Geographical Overview
Yan’an is located in northern Shaanxi Province, along the middle reaches of the Yellow River, between latitudes 35°21′–37°31′N and longitudes 107°41′–110°31′E. Nestled in the south-central Loess Plateau, it lies 371 kilometers north of Xi’an. The city borders Yulin to the north, the Guanzhong cities of Xianyang, Tongchuan, and Weinan to the south, Shanxi’s Linfen and Lüliang across the Yellow River to the east, and Gansu’s Qingyang to the west, covering a total area of 37,000 square kilometers. Yan’an experiences an inland arid to semi-arid climate with distinct seasons, abundant sunshine, and large diurnal temperature variations. The annual frost-free period averages 180 days, with a mean annual temperature of 11.0°C, 2,104.7 hours of sunshine, and 517.2 mm of precipitation.
Topography and Landforms
Yan’an is located in the middle reaches of the Yellow River, within the hilly and gully region of the Loess Plateau. Its landscape is predominantly characterized by the Loess Plateau and hills, with a northwest-to-southeast elevation gradient and an average altitude of approximately 1,200 meters. The northern Baiyu Mountain ranges from 1,600 to 1,800 meters in elevation, with its highest peak at the summit of Baiyu Mountain in WuguchengTownship, Wuqi County, reaching 1,809.8 meters; the lowest point is at Hou’erchuan in Jiyi Township, Yichuan County, at 388.8 meters, resulting in a relative elevation difference of 1,421 meters. The northern part is mainly composed of loess ridges, mounds, and gullies, accounting for 72% of the total area; the southern part is primarily characterized by loess tablelands and gullies, making up 19% of the area; while rocky mountainous regions constitute 9% of the total area. The western Ziwuling Mountain, running north-south, serves as the watershed between the Luo River and Jing River, and is one of the bedrock mountain ranges rising above the Loess Plateau, with elevations ranging from 1,500 to 1,600 meters and its main peak reaching 1,687 meters. The eastern Huanglong Mountain extends roughly north-south, with an elevation of 1,500 meters and its main peak (Daling) reaching 1,788.7 meters. The central Lao Mountain runs northwest-southeast, with an average elevation of 1,400 meters and its main peak (Dadunliang) at 1,464 meters. Huanglong Mountain and Lao Mountain are collectively known as the Liangshan Mountain Range, forming the skeletal framework of Yan’an’s topography.
Climate
Basic Climatological Data of Yan’an (Based on Statistics from 1991-2020) | ||||||||||||
Jan. | Feb. | Mar. | Apr. | May | Jun. | Jul. | Aug. | Sep. | Oct. | Nov. | Dec. | |
Avg. Temp (°C) | -5.4 | -1.1 | 5.3 | 12.2 | 17.1 | 21.3 | 23.2 | 21.5 | 16.3 | 9.8 | 2.8 | -3.7 |
Avg. High (°C) | 2.8 | 7.1 | 13.5 | 20.6 | 25.2 | 29.0 | 29.9 | 28.0 | 23.2 | 17.6 | 10.8 | 4.3 |
Extreme High (°C) | 10.4 | 16.2 | 23.8 | 29.9 | 32.3 | 34.7 | 35.3 | 33.4 | 30.1 | 24.5 | 19.4 | 11.4 |
Avg. Low (°C) | -11.2 | -7.0 | -1.2 | 4.9 | 9.8 | 14.5 | 17.8 | 16.8 | 11.6 | 4.6 | -2.5 | -9.2 |
Extreme Low (°C) | -20.0 | -11.8 | -8.8 | -2.4 | 2.0 | 7.9 | 11.3 | 11.2 | 3.7 | 0 | -11.7 | -19.6 |
Avg. Precipitation (mm) | 4.4 | 6.8 | 13.6 | 27.7 | 43.9 | 63.8 | 119.0 | 112.0 | 75.8 | 39.5 | 15.5 | 2.8 |
Rainy Days | 3.5 | 3.4 | 4.2 | 5.6 | 7.2 | 8.6 | 11.2 | 10.9 | 9.7 | 7.5 | 4.6 | 2.7 |
Avg. Wind Speed (m/s) | 1.4 | 1.5 | 1.8 | 1.9 | 1.8 | 1.6 | 1.5 | 1.4 | 1.4 | 1.4 | 1.4 | 1.5 |
Yan’an has a plateau continental monsoon climate, with its northern part belonging to a semi-arid region and the southern part to a semi-humid region. Winters are cold and dry with a long duration; spring sees rapid and variable temperature rises, prone to frost, and frequently accompanied by strong winds, sandstorms, and floating dust, often experiencing spring droughts. Summers are warm with concentrated rainfall, occasionally interrupted by mid-summer droughts, frequent thunderstorms, and occasional hail. Autumn brings rapid temperature drops, increased fog, early frosts, and overcast rainy weather. The diurnal temperature variation is large, with the annual average diurnal temperature difference across the region ranging from 11.1°C to 14.9°C, being the largest in Fuxian and the smallest in Luochuan. During the year, the diurnal temperature difference is larger from April to June, averaging 15–16°C, and smaller from July to September, averaging 11–12°C.
1.Temperature: The annual average temperature is 9.9°C, with an annual average maximum temperature of 17.7°C and an annual average minimum temperature of 4.1°C. The monthly average temperature in the hottest month (July) is 23.2°C, while in the coldest month (January) it is -5.4°C. The extreme maximum temperature recorded is 41.5°C (on June 22, 2005), and the extreme minimum temperature is -28.7°C (on December 26, 2002).
2. Precipitation: The annual average precipitation is 524.8 mm, with the maximum daily precipitation being 195.3 mm (on July 4, 2002). The annual number of days with precipitation ≥0.1 mm is 79.1, and with precipitation ≥50 mm is 7.8. The highest annual precipitation recorded is 772.8 mm (in 2013), while the lowest is only 346.1 mm (in 1997). Precipitation is mainly concentrated from May to September, with the highest average monthly precipitation occurring in July at 119.0 mm.
3. Sunshine: The annual sunshine duration is 2,408.9 hours, with May having the most at 246.0 hours and September the least at 167.1 hours. The annual sunshine percentage is 55%, reaching a maximum of 62% in December and a minimum of 46% in September.
4. Wind: The annual average wind speed is 1.5 m/s, with a maximum wind speed of 17.9 m/s from the north-northwest (NNW) direction recorded on July 12, 2017. The most frequent wind directions are north-northwest and calm (NNW, C).
5. Weather phenomenon days: Gales occur on 3.2 days; sandstorms on 0.3 days, mainly in April; heavy fog on 19.9 days, with September having the most at 8.7 days; hail on 23.2 days, mainly in June; thunderstorms on 26.4 days, with July having the most at 8.0 days; and the frost period lasts 185 days.
6. Sunrise and sunset times: On the spring equinox, sunrise is at 06:47 and sunset at 18:53; on the summer solstice, sunrise is at 05:24 and sunset at 20:04; on the autumn equinox, sunrise is at 06:30 and sunset at 18:38; on the winter solstice, sunrise is at 07:50 and sunset at 17:30.