Projections of climate change impacts on crop yields are inherently uncertain1. Uncertainty is often quantified when projecting future greenhouse gas emissions and their influence on climate2. ...However, multi-model uncertainty analysis of crop responses to climate change is rare because systematic and objective comparisons among process-based crop simulation models1, 3 are difficult4. Here we present the largest standardized model intercomparison for climate change impacts so far. We found that individual crop models are able to simulate measured wheat grain yields accurately under a range of environments, particularly if the input information is sufficient. However, simulated climate change impacts vary across models owing to differences in model structures and parameter values. A greater proportion of the uncertainty in climate change impact projections was due to variations among crop models than to variations among downscaled general circulation models. Uncertainties in simulated impacts increased with CO2 concentrations and associated warming. These impact uncertainties can be reduced by improving temperature and CO2 relationships in models and better quantified through use of multi-model ensembles. Less uncertainty in describing how climate change may affect agricultural productivity will aid adaptation strategy development and policymaking.
A geometrical method to determine the vertical distribution of a trace gas in the lower troposphere is presented. The technique is based on quasi-simultaneous measurements of diffuse solar radiation ...with spectrometric equipment observing the atmosphere from different viewing directions and a measurement of a distant lamp. Differential optical absorption spectroscopy (DOAS) algorithms are applied to retrieve the slant column densities (SCDs) of the analyzed compound. A recursive procedure involving the set of observed SCDs, the geometry of measurement, and several offline radiative transfer simulations provides the vertical profile of the target trace gas. This technique is applied to nitrogen dioxide Formula Omitted SCDs, and the results are compared to the output of the modeling system Gas Aerosol Modeling Evaluation System (GAMES). The correlation coefficient between the DOAS and GAMES Formula Omitted concentration profiles is 0.7 and shows a nonnegligible variability as a function of altitude and sky conditions.
The Oceansat-II Scatterometer has completed two years in orbit. The instrument has been declared operational, and the normalized radar cross section Formula Omitted and wind products are being made ...routinely available to the global operational Numerical Weather Prediction community. The Formula Omitted data from the sensor have been rigorously analyzed for the past two years. Efforts have been put to systematically correlate the biases observed in the data to the onboard functionality of the instrument and to precisely quantify these biases. These analyses have helped not only in the refinement of the ground-processing algorithm but also in the evaluation of sensor performance. This paper presents some of the analyses that have been carried out related to instrument noise calibration with reference to deep-space observations, estimation of biases in the signal bandwidth, and estimation of fixed remnant attitude biases. This paper also addresses the means for rectifying these instrument-related biases.
Tremendous efforts have been made to reduce the severe air pollution in China since 2013. However, the annual and peak fine particulate matter (PM
) concentrations during severe events in winter did ...not always reduce as expected. This is partially due to the inter-annual variation of meteorology, which affects the emission, transport, transformation, and deposition processes of air pollutants. In this study, the responses of PM
and ozone (O
) concentrations to changes in emission and meteorology from 2013 to 2015 were investigated based on ambient measurements and the Community Multi-Scale Air Quality (CMAQ) model simulations with anthropogenic emissions. It is found that emission reductions in 2014 and 2015 effectively reduced PM
concentrations by 23.9 and 43.5 μg/m
, respectively, but was partially counteracted by unfavorable meteorology. The negative effects from unfavorable meteorology were significant in extreme pollution events. For example, in December 2015, unfavorable meteorology caused a great increase (90 μg/m
) of PM
in Beijing. Reduction of primary PM and gaseous precursors led to 13.4 and 16.5 ppb increase of O
-8 h daily concentrations in the summertime in 2014 and 2015 in comparison of 2013, which was likely caused by the increase of solar actinic flux due to PM reduction. In addition, reduction of nitrogen oxides (NOx) emissions in areas with negative NOx-O
sensitivity could lead to an increase of O
formation when the reduction of volatile organic compounds (VOCs) was not sufficient. This unintended enhanced O
formation could also lead to higher O
in downwind areas. This study emphasizes the role of meteorology in pollution control, validates the effectiveness of PM
control measures in China, and highlights the importance of appropriate joint reduction of NOx and VOCs to simultaneously decrease O
and PM
for higher air quality.
OMAR V. MÜLLER CEVARCAM, Facultad de Ingeniería y Ciencias Hídricas, Universidad Nacional del Litoral and CONICET, Santa Fe, Argentina ERNESTO HUGO BERBERY Cooperative Institute for Climate and ...Satellites-Maryland, Earth System Science Interdisciplinary Center, University of Maryland, College Park, College Park, Maryland DOMINGO ALCARAZ-SEGURA Departamento de Botánica, Campus de Fuente Nueva, Universidad de Granada, Granada, Spain MICHAEL B. EK Environmental Modeling Center, NOAA/NCEP/NWS, College Park, Maryland (Manuscript received and in final form 30 June 2015) An incorrect version of Fig. 13a was published in Müller et al.
To quantitatively examine the sensitivity of the soil moisture retrieval over agricultural fields, first, we generated a database of radar backscattering coefficients using the first-order vector ...radiative transfer model for various leaf area indices (LAIs), incidence angles, frequencies, and polarizations. Then, soil moisture contents were retrieved from the backscattering coefficients of the database using the water-cloud model (WCM) and Oh et al. 's scattering model. Based on the sensitivity examination for Formula Omitted and Formula Omitted (incidence angle) on soil moisture retrieval, we propose validity regions of soil moisture retrieval over agricultural fields on the Formula Omitted- Formula Omitted plane at L-, C-, and X-bands for vv- and hh-polarizations in the form of Formula Omitted, where the constants Formula Omitted and Formula Omitted are determined in this letter for Formula Omitted-frequency band and pp-polarization. The validity regions were verified with inversion results from synthetic aperture radar (SAR) data of bean and wheat fields.
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