A Time-Series Analysis of Climate Variability in Urban and Agricultural Sites (Rome, Italy)

Abstract

Identifying early signals of climate change and latent patterns of meteorological variability requires tools analyzing time series data and multidimensional measures. By focusing on air temperature and precipitation, the present study compares local-scale climate regimes at two sites in Central Italy (urban Rome and a peri-urban cropland 10 km west of Rome), using descriptive and inferential statistics on both variables and a drought index (the Standardized Precipitation Index, hereafter SPI) recorded over the last 60 years (1958–2017). The present work assumes the importance of urban-rural gradients shaping local-scale climate regimes and spatial variability, with differential impacts on individual variables depending on territorial background and intrinsic biophysical characteristics. Considering together precipitations and minimum/maximum air temperature at month and year scale, the analysis developed here illustrates two coexisting climatic trends at distinctive spatial scales: A general trend toward warming—specifically influencing temperature regimes—and a more specific pattern evidencing changes in local-scale climate regime along the urban gradient, with a more subtle impact on both precipitations and temperatures. Empirical results indicate that climate variability increased over the study period, outlining the low predictability of dry spells typical of Mediterranean climate especially in the drier season (spring/summer). On average, absolute annual differences between the two sites amounted to 70 mm (more rainfall in the peri-urban site) and 0.9 °C (higher temperature in the urban site). A similar trend toward warming was observed for air temperature in both sites. No significant trends were observed for annual and seasonal rainfalls. SPI long-term trends indicate high variability in dry spells, with more frequent (and severe) drought episodes in urban Rome. Considering together trends in temperature and precipitation, the ‘urban heat’ effect was more evident, indicating a clearer trend toward climate aridity in urban Rome. These findings support the adoption of integrated strategies for climate change adaptation and mitigation in both agricultural systems and relict natural ecosystems surrounding urban areas.

Urban Climates and Climate Change

“…For many cities around the world, warming trends in minimum and maximum daily temperatures were calculated from stations located in urban environments. For some of them, the comparison with nonurban data shows that the trends are mainly related to large-scale climate change (129,130) without significant modification by cities. Nevertheless, Lee et al (131) studied several Asian megacities and found that the urbanization dynamics between 1992 and 2012 led to a modification of climatic trends.…”

“…Some work also looked at long-time series of precipitation observations. Although several climatological studies show an effect of cities on the intensification of precipitation, there is no evidence of an impact of cities on the evolution of climate trends (129,130,134). Nevertheless, based on an integrative indicator combining temperature and precipitation data, Salvati et al (130) showed an increase in drought events at the city site (Rome, Italy) relative to the rural site between 1958 and 2017.…”

Rural in Town: Traditional Agriculture, Population Trends, and Long-Term Urban Expansion in Metropolitan Rome

“…The climate is typically Mediterranean, with rainfall concentrated mainly in autumn and spring, and a mild temperature in winter. The average long-term annual rainfall and mean daily temperature in Rome were 700 mm and 16 • C, respectively [59]. Despite a relatively high human pressure, the original landscape typical of dry Mediterranean ecosystems was preserved in several woodlots and mixed agro-forest patches (Figure 1).…”

Future Climate Change Impact on Urban Heat Island in Two Mediterranean Cities Based on High-Resolution Regional Climate Simulations

“…On the other hand, Rome is a larger city of 3.7 million people, which is located in central-west Italy in a valley enclosed by mountains (Colli Albani, Sabatini and Tolfa mounts, not exceeding 1300 m). The climate of the city is similarly characterized by hot summers and mild winters, with mean annual temperature of~16.5 • C and mean annual precipitation of 802 mm [88]. * Cumulus parametrization is only used in d01 and d02.…”