INFLUENCE OF THE ARCTIC FRONT ON THE CLIMATE AND CROPS OF ICELAND

AGRICULTURE in a subarctic environment .L L such as that of Iceland is both restricted and hazardous. Only the hardiest of crops can be grown to maturity and even these are subject to extreme variations in yield. It is the purpose of this paper to examine recent trends in the production of Iceland's most important staple crop-potatoes-and to attempt to explain the regional and temporal changes which have taken place. In the period from 1935 to 1957, the annual production of potatoes in Iceland averaged about 7,800 metric tons (Fig. 1). It varied, however, from a low of less than 4,000 tons in 1949 to a high of just under 16,000 tons in 1953. If, during this period, any attempt was made to increase the country's over-all production in keeping with the island's rapid growth in population, it is clearly not discernible from the statistics. Year-to-year fluctuations are so great that they effectively obscure any longterm trends. Due to the fact that both the extreme minimum and the extreme maximum of production were recorded during the last nine years of the period, and because statistical data for these years are likewise more complete than earlier records, they were singled out for special attention. For each of these years indices of warmth and moisture were calculated for approximately 45-50 stations, located in all parts of the island. The growing-degree day was chosen as a measure of warmth, employing a threshold temperature of 60 C., or 430 F. As a measure of moisture, the amount of precipitation recorded during the summer halfyear (April through September) was used. Both sets of indices were totaled for the entire country and are presented graphically in Figure 2. In the first three years of the series (194951) the over-all conditions of warmth varied only slightly and there was a gradual downward trend in moisture. The summer of 1952, however, was markedly colder and drier, constituting, in fact, the coldest year in the series. By contrast, 1953 was the warmest on record, though only slightly more moist. Nineteen fifty-four repeated the cold and dry pattern of 1952, while 1955 shows up as the secondwarmest year in the series and, by all odds, the wettest. Nineteen fifty-six was again cold and dry, while in 1957 the index of warmth rose and the summer precipitation dropped to a nine-year low. Thus, apart from the first three years, there was something of a cyclic fluctuation from a cold, dry summer one year to a warm, moist one the next. It is of course impossible to generalize or stereotype patterns of weather over so large and diverse a region as the island of Iceland. Indeed, it has long been recognized that the high land which crosses the island from northwest to southeast serves as an effective "weather-divide." The area south and west of the divide comes under the influence of relatively warm and moist air masses moving in off the Atlantic; in contrast, the northern and eastern parts of Iceland are dominated largely by cooler, drier air masses moving down from the Arctic Ocean. (Fig. 3). Even when the entire island is under the influence of a single air mass, the weather patterns differ markedly on opposite sides of the divide. Thus it is more realistic to compare and contrast the two regions with one another, as in Figures 4 and 5, then to generalize for the island in toto. Figure 4 reveals that south of the divide the index of warmth rose from 1949 to 1951, while to the north it fell during those years. From 1952 onward, temperature fluctuations exhibit a roughly parallel trend on both sides of the divide, apart from 1955. That year was almost as warm as 1953 in the north, though it was one of the cooler years in the south. Figure 5 shows how divergent the indices of moisture have been in the two regions during the period under study. With only minor exceptions, whenever moisture increased in the south, it decreased in the north, and vice versa. The two years of 1950 and 1951 are particularly interesting in that the average precipitation in both regions was so similar. Indeed, 1951 is unique, for in that year the average precipita-