Average Annual Number Of Days Research Articles

Assessing the impact of climate change and reservoir operation on the thermal and ice regime of mountain rivers using the XGBoost model and wavelet analysis

AbstractThis study presents an analysis of the influence of climatic conditions and the operation of a dam reservoir on the occurrence of ice cover and water temperature in two rivers (natural and transformed by reservoir operations) located in the Carpathian Mountains (central Europe). The analyses are based on data obtained from four hydrological and two climatological stations. The Extreme Gradient Boosting (XGBoost) machine learning model was used to quantitatively separate the effects of climate change from the effects arising from the operation of the dam reservoir. An analysis of the effects of reservoir operation on the phase synchronization between air and river water temperatures based on a continuous wavelet transform was also conducted. The analyses showed that there has been an increase in the average air temperature of the study area in November by 1.2 °C per decade (over the period 1984–2016), accompanied by an increase in winter water temperature of 0.3 °C per decade over the same period. As water and air temperatures associated with the river not influenced by the reservoir increased, there was a simultaneous reduction in the duration of ice cover, reaching nine days per decade. The river influenced by the dam reservoir showed a 1.05 °C increase in winter water temperature from the period 1994–2007 to the period 1981–1994, for which the operation of the reservoir was 65% responsible and climatic conditions were 35% responsible. As a result of the reservoir operation, the synchronization of air and water temperatures was disrupted. Increasing water temperatures resulted in a reduction in the average annual number of days with ice cover (by 27.3 days), for which the operation of the dam reservoir was 77.5% responsible, while climatic conditions were 22.5% responsible.

Optimizing the Flood Limit Water Level of Reservoirs in Sediment-Laden Rivers under Changing Water and Sediment Conditions: A Case Study of the Xiaolangdi Reservoir

Optimizing the flood limit water level (FLWL) of reservoirs in sediment-laden rivers under changing water and sediment conditions is an important research topic that could improve comprehensive utilization benefits. Because reservoir operation has multiple objectives in sediment-laden rivers, this study established a water–sediment mathematical model, a comprehensive benefit evaluation model, and an evaluation index system. Taking the Xiaolangdi Reservoir of the Yellow River as an example, the operation mode of the FLWL under changing water and sediment conditions was studied. Under the scenarios of incoming sediment amounts of 300–800 million tons, when using the operation mode of gradually raising the FLWL, the sediment retention period was 4–13 years longer; the lower average annual siltation of the downstream channel and minimum bank-full discharge of the downstream channel after 50 years was larger by 150–260 m3/s than the operation mode of raising the FLWL at one time. However, with enhanced benefits of sediment blocking and siltation reduction, other benefits such as water resources supply, hydropower generation, and ecological improvement are reduced. The average annual number of days that do not meet the downstream water resources supply requirements, irrigation, and ecological improvement was increased by 0.64–2.16 days, and 91–197 million kW·h reduced average annual hydropower generation. The critical amount of incoming sediment was 350 million for conversion between the two FLWL operation modes, and it will increase to 450 million tons if the incoming runoff of the Yellow River increases by 20%. After constructing the Guxian Reservoir in the middle of the Yellow River, the critical amount of incoming sediment will increase to 600 million tons. This study is of great significance for improving the utilization efficiency of water resources and promoting the socio-economic development of river basins.

Analysis of the dynamics and precipitation regime in the cross-border region Poland-Belarus- Ukraine (2010-2018)


 
 
 The work analyzes the dynamics and regime of atmospheric precipitation in the cross-border region of Poland-Belarus-Ukraine during the period 2010-2018. This time period was chosen, in particular, due to the need to find the prerequisites for the strong shallowing of lake complexes and the depletion of groundwater in the Polish region in 2019, which caused significant social and scientific resonance. The source data for the statistical part of the work were archival information from 17 weather stations in the specified region for this period. The main results of the study: 1) the dynamics of the average monthly precipitation amounts for each meteorological station were calculated and analyzed (Lutsk, Svityaz, Manevychi, Kovel, Liubeshiv, Volodymyr, Rivne, Dubno, Sarny, Brody, Rava-Ruska, Kamianka-Buzka, Pinsk, Pruzhany, Terespol, Wlodawa, Zamosc), the average amounts of precipitation that fell during the warm season of the year (IV-X months) and the cold season of the year (XI-III months), average annual precipitation amounts and precipitation amounts for the entire period, which was investigated (2010-2018). All calculated indicators were compared with the data of the climatic norm of 1961-1990). The annual number of days with precipitation, the warm and cold periods of the year, and the average values of this indicator were also determined. Based on the results of the statistical analysis, charts, cartograms, and several diagrams were developed that visually represent the peculiarities of the dynamics of atmospheric precipitation in the studied region during the analyzed period (2010-2018). 2) on the basis of the calculated indicators, maps of the geographical distribution of precipitation amounts on the territory of the cross-border region Poland-Belarus-Ukraine during the studied period (annual amounts, cold and warm season amounts) were constructed. When comparing them with maps of the period of the 20th century. Changes in the geography of distribution and trends of modern growth of precipitation amounts in the study region were revealed. After the analysis, a number of conclusions and generalizations were made: 1. During the period 2010-2018 in the territory of the cross-border region Poland-Belarus- Ukraine, the average annual amounts of precipitation increased by 20-45 mm compared to the climatic standard, while the average annual number of days with precipitation decreased by 25-30%. 2. Annual amounts of precipitation exceeded 600 mm at almost all (16 out of 17) meteorological stations whose data were analyzed. 3. The distribution of days with atmospheric precipitation during the seasons of the year has changed. The ratio between the amounts of precipitation that fell in the warm and cold periods of the year changed from 75/25 to 60/40 on average. In general, in the studied region, there are trends towards a slight increase in annual precipitation amounts, a redistribution of precipitation amounts in liquid and solid state in favor of rains, and a reduction in the total number of days with precipitation during the year and a more even distribution of them during the warm and cold seasons, compared to the climatic norm.
 
 

Региональные особенности грозовой активности (на примере территории Кабардино-Балкарской Республики)

Introduction. Thunderstorm activity refers to one of the regional climatic characteristics of a limited area. Thunderstorms result in lightning discharges and an increase in the electric field strength of the surface layer of the atmosphere. Considered lightning discharges, which are divided into positive and negative. The number of thunderstorm days recorded on the territory of the KBR for the period from 2012 to 2022 was analyzed and calculated. It is shown that the relief and climate of the study area contribute to the heterogeneous development of thunderstorm processes. Materials and research methods. The lightning direction finding network of the Federal State Budgetary Institution "VGI" with spatially separated sensors LS8000 and LS7002 was used in the work. To determine the characteristics of thunderstorm activity, we used long-term data from the specified lightning direction finding network. The analysis of data from the LS8000 lightning direction finding system (GPS) confirms that ground-based lightning is unevenly distributed over the territory of the Kabardino-Balkarian Republic. For the analysis of thunderstorm activity, data over the period 2012 to 2022 were used. The following characteristics were studied the long-term course: the number of thunderstorm days in different months of the year; the total number of lightning of all types registered in the territory of the Kabardino-Balkarian Republic; number of lightnings of negative polarity; number of registered positive lightning; values (peak) of lightning currents in ground discharges; average air temperature for the warm period of the year. Research results and their discussion. During the studied period of time on the territory of the KBR, 869 days with a thunderstorm were recorded by the lightning registration system. A day was considered a thunderstorm if at least four lightning strikes were recorded per day. The largest number of days with 90 thunderstorms were noted in 2016 and 2018; the smallest number of days with thunderstorms was noted in 2022. This year, according to the data of Roshydromet, weather stations on the territory of the KBR, was marked as the driest year. The average annual number of days with thunderstorms in the considered time interval was 79 days, which is 19 more than recommended for lightning protection measures. Conclusions. The analysis performed showed a trend towards a decrease in thunderstorm activity on the territory of the Kabardino-Balkarian Republic, as well as the values of the number of lightning per year of negative polarity. Linear trend expressions for the indicated characteristics are obtained.

Synoptic circulation patterns associated with foehn days in Sofia in the period 1979–2014

Foehn is a well-known example of local atmospheric circulation and is an extreme weather event for wind gusts. It can cause rapid snowmelt in spring or spread of forest fire in summer, as well as significant economic losses. The foehn in Bulgaria is observed on the northern slopes of the mountains. For the period 1979–2014, 261 foehn days are registered north of the Vitosha mountain, where Sofia valley is located. The average annual number of foehn days is 8.1, 8.3, and 4.5 for the periods 1985–1994, 1995– 2004, and 2005–2014. After 2004, the average annual number of days with foehn decreases, and the lowest maximum wind gusts are registered. To check whether atmospheric circulation changes, could be the reason for this change two objective circulation classifications and a manual one are used to study the foehn occurrence in the Sofia valley. Based on the GrossWettertypen (GWT) catalogue of circulation patterns produced by the COST Action 733 and ten circulation types of the Jenkinson-Collison (JCT) catalogue of weather types the largest number of foehn days occur at the SW, W, and NW circulation patterns. GWT and JCT classifications with 26 types confirm the foehn occurrence during the W and SW flows, but add two more cyclonic types, the CW and CSW. For the foehn days in March 1979–2014, best agreement was found with the manual circulation classification with 26 types. A comparison between the decades 1995–2004 and 2005–2014 shows a substantial decrease in western and northwestern circulation types during the foehn days. An analysis of circulation types for all days confirms an overall reduction of W and NW circulation types after 2004.

Downscaling of Future Precipitation in China’s Beijing-Tianjin-Hebei Region Using a Weather Generator

To project local precipitation at the existing meteorological stations in China’s Beijing-Tianjin-Hebei region in the future, local daily precipitation was simulated for three periods (2006–2030, 2031–2050, and 2051–2070) under RCP 4.5 and RCP 8.5 emission scenarios. These projections were statistically downscaled using a weather generator (BCC/RCG-WG) and the output of five global climate models. Based on the downscaled daily precipitation at 174 stations, eight indices describing mean and extreme precipitation climates were calculated. Overall increasing trends in the frequency and intensity of the mean and extreme precipitation were identified for the majority of the stations studied, which is in line with the GCMs’ output. However, the downscaling approach enables more local features to be reflected, adding value to applications at the local scale. Compared with the baseline during 1961–2005, the regional average annual precipitation and its intensity are projected to increase in all three future periods under both RCP 4.5 and RCP 8.5. The projected changes in the number of days with precipitation are relatively small across the Beijing-Tianjin-Hebei region. The regional average annual number of days with precipitation would increase by 0.2~1.0% under both RCP 4.5 and RCP 8.5, except during 2031–2050 under RCP 8.5 when it would decrease by 0.7%. The regional averages of annual days with precipitation ≥25 mm and ≥40 mm, the greatest one-day and five-day precipitation in the Beijing-Tianjin-Hebei region, are projected to increase by 8~30% during all the three periods. The number of days with daily precipitation ≥40 mm was projected to increase most significantly out of the eight indices, indicating the need to consider increased flooding risk in the future. The average annual maximum number of consecutive days without precipitation in the Beijing-Tianjin-Hebei region is projected to decrease, and the drought risk in this area is expected to decrease.

Hailstorm risk assessment for crop areas in Moldova Region (Romania)

Estimating the impact of hail on agricultural land is needed in order to streamline damage reduction methods. In this regard, hail risk maps were prepared for the region of Moldova for the main types of crops (wheat and rye, corn, potato, sugar beet, sunflower, vegetables, orchards and vineyards). The methodology that we used consists in determining the risk map, as the product between the hazard map (average annual number of days with hail), the exposure map (agricultural crop value) and the vulnerability map (the percentage occupied by a certain agricultural crop in the administrative units). Areas with severe hail risk are in the eastern half of Vrancea County, the western part of Galati County and the northeastern part of Iasi County, where there are large areas cultivated with vines, orchards and vegetables. In Vaslui County, the most exposed ATUs are those in the vicinity of Bârlad, Fălciu Hills and the Huși wine area. Most AUs in Bacău and Suceava counties, in the southern part of Neamț County, are included in the medium and high-risk classes due to the suitable conditions for cultivating most plants and the higher frequency of hail. The ATUs from Botosani County are included in the low and medium risk classes. The lowest level of risk is registered in the case of AUs from the mountainous area, the Curvature Subcarpathians and the areas with higher altitudes from the Central Moldavian Plateau and Tutova Hills.

Сравнение данных глобальной сети локализации молний WWLLN и стандартных наблюдений на метеостанциях юга Дальнего Востока России

Standard observations at 20 weather stations were compared with data of the World Wide Lightning Location Network (WWLLN) in the south of the Russian Far East for the period of 2009-2018. Using two statistical methods, the estimates are obtained of the radii of the circular region of the WWLLN data sample, at which the best consistency of the WWLLN data with the number of days with thunderstorms according to weather station data is observed. It is shown that these radii are in the range from 12 to 36 km for all stations, with an average value of 23 km. Daytime radii are smaller than nighttime ones, the average values for all stations are equal to 21 and 26 km, respectively. It is demonstrated that an increase/decrease in the radius of the WWLLN data sample by 1 km leads to an increase/decrease in the average annual number of days with WWLLN lightnings relative to weather reports by ~1 day.

Hail characteristics in Serbia based on data obtained from the network of hail suppression system stations

AbstractSerbia is located in the mid‐latitudes of the Northern Hemisphere and is exposed to frequent hailfall. Consequently, a hail suppression system was gradually developed during the last 54 years. In this study, data from densely distributed hail suppression stations were used to better understand the hail characteristics. Two data subsets are differentiated: the first from the territory of Serbia, excluding the northern province of Vojvodina, during 1981–2015 (P1) and the second from the entire territory of Serbia during 2002–2015 (P2). The distribution of hail size shifted to smaller diameters in P2 compared to P1. The hailfall lasted less than 5 min in about 75% of events while the duration was greater than or equal to 10 min in only 8%. The influence of Serbia's complex orography on hailfall is reflected in the greater average annual number of days with hailfall in mountainous areas, with a maximum mean value of 1.2 in the southwestern part of Serbia, while the maximum number was 2.7. Hail and small hail occurred mainly in the afternoon and evening, with 92.24% of cases being observed from 12:00 to 21:00 local time (UTC + 1). A positive monotonic trend in the annual number of days with hailfall was observed. In both subsets, there was no statistically significant trend in hail frequency. The average seasonal duration of hail and small hail falls showed a decreasing trend in P1. Results showed that the first occurrence of hail falls did not appear earlier in the season.

Analysis of the meteorological situation in the conditions of icing and ice

The article is devoted to the study of the problem of ensuring the safety of aircraft on the territory of the Republic of Belarus and, directly, on the territory of the Minsk airfield. Icing and ice are some of the most dangerous meteorological phenomena for aviation. In order to prevent accidents related to these phenomena, it is necessary to have a clear idea of the laws of their occurrence and distribution, as well as their relationship to each other. To study the spatial and temporal patterns of ice distribution, the actual meteorological data of Belhydromet for 1989–2016 were processed at all meteorological stations of the Republic of Belarus. Also, charts of the chronological progress of the average monthly number of days with ice and the average annual number of days with ice at all meteorological stations on the territory of the Republic of Belarus for the above period were constructed and analyzed. The tendency to change the average annual number of days with ice over the period from 1989 to 2016 is analysed. The icing analysis for 2014–2018 was also carried out according to the data of the Civil Aviation Meteorological Station «Minsk». The accompanying meteorological elements, such as the shape of the clouds, the direction and strength of the wind, air temperature, as well as the synoptic situation, are analysed. The map of the spatio-temporal distribution of ice is constructed using ArcGIS by the method of equal intervals.

Population Dynamics of the Bream Abramis brama in Lake Peipus

Population dynamics of the bream Abramis brama in lakes Peipsi and Pihkva for the period from 1980 to 2009 has been studied by means of cohort models. Bream stock increased steadily in Lake Pihkva until 1999 and in Lake Peipsi until 2004, however then a trend towards a decrease of stock down to the level of early 1980s has been detected. In the 2000s a decrease in the population average age has been registered; it could be explained by both an increase in fishing intensity and high recruitment rates of the late 1990s. Highly abundant bream generations emerged in both lakes simultaneously. In late 2000s low level of recruitment was noted in both lakes. The qualitative relationship between stock and recruitment is best described by Ricker’s curve. It has been shown that bream recruitment depends on water transparency, water temperature, average annual number of days with air temperature above 20°С, and average annual water level. The existing fishery pressure on the stock of bream is close to optimal. A further increase in fishing intensity in both lakes is impractical. The current level of equilibrium yield can be achieved with much lower fishing intensity.

Dustiness and Aerodynamics of Air in Central Asian Cities

One of the adverse meteorological factors for the cities of Central Asia are dust storms and haze. The average annual number of days with haze in the cities of Central Asia reaches from 10 to 20 days. Among them, the “Afghan” wind stands out. ( garmessel - fiery, hot, dry wind ), suddenly begins dusty storm in the deserts Afghanistan. It causes significant damage to the health of the population and the economies of Central Asian countries. The article describes the characteristics of the origin of dust and the process of dust transfer of wind. Research has shown that the process of transporting natural dust begins with the movement of particles with a diameter of 100–500 microns. The main types of occurrence and distribution of dust in cities are identified. The main results of field observations on measuring the content of fine dust were carried out in the atmospheric air of the urban environment. The paper also applied computer simulation technologies that can significantly simplify the analysis of dust and wind conditions. The analysis of urban greening is presented. The practical implementation of the proposed methods creates a real opportunity to improve the quality indicators of the atmospheric air of cities with a complex landscape location in the summer, which will directly affect the improvement of people’s health.

High Temperature Reduces the Viability of Pollen from Upland Cotton in China

The viability of pollen grains from upland cotton (Gossypium hirsutum L.) has an important influence on fertilization and fiber yield and quality, and high temperature adversely affects cotton pollen grain development. However, the effects of high temperature on the vigor of pollen grains and cultivars having pollen grains resistant to high temperature in different regions have not been reported. The purpose of this study was to evaluate how high temperatures influence the viability of pollen from upland cotton and determine the high‐temperature risk to pollen vigor in upland cotton cultivars in major cotton‐producing regions in China. In this study, pollen grain germination was performed in vitro by culturing pollen grains in medium to detect cotton pollen grain viability. Pollen germination rates decreased significantly when the maximum daily temperature was ≥35°C for three consecutive days. The resistance of pollen vigor to high temperatures significantly differed among cultivars. According to the average annual number of days with temperatures ≥35°C from June to August in the main cotton‐producing areas in China within a 10‐yr period, the risk of high temperature affecting pollen vigor can be divided into five levels. Seventeen cultivars (lines) resistant to high temperatures were selected from 206 upland cotton cultivars, and four simple sequence repeat (SSR) markers were found to be associated with pollen germination rates under high temperature. This study clarified the degree of high‐temperature risk in major cotton‐producing areas in China and provided guidance for the selection of suitable heat‐resistant cultivars.Core Ideas Pollen germination rates decreased significantly when the maximum daily temperature was ≥35°C for three consecutive days. The heat resistance index was calculated to evaluate the differences in the heat resistance among the different cultivars. Resistance of pollen vigor to high temperature significantly differed among cultivars. Four simple sequence repeat markers associated with pollen germination rates under high temperature were identified.

Modeling droughty soils at regional scales in Pacific Northwest Forests, USA

Natural resource managers need better estimates of water storage and supply in forested landscapes. These estimates would aid planning for management activities that maintain and enhance forest health and productivity and help prepare forested landscapes for a changing climate. In particular, low soil moisture in combination with high evaporative demands can induce significant stresses on forests, increasing vulnerability to attacks of insect and disease, as well as increasing wildfire risk. Although high-resolution soils data exist for much of the Pacific Northwest, regional-scale datasets that identify forested areas potentially vulnerable to soil moisture-related drought do not exist. In this study, we used readily available spatial datasets depicting available water supply, soil depth, and evapotranspiration to model the likelihood that soils experience prolonged summer drying. To calibrate the model, we examined soil profile descriptions, lab data, and soil moisture curves for 25 sites throughout the Pacific Northwest and estimated the average annual number of days that soil moisture drops to levels at or below the permanent wilting point, a theoretical lower limit of plant-available water. Using this approach, we found statistically significant relationships between the independent variables and broad classes of soil moisture levels representing the highest and lowest levels of plant-available moisture. We then used these relationships to create a landscape-level droughty soil index for the Pacific Northwest. We expect that this approach can be further developed to include additional soil moisture data outside Washington and Oregon and enhanced with other explanatory variables such as topographic position, elevation, and vegetation type. With the addition of vegetation-related data, in particular, the current modeling approach can aid in identifying vulnerable landscapes in the context of managing for increased forest resiliency in the Pacific Northwest.

Health care use and economic burden of patients with diagnosed chronic obstructive pulmonary disease in Korea.

The prevalence and economic burden of chronic obstructive pulmonary disease (COPD) are increasing worldwide. However, little information is available concerning COPD-associated health care use and costs in Korea. To analyse 1) health care use, medical costs and medication use in 2009, and 2) changes in costs and medication use over 5 years (2006-2010). Using the database of the Korean Health Insurance Review and Assessment Service, COPD patients were identified by searching on both ICD-10 codes and COPD medication. RESULTS A total of 192,496 COPD patients were identified in 2009. Total medical costs per person were US$2803 ± 3865; the average annual number of days of out-patient care and days of hospitalisation were respectively 40 ± 36 and 11 ± 33. Methylxanthine and systemic beta-agonists were the most frequently used drugs. However, the number of prescriptions for long-acting muscarinic antagonist increased rapidly. The total cost of COPD-related medications increased by 33.1% over 5 years. The present study provides new insight into health care use and the economic burden of COPD in Korea. Changing patterns of COPD-related medication use could help inform COPD management policies.

A Synoptic Climatological Approach to Assess Climatic Impact on Air Quality in South-central Canada. Part II: Future Estimates

Using within-weather-group air pollution prediction models developed in Part I of this research, this study estimates future air pollution levels for a variety of pollutants (specifically, carbon monoxide – CO, nitrogen dioxide – NO2, ozone – O3, sulphur dioxide – SO2, and suspended particles – SP) under future climate scenarios for four cities in south-central Canada. A statistical downscaling method was used to downscale five general circulation model (GCM) scenarios to selected weather stations. Downscaled GCM scenarios were used to compare respective characteristics of the weather groups developed in Part I; discriminant function analysis was used to allocate future days from two windows of time (2040–2059 and 2070–2089) into one of four weather groups. In Part I, the four weather groups were characterised as hot, cold, air pollution-related, and other (defined as relatively good air quality and comfortable weather conditions). In estimating future daily air pollution concentrations, three future pollutant emission scenarios were considered: Scenario I – emissions decreasing 20% by 2050, Scenario II – future emissions remaining at the same level as at the end of the twentieth century, and Scenario III – emissions increasing 20% by 2050. The results showed that, due to increased temperatures, the average annual number of days with high O3 levels in the four selected cities could increase by more than 40–100% by the 2050s and 70–200% by the 2080s (from the current areal average of 8 days) under the three pollutant emission scenarios. The corresponding number of low O3 days could decrease by 4–10% and 5–15% (from the current areal average of 312 days). For the rest of the pollutants, future air pollution levels will depend on future pollutant emission levels. Under emission Scenarios II and III, the average annual number of high pollution days could increase 20–40% and 80–180%, respectively, by the middle and late part of this century. In contrast, under Scenario I, the average annual number of high pollution days could decrease by 10–65%.

Urban Modification of Freezing-Rain Events

Abstract A new national database for freezing-rain occurrences during the 1945–2000 period provided an opportunity for a study of the potential urban effects on freezing-rain events. Numerous past studies of snowfall events in urban areas have defined decreases of 10%–35% related to the urban heat island. The heat island, which acts to elevate near-surface temperatures, could also keep some freezing-rain situations from occurring in the city. The study involved four cities in the Midwest and Northeast for which the average annual number of days with freezing rain are three or more, for which data from in-city stations existed, and for which data for several surrounding rural stations existed. The two largest qualifying cities, New York City, New York, and Chicago, Illinois, had sizable reductions in average and maximum annual freezing-rain-day frequencies, ranging from 16% to 43% less than values of surrounding rural stations, and their freezing-rain “seasons” were 1–2 months shorter than those in surroun...

Heat stress in Greece.

For 12 selected synoptic stations of the Greek Weather Service, the daily 12 UTC values of the thermal index Predicted Mean Vote (PMV) were calculated for the years 1980 to 1989. The locally varied occurrence of diverse thermal sensation and particularly of strong heat stress were analysed in relation to the human-biometeorological significance. With the help of a statistical model, PMV values of individual stations were transformed into a high-resolution bioclimatic map. The map presents the average annual number of days with at least strong heat stress (PMV > 3.0).

PART‐TIME WORKING IN IRELAND

The subject of part‐time work is one which has become increasingly important in industrialised economies where it accounts for a substantial and growing proportion of total employment. It is estimated that in 1970, average annual hours worked per employee amounted to only 60% of those for 1870. Two major factors are attributed to explaining the underlying trend towards a reduction in working time: (a) the increase in the number of voluntary part‐time employees and (b) the decrease in average annual number of days worked per employee (Kok and de Neubourg, 1986). The authors noted that the growth rate of part‐time employment in many countries was greater than the corresponding rate of growth in full‐time employment.

Fog Frequency in the United States

r IHIRTY years ago the Geographical Review published a map of fog distribution over the United States, by Robert G. Stone.' Five years later a map of Average Annual Number of Days with Dense Fog appeared as one of forty-six maps depicting climates of the United States in Climate and Man, the 1941 Yearbook of Agriculture.2 No other fog maps for the entire country have since appeared, and both Stone's map and the Climate and Man map have been widely reprinted and adapted.3 A new map showing fog distribution over the conterminous United States, based on averages at 251 first-order Weather Bureau stations through 1960, is presented here as Figure 1. Stone's map (Fig. 2) was based on mean values for the full period of record ... (through 1931 or 1932) ... for 410 stations in all, including many non-Weather Bureau observatories and about loo stations outside the United States proper. His primary basic were 30-year means, 1901-1930, for 108 United States stations and 26 Mexican stations; in addition, data were obtained from about 5oo lighthouses.4 The Climate and Man map (Fig. 3) was based on 200 first-order Weather Bureau stations, period 1899-1938.