Securing Biodiversity in Breckland - European Commission

Evidence of Climatic Change: Long-Term Trends in WeatherRainfallSince 1905, Breckland has become wetter. Total rainfall in each of winter, spring and autumnincreased significantly between 1905 and 2007 (Table 17). The biggest seasonal increase was forwinter rainfall that rose by 21.2 mm (0.206 mm yr -1 ± 0.127 SE); 14.6 % relative to the winter meanover this time period. In contrast, the total rainfall recorded in summer showed no long term trendover this period (Figure 15).The number of extreme rainfall events increased significantly for all seasons between 1905 and2007 (Table 17). However, there were no changes in the number of extreme drought events perseason.TemperatureIn Breckland the weather, in terms of temperature, has become less continental, with milderwinters, milder nights in spring and summer and fewer frosts. Mean daily minimum airtemperatures were lower in the mid twentieth century in all four seasons than in recent decadesand increased significantly from 1949 to 2008, for all four seasons (Table 17, Figure 16). Duringwinter, the increase in mean daily minimum temperature between 1949 and 2008 was 2.4 °C (0.04°C yr -1 ± 0.009 SE), a substantial change compared to a long term winter mean minimum of 0°C. Forspring, daily minima increased substantially, by 1.7 °C compared to a long term mean of 2.8 °C (anincrease of 61%).Air frost became significantly less frequent in both spring and winter between 1949 and 2008 (Table17). Daily minimum air temperatures and number of air frosts are conservative estimates of theactual degree of frost stress for plants and invertebrates. Minimum air temperatures presentedhere are much higher than the minimum grass temperatures recorded; for example the averageminimum air temperature for December 2007 was 1.16°C, however the average minimum grasstemperature for the month was -2.35°C. The mean daily maximum temperature in winter andspring increased significantly between 1949 and 2008; for winter the temperature change issubstantial, 1.9 °C compared to a long term mean of only 7.2 °C (26%). However, mean dailymaxima during summer and autumn have not changed; since 1949 Breckland has not becomehotter.93