Park type (f
1)
Nanjing is located in the western section of the Ningzhen Mountain Range. The Yangtze River runs through the area from southwest to east. The overall terrain and landform gradually transition from the low hills in the southwest and northwest to the Yangtze River valley plain in the middle. It can be divided into four types: mountain, hill, upland and plain31.
Taking into account the construction theme, surface form and resource types of country parks, the 43 country parks types are classified, and their types can be divided into five types: wetland country parks, humanistic country parks, mountainous country parks, idyllic country parks and forest country parks. First of all, water is an important medium for spreading diseases after ingestion or contact with pathogenic microorganisms, such as cholera, hepatitis A, typhoid fever, etc. Eight of the 37 statutory infectious diseases in China are all waterborne infectious diseases22. The wetland type country parks are close to water sources, and if they are not properly protected, they will be easily affected by them, so they are classified as Class I. The humanistic landscape is a non-renewable resource, and Nanjing enjoys the reputation of “ancient capital of six dynasties” and “capital of ten generations”, with nearly 2500 years of city history and about 450 years of capital history and rich cultural and material relics above and below ground. Therefore, the humanistic type park is set as Class II; the mountainous type country park mainly contains uncertainties in terms of traffic and site topography and geological conditions, and is set as Class III; the idyllic type country park has flat topography, convenient transportation, high integration of land parcels and relatively complete infrastructure, and is set as Class IV. Forested country parks are open and have excellent ecological environment. Large areas of dense forest can play a role of isolation and provide a good forest rehabilitation environment for patients32, so this type of country park is set as Class V.
Effective safe haven area(f
2)
The siting of emergency medical facilities should take into account the lower limit of effective safe haven area. 2020 With the outbreak of New Crown Pneumonia, the first nationwide major public health emergencies level I response was launched. Referring to the construction and use of Xiaotangshan, Huoshenshan and Leishenshan hospitals, the data of the New Crown Pneumonia epidemic is used as the basis, i.e., when the emergency medical facility is a single-story building, its effective land area should be no less than 4.7 hm233. The effective shelter area in the urban disaster prevention and avoidance function green space refers to the actual area that can be used for disaster prevention and avoidance after deducting the area of water, building (structure) and its falling objects and collapse influence (the radius of the influence area is calculated by 50% of the height of the building (structure)), the dense area of trees, the area of slope greater than 15% and the rescue channel, etc. It is also stipulated that the effective shelter area of the country park as a long-term shelter green space is not less than 30 hm2. According to the statistics of Nanjing country parks, 43 country parks with effective refuge areas ranging from 17.62 to 8110.85 hm2 are in line with the lower limit of land requirement for emergency medical facilities. The country parks with an effective shelter area of 4.7–30 hm2 are classified as Class I, between 30 and 150 hm2 as Class II, 150–750 hm2 as Class III, 750–3750 hm2 as Class IV, and > 3750 hm2 as Class V.
Spatial fragmentation(f
3)
Spatial patchiness is the most common form of landscape pattern, reflecting the heterogeneity of the landscape; fragmentation characterizes the degree of fragmentation of the park by water systems, roads, structures, etc., reflecting the complexity of the park’s spatial structure34. Emergency medical facilities require a single, homogeneous and continuous building site within the park, so parks with a low number of spatial patches and low landscape fragmentation are more suitable as target sites. Landscape fragmentation35. The ratio of the number of patches to the corresponding area is usually used, i.e. Ci = Ni/Ai. The larger the fragmentation degree, the more fragmented the internal space of the park is, and the smaller the area of effective risk-avoidance patches is, which is not conducive to the construction of emergency medical facilities and later expansion. The statistical results showed that the spatial fragmentation of 43 country parks ranged from 0.0003 to 0.1703. According to the fragmentation distribution characteristics, the natural interruption point method was used to classify them, so 0.0003–0.0047 was class V, 0.004701–0.0120 was class IV, 0.012001–0.0240 was class III, 0.024001–0.0511 was level II, 0.051101–0.1703 for level I.
Distance from water source(f
4)
Nanjing is a riverside port city straddling both sides of the Yangtze River. The water area of Nanjing accounts for about 11% of the city, and there are three water systems in its territory: the Yangtze River, the Huai River, and Taihu Lake, of which the Yangtze River system is the main water system in Nanjing, which can be subdivided into four sub-water systems, including the Chu River, the Yangtze River along the Nanjing River, the Qinhuai River, and the Suiyang River, involving all districts and counties of Nanjing, with a watershed area of 6287.7 km2, accounting for 95.49% of the total land area of Nanjing. The above water systems enter the study area to form various types of surface water sources such as rivers, lakes, wetlands and reservoirs. In the “technical specifications for the delineation of drinking water source protection zones”, different types of water sources such as rivers, lakes, reservoirs and water protection zones are delineated in the land area of protection, of which the scope of protection for large reservoirs is most strictly defined. River-type water sources, primary and secondary land area protection range to the coastal depth and the horizontal distance of the river bank not less than 50 m and 1000 m for the boundary. Lakes, reservoirs type water sources, primary protection including lakes, reservoirs, water intake side of the normal water level above the 200 m land area; secondary protection, and according to the scale of lakes, reservoirs are divided into “not less than 3000 m outside the primary protection zone”, “above the normal water level (the first protection zone (outside the primary protection zone), the horizontal distance of 2000 m area” two division methods. Combined with the characteristics of the type of water sources within the city of Nanjing, in accordance with the principle of strict division, the above division boundaries integration, set 200 m within the land area (including water sources) for the I level, 200–500 m for the II level, 500–1000 m for the III level, 1000–2000 m for the IV level, > 2000 m for the V level.
Wind direction(f
5)
In the Guidelines for the Site Selection, Design, Construction and Operation Management of Emergency Infectious Disease Hospitals, it is stated that the site selection of emergency medical facilities should be located in the direction of the prevailing downwind of the urban area all year round. Nanjing belongs to the northern subtropical humid monsoon climate zone, which is influenced by the Eurasian continental air mass in winter with northeasterly winds, and by the Eurasian low pressure area in summer with southeasterly winds. The wind frequency calculation method of 16 rows of longitude points was used to quantitatively evaluate the wind frequencies in each direction in Nanjing, centering on the core area. The meteorological data of Nanjing were counted, and the wind frequencies of its sixteen wind directions are shown in Table 3. The wind frequencies in each direction were mainly distributed below 12%, and with reference to the natural intermittent point method grading, they were divided into five frequency bands of 10.44–11.36%, 9.02–9.27%, 6.02–6.73%, 3.68–4.45%, and 2.99–3.26%, and the parks in the upwind area corresponding to the wind direction were assigned as I, II, III, IV, and V in turn.
Distance from the central city area(f
6)
The Guidelines for the Selection, Design, Construction and Operation of Emergency Infectious Disease Hospitals and the Architectural Design Guidelines for Hospitals for Patients with Infectious Atypical Pneumonia both state that “avoiding densely populated urban areas” is an important principle for site selection. According to the distribution characteristics of country parks in Nanjing, the boundary of Nanjing central city planning area is used as the starting boundary, and the area is divided into I, II, III, IV and V levels from near to far with 15 km as the first level.
Hydrogeology(f
7)
Medical waste carries a large number of pathogens, heavy metals and organic pollutants, which can produce a variety of harmful leachate after rainwater and biological hydrolysis. In order to avoid the harmful leachate from entering the soil with the rainwater and thus causing pollution to the groundwater, emergency medical facilities are usually built on sites with high terrain and low groundwater level and not easy to infiltrate. The stratigraphy of Nanjing belongs to the lower Yangzi subzone of the Yangzi stratigraphic region, and the deep groundwater in the region can be divided into three major types: loose rock pore water, carbonate karst water and clastic rock fracture water36. The hydrogeological profile of the 43 study sites was analyzed, and country parks located in potential inundation areas were classified as Class I. Those located in areas with exposed carbonate fissure water and exposed carbonate fissure water cover with water enrichment > 1000 m3/d were classified as Class II. Those located in areas with intrusive magmatic fissure water, magmatic fissure water ejected rock, loose rock pore water, clastic rock Fissure water, carbonate fissure water exposed rock, carbonate fissure water exposed class cover and the degree of water richness in the area of 100–1000 m3/d is set as level III, located in the magmatic rock fissure water ejected rock, clastic rock fissure water and the degree of water richness < 100 m3/d and loose rock pore water and the degree of water richness in the area of 10-100 m3/d is set as level IV, located in loose rock pore water and the degree of water richness in the area of < 10 m3/d is set as level III. Water and water-rich degree in the < 10 m3/d area is set to level V.
Traffic duration(f
8)
During the outbreak of the epidemic, according to the “five centralized” treatment principle of COVID-19, a large number of critically ill patients need to be transferred from the designated treatment institutions in the urban area to the emergency medical facilities through negative pressure ambulance, so the speed of traffic is very critical. During the COVID-19 outbreak, there were 5 designated COVID-19 treatment hospitals set up in Nanjing (Table 4). In the same period, the traffic time of each country park was measured by the digital map navigation system in driving mode, using the above five designated hospitals as the starting point, and the longest traffic time was evaluated according to the principle of strict evaluation. The longest traffic time in the 43 country parks was about 2.5 h. The traffic duration was divided into five periods: ≥ 105 min, 90–105 min, 75–90 min, 60–75 min, and < 60 min, which were divided into I, II, III, IV, and V levels in order.