LONG-TERM VARIABILITY OF THE HYDROCLIMATE .1 Eastern Canada

While seasonal temperatures have generally increased over the past century in western and central Canada, temperatures in the Atlantic coastal region and the eastern Canadian Arctic have tended to become lower, particularly during fall and winter since the 1960s (Gullet &

Skinner, 1992; Gan, 1995). Trends and patterns of precipitation are less obvious. According

to Gan (1995), for the 1948 -1989 period, less than 20 % of 145 station records examined from across Canada showed any significant change in total precipitation and these were about equally distributed between increasing and decreasing amounts. There was no apparent spatial pattern to these changes, nor was there any significant association between changes in temperature and precipitation (Gan, 1995). A different result was obtained by Groisman &

Easterling (1994), who found a significant increase between 1950 and 1990 in total precipitation for the northeastern United States and adjacent parts of Canada, as well as a significant increase in snowfall for Canada north of 55”N. Brown & Goodison (1996) identified a significant increase in winter and spring snowfall in Atlantic Canada between 1971 and 1992. In a major reanalysis of snow depth data for Canada for the period 1946 - 1995, Brown & Braaten (1998) found that winter and early spring snow depths decreased significantly over much of Canada; however, Newfoundland was shown to have experienced a slight but not statistically significant increase in winter and spring snow depth and duration of snow cover.

The climatological relationship between snowfall and temperature for Canada over the past century was recently investigated by Davis et al. (1999). They found regional differences in the response to a given change in winter temperature such that, in the case of an increase in temperature, the more northerly and continental locations experienced an increase in snowfall. In the same circumstances, the more southerly and coastal locations experienced a decrease in snowfall, though not necessarily a decrease in total precipitation.

The relationship was found to vary from month to month, such that the “zero line” marking the change in sign of the slope of the snowfall-temperature relationship migrates from north to southeast with the advance of fall and winter, reaching its maximum southerly extent in February, before retreating northward again. For Newfoundland and southeast Labrador, the relationship is negative in all months; that is, less snowfall is associated with higher winter temperatures and more with lower temperatures. The January position of the zero line coincides with the -12°C January mean temperature (Davis et al., 1999).

3.2 Recent trends in Newfoundland

The long-term variability of seasonal temperature and precipitation for Newfoundland has been evaluated using records from low-elevation, mainly coastal stations (Banfield & Jacobs, 1998). That analysis used the recently homogenized historical monthly temperature and precipitation database for Canadian locations, prepared by the Atmospheric Environment Service of Environment Canada using objective procedures to overcome various sources of inhomogeneity (Mekis & Hogg 1997; Vincent & Gullett 1997; Vincent 1998; Vincent &

Gullett 1998). Of the Newfoundland station series selected for analysis, those for St. John’s and the composite record for Belle Isle/St. Anthony at the northern tip of the island could be extended back as far as 1895.

When a linear regression model was applied to the century-long series (1895-1995) for St. John’s and Belle Isle/St. Anthony, no significant trend was found for summer temperature at either station, in agreement with the regional studies reviewed above. With respect to winter (December through March) mean temperature, the analysis showed trends at both locations to be slight but statistically non-significant, indicating no significant increase or decrease of temperature for this period as a whole. However, examination of the winter series after smoothing using 5-year moving averages revealed a pattern of alternating modes with temperatures significantly above or below the series average. Using quasi-objective criteria - that a mode shift was said to have occurred when the departure of the smoothed series from the overall mean equaled or exceeded one standard deviation and persisted for a

52

decade or more - the records could be separated into five epochs common to both St. John’s and Belle Isle/St. Anthony. These periods are demarcated in Figure 3, with the corresponding epoch-mean winter temperatures at these two stations presented in Table 1. One of the most striking features of the winter record is the substantial decline in temperatures that took place between epochs IV and V, over a relatively short period between 1969 (one of mildest winters on record throughout the province) and 1972. The absolute decline in temperature was especially marked to the north, amounting to a cooling by almost 7 “C of the seasonal mean at Belle Isle/St. Anthony during this three-year period. The latter years of the 1970’s decade saw a temporary moderation that included some mild winters between 1979 and 1983 (as elsewhere in Canada), but this was followed by a resumption of cooling until the first half of the1990’s decade. This latter episode represents a significant contrast with much of central and western Canada, where winter temperatures continued their general upward trend.

0 3 0 -6 B -9 -12 -15

1895 1915 1935 1955 1975 1995

Figure 3. Historical record of mean winter temperature at St. John’s

Airport (STJA) and Belle Isle/St. Anthony (BUSTA), 1895 - 1995.

Five-year moving averages (bold) are superimposed upon the inter-annual record.

The most reliable precipitation records for Newfoundland extend back to around 1940 at synoptic (airport) reporting stations on the island, though it should be noted that the generally exposed situation at such stations raises questions concerning representiveness of measurements during periods of strong winds, especially for snowfall. Table 2 from Banfield

& Jacobs (1998) contrasts the mean winter and summer total precipitation at St. John’s, Gander and Stephenville for the relatively warm period of 1943-1971 and the subsequent cold epoch of 1972-1996. The clearest spatially defined signal is that of increased amounts at Stephenville after 1972, which is apparent for winter, summer and the annual total (all significantly greater than for the preceding period). At Gander and St. John’s winter precipitation has also shown significant change since 1972, but in opposing directions.

Furthermore, a significant increase in winter snowfall (amount and frequency of occurrence) has occurred at Stephenville and Gander since the start of the colder post-1972 epoch, though not at St. John’s.

Table 1. Mean winter temperature at St. John’s and St. Anthony/Belle Isle for Epochs I-V

Table 2. Comparison of seasonal temperature and precipitation at Newfoundland Stations for 1943-1971 and 1972-1996 comprehensive analysis of Newfoundland streamflow records for secular change or long-term

54

variability has yet to be carried out. However, from the earlier discussion of differences in month were the differences statistically significant at the 95% confidence level. This limited analysis suggests that interannual, not decadal-scale, variability dominates the streamflow records, but further investigation is needed to confirm this.

3.3 Snowcover-climate relations for the Grand Lake Basin

Although long-term snow survey data exist for some locations in Newfoundland, there has been little analysis of these records. An exception, which demonstrates the climatological potential of such specialized private data sets, is the annual late-winter snow survey of the consist of three separate, near-circular small clearings occurring within an approximately level, natural forest area of 1000-2000 m*. Since 1988 the measurements have utilised a Water Survey of Canada snow sampler having metric water equivalent graduation; previously the Mount Rose sampler was used. With the advent of helicopter support the survey duration is now typically 2-3 days, though in the earlier years it took much longer. At each location mean snow depth, water equivalent and density are determined, leading to average values of these quantities for each of the physical sub-divisions of the basin. The results of the survey and the implications for the spring flood are presented as an annual internal report (Deer Lake Power Company, 1999). Banfield (1991) carried out a detailed analysis of those records, which has been updated and summarised for the purposes of this review.

Typically, a net accumulation of snow develops over the basin from late November until March, though this may be punctuated by thawing periods of varying intensity, especially at the lower elevations during relatively milder winters. The long term mean depth of snow at the time of the March survey, averaged for seven of the survey locations for which a continuous series extends from 1934 -1999, is 85 cm (standard deviation 24 cm); mean snowpack water content averaged 26 cm (s.d. = 9 cm), with a mean density of 308 kg me3 (s.d. = 41 kg ms3). Owing to logistical and manpower limitations, some sections of the basin are less than ideally sampled, whilst at exposed elevations above the tree line the reduction in snow cover due to wind drifting and sublimation may be considerable.

* Snow Survey Location (since 1934) A Climatolcgical Statian

Islavatlon ssl; year Opened,

Comer Brook Lake

-

NEWFOUNDLAND

/3

Figure 4. Grand Lake watershed, showing locations of snow survey sites and climate stations used in the study (Banfield, 1991).

The spring flood, comprising the snowmelt plus springtime precipitation, is by far the most important seasonal contribution to the annual runoff into the reservoir of Grand Lake.

For a year with average snow depth and density over the basin, the volumetric water content of the late March snow blanket would contribute approximately 25% of the average annual watershed runoff or yield. This figure increases to approximately 45% of annual yield when an average amount of springtime precipitation (between April l-June 15) is added to the snowmelt contribution. Hence, the snow survey constitutes a crucial first step in a quantitative procedure designed to provide advance knowledge of spring flood magnitude and subsequent optimisation of operating priorities for the watershed.

As in other parts of Newfoundland, the Grand Lake watershed area has experienced temporal fluctuations in its seasonal climate during the 20th century. In the present context the winter season is defined as the months of December through March and it is clear that the variability in mean temperature for this season has had significant implications for the snow cover and hence spring runoff over the catchment. Table 3 and Figure 5 summarise the highly significant inter-relationships between mean winter temperature at Deer Lake (an Environment Canada climate station adjacent to the catchment), the amount of rainfall during winter, and the late winter snowpack water content derived from the March survey. Since

1934 the periods with mildest winters have been the 1950’s, late 1960’s, early 1980’s and three of the most recent four winters (1996, 1998 and 1999). During each of these phases there has generally been a diminished snowpack and hence less water content for the ensuing spring flood. The amount of snowfall during the winter, in itself, is not the most significant determinant of the March snowpack volume, but rather the amount of rainfall, as a function of the temperature, is more important in this respect. Conversely, during the coldest phases of the winter record (1930’s, early-mid 1970’s and early-mid 1990’s) the March snowpack water volume tended, overall, to be greater, but exceptions characterise particularly cold

56

winters having less snowfall, such as 1959 and 1972. These basin-scale results are consistent with the general pattern of a negative temperature-snowfall relationship for the Newfoundland region identified by Davis et al. (1999).

Table 3: Correlation between winter climate and March snowpack water content in the Grand Lake Watershed, based upon period 1933- 1999. Coefficients marked “* *” are significant at the 99% level.

RAIN SNOW SNOW Hz0

TMEAN .431** -.067 -.496**

RAIN -.072 -.541**

SNOW .068

TMEAN:

RAIN:

SNOW:

SNOW H20:

Mean air temperature at Deer Lake, December through March Total rainfall at Deer Lake, December through March

Total snowfall at Deer Lake, December through March

Water equivalent of the late March snowpack over Grand Lake basin, derived from the annual snow survey.

Figure 5. Late-March snowpack water content and December-March mean temperature for the Grand Lake watershed.

3.4 Hydroclimate of the Long Range Mountains

No long-term climate data exist for the Long Range Mountains, although their more northerly location and higher elevations suggest a relatively reliable winter/spring snowcover, compared with the rest of the island. As noted, this supposition is supported by the mean hydrographs of streams emerging from the mountains. Recent studies based on automated climate stations and seasonal snow surveys on the Big Level Plateau in the Gros Mome National Park (Jacobs et al. 1998) have given some indication of the hydroclimatic regime in

the central part of the range. Comparisons with lower stations suggest November through April precipitation totals of 140 to 150 cm (w.e.), with 80% of that falling as snow. Short- term temperature comparisons indicate a mean lapse rate of 0.6 “C /lOO m, and an estimated long-term mean temperature at the 800 m a.s.1. summit of 9.5 “C in July and -12.5 “C in February. The plateau is windy, with prevailing southwesterlies for October to March averaging more than 30 km hr-’ and storm gusts reaching 200 km hr-‘. Such conditions favor the formation and persistence of late-lying snowbeds, mainly on moderate north-facing slopes (Figure 6). These are an important feature of the regional ecology, especially in relation to caribou and a distinctive alpine flora that is a consequence of the presence of the snowbeds and the nutrients provided by caribou that are attracted to them in summer (Brouillet et al.

1998).

Figure 6. Long Range Mountains: viewed at the end of June looking eastward over the Big Level plateau. Snowbeds visible on north-facing slopes will typically remain until early August.

The accumulating observational record from the Big Level plateau has been extended by statistical comparison with records from adjacent coastal stations dating to the 1940s (Martin et al. 1999). The results tend to confirm the supposition that, within the limits of the interannual and interdecadal variability observed in the Newfoundland climate over the past half-century, the seasonal snowcover at the alpine zone is a relatively constant feature from one year to the next. Since the mean winter temperatures on the plateau are near or below the temperature coinciding with the regional “zero-line” in the snowfall-temperature relationship identified by Davis et al. (1999), it is possible that winter snowfall above 700 m a.s.1. is positively associated with regional winter temperature anomalies, in contrast to what is

58

observed at lower elevations. Several more years of observations will be required to confirm this.

Seasonal surveys on the Big Level plateau have included sampling of the snowpack and streams for chemical analysis, revealing interannual variations in the hydrochemical regime (Jacobs et al., 1998). In colder winters, such as 1996-97, the load of deposited that in milder winters, such as 1998 and 1999, frequent thaws and rain-on-snow events result in a distributed release of meltwater and dissolved chemical load, as has been observed by MacLean et al. (1995) in central Ontario. Thus, for a given loading of atmospheric pollutants to the snow through the course of a winter, the timing and magnitude of the maximum concentration of dissolved chemicals delivered to headwater streams is seen to depend on the amount and frequency of winter rainfall events, that being largely dependent on winter temperature.

4. CONCLUSIONS

The hydroclimate of Newfoundland is characterized by generally high effective precipitation on an annual basis, although there is significant seasonality to precipitation and runoff regimes. Seasonal snowcover plays an important role in the timing and distribution of runoff, with winter temperature and rainfall the controlling factors. As a consequence, distinct differences exist between mean hydrographs for low, more southerly basins and those in the north and at higher elevations. In the former, peak runoff normally occurs in fall and winter, while in the latter there is a distinct spring peak in the flow. These temperature-driven spatial patterns might be expected to have a parallel in the temporal record of interannual and longer-term variability. While there has been significant interdecadal variability of winter temperature and precipitation over the region, and a general tendency toward greater winter precipitation in colder periods, the nature of the hydrologic response of these events is less this tentative conclusion applies to other anthropogenic pollutants. Analysis of the aquatic chemistry (Clair et al., 1997) has thus far given ambiguous results, but might be reinterpreted as giving greater weight to local sources of some contaminant species such as SO4, if not others. Little is known about trace contaminants such as heavy metals and organic pollutants in Newfoundland waters. Given the relationship seen between the winter rain-snow ratio and

the temporal distribution of contaminant concentrations in runoff, climate variability and change can be expected to have significant effects on surface water chemistry.

Basin-specific investigations, such as the Grand Lake watershed study of Banfield (1991) and proposed interdisciplinary studies in other basins, offer the best means of advancing knowledge about the hydroclimate and pollution chemistry of Newfoundland. In conjunction with data from conventional hydrometric and climate networks, such intensive studies provide a baseline against which monitoring for change can be carried out. In addition to new research and data-gathering efforts, more use needs to be made of existing data sets held by government agencies and firms such as hydroelectric companies.

5. ACKNOWLEDGEMENTS

The authors wish to acknowledge the assistance of staff of Gros Mome National Park and Deer Lake Power Company, among others, in some of the research activities reviewed here.

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