2. Annual summaries of the climate system in (c) Summer (June – August 2010, Fig. 2.1.4c) 2010 Japan experienced its hottest summer in more than 100 years. The seasonal mean temperature in 2.1 Climate in Japan Japan, which is the average value for 17 observatory 2.1.1 Average surface temperature, precipitation stations deemed to be relatively unaffected by the amounts and sunshine durations urban heat island effect, was the highest on record The annual anomaly of the average surface since 1898. In particular, August was so hot that temperature over Japan (averaged over 17 monthly mean temperature records for August were observatories confirmed as being relatively unaffected broken at 77 out of 154 observatories in Japan. by urbanization) in 2010 was 0.86°C above normal Seasonal precipitation amounts were significantly (based on the 1971 – 2000 average), and was the above normal on the Sea of Japan side of northern fourth highest since 1898. On a longer time scale, Japan due to the influence of a series of fronts. average surface temperatures have risen at a rate of (d) Autumn (September – November 2010, Fig. about 1.15°C per century since 1898 (Fig. 2.1.1). 2.1.4d) Seasonal mean temperatures were above normal 2.1.2 Seasonal features nationwide and significantly above normal in northern (a) Winter (December 2009 – February 2010, Fig. Japan. Due to severe late summer heat in the first half 2.1.4a) of September, records for the frequency of extremely Although seasonal mean temperatures were hot days (defined as those with maximum daily above normal nationwide, the intraseasonal temperatures of 35°C or over) for September were temperature variation was large. Due to cold spells, broken at 46 out of 154 stations. Seasonal many areas on the Sea of Japan side were hit by heavy precipitation amounts were significantly above normal snowfall in the middle of December, the first half of in Okinawa/Amami. January, and the first ten days of February. In early February, Niigata on the Sea of Japan side of eastern Japan was hit by heavy snowfall and had a maximum snow depth of 81 cm, which was the highest level since the winter of 1984/85. (b) Spring (March – May 2010, Fig. 2.1.4b) The intraseasonal temperature variation was very large nationwide. In the first and second ten-day period of March and in the first ten days of May, temperatures were significantly above normal nationwide due to warm air advection from the south. Conversely, in the last ten days of March, the latter half of April and the last ten days of May, temperatures were below normal nationwide due to a series of cold spells. Since cyclones and fronts frequently passed near mainland Japan, seasonal precipitation amounts were significantly above normal in northern, eastern and western Japan, and seasonal sunshine duration amounts were significantly below normal in northern Japan and on the Sea of Japan side of eastern and western Japan. 6 Fig. 2.1.1 Long-term change in the annual anomaly of average surface temperature over Japan The bars indicate the annual anomalies of the average surface temperature for each year. The blue line indicates the five-year running mean, and the red line indicates the long-term linear trend. Table 2.1.1 Regional average and rank of annual mean temperature anomaly, annual precipitation ratio and annual sunshine duration ratio for divisions and subdivisions (2010) 7 Table 2.1.2 Number of observatories reporting record monthly mean temperatures, precipitation amounts and sunshine durations (2010) From 154 surface meteorological stations across Japan Temperature Precipitation amount Sunshine duration Highest Lowest Heaviest Lightest Longest Shortest January 1 February 1 2 March 9 1 6 April 7 9 May June 4 2 July 2 4 6 August 77 4 September 3 1 7 October 2 5 November 1 December 2 12 3 Table 2.1.3 Onset/end of the Baiu (Japan’s rainy season) for individual regions (2010) Average Average date of date of Area-averaged precipitation Regions Onset of rainy onset of End of rainy end of ratio during season* rainy season season* rainy season rainy season (1971 – (1971 – ％ 2000) 2000) ( ) Okinawa 6 May 8 May 19 June 23 June 97 Amami 6 May 10 May 15 July 28 June 94 Southern 12 June 29 May 20 July 13 July 167 Kyushu Northern 12 June 5 June 17 July 18 July 111 Kyushu Shikoku 13 June 4 June 17 July 17 July 121 Chugoku 13 June 6 June 17 July 20 July 103 Kinki 13 June 6 June 17 July 19 July 135 Toukai 13 June 8 June 17 July 20 July 96 Kanto- 13 June 8 June 17 July 20 July 101 Koushin Hokuriku 13 June 10 June 17 July 22 July 94 Southern 14 June 10 June 18 July 23 July 115 Tohoku Northern 16 June 12 June 18 July 27 July 119 Tohoku * The onset/end of the rainy season normally has a transitional period of about five days. The dates shown in the table denote the middle day of this period. 8 Fig. 2.1.2 Five-day running mean temperature anomaly for divisions (January – December 2010) Fig. 2.1.3 Annual climate anomaly/ratio over Japan in 2010 9 (a) Winter (b) Spring (c) Summer (d) Autumn Fig. 2.1.4 Seasonal anomalies/ratios over Japan in 2010 (a) Winter (December 2009 to February 2010), (b) spring (March to May), (c) summer (June to August), (d) autumn (September to November) 10 2.2 Climate around the world (9) Low temperatures in Europe (January – February, November – December) 2.2.1 Global average surface temperature (10) High temperatures and light precipitation amounts The annual anomaly of the global average surface around western Russia (June – August) temperature in 2010 (i.e., the average of the near-surface (11) High temperatures from the Middle East to western air temperature over land and the SST) was 0.34±0.12°C Africa (all year round) above normal (based on the 1971 – 2000 average), which (12) High temperatures around Madagascar (all year was the second highest since 1891. On a longer time scale, round) global average surface temperatures have risen at a rate of (13) High temperatures around eastern North America (all about 0.68°C per century since 1891 (Fig. 2.2.1). year round) (14) Low temperatures around the southeastern USA 2.2.2 Regional climate (February – March, December) Annual mean temperatures were above normal in (15) Heavy precipitation amounts around the Caribbean most parts of the world except over the area from western Sea (June – December) to central Siberia, in Europe and in Australia (Fig. 2.2.3). (16) High temperatures in northern South America Extremely high temperatures were frequently observed (January – November) around low latitudes between 30°S and 30°N, around (17) Low temperatures in southern South America (May, western Russia and around eastern North America, while July – August, December) extremely low temperatures were observed in Europe (18) Heavy precipitation amounts in eastern Australia from January to February and from November to (December) December, and around the southeastern USA from February to March and in December (Fig. 2.2.5). 2.2.3 Tropical cyclones over the western North Annual precipitation amounts were above normal in Pacific Indonesia, around Pakistan, and in eastern Europe, In 2010, 14 tropical cyclones with maximum wind western Africa, the northwestern USA, around the speeds of 17.2 m/s or higher formed in the western North Caribbean Sea and in Australia, while they were below Pacific. The number is the least since 1951. Seven of them normal in southwestern South America (Fig. 2.2.4). approached within 300 km of the Japanese archipelago, Extremely heavy precipitation amounts were frequently and two made landfall on Japan. The normal numbers (i.e., observed in northeastern China, around southern the 1971–2000 average) of formation, approach and Indonesia and around the Caribbean Sea, while extremely landfall are 26.7, 10.8 and 2.6, respectively. light precipitation amounts were frequently seen in The tracks of tropical cyclones in 2010 are shown in southwestern South America (Fig. 2.2.6). Figure 2.2.7. The number of formation in 2010 is fewer Major extreme events and weather-related disasters than normal, particularly over the sea east of the in 2010 were as follows (Fig. 2.2.2): Philippines. Only five tropical cyclones formed south of (1) Low temperatures around western Siberia (January – latitude 20 degrees north and east of longitude 120 degrees February, December) east (16.1 is the 1971–2000 average frequency). This was (2) Low temperatures around Mongolia (February – April, considered that a result of the strong North Pacific High December) and suppressed convective activities over the sea east of (3) High temperatures around Japan (June – September) the Philippines. (4) Torrential rains in central China (August) (5) Typhoons and heavy precipitation amounts from Western Japan to Thailand (October) (6) High temperatures in Southeast Asia (all year round) (7) Heavy precipitation amounts around southern Indonesia (July – October) (8) Heavy precipitation amounts around Pakistan (June – September) 11 Fig. 2.2.1 Long-term change in the annual anomaly of global average surface temperature The bars indicate the annual anomalies of the global average surface temperature for each year. The error bars indicate 90% confidence intervals. The blue line indicates the five-year running mean, and the red line indicates the long-term linear trend. Fig. 2.2.2 Extreme events and weather-related disasters in 2010 Schematic representation of major extreme climatic events and weather-related disasters that occurred during the year 12 Fig.