Publications by authors named "Ehsan Najafi"

4 Publications

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Larger-scale ocean-atmospheric patterns drive synergistic variability and world-wide volatility of wheat yields.

Sci Rep 2020 03 23;10(1):5193. Epub 2020 Mar 23.

Civil Engineering Department, The City College of New York, The City University of New York, New York City, 10031, USA.

Diagnosing potential predictability of global crop yields in the near term is of utmost importance for ensuring food supply and preventing socio-economic consequences. Previous studies suggest that a substantial proportion of global wheat yield variability depends on local climate and larger-scale ocean-atmospheric patterns. The science is however at its infancy to address whether synergistic variability and volatility (major departure from the normal) of multi-national crop yields can be potentially predicted by larger-scale climate drivers. Here, using observed data on wheat yields for 85 producing countries and climate variability from 1961-2013, we diagnose that wheat yields vary synergistically across key producing nations and can also be concurrently volatile, as a function of shared larger-scale climate drivers. We use a statistical approach called robust Principal Component Analysis (rPCA), to decouple and quantify the leading modes (PC) of global wheat yield variability where the top four PCs explain nearly 33% of the total variance. Diagnostics of PC1 indicate previous year's local Air Temperature variability being the primary influence and the tropical Pacific Ocean being the most dominating larger-scale climate stimulus. Results also demonstrate that world-wide yield volatility has become more common in the current most decades, associating with warmer northern Pacific and Atlantic oceans, leading mostly to global supply shortages. As the world warms and extreme weather events become more common, this diagnostic analysis provides convincing evidence that concurrent variability and world-wide volatility of wheat yields can potentially be predicted, which has major socio-economic and commercial importance at the global scale, underscoring the urgency of common options in managing climate risk.
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http://dx.doi.org/10.1038/s41598-020-60848-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7090071PMC
March 2020

Data of variability and joint variability of global crop yields and their association with climate.

Data Brief 2019 Apr 8;23:103745. Epub 2019 Mar 8.

Civil Engineering Department, The City College of New York, The City University of New York, New York City, 10031, USA.

We present the output data of Robust Principal Component Analysis (RPCA) applied to global crop yield variability of maize, rice, sorghum and soybean (MRSS) as presented in the publication "Climate drives variability and joint variability of global crop yields" (Najafi et al., 2019). Global maps of the correlation between all the principal components (PCs) acquired from the low rank matrix (L) of MRSS and Palmer Drought Severity Index (PDSI), air temperature anomalies (ATa) and sea surface temperature anomalies (SSTa) are provided in this article. We present co-varying countries, impacted cropland areas across global countries, and 10 global regions by climate and the association between PCs and multiple atmospheric and oceanic indices. Moreover, the joint dependency between PCs of MRSS yields are presented using two different approaches.
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http://dx.doi.org/10.1016/j.dib.2019.103745DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6660635PMC
April 2019

Climate drives variability and joint variability of global crop yields.

Sci Total Environ 2019 Apr 17;662:361-372. Epub 2019 Jan 17.

Civil Engineering Department, The City College of New York, The City University of New York, 10031 New York City, USA; NOAA Center for Earth System Sciences and Remote Sensing Technologies (NOAA-CREST), The City College of New York, The City University of New York, 10031 New York City, USA.

In this study, long-term national-based yields of maize, rice, sorghum and soybean (MRSS) from 1961 to 2013 are decomposed using Robust Principal Component Analysis (RPCA). After removing outliers, the first three principal components (PC) of the persistent yield anomalies are scrutinized to assess their association with climate and to identify co-varying countries and crops. Sea surface temperature anomalies (SSTa), atmospheric and oceanic indices, air temperature anomalies (ATa) and Palmer Drought Severity Index (PDSI) are used to study the association between the PCs and climate. Results show that large-scale climate, especially El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) are strongly correlated with crop yield variability. Extensive maize harvesting regions in Europe and North America, rice in South America, Oceania and east of Asia, sorghum in west and southeast of Asia, North America and Caribbean and soybean in North and South America, Oceania and south of Asia experienced the influence of local climate variability in this period. Sorghum yield variability across the globe exhibits significant correlations with many atmospheric and oceanic indices. Results indicate that not only do the same crops in many countries co-vary significantly, but different crops, in particular maize, in different PCs also co-vary with other crops. Identifying the association between climate and crop yield variability and recognizing similar and dissimilar countries in terms of yield fluctuations can be informative for the identified nations with regard to the periodic and predictable nature of many large-scale climatic patterns.
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http://dx.doi.org/10.1016/j.scitotenv.2019.01.172DOI Listing
April 2019

Prevalence and Associated Risk Factors of Hyperglycemia and Diabetes Mellitus Among HIV Positive Patients in Tehran, Iran.

Infect Disord Drug Targets 2019 ;19(3):304-309

Iranian Research Center for HIV/AIDS, Iranian Institute for Reduction of High-Risk Behaviors, Tehran University of Medical Sciences, Tehran, Iran.

Background: The introduction of Antiretroviral Therapy (ART) has resulted in the emergence of some metabolic complications including hyperglycemia and diabetes mellitus among HIV positive patients. The aim of this study was to investigate the prevalence of hyperglycemia, diabetes mellitus and their associated risk factors in HIV positive patients.

Methods: This cross-sectional study was conducted on HIV positive patients who visited Voluntary Counseling and Testing (VCT) center of Imam Khomeini Hospital, Tehran, Iran (2004-2013). Medical records of patients were reviewed retrospectively. A logistic regression model was applied for analysis of the association between glycemic status and relevant risk factors.

Results: Out of 480 patients who were included in this study, 267 (55.6%) had hyperglycemia, including 28 (5.8%) with diabetes mellitus and 239 (49.8%) with pre-diabetes. The higher frequency of hyperglycemia, was found to be significantly associated with older age (OR for patients ˃40 years old, 2.260; 95% CI, 1.491, 3.247), male gender (OR, 1.555; 95% CI, 1.047, 2.311), higher Body Mass Index (OR for patients with BMI˃25 Kg/m², 1.706; 95% CI, 1.149, 2.531) and prolonged duration of HIV infection (OR for patients with duration of HIV infection ≥60 months, 2.027; 95% CI, 1.372, 2.992).

Conclusion: Hyperglycemia, especially pre-diabetes, is highly frequent among Iranian people living with HIV. Male gender, older age, prolonged duration of HIV infection, and higher BMI were associated with a higher prevalence of hyperglycemia. Hence, it is important to screen all HIV infected patients at the time of diagnosis and then periodically for hyperglycemia.
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http://dx.doi.org/10.2174/1871526518666180723152715DOI Listing
February 2020