Dalian has a monsoon-influenced humid continental climate (Köppen Dwa), characterised by humid summers due to the East Asian monsoon, and cold, windy, dry winters that reflect the influence of the vast Siberian anticyclone. Except for winter, the city experiences a one-month seasonal lag due to its position on the Liaodong Peninsula. The monthly 24-hour average temperature ranges from −3.9 °C (25.0 °F) in January to 24.1 °C (75.4 °F) in August. Annual precipitation averages 602 millimetres (23.7 in) but is heavily concentrated in the summer months and can vary greatly from year to year. Due to the coastal location, the mean diurnal temperature variation annually is small, at 6.75 °C (12.2 °F). The monthly percent of possible sunshine ranges from 49% in July to 68% in September and October, with 2,740 hours of bright sunshine annually. The annual mean temperature is 10.90 °C (51.6 °F). Extremes since 1951 have ranged from −21.1 °C (−6 °F) on 4 January 1970 to 36.6 °C (98 °F) on 14 July 2015.
One of the most heavily developed industrial areas of China, Dalian municipal area today consists of Dalian proper and the smaller Lüshunkou (formerly Lüshun city, known in Western and Russian historic references as Port Arthur), about forty nautical miles (74 kilometres; 46 miles) farther along the Liaodong Peninsula. Historical references note that the Russian designed city of Dalniy (Alt. Dalney), on the south side of Dalian Bay was 40 kilometres (25 miles) from Port Arthur/Lüshun (known today as Lüshunkou or literally, Lüshun Port).
Dalian is located on Korea Bay north of the Yellow Sea and roughly in the middle of the Liaodong peninsula at its narrowest neck oristhmus. With a coastline of 1,906 km (1,184 mi), it governs the majority of the Liaodong Peninsula and about 260 surrounding islands and reefs. It is seated at south-south-west of the Yalu River, and its harbour entrance forms a sub-bay known as Dalian Bay.
In 2001, The United Nations Environment Programme awarded the Dalian Municipal Government for its outstanding contribution to the protection of the environment.
The average content of the four pollutants in the air reached Class Ⅱ of National Ambient Air Quality Standards and there were 353 days with Air Pollution Index (API) over Class Ⅱ (Good), including 108 excellent days with Class Ⅰ (Superior). Dalian frequently ranks Grade 2 for air pollution according to State Environmental Protection Administration. However, the environmental effects of economic growth are of concern, according to Dalian Environmental Protection Agency, during the first half of 2011, respirable particles in the air increased significantly, with an average 40% higher than 2010.
The water quality of offshore marine space remained stable overall. The annual average content of monitoring indicators for water quality met Class-II of the National Seawater Quality Standard, with the exception of Inorganic Nitrogen in Dalian Bay and the city’s southern coast. The water quality of drinking water sources is considered good and complies with Class-III of Environmental Quality Standards for Surface Water.
Recent events have had a major environmental impact on the city. In July 2010, the explosion of two petroleum pipelines released 11,000 barrels of oil into the Yellow Sea, according to official statements. Rick Steiner, an American marine conservationist working with Greenpeace, says that the figure could be upwards of 400,000. It was reported as the largest oil spill to occur in China, and involved 2,000 firefighters. The oil spill stretched for at least 50 square kilometres (19 sq mi). 800 fishing boats were mobilized for the cleanup. The incident caused President Hu Jintao and Premier Wen Jiabao to intervene, and Vice Premier Zhang Dejiang moved in to help direct the rescue work. A researcher with the China Environmental Science Research Institute, said that “the impact on marine life and on humans – as the pollution enters the food chain – could last 10 years.” This has compounded aquatic pollution, affecting the city’s fishing industry.
In August 2011, a dike protecting the petrochemical Fujia Factory in Jinzhou District was breached due to a typhoon. Authorities have ordered the plant to be shut down. Around 12,000 residents protested as the factory, which originally was intended to be based in Xiamen, did not receive official approval to operate in Dalian. Municipal authorities ruled that the facility must move, leaving taxpayers to pay the expensive cost of relocation.
Concerns have been raised over mounting traffic due to “bad urban design” and that the growing rate of car ownership is affecting air quality. The United States National Academy of Engineering have raised concern about rising traffic in Dalian stating that “rapid growth of traffic in Dalian and in similar Chinese cities will repeat the air quality and energy consumption mistakes of Los Angeles and other U.S. cities, if not better managed.”