the leading patterns of annual mean SST variability consisting of a Pacific El Niño–Southern Oscillation (ENSO)-like pattern, a pattern that resembles the Atlantic multidecadal oscillation (AMO), and a global trend pattern. One of the key findings is that all of the AGCMs produce broadly similar (though different in detail) precipitation responses to the Pacific forcing pattern, with a cold Pacific leading to reduced precipitation and a warm Pacific leading to enhanced precipitation over most of the United States. While the response to the Atlantic pattern is less robust, there is general agreement among the models that the largest precipitation response over the United States tends to occur when the two oceans have anomalies of opposite signs. Further highlights of the response over the United States to the Pacific forcing include precipitation signal-to-noise ratios that peak in spring, and surface temperature signal-to-noise ratios that are both lower and show less agreement among the models than those found for the precipitation response. The response to the positive SST trend forcing pattern is an overall surface warming over the world’s land areas, with substantial regional variations that are in part reproduced in runs forced with a globally uniform SST trend forcing. The precipitation response to the trend forcing is weak in all of the models. It is hoped that these early results, as well as those reported in the other contributions to this special issue on drought, will serve to stimulate further analysis of these simulations, as well as suggest new research on the physical mechanisms contributing to hydroclimatic variability and change throughout the world.

scholarly journals Decomposing the sources of SARS-CoV-2 fitness variation in the United States

2021 ◽  
Vol 7 (2) ◽  
Author(s):  
Lenora Kepler ◽  
Marco Hamins-Puertolas ◽  
David A Rasmussen
Keyword(s):  
United States ◽  
Spatial Heterogeneity ◽  
Genetic Factors ◽  
Population Level ◽  
The United States ◽  
Host Population ◽  
Viral Population ◽  
Extrinsic Factors ◽  
Transmission Rates ◽  
Fitness Effects

Abstract The fitness of a pathogen is a composite phenotype determined by many different factors influencing growth rates both within and between hosts. Determining what factors shape fitness at the host population-level is especially challenging because both intrinsic factors like pathogen genetics and extrinsic factors such as host behavior influence between-host transmission potential. This challenge has been highlighted by controversy surrounding the population-level fitness effects of mutations in the SARS-CoV-2 genome and their relative importance when compared against non-genetic factors shaping transmission dynamics. Building upon phylodynamic birth–death models, we develop a new framework to learn how hundreds of genetic and non-genetic factors have shaped the fitness of SARS-CoV-2. We estimate the fitness effects of all amino acid variants and several structural variants that have circulated in the United States between February 2020 and March 2021 from viral phylogenies. We also estimate how much fitness variation among pathogen lineages is attributable to genetic versus non-genetic factors such as spatial heterogeneity in transmission rates. Before September 2020, most fitness variation between lineages can be explained by background spatial heterogeneity in transmission rates across geographic regions. Starting in late 2020, genetic variation in fitness increased dramatically with the emergence of several new lineages including B.1.1.7, B.1.427, B.1.429 and B.1.526. Our analysis also indicates that genetic variants in less well-explored genomic regions outside of Spike may be contributing significantly to overall fitness variation in the viral population.

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