Frost Dates Research Articles

Trends of spring time frost events and phenological dates in Central Europe

¶Over large parts of the Northern Hemisphere’s continents temperature has been increasing during the last century. Particularly minimum temperatures show a more pronounced increase than maximum temperatures. Not only the phenological seasons, but also the potentially plant damaging late frost events are governed by the atmosphere. In case of a rise of minimum temperatures one would expect phenological phases and spring late frost events to occur earlier. In this work the question is elucidated whether plant phenology shifts at a higher or lower rate towards earlier occurrences than potential plant damaging events, like spring late frost events. Frost events based on the last occurrence of daily minimum temperatures below a certain threshold have been moving faster to earlier occurrence dates than phenological phases during the last decades at 50 climate stations in Central Europe. Trend values of frost time series range around −0.2 days/year and of phenological time series are between −0.2 and 0.0 days/year over the period from 1951–1997. ‘Corylus avellana beginning of pollination’ is the only one of the 13 phases considered here with a lower trend value of −0.28 days/year. Early phases are more adapted to below zero temperatures and therefore follow more closely the temperature variability. Later phases seem to have more reason to be concerned about possible late frost events and react more cautiously towards higher spring temperatures and earlier last frost dates. The risk of late frost damage for plants should have been lower during the last decade as compared to the previous decades.

RECENT CHANGES IN FROST DAYS AND THE FROST-FREE SEASON IN THE UNITED STATES

One of the signals expected with greenhouse warming is a change in what are now considered extreme temperatures. In this paper one type of extreme is examined for the 1948–99 period, that is, a change in the number of days when the minimum daily temperature dips below freezing or “frost days.” This is approached by looking at two questions: 1) have there been changes in the number of frost days per year, or per season, and 2) are there trends in the dates of the first autumn frost, last spring frost, and length of the frost-free season? Results show that the country as a whole has experienced a slight decrease in the number of days, with the biggest decreases in the winter and spring. Changes in frost dates for autumn show small changes to a later date, but the date of the last-spring freeze shows a distinct move to an earlier date. This results in an increase in the frost-free season. However, there is a distinct spatial pattern to the results that is consistent with the spatial pattern of annual temperature trends for the twentieth century. The geographical pattern shows the western United States with the largest decreases in frost days, and increases in frost-free season length. But the southeast United States, which is one of the few areas of the world showing cooling over the twentieth century, has no significant changes in the number of frost days or the frost-free season.

Examining the onset of spring in China

The onset of spring is a critical time in mid-latitude atmosphere-biosphere interactions. Deciduous plants resume growth after winter dormancy, and their activities cause land surfaces to become more active agents in energy and mass exchanges. The progress of spring plant develop- ment driving these changes can be conveniently monitored by observation of plant life-stage (phe- nological) events. Thus, phenological data can play a crucial role in understanding and monitoring springtime vegetation and climate dynamics, especially about potential changes over time. Although global-scale phenological monitoring is not yet possible, alternative strategies are available to assess these impacts. In this paper, a simple phenological model, driven by surface-level daily maximum- minimum temperatures is employed as a surrogate measure of the onset of spring in China. Con- trasting with results from similar studies in North America and Europe, the onset of spring plant growth in China has no apparent change over 1959-1993. However, during the same period, last spring frost (-2.2°C) dates have become markedly earlier (by 6 d), with the greatest change occurring in the northeast portions of the country. First autumn frost dates have also become later (by 4 d), especially in north-central China. Combining these 2 changes, the frost period has decreased by 10 d over many northern regions of the country. A shorting frost period is consistent with decreasing diurnal temperature ranges and day-to-day temperature differences during spring and autumn in China, reported by previous research.

Developmental Consequences of Cold Temperature Stress at Transplanting on Seedling and Field Growth and Yield. II. Muskmelon

For the earliest yields of spring melons, muskmelon [Cucumis melo L. (Reticulatus Group)] fields in the southeast United States may be transplanted in late winter before the last frost date. Seedlings may be exposed to cold temperatures cycling between almost freezing and optimal for weeks before warm weather predominates and such exposure may reduce later growth and yields. To test whether cold stress may reduce growth and yield, `Athena' muskmelon seedlings were subjected to cold stress at 2 ± 1 °C then transferred to a greenhouse at 29 ± 5 °C before field transplanting. In 1997, cold exposure durations were 3, 6, or 9 h and were repeated (frequency) for 1, 3, 6, or 9 d before transplanting. In 1998, duration levels were not changed but frequencies were 3, 6, or 9 d. In 1997, as cold stress increased, seedling shoot and root fresh and dry weights, height, leaf area, and leaf chlorophyll content decreased linearly, but shoot carbohydrates decreased curvilinearly and stabilized with ≈54 hours cold stress. In 1998, all seedling growth characteristics except leaf chlorophyll content decreased linearly as cold stress exposure increased. Leaf chlorophyll content decreased curvilinearly as cold stress increased to 36 h, but leveled off with more hours of cold stress. Even 1 week after transplanting, plants exposed to cold stress for up to 81 h continued to transpire more than control plants. In both years, vining (date first runner touched the ground) and male and female flowering were delayed significantly with increasing cold stress, but fruit set was affected only in 1998. Cold stress in 1998 delayed earliness with early fruit weight and number per plot decreasing as cold stress exposure increased. Total yields decreased linearly in both years as cold stress increased with 21 to 32 hours causing 10% yield reduction in 1997 and 1998, respectively. Results indicate a potential risk exists for yield reduction if `Athena' muskmelon is planted weeks before last frost dates.

HIGH-QUALITY SPATIAL CLIMATE DATA SETS FOR THE UNITED STATES AND BEYOND

A number of peer-reviewed, spatial climate data sets of excellent quality and detail for the United States arenow available. The data sets are suitable for a variety of modeling, analysis, and decision-making activities. Theseproducts are the result of collaboration between Oregon State Universitys Spatial Climate Analysis Service and USDANRCS, NOAA Office of Global Programs, NOAA National Climatic Data Center, NASA, Environment Canada, and otheragencies. The development of these high-quality maps was made possible through the development and use of PRISM, aknowledge-based climate analysis system that uses point climate data, a digital elevation model, and other spatial datasets to generate gridded, GIS-compatible estimates of annual, monthly and event-based climatic elements. Mappedelements currently available for the United States include 1961-1990 mean monthly and annual precipitation, maximumand minimum temperature, dew point temperature, relative humidity, snowfall, heating and cooling degree days, growingdegree days, median last spring and first fall frost dates, median freeze-free season length, and others. In addition,century-long gridded time series of monthly precipitation and minimum and maximum temperature for the lower 48 stateswill be available in 2001. Map products for other countries, including China and Canada, are nearing completion.

Quality and variability of long term climate data relative to agriculture

Climate data quality concerns prompted this study. The objective was to ascertain the impact of air temperature inhomogeneities on derived weather variables, such as growing-degree days, frost dates and heat stress, and to develop adjustment methodologies. Daily weather data spanning 1893–1989 from 34 Iowa stations were used for computation. Direct comparisons for each weather station and derived variable were made between all possible weather station combinations and a geographical mean data set. The latter was computed by using all available weather stations. For all derived weather variables studied, most weather stations revealed some type of notable inhomogeneity over the long period. Homogeneous weather stations were indeed rare. Individual time series exhibiting different levels of stability were common as were those exhibiting sharp discontinuities. Many, but not all, discontinuities could be traced to station histories. The use of the geographical mean data sets provided a rapid method to screen candidate weather stations, and could be used to correct discontinuities if they were not too numerous. More precise adjustments could, however, be made by using one or two nearby weather stations that were identified as being extremely stable. This process was more tedious because the stable periods were usually short. Climate resources are a valuable asset for mankind. However, data quality needs to be scrutinized before subsequent climate analyses.

ASSESSING THE ONSET OF SPRING: A CLIMATOLOGICAL PERSPECTIVE

This study is part of a program to examine spring plant-climate interactions in the major agricultural regions of eastern North America. The project's objectives were to: (1) document the yearly onset of the spring green wave and associated phenomena from 1908 to 1987 using phenological models, and (2) analyze regional dynamics and recent changes. Examining past variations in the green wave provides a context within which present and future variations can be assessed. Spring index dates, last -2.2°C (28°F) frost dates, and the difference between these two dates (termed the damage index) were generated for selected United States Daily Historical Climatology Network (HCN) stations between 1908 and 1987. The results show considerable geographic and temporal variations over the study period, and suggest that the threat of late spring frost damage may have decreased slightly from about 1960 to 1987. In future research, an improved version of the spring index (and associated surface phenological data) will be c...

Genetic variation in red alder (Alnusrubra) in relation to native climate and geography

Genetic variation was examined within and among populations of red alder (Alnusrubra Bong.) from elevational gradients in four river drainages of the Pacific Northwest. Wind-pollinated progenies of 120 trees were grown for 3 years in a common garden environment and measured for growth and shoot phenology. Variation in top weight, bud flush, and leaf abscission was analyzed in relation to native climate and elevation and compared with sympatric species. Strong geographic patterns of variation were observed for all measured traits, apparently reflecting adaptations to highly variable climates within the region studied. Growth traits were correlated with temperature amplitude and length of growing season. Growth rhythm in bud flushing and growth cessation was related to two important environmental cues, spring thermal sums and fall frost dates. Overall levels of variation in red alder appeared to be similar to several sympatric conifers, although variation within populations of red alder was lower. The latter finding may be due to the demography of the riparian populations sampled, or perhaps a characteristic of the species and its colonizing life history.

Implications of spatial averaging weather and soil moisture data for broad scale modelling activities

Abstract. Spatial averaging of data before or after modelling has important implications for large area land evaluation studies. Two procedures are evaluated for the spatial averaging of weather and soil moisture data before and after modelling (procedures A and B, respectively). The Thiessen polygon weighting technique is applied to a network of weather stations to derive daily weather values for the period 1955 to 1985 for 12 selected Agroecological Resource Areas (ARAs) on the Canadian prairies. These values are used in the model for procedure A. The components of the soil moisture balance for spring wheat are estimated with a budgeting model, assuming wheat is grown continuously for 30 years on soils with available water‐holding capacities (AWCs) of 150 and 250 mm. In procedure B, the data from individual stations are used as input to the model and the same Thiessen polygon weighting coefficients are applied to the output variables. A comparison of the two procedures shows no significant difference for temperature‐related variables such as frost dates, harvest date and cumulative potential evapotranspiration. The differences for moisture‐related variables (soil moisture content at sowing, cumulative actual evapotranspiration, runoff and deep drainage) are often statistically significant, but the absolute differences are less than 10 mm at probability levels ranging from 10 to 90%. For many practical applications the two procedures give similar results.

RATING CLIMATE IN SOUTHWESTERN ONTARIO FOR HORTICULTURAL CROPS

A climatic rating scheme was developed for qualitative assessment of land areas in southwestern Ontario for all commercial edible horticultural crops grown in the region. The general approach was to place the crops into three main groups — frost susceptible, frost tolerant, and winter temperature susceptible perennials. A four-point rating system was used to place areas into "very good", "good", "fair," or "poor" categories based on restrictions produced by the critical climatic factors appropriate for each group of crops. The Corn Heat Unit (CHU) map was used as the primary criterion to subdivide the area for the four-point rating. Secondary climatic features appropriate for each crop group were used to further subdivide the crops into subgroups. The climatic features used for the secondary subdivision were spring and fall frost dates, spring and summer maximum temperatures, and winter minimum temperatures. This scheme is the first step in developing a system that can be used to rate areas for their ability to produce edible commercial horticultural crops in this region of Ontario. It should prove useful when combined with soil ratings for these crops.Key words: Vegetable, fruit crop, growing season, winter/spring conditions, land rating

Autumn Frost Damage on Young Picea sitchensis 1. Occurrence of Autumn Frosts in Scotland compared with Western North America

Dates of first autumn air frosts (in Stevenson screens) of −2.5°C and 4.5°C were obtained for 42 meteorological stations in northern Britain with runs of 18 to 116 years. Frequency distributions of first frost dates were approximately normal. Altitude, distance from the sea, latitude and distance from the NWSE axis of Britain together accounted for 75% and 81% of the variation in dates of first −2.5°C and −4.5°C frosts, respectively, at the 42 stations. The variance in dates of first frosts decreased from lowland coastal to upland inland sites. Multiple regressions were used to produce maps of first frost dates in 20 × 20 km grid squares of Scotland. Dates of first 28°F (−2.2°C) and 24°F (−4.4°C) frosts were obtained for 20 sites in western North America, spanning the natural range of P. sitchensis . Mean dates were earlier, and variances decreased, from south to north. Upland sites like Eskdalemuir and Kielder Castle experience –2.5°C and −4.5°C frosts earlier in the autumn than all coastal stations in western North America south of about latitude 58°N (between Cordova and Sitka), and about 4 weeks earlier than at Masset on the Queen Charlotte Islands. Thus, P. sitchensis from Q.C.I. and further south may often experience autumn frosts in Scotland before the trees have experienced the cool/short days that they require to induce frost hardening.

Cloudiness and wind speed as factors in a climatic anomaly

Since 1940, Calgary's mean annual temperature has declined 0.3 °C from the mean value established during a warmer era, 1905–1940. However, the length of the frost-free period increased from an average of 109 days in the warmer period to 119 days in the cooler one. These changes are underscored by an advance of the probable date of the last spring frost, and a delay of the probable date of the first frost of autumn. Probabilities are computed for various critical frost dates. The belief is expressed that the discrepancy of a longer growing season in the face of declining growing season temperature is related to an observed increase in mean cloudiness during the growing season. It is also demonstrated that strong winds could have been a factor in promoting the anomaly. DOI: 10.1111/j.2153-3490.1981.tb01727.x

Estimating minimum temperature and climatological freeze risk in hilly terrain

Differences between weather station and on-farm minimum temperatures in hilly terrain were related to general weather parameters, using stepwise multiple linear regression and correlation techniques. Opacity (cloud cover) and wind speed were the most significant parameters, explaining up to 79% of the variation in night-time temperature differences between base station and field sites 20–40 km away. Considering dew point depression, days since 0.25 cm rainfall, absolute minimum temperature, cloud base height, opacity as quadratic and an exponential relationship did not improve the regression estimates significantly. Standard error of estimates ranged from 0.8°C for sites on hilltops to 2.3°C for valley bottoms. In independent data tests using 19 cases, the average minimum temperature difference between the base station and a high risk site was estimated within 0.4°C of the measured value. Significance of the regression relationships increased proportionally with distance down the slopes. Base station-site minimum temperature differences on relatively clear calm nights averaged near 1°C on hilltops, 2° to 3°C midway down slopes and 5° to 6°C in the hollows. Regression equations developed from short-term temperature measurements at more than 50 sites were used to estimate daily site minimum temperatures for a 21-year period. Spring and fall freeze probabilities for critical temperatures of 32°, 30° and 28°F (0.0°, −1.1° and −2.2°C) were then calculated for each site using standard climatological techniques. Estimated average freeze dates in hollows were up to 34 days later in spring and 39 days earlier in fall than on hilltops. Average dates of spring and fall freeze occurrences were delayed and advanced respectively about 6 days for each degree (C) drop in critical temperature. In independent data tests the average spring and fall ground frost dates at the base station were estimated within 2 days of measured values, using similar techniques. Minimum temperatures measured by traverses on a clear, calm night were highly correlated with estimated frost dates ( R = 0.99).

A Geographical Study of New England Temperatures

F all the elements of climate, temperature plays the most significant role in New England. The precipitation is generally adequate for all crops raised within the temperature limits. Wind, sunshine, cloudiness, and humidity are minor in their effects. These statements are an outgrowth of a study in which twenty-nine isothermal maps were constructed, showing the mean monthly, mean seasonal, mean annual, highest, and lowest temperatures, mean annual range, frost dates, and length of frost-free season.' Seventeen of these maps are reproduced here.