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Climate of the Republic

The Republic occupies a peninsula at the northern edge of Asia Minor, with sea on three sides and land frontiers only in the south. It lies in the temperate transition zone, between the maritime climates of the north-west and the drier continental interiors to the east. The weather is changeable and extremes are few.

ZoneTemperate transitional

Normals period1991 to 2020, revised each decade

Annual rainfallFrom above 1,200 mm on the Kelvaqui moor to below 500 mm in the Quintorum basin

Dry seasonNone anywhere except the eastern interior

SnowLying six to ten weeks on the Vandorum high ground, occasional and brief elsewhere

Highest groundVandorum upland, western region

Strongest windsBelvacius hills, south-eastern region

Position and the controls on the climate

Three controls govern the pattern. The first is the sea, which surrounds the peninsula on three sides and holds the annual temperature range of the coasts to about fourteen degrees. The second is the westerly flow, which delivers the greater part of the year's rainfall and weakens with distance from the north-western shore. The third is relief: the Vandorum upland in the west and the Belvacius hills in the south-east lift the air that crosses them and shelter the ground behind.

The peninsula lies between two air masses. Maritime air from the north-west arrives cool and moist through most of the year. Continental air from the east arrives dry, hot in summer and cold in winter, and reaches the western plain only when the westerly flow slackens. The frequency with which the boundary between them passes over the territory accounts for the changeability of the weather and for the absence of long settled spells.

The four local climates

Four local climates are conventionally distinguished, and the division is the one taught in schools. It describes the observed record and has no administrative effect.

Local climates, normals of 1991 to 2020
Local climate	Sub-regions	January mean	July mean	Annual rainfall	Character
Maritime coast	Lindoma, Merrisoma, Kelvaqui, Leriduson	4.2 °C	19.6 °C	780 to 1,050 mm	Mild, wet, windy, small annual range, frequent low cloud
Western upland	Vandorum, Corvaluri, upper Tessilius	0.8 °C	16.4 °C	1,050 to 1,240 mm	Cool and wet, snow lying six to ten weeks, cloud on the summits
Continental interior and east	Anselaqui, Thurioma, Quintorum, Marnaqui, Ravelluri, Cortius, Belvacius, Esteveduson, Sornorum, Halvorum, Durorilaqui	-1.4 °C	23.8 °C	480 to 690 mm	Warm summers, cold winters, summer rainfall maximum, thunderstorms
Sheltered south-west	Ombraqui, western Aspreduson	6.1 °C	22.9 °C	640 to 810 mm	Warmest and sunniest, long growing season, orchard and vine

Figures are areal means over the sub-regions named and conceal local variation, which on the western upland exceeds five degrees between valley floor and summit. The eastern seaboard at Ravelluri and Cortius is two to three degrees warmer in the winter than the group mean, the sea moderating a district that is otherwise continental in its rainfall regime.

The rainfall gradient

Rainfall falls steadily with distance from the north-western coast. The Kelvaqui moor receives above 1,200 mm a year and is covered in blanket peat in consequence. The Quintorum basin, about 180 km to the south-east and sheltered by the interior divide at Ilvara, receives below 500 mm, and its soils are fertile and drought-prone together. Between these two the gradient is close to linear, at roughly 3.9 mm for each kilometre travelled inland.

The seasonal distribution turns over along the same line. On the maritime coasts the wettest months are November to January and the driest are June and July. In the interior and the east the maximum falls in June and July, delivered by convective storms in a small number of heavy days, and the winter is the drier half of the year. The east therefore receives less rain in fewer events, which is the combination that governs both its irrigation regime and its flood behaviour.

Wind

Prevailing winds are westerly and south-westerly through most of the year. Mean speed at 10 m exceeds 6.5 m/s on the exposed north-western coast and falls below 3.2 m/s in the sheltered south-west. The Belvacius hills hold the strongest resource in the Republic, with a mean above 8 m/s at 100 m on the ridge lines, and the wind installations above Corcina have been developed there since 1998.

Gales of force 8 and above are recorded on the north-western coast on about eighteen days a year and inland on fewer than three. The strongest gust in the instrumental record was 47 m/s at the Maravel headland in February 1962. Storm surge on the north-western bay is the principal wind-driven hazard, and the tide gauges at Merrisoma and Lindoma feed the surge model described under REP-FEW.

The sea, the lagoon and the marsh

Sea surface temperature ranges from about 8 °C in February to about 21 °C in August on the northern coast, and runs one to two degrees warmer on the eastern seaboard. The Ravelluri lagoon, brackish and shallow behind its dune barrier, warms and cools far faster than the open sea and reaches above 26 °C in a settled August. That behaviour governs the ecology of the lagoon and is monitored continuously by the coastal station at Marendo, whose series supports the assessment of Ravellura marendensis.

The Merrisoma salt marsh behind the north-western bay is the largest intertidal system in the Republic and the principal wintering ground for migratory birds on this coast. Air frost is rare over the marsh and the frost-free season there is the longest recorded on any western station.

What the normals do and do not tell

Reading the normals

A normal is a thirty-year mean and describes the period from which it was calculated. The 1991 to 2020 normals are already warmer than the 1961 to 1990 set they replaced, by about 0.9 degrees in the annual mean, so a season described as average against the current normals would have been described as warm against the earlier ones.

Normals also conceal the distribution behind them. Two sub-regions with the same July mean can differ by six degrees in the temperature exceeded on one day in twenty, and the Quintorum basin differs from the maritime coast in exactly that way.