Study area
The Algeria region is in North African continent, and it is classified as the largest African country covering an area of approximately 2,381,741 km2 (Fig. 1). It extends from the Mediterranean coast in the North until the Sahara Desert in the South. It is bordered to the East by Tunisia and Libya, to the southeast by Niger, to the southwest by Mali, and to the West by Mauritania, Western Sahara, and Morocco. The nation holds a very special spot in the Mediterranean Basin with its geostrategic position and its demographic and economic weight. According with National Office of Statistic (Algeria), more than 43 million of habitants were estimated in 2018 with the higher density mainly concentrated in the North of the country along the Mediterranean coastline. The climatic conditions of the nation could vary considerably from North to South. Specifically, the coastal area has characterized by a Mediterranean climate, while the high plateaus are characterized by hot summers and cold low rainy winters. The Sahara Desert, in the South of the region, instead, represents a true example of extreme climate with very rare rain and strong differences in temperature between day and night. The rainfall regime can be classified as abundant along the coastal zone (North), ranging from 400 to 700 mm for year, with a substantial increasing precipitation pattern moving from West to East. Precipitations become even more abundant in the northern part of East Algeria, reaching 1200 mm in some years. The average temperature and humidity during summer range between 21 and 36 °C and 70 and 90%, respectively. In winter, instead the average temperature and humidity range from 8 to 12 °C and from 50 to 80%, respectively. Winters are so characterized by not too rigid temperatures but by very high relative humidity. In the high plateaus, the yearly rainfall substantially decreases ranging among 100 m and 400 mm, mainly occurring during the months of October and December. The average maximum and minimum temperatures in winter are 16 °C and − 2 °C, respectively, with sporadic snowfall on the highest peaks, while during summer, they are 42 °C and 10 °C, respectively. The relative humidity is moderate, varying from 30 to 60% in summer and from 60 to 80% in winter. In the Algerian Sahara’s desert, the climate is classified as extremely arid to hyper-arid with the almost entirely absence of rainfall during the year, except for torrential rains. In this area, a significant difference in temperature between the day and the night also occurs. In winter, during the day, the temperature ranges from 20 to 30 °C with cold nights (− 5 to 10 °C). In summer, instead the temperature can reach 47 °C during the day and 30 °C at the night. The relative humidity is low during all the year (less than 40%). Fourteen Algerian cities have been selected in different climatic regimes for this study, including (i) Algiers, Annaba, Jijel, Oran, and Blida in humid to sub-humid climate; (ii) Setif, Batna, Djelfa, Tiaret, and Naâma in semi-arid climate, (iii) Ouargla and Bechar in arid climate; and (iv) Tamanrasset and Adrar in hyper-arid climate (Fig. 1). The location of all cities center is reported in Table 1.
Table 1 Geographic location of cities studied Data collection
Data of COVID-19 daily new cases were collected considering the fourteen Algerian cities from April 1, 2020, to August 31, 2020. The data was made available from the Algerian Ministry of Health (http://covid19.sante.gov.dz/carte/#pll_switcher).
To correlate the COVID-19 case with meteorological condition, a representative weather station was chosen for each city. The geographic characteristics of all the weather stations are reported in Table 2. The daily meteorological data, including maximum temperature (TMAX) (°C), minimum temperature (TMIN) (°C), and relative humidity (RHD) (%), were obtained from the National Weather Center (ONM) (https://www.meteo.dz/previsions/carte).
Table 2 Weather stations of the study area Data analysis
The effect of meteorological factors such as wind speed, temperature, sunshine hours, rainfall, and humidity on COVID-19 cases was usually examined using the Spearman correlation test (Rendana 2020), Pearson correlation, Kendall’s rank correlation (Doğan et al. 2020; Shahzad et al. 2021), autoregressive distributed lag (ARDL) (Doğan et al. 2020), and linear regression method. Specifically, in this study, a linear regression method was utilized to investigate the interconnection among new cases of COVID-19 and the available factors.
First, a descriptive statistical of epidemiological data (daily new cases of COVID-19) along with daily meteorological factors during the period April 1, 2020–August 31, 2020, in the fourteen Algerian cities was also performed. Secondly, given the spatial and temporal variability of climate characteristics, the linear regression method was used to explore the relationship among daily meteorological factors and correspondent new cases of COVID-19. The number of daily new cases was chosen as dependent variables, while the daily meteorological factors were selected as independent variables. The formula used was as follows:
$$Y=\alpha +{\beta }_{1}{X}_{1}+{\beta }_{2}{X}_{2}+\dots +{\beta }_{n}{X}_{n}1)$$
where Y is the linear function indicating a set of predictor variables, α indicates a numerical constant that represents an intercept, n is the number of predictor variables, X represents those meteorological factors that are significantly associated with epidemiological data, and finally β is the regression coefficients of X. Each β reflects how Y will change with the X, which is associated with the β, when all other X variables are constant (Jaccard et al. 2006). This analysis was performed in Origin Pro 2019b software.
Based on the statement of the World Health Organization (WHO) which reported an incubation period for COVID-19 between 2 and 10 days with a mean incubation period of 5.2 days (WHO 2020), 5 days lag time to assess the correlation between the new cases of COVID-19 and climate’s factor variability has been considered (temperature and relative humidity).