Number Of Cold Days Research Articles

Not Cool: On the Loss of Cold Weather in the Canadian Arctic

ABSTRACT Most studies of climate change in the Arctic report how much warmer the climate is getting. In this study we use 1950–2020 daily observed minimum temperatures at 34 weather stations in Canada’s north to examine how rapidly the region is losing annual occurrences of cold weather (−30°C or colder). Kendall–Theil trend analysis is used to assess the strength and significance of trends. Twenty-nine of the stations were found to have significant negative trends, with an average of 4.89 fewer annual cold days per decade; on average, the stations have lost over 40% of their cold days in recent decades. An ensemble of downscaled Coupled Model Intercomparison Project, phase 5 (CMIP5) models is used to show how the numbers of cold days are projected to change in the coming decades with the representative concentration pathway (RCP4.5 and RCP8.5) scenarios. Finally, we discuss the implications of the loss of cold weather in the Canadian Arctic and beyond.

Simulating compound weather extremes responsible for critical crop failure with stochastic weather generators

Abstract. In 2016, northern France experienced an unprecedented wheat crop loss. The cause of this event is not yet fully understood, and none of the most used crop forecast models were able to predict the event (Ben-Ari et al., 2018). However, this extreme event was likely due to a sequence of particular meteorological conditions, i.e. too few cold days in late autumn–winter and abnormally high precipitation during the spring season. Here we focus on a compound meteorological hazard (warm winter and wet spring) that could lead to a crop loss. This work is motivated by the question of whether the 2016 meteorological conditions were the most extreme possible conditions under current climate, and what the worst-case meteorological scenario would be with respect to warm winters followed by wet springs. To answer these questions, instead of relying on computationally intensive climate model simulations, we use an analogue-based importance sampling algorithm that was recently introduced into this field of research (Yiou and Jézéquel, 2020). This algorithm is a modification of a stochastic weather generator (SWG) that gives more weight to trajectories with more extreme meteorological conditions (here temperature and precipitation). This approach is inspired by importance sampling of complex systems (Ragone et al., 2017). This data-driven technique constructs artificial weather events by combining daily observations in a dynamically realistic manner and in a relatively fast way. This paper explains how an SWG for extreme winter temperature and spring precipitation can be constructed in order to generate large samples of such extremes. We show that with some adjustments both types of weather events can be adequately simulated with SWGs, highlighting the wide applicability of the method. We find that the number of cold days in late autumn 2015 was close to the plausible minimum. However, our simulations of extreme spring precipitation show that considerably wetter springs than what was observed in 2016 are possible. Although the relation of crop loss in 2016 to climate variability is not yet fully understood, these results indicate that similar events with higher impacts could be possible in present-day climate conditions.

Analysis of Climate Change and Extreme Climatic Events in the Lake Victoria Region of Tanzania

The understanding of climate change impacts and the associated climate extreme events at regional and local scales is of critical importance for planning and development of feasible adaptation strategies. In this paper, we present an analysis of climate change and extreme climate events in the Lake Victoria region of Tanzania, focusing on the Kagera and Geita regions. We use daily simulated climate variables (rainfall and minimum and maximum temperatures) from the Coordinated Regional Climate Downscaling Experiment Program Regional Climate Models (CORDEX_RCMs) for the analysis. Extreme climate event, rainfall, and minimum and maximum temperatures time series during historical (1971–2000) climate condition are compared to future climate projection (2011–2100) under two Representative Concentration Pathway (RCP): RCP 4.5 and RCP 8.5 emission scenarios. The existence, magnitude, and statistical significance of potential trends in climate data time series are estimated using the Mann–Kendall (MK) non-parametric test and Theil-SEN slope estimator methods. Results show that during historical (1971–2000) climate, the Lake Victoria region of Tanzania experienced a statistically significant increasing trend in temperature. The annual minimum and maximum temperatures in the Kagera and Geita regions have increased by 0.54–0.69°C, and 0.51–0.69°C, respectively. The numbers of warm days (TX90p) and warm nights (TN90p) during the historical climate have increased, while the numbers of cold days (TX10p) and cold nights (TN10p) have decreased significantly. However, in future climate condition (2011–2100) under both RCP 4.5 and RCP 8.5 emission scenarios, the Lake Victoria region is likely to experience increased temperatures and rainfall. The frequency of cold events (cold days and cold nights) is likely to decrease, while the frequency of warm events (warm days and warm nights) is likely to increase significantly. The number of consecutive wet days, the intensity of very wet days, and the number of extreme wet days are likely to increase. These results indicate that in future climate condition, socioeconomic livelihoods of people in the Kagera and Geita regions are likely to experience significant challenges from climate-related stresses. It is, therefore, recommended that appropriate planning and effective adaptation policies are in place for disaster risk prevention.

ОБОСНОВАНИЕ ПРИМЕНЕНИЯ ТЕПЛОВОЙ ПОДГОТОВКИ НА АВТОМОБИЛЯХ В РАЗНЫХ КЛИМАТИЧЕСКИХ ЗОНАХ

The paper presents the rationale for the feasibility of using an autonomous liquid heater for thermal preparation of the engine in different climatic zones. A comparison is made of operating costs when using an autonomous liquid heater and a car alarm with the function of maintaining the optimum temperature. Several large settlements of the Tyumen region were selected for a comparative calculation. Using climatic portals, the average number of cold days over three years was selected and the number of cold engine starts in each city was determined. The objects of the study were Toyota Land Cruiser Prado cars with different power plants: diesel and gasoline. The calculation does not consider the effect of the autonomous heater on the comfort of use and the technical condition of the vehicle, only the current fuel costs during daily operation are taken into account. In the course of the calculations, it was found that at ambient temperatures up to -150C for a gasoline car and -170C for a diesel car, the use of a pre-starting autonomous liquid heater is not economically viable. The required number of days is also determined to obtain economic benefits from the pre-heater, taking into account the cost of its installation on cars with gasoline and diesel engines. Using the results of the study, it can be concluded that not in all settlements it is advisable to install preheaters. The severity of the climate in some cities does not pose a big threat to a guaranteed cold engine start and may be limited only by using the remote engine start function built into the security system.

A historical perspective on Australian temperature extremes

Global temperature increases are most clearly detected in the shifting distribution of extreme events. Australia’s warming climate has resulted in significant changes in the frequency of temperature extremes, with a general increase in heatwaves and a reduction in the number of cold days. Here, we present the longest historical analysis of daily Australian temperature extremes and their societal impacts compiled to date. We use a newly consolidated early instrumental dataset and a range of historical sources for the South Australia region of Adelaide—the nation’s driest state, containing the most heatwave-affected city in Australia—to investigate any changes in the characteristics of daily temperature extremes back to 1838. We identify multidecadal variability in heatwave and snow event frequency with a peak in the early twentieth century, with an overall decrease in cold extremes and an increase in heatwaves in the region over the 1838–2019 period. Documentary and instrumental records show a decrease in the number of snow events in Adelaide, and a clear increase in the number of heatwaves since the late twentieth century. To gain dynamical insight into historical extremes in South Australia, detailed case studies are presented to compare the synoptic characteristics of historical hot and cold extremes and their impacts. We place a particular emphasis on lesser-known events of the pre-1910 period and rare low-elevation snowfall. Significantly, this is the first study to provide long-term evidence for a reduction of low-elevation snow events and cold outbreaks in Australia. Finally, a discussion is provided on the value and limitations of using historical instrumental and documentary data to assess long-term changes in Australian temperature extremes and their potential to improve future climate change risk assessment.

Spatial variance of spring phenology in temperate deciduous forests is constrained by background climatic conditions

Leaf unfolding in temperate forests is driven by spring temperature, but little is known about the spatial variance of that temperature dependency. Here we use in situ leaf unfolding observations for eight deciduous tree species to show that the two factors that control chilling (number of cold days) and heat requirement (growing degree days at leaf unfolding, GDDreq) only explain 30% of the spatial variance of leaf unfolding. Radiation and aridity differences among sites together explain 10% of the spatial variance of leaf unfolding date, and 40% of the variation in GDDreq. Radiation intensity is positively correlated with GDDreq and aridity is negatively correlated with GDDreq spatial variance. These results suggest that leaf unfolding of temperate deciduous trees is adapted to local mean climate, including water and light availability, through altered sensitivity to spring temperature. Such adaptation of heat requirement to background climate would imply that models using constant temperature response are inherently inaccurate at local scale.

A novel approach for exploring climatic factors limiting current pest distributions: A case study of Bemisia tabaci in north-west Europe and assessment of potential future establishment in the United Kingdom under climate change.

Bemisia tabaci (the tobacco whitefly) is an important agricultural pest of global significance primarily because of its ability to transmit multiple damaging plant viruses. To date, UK outbreaks of the whitefly have been restricted to glasshouses and there are no records of the whitefly establishing outdoors during the summer. This is despite the fact that annual degree-day models (that estimate accumulated warmth over the year above the development threshold), indicate that B. tabaci has the thermal potential for multiple summer generations in the UK. A set of 49 climate indices calculated using the present day climate (1986–2015) were therefore compared between the UK and the south of France, where B. tabaci is able to establish outdoors, to identify the factors limiting its establishment. The number of cold days and nights in summer, as well as the time spent within the whitefly’s optimum temperature range, were most significantly different between the two areas. These indices may impact the development of B. tabaci and offer an explanation for the absence of the whitefly outdoors in the UK during the summer. Further analyses undertaken with climate projections suggest that in a 2–4°C warmer world this pest could pose a risk to outdoor UK crops in July and August. A clear south-north gradient can be demonstrated for these indices. Linking any possible northwards spread of B. tabaci populations outdoors in France with changes in these indices could therefore provide an important indicator of any change in the risks of outdoor populations of this species developing in the UK. The effectiveness of climate indices in pest risk analysis is compellingly demonstrated, and it is recommended that in-depth comparisons of climatic indices between areas of pest presence and absence are conducted in other situations where forecasting the risks of pest establishment are complex and challenging.

IDENTIFIKASI PERUBAHAN CURAH HUJAN DAN SUHU UDARA MENGGUNAKAN RCLIMDEX DI WILAYAH SERANG

Data iklim dianalisis untuk mengidentifikasi perubahan besaran parameter iklim maupun peristiwa iklim ekstrem. Data yang menjadi kajian berasal dari Stasiun Meteorologi Serang, Banten. Tujuan penelitian ini adalah menganalisis karakterisktik data cuaca stasiun pengamatan cuaca Serang terutama pada suhu udara dan curah hujan serta mengidentifikasi perubahan pada pola dan nilai kedua parameter tersebut. Pengolahan data dilakukan dengan menggunakan RClimdex untuk mengetahui adanya perubahan jangka panjang suhu dan curah hujan. Secara keseluruhan slope indeks suhu udara pada stasiun pengamatan Serang mengalami penurunan diantaranya indeks TX10p dan TN10p, yang mengindikasikan jumlah hari dengan suhu minimum pada siang hari dan malam hari mengalami penurunan. Pada stasiun Serang slope indeks suhu udara (TN90p) cenderung meningkat yang mengindikasikan suhu minimum lebih hangat. Indeks curah hujan hampir seluruhnya mengalami penurunan kecuali CDD yang menunjukkan peningkatan jumlah hari tanpa hujan berturut-turut di wilayah Serang.

Cold spells in Poland and Germany and their circulation conditions

The primary objective of this paper was to determine the circulation conditions of the occurrence of cold spells in Poland and Germany. The observed inconsiderable warming slightly contributed to a change in the number of cold days and cold spells. The occurrence of cold spells in Poland and Germany was related to considerably more active and intensive pressure systems than on average in the winter season in the studied years. A strong high pressure system was located over much of the continent, blocking westerly circulation. During the occurrence of cold spells, negative anomalies of isobaric surface heights were recorded with the greatest anomalies being in the 300–250 hPa heights. The highest air temperature anomalies were recorded on the lowest isobaric levels, where they amounted to <−10°C. On average, anomalies on the 300 hPa isobaric level began developing approximately 9 days before the beginning of cold spells over the study area. The decay of cold spells was not related to rapid exchange of air masses, but rather to gradual weakening of anomalies in the upper troposphere, and their shifting westwards.

Temporal Characteristics of Heat Waves and Cold Spells and Their Links to Atmospheric Circulation in EURO-CORDEX RCMs

We study summer heat waves and winter cold spells and their links to atmospheric circulation in an ensemble of EURO-CORDEX RCMs in Central Europe. Results of 19 simulations were compared against observations over 1980–2005. Atmospheric circulation was represented by circulation types and supertypes derived from daily gridded mean sea level pressure. We examined observed and simulated characteristics of hot and cold days (defined using percentiles of temperature anomalies from the mean annual cycle) and heat waves and cold spells (periods of at least three hot/cold days in summer/winter). Although the ensemble of RCMs reproduces on average the frequency and the mean length of heat waves and cold spells relatively well, individual simulations suffer from biases. Most model runs have an enhanced tendency to group hot/cold days into sequences, with several simulations leading to extremely long heat waves or cold spells (the maximum length overestimated by up to 2-3 times). All simulations also produce an extreme winter season with (often considerably) higher number of cold days than in any observed winter. The RCMs reproduce in general the observed circulation significantly conducive to heat waves and cold spells. Zonal flow reduces the probability of temperature extremes in both seasons, while advection of warm/cold air from the south-easterly/north-easterly quadrant plays a dominant role in developing heat waves/cold spells. Because of these links, the simulation of temperature extremes in RCMs is strongly affected by biases in atmospheric circulation. For almost all simulations and all circulation supertypes, the persistence of supertypes is significantly overestimated (even if the frequency of a given supertype is underestimated), which may contribute to development of too-long heat waves/cold spells. We did not identify any substantial improvement in the EURO-CORDEX RCMs in comparison to previous ENSEMBLES RCMs, but the patterns of the biases are generally less conclusive as to general RCMs’ drawbacks.

Long‐Term Changes in Wintertime Temperature Extremes in Moscow and Their Relation to Regional Atmospheric Dynamics

AbstractInterannual variability and long‐term changes in winter air temperature extremes in Moscow (1949–2017) are investigated using observational and reanalysis data. Significant interdecadal changes in principal characteristics of temperature extremes are revealed. Strong warming (0.50 °K per decade) is identified contrasting to the previously identified summer trend of 0.25 °K per decade. This is attributable to middle‐to‐late winter. Winter and summer daily air temperature variabilities are fundamentally different with wintertime anomalies strongly negatively skewed, while summer displays Gaussian variability. A reduction in the number of cold days and an increase in warm days in December and March are found. In January and February, the probability of warm extremes increases, while the probability of cold extremes remains constant. Intensification of January extremes (cold and warm) is revealed along with daily temperature variability reduction. In aggregate, potential shortening of Moscow's winter season, suppression of the previously strong seasonal cycle in daily temperature variability, and intensification of midwinter extremes are identified. Dynamical linkages are found to North Atlantic and Mediterranean storm track variability as well as synoptic activity over the Barents‐Kara Seas. Lagrangian analysis shows associations of wintertime extreme warm events to air masses originating over the North Atlantic and Mediterranean regions. Air masses implicated in cold extremes are mostly of Siberian and Arctic origin. On interannual time scales cold event frequency in Moscow is impacted by the negative phase of North Atlantic Oscillation, whereas frequency of warm events is influenced by the positive phase of North Atlantic Oscillation and the negative phase of Scandinavian teleconnection.

Circulation‐Conditioned Wintertime Temperature Bias in EURO‐CORDEX Regional Climate Models Over Central Europe

AbstractWe analyze circulation‐conditioned wintertime temperature biases in regional climate models (RCMs) over Central Europe and link them to simulation of cold days. Daily minimum and maximum temperatures from the European Coordinated Regional Climate Downscaling Experiment RCMs are evaluated against reference data from the E‐OBS gridded data set. Flow direction is analyzed through u‐ and v‐wind components at the 850‐hPa pressure level taken from the ERA‐Interim reanalysis. Cloud cover and snow‐area fraction from the same reanalysis are used to associate the temperature biases with physical mechanisms. Distribution of flow directions during cold days is evaluated using efficiency coefficients, calculated as ratios of the relative abundance of flow directions during cold days and their wintertime climatology. RCMs driven by the reanalysis have both positive and negative minimum temperature biases, ranging from +0.7 to −2.7 °C. By contrast, all reanalysis‐driven RCMs have negative maximum temperature biases, especially during northerly and westerly advection, which is probably related to overestimated cloud cover. The too‐cold westerly and northerly flows are associated with an overestimated number of cold days and relatively high values of efficiency coefficients under these directions. Efficiency coefficients are simulated better under southeasterly advection, during which the temperature bias tends to be the lowest. The results suggest that simulated cold events should be analyzed and interpreted with caution, since they may develop also under zonal flow in some models, which contradicts observations.

How have daily climate extremes changed in the recent past over northeastern Argentina?

Abstract Changes in climate extremes affect socioeconomics and natural systems in northeastern Argentina (NEA) and may increase its vulnerability leading to unprecedented disasters. This study investigates the long-term changes and interannual variability of daily temperature and precipitation climate extremes and assesses to what extent global reanalyses reproduce the observed variability in the recent past. Datasets include quality-controlled observations (1963–2013) and ERA-Interim and NCEP2 reanalyses (1979–2011). Climate extremes are characterized spatially and temporally by 15 indices proposed by the Expert Team on Climate Change Detection and Indices. The leading modes of the area-averaged index time series were obtained by means of a Singular Spectrum Analysis, while the spatial distribution of mean changes was estimated by fitting nonparametric linear trends to each index time series. The results show that temperature extremes are changing towards warmer conditions. The number of warm days has been increasing since 1990 while the number of cold days has been decreasing. Warm and cold nights show a significant signal of warming that seems to be stabilizing in recent decades. Heat waves almost double the frequency and duration of cold waves, and the duration of heat waves increased while cold spells decreased in last decades. Longer heat waves are related to longer dry spells. On the other hand, the number of frost days remained stable although they exhibit high interannual and decadal variability. As well, intense precipitation events in most of the region increased steadily since 1970. The annual maximum amount of 1-day and 5-day precipitation events increased from the 1970s to the 2000s, stabilizing in recent years. The ERA-Interim and NCEP2 reanalyses represent climate extremes with different success. ERA-Interim can recognize temperature extremes in time and space, while the older NCEP2 presents systematic positive errors and has some difficult to replicate the interannual variability of the number of summer days. Both reanalyses reproduce dry spells and the annual maximum 5-day precipitation with large biases, which are particularly noticeable at each observation station. Although reanalyses would be expected to add information for climate extremes in areas of scarce observations like northeastern Argentina, they still need to be used with great caution and only as a complement to observations, especially in studies focusing on precipitation extremes.

Cold Waves in Poznań (Poland) and Thermal Conditions in the City during Selected Cold Waves

The objective of the paper was to characterize the occurrence of cold days and cold waves in Poznań in the years 1966/67–2015/16, as well as to characterize thermal conditions in the city during selected cold waves in the years 2008/09–2015/16. The study was based on daily data on maximum and minimum air temperature for station Poznań-Ławica from the years 1966/67–2015/16 and daily air temperature values from eight measurement points located in the territory of the city in different types of land use from the years 2008/08–2015/16. In addition, to characterize thermal conditions during selected days forming cold waves, satellite images were used, on the basis of which the land surface temperature (LST) was calculated. A cold day was defined as a day with daily maximum temperature (Tmax) below the value of 5th annual percentile of Tmax, and a cold wave was defined as at least five consecutive cold days. The study showed an increase in Tmax in winter, which translated to a decrease in the number of cold days over the last 50 years, although the changes were not statistically significant. Thermal conditions in the city showed high variability in the winter season and during the analyzed cold waves.

Unidirectional trends in annual and seasonal climate and extremes in Egypt

The presence of short- and long-term autocorrelations can lead to considerable change in significance of trend in hydro-climatic time series. Therefore, past findings of climatic trend studies that did not consider autocorrelations became a questionable issue. The spatial patterns in the trends of annual and seasonal temperature, rainfall, and related extremes in Egypt have been assessed in this paper using modified Mann-Kendal (MMK) trend test which can detect unidirectional trends in time series in the presence of short- and long-term autocorrelations. The trends obtained using the MMK test was compared with that obtained using standard Mann-Kendall (MK) test to show how natural variability in climate affects the trends. The daily rainfall and temperature data of Princeton Global Meteorological Forcing for the period 1948–2010 having a spatial resolution of 0.25° × 0.25° was used for this purpose. The results showed a large difference between the trends obtained using MMK and MK tests. The MMK test showed increasing trends in temperature and a number of temperature extremes in Egypt, but almost no change in rainfall and rainfall extremes. The minimum temperature was found to increase (0.08–0.29 °C/decade) much faster compared to maximum temperature (0.07–0.24 °C/decade) and therefore, a decrease in diurnal temperature range (− 0.01 to − 0.16 °C/decade) in most part of Egypt. The number of winter hot days and nights are increasing, while the number of cold days is decreasing in most part of the country. The study provides a more realistic scenario of the changes in climate and weather extremes of Egypt.

Air temperature conditions in northern Nordaustlandet (NE Svalbard) at the end of World War II

This article presents the results of an investigation into air temperature conditions in northern Nordaustlandet (NE Svalbard) based on meteorological observations made by German soldiers towards the end of World War II (1944/1945) and 4 months after its end. Traditional analysis using mean monthly data was supplemented by a detailed analysis based on daily data: maximum temperature, minimum temperature and diurnal temperature range. The latter kind of data made it possible to study such aspects of climate as the number of “characteristic days” (i.e., the number of days with temperatures exceeding specified thresholds), day‐to‐day temperature variability, and duration, onset and end dates of thermal seasons. The results from Nordaustlandet for the warmest period of the early 20th century warming period (ETCWP) were compared with temperature conditions both historical (the end part of the Little Ice Age) and contemporary (different sub‐periods taken from the years 1981–2017) to estimate the range of warming during the ETCWP.Analysis reveals that the expedition year 1944/1945 in Nordaustlandet was, in the majority of months, the warmest of all analysed periods, that is, both historical and contemporary periods. The study period was markedly warmer than 1981–2010 (mean annual −6.5 vs. −8.4 °C) but colder than the periods 2011–2016 (−5.7 °C) and 2014–2017 (−5.8 °C). The majority of mean monthly air temperatures in the ETCWP lies within two standard deviations of the modern 2014–2017 mean. This means that values of air temperature in the study period lie within the range of recent temperature variability. All other thermal characteristics show changes in accordance with expectations associated with general warming of the Arctic (i.e., a decrease in diurnal temperature range and number of cold days, and an increase in number of warm days). The latter days were most common in the ETCWP.

Mean and extreme temperatures in a warming climate: EURO CORDEX and WRF regional climate high-resolution projections for Portugal

Large temperature spatio-temporal gradients are a common feature of Mediterranean climates. The Portuguese complex topography and coastlines enhances such features, and in a small region large temperature gradients with high interannual variability is detected. In this study, the EURO-CORDEX high-resolution regional climate simulations (0.11° and 0.44° resolutions) are used to investigate the maximum and minimum temperature projections across the twenty-first century according to RCP4.5 and RCP8.5. An additional WRF simulation with even higher resolution (9 km) for RCP8.5 scenario is also examined. All simulations for the historical period (1971–2000) are evaluated against the available station observations and the EURO-CORDEX model results are ranked in order to build multi-model ensembles. In present climate models are able to reproduce the main topography/coast related temperature gradients. Although there are discernible differences between models, most present a cold bias. The multi-model ensembles improve the overall representation of the temperature. The ensembles project a significant increase of the maximum and minimum temperatures in all seasons and scenarios. Maximum increments of 8 °C in summer and autumn and between 2 and 4 °C in winter and spring are projected in RCP8.5. The temperature distributions for all models show a significant increase in the upper tails of the PDFs. In RCP8.5 more than half of the extended summer (MJJAS) has maximum temperatures exceeding the historical 90th percentile and, on average, 60 tropical nights are projected for the end of the century, whilst there are only 7 tropical nights in the historical period. Conversely, the number of cold days almost disappears. The yearly average number of heat waves increases by seven to ninefold by 2100 and the most frequent length rises from 5 to 22 days throughout the twenty-first century. 5% of the longest events will last for more than one month. The amplitude is overwhelming larger, reaching values which are not observed in the historical period. More than half of the heat waves will be stronger than the extreme heat wave of 2003 by the end of the century. The future heatwaves will also enclose larger areas, approximately 100 events in the 2071–2100 period (more than 3 per year) will cover the whole country. The RCP4.5 scenario has in general smaller magnitudes.

The Effects of Forest Area Changes on Extreme Temperature Indexes between the 1900s and 2010s in Heilongjiang Province, China

Land use and land cover changes (LUCC) are thought to be amongst the most important impacts exerted by humans on climate. However, relatively little research has been carried out so far on the effects of LUCC on extreme climate change other than on regional temperatures and precipitation. In this paper, we apply a regional weather research and forecasting (WRF) climate model using LUCC data from Heilongjiang Province, that was collected between the 1900s and 2010s, to explore how changes in forest cover influence extreme temperature indexes. Our selection of extreme high, low, and daily temperature indexes for analysis in this study enables the calculation of a five-year numerical integration trail with changing forest space. Results indicate that the total forested area of Heilongjiang Province decreased by 28% between the 1900s and 2010s. This decrease is most marked in the western, southwestern, and northeastern parts of the province. Our results also reveal a remarkable correlation between change in forested area and extreme high and low temperature indexes. Further analysis enabled us to determine that the key factor explaining increases in extreme high temperature indexes (i.e., calculated using the number of warm days, warm nights, as well as tropical nights, and summer days) is decreasing forest area; data also showed that this factor caused a decrease in extreme low temperature indexes (i.e., calculated using the number of cold days and cold nights, as well as frost days, and ice days) and an increase in the maximum value of daily minimum temperature. Spatial data demonstrated that there is a significant correlation between forest-to-farmland conversion and extreme temperature indexes throughout most of our study period. Spatial data demonstrated that there is a significant correlation between forest-to-farmland conversion and extreme temperature indexes throughout most of our study period. Positive correlations are also present between decreasing forest area, the more frequent occurrence of extreme high temperature events, and a rise in the maximum value of daily minimum temperature. At the same time, we found clear negative correlations between decreasing forest area and less frequent occurrence of extreme low temperature events.

Investigation of Arctic air temperature extremes at north of 60°N in winter

Air temperature is a key index reflecting climate change. Air temperature extremes are very important because they strongly influence the natural environment and societal activities. The Arctic air temperature extremes north of 60°N are investigated in the winter. Daily data from 238 stations at north of 60°N from the global summary of the day for the period 1979–2015 are used to study the trends of cold days, cold nights, warm days and warm nights during the wintertime. The results show a decreasing trend of cold days and nights (rate of–0.2 to–0.3 d/a) and an increasing trend of warm days and nights (rate of +0.2 to +0.3 d/a) in the Arctic. The mean temperature increases, which contributes to the increasing (decreasing) occurrence of warm (cold) days and nights. On the other hand, the variance at most stations decreased, leading to a reduced number of cold events. A positive AO (Arctic Oscillation) index leads to an increased (decreased) number of warm (cold) days and nights over northern Europe and western Russia and an increased (decreased) number of cold (warm) days and nights over the Bering Strait and Greenland. The lower extent of Arctic autumn sea ice leads to a decreased number of cold days and nights. The occurrences of abrupt changes are detected using the Mann-Kendall method for cold nights occurring in Canada in 1998 and for warm nights occurring in northwestern Eurasia in 1988. This abrupt change mainly resulted from the mean warming induced by south winds and an increased North Atlantic sea surface temperature.

Risk of sudden cardiac death in relation to season-specific cold spells: a case–crossover study in Finland

ObjectiveTo test a priori hypothesis of an association between season-specific cold spells and sudden cardiac death (SCD).MethodsWe conducted a case–crossover study of 3614 autopsy-verified cases of SCD in the Province...