Frost Occurrence Research Articles

SPATIOTEMPORAL EVALUATION OF NOCTURNAL COLD AIR DRAINAGE OVER A SIMPLE SLOPE USING THERMAL INFRARED IMAGERY

Measurements of climatic processes such as cold air drainage flows are problematic over mountainous areas. Observation of cold air drainage is not available in the existing observation network and it requires a special methodology. The main objective of this study was to characterize the cold air drainage over regions with a slope. A high resolution infrared camera, a meteorological station and Digital Elevation Model (DEM) were used. The specific objective was to derive nocturnal cold air drainage velocity over the slope. To address these objectives, a number of infrared measurement campaigns were conducted during calm and clear sky conditions over an agricultural zone (blackcurrant farm) in Canada. Using thermal infrared images, the nocturnal surface temperature gradient were computed in hourly basis. The largest gradient magnitudes were found between 17h -20h. The cooling rates at basin area were two times higher in comparison to the magnitudes observed within slope area. The image analysis illustrated this considerable temperature gradient of the basin may be partly due to transport of cold air drainage into the basin from the slope. The results show that thermal imagery can be used to characterize and understand the microclimate related to the occurrence of radiation frost in the agricultural field. This study provided the opportunity to track the cold air drainage flow and pooling of cold air in low lying areas. The infrared analysis demonstrated that nocturnal drainage flow displayed continuous variation in terms of space and time in response to microscale slope heterogeneities. In addition, the analysis highlighted the periodic aspect for cold air drainage flow.

SPATIOTEMPORAL EVALUATION OF NOCTURNAL COLD AIR DRAINAGE OVER A SIMPLE SLOPE USING THERMAL INFRARED IMAGERY

Abstract. Measurements of climatic processes such as cold air drainage flows are problematic over mountainous areas. Observation of cold air drainage is not available in the existing observation network and it requires a special methodology. The main objective of this study was to characterize the cold air drainage over regions with a slope. A high resolution infrared camera, a meteorological station and Digital Elevation Model (DEM) were used. The specific objective was to derive nocturnal cold air drainage velocity over the slope. To address these objectives, a number of infrared measurement campaigns were conducted during calm and clear sky conditions over an agricultural zone (blackcurrant farm) in Canada. Using thermal infrared images, the nocturnal surface temperature gradient were computed in hourly basis. The largest gradient magnitudes were found between 17h -20h. The cooling rates at basin area were two times higher in comparison to the magnitudes observed within slope area. The image analysis illustrated this considerable temperature gradient of the basin may be partly due to transport of cold air drainage into the basin from the slope. The results show that thermal imagery can be used to characterize and understand the microclimate related to the occurrence of radiation frost in the agricultural field. This study provided the opportunity to track the cold air drainage flow and pooling of cold air in low lying areas. The infrared analysis demonstrated that nocturnal drainage flow displayed continuous variation in terms of space and time in response to microscale slope heterogeneities. In addition, the analysis highlighted the periodic aspect for cold air drainage flow.

Using the internet of things to monitor low adhesion on railways

Adhesion refers to the ‘slipperiness’ of the rails due to surface contaminants such as leaves, rust, oil and grease, exacerbated by small amounts of atmospheric moisture from drizzle, dew or fog. Low adhesion is an issue on the railways because it reduces acceleration and braking efficiency. This leads to platform overruns and signals passed at danger, putting the travelling public at risk, as well as contributing significantly to service delays. In response, high-resolution forecasting systems have been developed that take into account site-specific leaf-fall forecasts, rail and dew-point temperature to estimate the occurrence of dew, frost, light rain and fog. However, in order to validate models, data are required from a high-resolution monitoring network that is able to capture observations of rail moisture and leaf-fall contamination. This paper investigates the feasibility of harnessing the emerging internet of things to develop a high-resolution, but low-cost, rail moisture monitoring network. A low-cost, self-contained sensor was developed and tested, with positive results, against existing, more expensive sensors in both a laboratory and field setting. The paper concludes with a blueprint documenting an approach to improve the spatial resolution of moisture measurements across the network.

English

Aloysia triphylla, also known as lemon verbena is a medicinal plant with aromatic leaves which produce essential oil rich in citral and has great importance for pharmaceutical and cosmetic industries. The objective of this study was to evaluate the effect of frost on the chemical composition and yield of A. triphylla essential oil. The experiment was conducted at the Campus of UFSM in Frederico Westphalen, Rio Grande do Sul, in July 2014. A complete randomized design with three repetitions was used where three random collections and extractions occurred before and after the occurrence of frost. The oil was obtained via hydrodistillation and analyzed by a process of gas chromatography and mass spectrometry. The total yield obtained from leaves before frost was 0.162% and 0.187% after frost. Essential oil composition was largely not affected by the presence of frost; however, of the macro components, limonene was observed to be most sensitive to frost, accounting for 14.36% of essential oil content before and 10.15% after frost. Key words: Chemical composition, secondary metabolites, low temperatures.

Recent changes in southern Australian frost occurrence: implications for wheat production risk

Frost damage remains a major problem for broadacre cropping, viticulture, horticulture and other agricultural industries in Australia. Annual losses from frost events in Australian broadacre agriculture are estimated at between $120 million and $700 million each year for this sector. Understanding the changing nature of frost risk, and the drivers responsible, are important steps in helping many producers manage climate variability and change. Our analysis, using Stevenson screen temperature thresholds of 2°C or below as an indicator of frost at ground level, demonstrates that across southern Australia, despite a warming trend of 0.17°C per decade since 1960, ‘frost season’ length has increased, on average, by 26 days across the whole southern portion of Australia compared with the 1960–1990 long-term mean. Some areas of south-eastern Australia now experience their last frost an average 4 weeks later than during the 1960s. The intersection of frost and wheat production risk was quantified at 60 sites across the Australian wheatbelt, with a more in-depth analysis undertaken for 15 locations across Victoria (i.e. eight sites common to both the National and Victorian assessments and seven sites exclusive to the Victorian analysis). The results of the national assessment highlight how frost-related production risk has increased by as much as 30% across much of the Australian wheatbelt, for a range of wheat maturity types, over the last two decades, in response to an increase in later frost events. Across 15 Victorian sites, sowing dates to achieve anthesis during a period with only a 10% chance of a 0°C night occurring shifted by 23 days (6 June) for the short-season variety, 20 days (17 May) for the medium-season variety and 36 days later (9 May) for the long-season variety assessed.

The Study of Frost Occurrence in Free State Province of South Africa

The study investigated the cessation, onset, and duration of light, medium, and heavy frost in Free State province of South Africa using minimum temperatures from 1960 to 2015. Trends in the frost indices were assessed using the Man-Kendall test. Onset of frost varied spatially with earlier onset over the northern, eastern, and southeastern parts. Areas of early onset also experience late cessation of frost resulting in shorter growing period of less than 240 days. The western parts have longer growing period exceeding 240 days due to earlier cessation of frost and relatively late onset of frost. Trends for the frost-free period (growing period) show contrasting negative and positive trends with isolated significant trends.

Managing impact of climatic vagaries on the productivity of wheat and mustard in India

Wheat and mustard crop is highly vulnerable, particularly in the semi-arid and arid regions of India. The climate is warming through the processes such as CO2 and changed pattern of temperature and precipitation resulting in heat and drought stresses, respectively. The effect of increasing temperature during grain filling stage of wheat causes substantial reduction in grain yield. The effect of low temperature (frost) during podding and seed development stage in mustard causes freezing injury in seeds and sizable reduction in seed yield. In this review paper response of wheat and mustard crop to weather extremes and management practices such as time of sowing, selection of resistance cultivars, mulching, seed priming, foliar spray of salts, use of extra irrigation water, foliar spray of micronutrients, sprinkler, wind barrier etc. to mitigate the temperature and moisture stress effect on the productivity of wheat and mustard crop have been discussed. Above ground dry weight of wheat and its rate decreased with increasing water stress at each stage. The averaged values of damage threshold temperatures compiled from the literature were 31 °C for flowering and 35 °C for grain filling of wheat. Changes in average daily maximum temperature during flowering and grain filling had a negative effect on grain yield of 518 kg/ha and 1140 kg/ha, respectively for every 1 degree increase in average maximum temperature in South Australia. Temperature rise would be most harmful for the crop in eastern region, followed by central and northern India, where winter season temperature is comparatively higher than northern region. Rainfed mustard was less vulnerable to temperature rise in northern India as compared to other two central and eastern India. Rise in atmospheric temperature reduced leaf area index, grain number as well as weight of grains which was in turn reflected in yield of mustard crop. Seed yield reduction occurred by low water availability during stem elongation, flowering and pod development in mustard. Priming with moringa water extract and ascorbate substantially improved the tissue water status, membrane stability, gas exchange, water productivity of the plant. Late sown wheat crop faces high temperature stress during ripening phase. Delayed sowing reduces the tillering period and hot weather during critical period of grain filling lead to forced maturity thereby reduces the grain yield. Application of mulches in wheat produced higher grain yield over without much wheat. Organic mulches provided better soil water status and improved plant canopy in terms of biomass, root growth, leaf area index and grain yield as compared to inorganic mulch. The foliar spray of KNO3 (0.5%) at 50 per cent flowering stage, 1.0 per cent KNO3 during anthesis stage, 2.5 mM of arginine, spray of zinc, extra irrigation water during grain filling stage increased the productivity of wheat under high temperature stress.
 Light irrigation in mustard crop one day before frost occurrence protects from frost damage by improving heat transfer and heat capacity. Plastic mulch raises the surface temperature of the soil nearly 10 °C over bare soil. Smoke particles are usually less than 1 µm in size, reflect visible radiation but trap the long wave radiation and so are effective in preventing rapid cooling of surface near ground. Mixing air and liquid materials in the right proportion to create many small bubbles is the secret to generate foam with low thermal conductivity. Organic mulches (straw and saw dust) provided better soil water status over ash mulch.

Prediction of Frost Occurrences Using Statistical Modeling Approaches

We developed the frost prediction models in spring in Korea using logistic regression and decision tree techniques. Hit Rate (HR), Probability of Detection (POD), and False Alarm Rate (FAR) from both models were calculated and compared. Threshold values for the logistic regression models were selected to maximize HR and POD and minimize FAR for each station, and the split for the decision tree models was stopped when change in entropy was relatively small. Average HR values were 0.92 and 0.91 for logistic regression and decision tree techniques, respectively, average POD values were 0.78 and 0.80 for logistic regression and decision tree techniques, respectively, and average FAR values were 0.22 and 0.28 for logistic regression and decision tree techniques, respectively. The average numbers of selected explanatory variables were 5.7 and 2.3 for logistic regression and decision tree techniques, respectively. Fewer explanatory variables can be more appropriate for operational activities to provide a timely warning for the prevention of the frost damages to agricultural crops. We concluded that the decision tree model can be more useful for the timely warning system. It is recommended that the models should be improved to reflect local topological features.

Climate-induced mortality of spruce stands in Belarus

The aim of this work is an analysis of the causes of spruce (Picea abies L.) decline and mortality in Belarus. The analysis was based on forest inventory and Landsat satellite (land cover classification, climate variables (air temperature, precipitation, evaporation, vapor pressure deficit, SPEI drought index)), and GRACE-derived soil moisture estimation (equivalent of water thickness anomalies, EWTA). We found a difference in spatial patterns between dead stands and all stands (i.e., before mortality). Dead stands were located preferentially on relief features with higher water stress risk (i.e., higher elevations, steeper slopes, south and southwestern exposure). Spruce mortality followed a series of repeated droughts between 1990 and 2010. Mortality was negatively correlated with air humidity (r = –0.52), and precipitation (r = –0.57), and positively correlated with the prior year vapor pressure deficit (r = 0.47), and drought increase (r = 0.57). Mortality increased with the increase in occurrence of spring frosts (r = 0.5), and decreased with an increase in winter cloud cover (r = –0.37). Spruce mortality was negatively correlated with snow water accumulation (r = –0.81) and previous year anomalies in water soil content (r = –0.8). Weakened by water stress, spruce stands were attacked by pests and phytopathogens. Overall, spruce mortality in Belarussian forests was caused by drought episodes and drought increase in synergy with pest and phytopathogen attacks. Vast Picea abies mortality in Belarus and adjacent areas of Russia and Eastern Europe is a result of low adaptation of that species to increased drought. This indicates the necessity of spruce replacement by drought-tolerant indigenous (e.g., Pinus sylvestris, Querqus robur) or introduced (e.g., Larix sp. or Pseudotsuga menzieslii) species to obtain sustainable forest growth management.

Use of LST images from MODIS/AQUA sensor as an indication of frost occurrence in RS

ABSTRACTAlthough frost occurrence causes severe losses in agriculture, especially in the south of Brazil, the data of minimum air temperature (Tmin) currently available for monitoring and predicting frosts show insufficient spatial distribution. This study aimed to evaluate the MDY11A1 (LST – Land Surface Temperature) product, from the MODIS sensor on board the AQUA satellite as an estimator of frost occurrence in the southeast of the state of Rio Grande do Sul, Brazil. LST images from the nighttime overpass of the MODIS/AQUA sensor for the months of June, July and August from 2006 to 2012, and data from three conventional weather stations of the National Institute of Meteorology (INMET) were used. Consistency was observed between Tmin data measured in weather stations and LST data obtained from the MODIS sensor. According to the results, LSTs below 3 ºC recorded by the MODIS/AQUA sensor are an indication of a favorable scenario to frost occurrence.

Biostimulant usage for preserving strawberries to climate damages

Bogunovic I., Duralija B., Gadze J., Kisic I. (2015): Biostimulant usage for preserving strawberries to climate damages . Hort. Sci., 42: 132–140. Climate changes affect horticultural production through the occurrence of late spring frosts. Therefore plant manage ment is gaining more importance with the aim of improving plant condition. The research deals with the biostimulator containing amino-acids of animal origin (porcine blood) which can be obtained by chemical and/or enzymatic hydrolysis of an organic matrix. During vegetation period different cultivars of strawberries were included in the experiment: Asia, Alba and Clery. The effects of biostimulator on resistance to frost, yields and pomological characteristics were studied at three treatments (0.5 , 1.0 and 1.5 g/plant, and control 0 g/plant). The results showed that all investigated cultivars had a positive response to biostimulant application regarding the frost resistance. Natural frost resistance was the strongest for cv. Clery. Significantly lowest percentage of damage was recorded for cv. Alba at 1.5 g and cvs Clery and Alba at 0.5 g. In the case of late spring frosts and other climatic hazards for growing outdoors cvs Clery and Alba are recommended. All cultivars recorded decreased yields. The difference in yields between cultivars was a consequence of frost damages.

A UTILIZAÇÃO DE OBJETOS DE APRENDIZAGEM NO ESTUDO DO ORVALHO E DA GEADA NO 6º ANO DO ENSINO FUNDAMENTAL

The occurrence of dew and frost is a situation, accordint to the climatic rhythm, common in the southern Brazil. Most textbooks discusses this subject in a static way. This hinders that the student visualize the dynamics of the phenomenon. Given this difficulty we propose didactic teaching resources to assist the teacher in this practice and provide to the student an interation with the phenomena. Facing the possibility of the student to interact with new media related to education, the learning objects may serve as a link between these media and the teaching of climatology, specificall in the teaching of dew and frost. With the assistance of a digital video decoder (DVD) it was possible to make the lessons more dynamic and interactive, because with this instrument and the creativity of the teacher, it is possible to make the lessons, and specially geography, more attractive. Within this perspective that the present work was proposed, wich materialized in a school on the outskirts of Santa Maria, RS. Using class periods of the fifth year, these became full of cooperativeness among academics. The evaluation of the results was positive, wich shows the effectiveness of the learning object applied.

Hemispheric asymmetry in martian seasonal surface water ice from MGS TES

The Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) visible/near-infrared and thermal infrared bolometers measured planetary broadband albedo and temperature for more than three Mars years. As seasons progress on Mars, surface temperatures may fall below the frost point of volatiles in the atmosphere (namely, carbon dioxide and water). Systematic mapping of the spatial and temporal occurrence of these volatiles in the martian atmosphere, on the surface, and in the subsurface has shown their importance in understanding the climate of Mars. We examine TES daytime albedo, temperature, and atmospheric opacity data to map the latitudinal and temporal occurrence of seasonal surface water frost on Mars. We expand on previous work by looking at the behavior of water frost over the entire martian year, made possible with comprehensive, multi-year data. Interpretations of frost are based on albedo changes and the corresponding daytime temperature range. Data is considered consistent with water frost when there are significant albedo increases (>0.05 relative to frost-free seasons) and the observed temperatures are ∼170–200K. We argue the presence of extensive water frost in the northern hemisphere, extending from the pole to ∼40°N, following seasonal temperature trends. In the north, water frost first appears near the pole at Ls=∼160° and is last observed at Ls=∼90°. Extensive water frost is less evident in southern hemisphere data, though both hemispheres show data that are consistent with the presence of a water ice annulus during seasonal cap retreat. Hemispherical asymmetry in the occurrence of seasonal water frost is due in part to the lower (∼40%) atmospheric water vapor abundances observed in the southern hemisphere. Our results are consistent with net transport of water vapor to the northern hemisphere. The deposition and sublimation of seasonal water frost may significantly increase the near-surface water vapor density that could substantially extend the geographic occurrence of stable ground ice.

Assessing the extent and the environmental drivers of Eucalyptus globulus wildling establishment in Portugal: results from a countrywide survey

Tasmanian blue gum (Eucalyptus globulus) has been increasingly used in forestry outside its native range, and is nowadays one of the most important pulpwood species in the world. E. globulus has great economic importance in many countries, and in Portugal it has recently become the most widespread tree species. However, there is also an increasing concern about the potential ability of eucalypts to naturally establish from seed (wildling establishment), because of negative ecological and economic impacts this could cause. The natural establishment of this fast-growing exotic species may have undesirable consequences, but little is known about its distribution, or which are the factors influencing its occurrence. In order to investigate these issues, we characterized wildling occurrence and abundance along 3111 roadside transects adjacent to eucalypt plantations distributed throughout continental Portugal. Eucalypt wildlings were found in 60 % of the sampled transects and across all natural regions, with densities ranging from 0 to 10,000 plants ha−1 (mean = 277 plants ha−1). The potential influence of environmental variables on wildling establishment from plantations was assessed using boosted regression trees. The abundance of wildlings was found to be primarily affected by precipitation and distance from the sea (used as a surrogate of thermal amplitude), although topography, frost occurrence and soil type also played a significant role. Plant density peaked at around 1500 mm of annual precipitation and it decreased with both decreasing and increasing precipitation, reaching the lowest values below 800 mm and above 2400 mm. Eucalypt wildlings were also more abundant in areas with milder temperatures, namely closer to the sea (with lower thermal amplitude) and with lower number of frost days. Finally, plant density also seemed to be favoured in areas with intermediate elevation, higher slope and with certain soil types (namely Cambisols and Podzols). Knowing the regions with higher wildling density and understanding the factors influencing plant establishment may help managers to establish and prioritize eventual control plans in regions with higher probability of recruitment.

Frost, Portulacaria afra Jacq., and the boundary between the Albany Subtropical Thicket and Nama-Karoo biomes

Numerous shrublands exist in areas where soil moisture should support tree growth. In South Africa, the dwarf shrublands of the Nama-Karoo biome and tree-dominated vegetation of the Albany Subtropical Thicket biome share a boundary that is often abrupt. This boundary is not associated with edaphic or rainfall transitions. Field observations and leaf-level experiments suggest that the vulnerability of thicket species to frost damage is responsible for this thicket–shrubland boundary. We tested this hypothesis by establishing cuttings of Portulacaria afra (spekboom) – a dominant thicket succulent shrub that is a keystone species in arid forms of thicket – in two separate transplant experiments. Firstly across a topographic gradient from frost-free, thicket clad slopes to frost-prone, karoo shrubland dominated valley floor; and secondly, inside and outside a thicket clump in the frost-prone valley floor. We quantified the effects of frost on spekboom by measuring photosynthetic efficiency (Fv/Fm), leaf number, estimating the percentage of healthy stem before and after frost events in June 2013. Frost-exposed spekboom cuttings rapidly underwent declines in photosynthetic efficiency, followed by severe leaf and stem necrosis; herbivores played no role in these declines. Those planted on the frost-free valley slopes or under the frost-protecting thicket canopy on the valley floor remained largely unaffected. This supports the hypothesis that frost-exposure is likely to be the main factor determining the growth rates, and ultimately survival of spekboom. These results suggest that frost occurrence is an important factor involved in determining the boundaries between the arid, and spekboom-rich subtypes of Albany Subtropical Thicket, and the frost tolerant shrublands of the Nama-Karoo.

Impact of climate change on wheat flowering time in eastern Australia

The flowering time of wheat is strongly controlled by temperature and is potentially highly sensitive to climate change. In this study, we analysed the occurrence of last frost (days with minimum temperature under 2°C) and first heat (days with maximum temperatures exceeding 30°C) events of the year to determine the optimum flowering date in the wheat belt of New South Wales (NSW), eastern Australia. We used statistically downscaled daily maximum and minimum temperature data from 19 Global Climate Models (GCMs) with a vernalizing–photothermal model in order to simulate future flowering dates and the changes in frost and hot days occurrence at flowering date (± 7 days) for two future scenarios for atmospheric greenhouse gas concentrations (RCP4.5 and RCP8.5) in 2040s (2021–2060) and 2080s (2061–2100). Relative to the 1961–2000 period, the GCMs projected increased daily maximum and minimum temperatures for these future periods, accompanied by reduced frost occurrence and increased heat stress incidence. As a consequence, by the 2080s, simulations suggest a general advance in spring wheat flowering date by, on average, 10.2 days for RCP4.5 and 17.8 days for RCP8.5 across the NSW wheat belt. Winter wheat flowering dates were delayed by an average of 2.4 days for RCP4.5 and 14.3 days for RCP8.5 in the warmest parts of the region (the northwest) due to reduced cumulative vernalization days (requiring cool conditions). In the cooler regions (the northeast, southeast and southwest), flowering date occurred earlier by 6.2 days for RCP4.5 and 6.7 days for RCP8.5 on average. Moreover, in the western parts of the wheat belt the delay of winter wheat flowering date was about 9.5 days longer than that in the eastern parts. As a result of phenological responses to increasing temperatures, current wheat varieties may not be suitable for future climate conditions, despite reduced frost risk. In the future, it may be necessary to use longer-season wheat varieties and varieties with increased heat-stress resistance.

Effects of environmental factors and management practices on microclimate, winter physiology, and frost resistance in trees.

Freezing stress is one of the most important limiting factors determining the ecological distribution and production of tree species. Assessment of frost risk is, therefore, critical for forestry, fruit production, and horticulture. Frost risk is substantial when hazard (i.e., exposure to damaging freezing temperatures) intersects with vulnerability (i.e., frost sensitivity). Based on a large number of studies on frost resistance and frost occurrence, we highlight the complex interactive roles of environmental conditions, carbohydrates, and water status in frost risk development. To supersede the classical empirical relations used to model frost hardiness, we propose an integrated ecophysiologically-based framework of frost risk assessment. This framework details the individual or interactive roles of these factors, and how they are distributed in time and space at the individual-tree level (within-crown and across organs). Based on this general framework, we are able to highlight factors by which different environmental conditions (e.g., temperature, light, flood, and drought), and management practices (pruning, thinning, girdling, sheltering, water aspersion, irrigation, and fertilization) influence frost sensitivity and frost exposure of trees.

Frost trends and their estimated impact on yield in the Australian wheatbelt.

Radiant spring frosts occurring during reproductive developmental stages can result in catastrophic yield loss for wheat producers. To better understand the spatial and temporal variability of frost, the occurrence and impact of frost events on rain-fed wheat production was estimated across the Australian wheatbelt for 1957-2013 using a 0.05 ° gridded weather data set. Simulated yield outcomes at 60 key locations were compared with those for virtual genotypes with different levels of frost tolerance. Over the last six decades, more frost events, later last frost day, and a significant increase in frost impact on yield were found in certain regions of the Australian wheatbelt, in particular in the South-East and West. Increasing trends in frost-related yield losses were simulated in regions where no significant trend of frost occurrence was observed, due to higher mean temperatures accelerating crop development and causing sensitive post-heading stages to occur earlier, during the frost risk period. Simulations indicated that with frost-tolerant lines the mean national yield could be improved by up to 20% through (i) reduced frost damage (~10% improvement) and (ii) the ability to use earlier sowing dates (adding a further 10% improvement). In the simulations, genotypes with an improved frost tolerance to temperatures 1 °C lower than the current 0 °C reference provided substantial benefit in most cropping regions, while greater tolerance (to 3 °C lower temperatures) brought further benefits in the East. The results indicate that breeding for improved reproductive frost tolerance should remain a priority for the Australian wheat industry, despite warming climates.

Changes of temperature-related agroclimatic indices in Poland

The agricultural sector in Poland is of considerable social and economic importance for the nation. Climate variability and change are of primary relevance to this largely climate-dependent sector. Changes in seven temperature-related agroclimatic indices (lengths of the growing season and of the frost-free season, days of occurrence of the last spring frost and of the first autumn frost; and annual sums of growing degree-days for three values of temperature threshold) in Poland in 1951–2010 are examined. As expected, they generally correspond to the overwhelming and ubiquitous warming. Many, but not all, detected trends are statistically significant. However, for some indices, strong natural variability overshadows eventual trends. Projections of temperature-related agroclimatic indices for the future, based on regional climate models, are also discussed.

Frost periods and frost-free periods in Poland and neighbouringcountries

AbstractThe main objective of this article is to analysethe multiannual variability of frost occurrence and thelength of the frost-free period in Poland and neighbouringcountries between 1971 and 2010. A frost day was de-fined as a day onwhich the minimum temperaturewas below0°C and the maximum temperature was above 0°C.On average, between March and November, there were 30frost days in Poland and neighbouring countries, and theirnumber ranged between 12 and 61. In the analysed multiannualperiod, there was a statistically significant tendencyfor the last spring frost to be earlier. Conversely,the first autumn frost occurred increasingly late, althoughthe changes were not statistically significant. All but threestations (Augsburg, Kaliningrad, Olsztyn) recorded an increasein the length of frost-free periods, which was statisticallysignificant in 51% of stations. The pressure conditionconducive to the occurrence of frosts was anticycloniccirculation, as confirmed by the SLP and z500 hPa mapswhich were drawn up, and the Grosswetterlagen (GWL)classification types which were distinguished.