Environmental aspects

BODIES OF WATER

The region has several hydrographic systems that differ in terms of origin, evolution and subsequent remodelling of the different substrates they continue to erode. To the north, the western and southern slopes of the Prenestini Mountains are drained by a system of streams and tributaries of the Aniene, to the west, and of the Sacco River, to the east. The hydrographic network of the volcanic Albani hills is, instead, a typical radial centrifuge system with a myriad of channels and streams scoring the area outside the Tuscolano-Artemisio rim.

Of these, the southern and western slope, respectively, feed the Aniene and Tiber Rivers, those on the eastern and southern slopes run more or less directly to the Tyrrhenian Sea and, finally, the streams on the north-east slope and those in the southern Prenestina area are tributaries of the Sacco River. The waters gathered in the Molara river valley — a low-lying area between the external Tuscolano-Artemisio rim and internal portion of the Faete zones — flow into the Pantano della Doganella Lake from the north-east; the overflow from this lake runs through the Algido, a tributary of the Sacco River.

Even if outside the municipal district, the lacustrine basins of Nemi and Albano mark the hydrographic features of the Roman Castles area. Fed by rainwater falling in the respective basins, and by some springs, the lakes do not have natural emissaries, but rather the outflow runs along tunnels excavated in ancient Roman times.

CLIMATE

The climate of the district is the result of a wide range of variables related to the isolation of the two mountain systems: the Prenestini Mountains to the NE and the Laziale Volcano to the SW. Exposure, altitude, winds, rainfall, temperature, humidity, distance from the sea, type of plant cover, presence of lacustrine basins and deep ditches create a myriad of meso- and micro-climates.

The entire region is affected by a warm, temperate, Mediterranean climate with extended summers and mild winters where temperatures rarely fall below 0°C, even during the coldest months. In the Prenestina area the peak temperatures — averaged taking the values recorded at the weather stations in the northern and southern Prenestini mountains — fall within the 13°C-22°C range: the minimums between 4°C and 12°C. The daily temperature range is relatively low in the winter and relatively high in the summer, and can even be quite significant in spring and fall. The area suffers from a lack of uniform rainfall. The rainfall features sub-Mediterranean and Apennine characteristics with high concentrations and great humidity in spring, and even more so, in the autumn months. The peak is in November when the average monthly rainfall is on the order of 150 mm; the driest month, August, logs in with just 34 mm. The average monthly rainfall is moderate-to-high throughout all months of the year and average annual rainfall is on the order of 1,357 mm at the Zagarolo weather station. Therefore the Prenestina region climate can be classified as moist with moderate water deficiencies in the summer. In the Roman Castles area, the average peak temperatures range between 15°C and 22°C, the minimums between 9°C and 12°C.

The daily temperature ranges are relatively low in the winter and relatively high in the summer, and can even be significant in spring and fall. The average winter temperatures for all stations hovers at values above 5°C with the absolute minimum rarely dropping below 0°C. Monthly rainfall peaks in November and drops to a minimum in the summer, between July and August; the relative maximum rainfall occurs during the spring. The fall-winter period sees approximately 2/3 of the total rainfall while the values in summer are just 2/3 that seen in spring.

The average annual rainfall is 942 mm and the pluviometric system is typical of the mesomediterranean areas with a shortage of water in summer. The rain is distributed following the progression of the slopes with peak values achieved in the highest zones and minimums in the low-lying areas; however, this varies widely between the southern and northern slopes of the Albani hills. This phenomenon, called STATU, is the result of the fact that the Laziale Volcano blocks the moisture-laden winds blowing in from the Tyrrhenian Sea. As the mass of air rises, it cools and this, in turn, reduces its ability to hold vaporised water; the excess then precipitates in the form of orographic rain, mainly on the slopes facing S-SW.

When the mass of air reaches the opposite slope, it descends and warms up again but, since it is now devoid of any water vapour, it rarely leads to rain. This means that the climate conditions are more xerothermal on the northern slope than on the southern slope, even in sites at the same altitude.