Total and cause-specific mortality attributable to cold spells in China:A multicity and multicounty study

Climate change has resulted in an increase in the frequency and intensity of extreme cold weather events,but few multicity or multicounty researches have explored the association between cold spells and mortality risk and burden.We collected daily data on climate,sociodemo-graphic factors and mortality in 18 cities/counties across 11 geographical regions for the period of November to March 2014-2018.A distributed lag nonlinear model was used to examine the association between cold spells and mortality after adjustment for confounding factors.Twelve definitions of cold spells were used.Multi-meta regression analysis was applied to pool the impacts over different regions.Cold spells were significantly associated with all-cause mortality at lag 0-21(CRR:1.38,95%CI:1.21,1.57).In addition to respiratory diseases and cir-culatory system diseases,digestive,endocrine and nervous system diseases and injury were also affected by cold spells.The magnitude of the impacts of cold spells on mortality varied among the diseases investigated,with the highest risk estimate found for influenza and pneumonia(CRR:2.00,95%CI:1.45,2.76)and the lowest estimate found for injury(CRR:1.26,95%CI:1.09,1.46).The fraction of all-cause mortality attributable to cold spells was 2.31%(95%CI:0.90%,3.46%).Among the regional differences,the attributable burden of all-cause mortality was higher in rural areas and subtropical monsoon climate zone,with attributable fractions of 2.85%(95%CI:1.23%,4.11%)and 3.36%(95%CI:0.55%,5.35%),respectively.Cold spells increased mortality from a range of diseases.Women,older adults and residents of rural areas and subtropical monsoon climate zone were more vulnerable to cold spells impacts.The findings may help to formulate preventive strategies and early warning response plans to reduce mortality burden of extreme cold events.

Impact of Cold Spells on Ischemic Stroke Severity and Clinical Outcomes in Tianjin, China

There are several studies on the impact of extreme weather on the incidence and mortality of stroke, but the research on the effect of extreme weather events on severity and outcome of ischemic stroke is scarce. This study aimed to evaluate the impact of cold spells on the severity and clinical outcomes of patients with initial acute ischemic stroke in a hospital-based study. We enrolled 553 patients with initial ischemic stroke during the cold seasons between 2016 and 2019. Patients were separated into the mild stroke group and moderate-to-severe stroke group according to the National Institutes of Health Stroke Scale(NIHSS) of the U.S., and good outcome group and poor outcome group according to modified Rankin Scale(mRS) scores. There are nine different definitions of cold spells according to intensities and duration time. After adjustment for climate factors, air quality index, and common risk factors, it is found that cold spells were associated with moderate-to-severe neurological deficits and clinical outcomes in overall ischemic stroke patients. Furthermore, the delay effect for stroke severity started at the beginning of the cold wave(Lag 0) and lasted up to 14 days(Lags 0–14). In addition, when a cold spell was set as a daily mean temperature < 3rd or 5th percentile and with a duration ≥ 2 or 3 consecutive days, cold spells had a significant impact on clinical outcomes, and there was a definite delay effect of at least 7 days(Lags 0–7) and it lasted up to 14days(Lags 0–14). At last, we concluded that cold spells may be a contributory factor for more severe neurological deficits and worse outcomes in patients with initial ischemic stroke.

Circulation Characteristics of Persistent Cold Spells in Central–Eastern North America

The circulation patterns of persistent cold weather spells with durations longer than 10 days in central-eastern North America （United States and Canada; 32° 52°N, 95°-65°W） are investigated by using NCEP reanalysis data from 1948 to 2014. The criteria for the persistent cold spells are： （1） three-day averaged temperature anomalies for the regional average over the central-eastern United States and Canada must be below the 10th percentile, and （2） such extreme cold spells must last at least 10 days. The circulation patterns associated with these cold spells are ex- amined to find the common signals of these events. The circulation anomaly patterns of these cold spells are categor- ized based on the E1 Nifio--Southern Oscillation, Arctic Oscillation （AO）, and other climate indices. The atmospheric circulation patterns that favor the cold spells are identified through composites of geopotential height maps for the cold spells. Negative AO phases favor persistent cold spells. Phases of sea surface temperature （SST） modes that are associated with warm SSTs in the eastern extratropical Pacific also favor persistent cold events in the study region. Stratospheric polar vortex breakdown alone is not a good predictor for the regional extreme cold spells in central-eastern North America. The meridional dispersions of quasi-stationary Rossby waves in the Pacific-North America sector in terms of cut-off zonal wavenumber modulated by background flow are analyzed to provide insight into the difference in evolution of the cold spells under different mean AO phases. The waveguide for AO 〉 1 is in a narrow latitudinal band centered on 40°N, whereas the waveguide for AO 〈 -1 is in a broader latitudinal band from 40° to 65°N. The circulation patterns and lower boundary conditions favorable for persistent cold spells identified by this study can be a stepping-stone for improving winter subseasonal forecasting in North America.