The climatic differences, and especially of precipitations, determine a scarcity in eastern Greece, and a relative abundance of running waters in western Greece. So that almost all the watercourses of eastern Greece have a torrential regime and often, indeed, for a large part of the year their riverbed is completely dry; while western Greece, with the Arctic, the Aspropotamus and the Alphaeus, belong to the major rivers of the entire region, when abstracting from the Macedonian ones, which only partially flowed into Greek territory. The presence of extensive alluvial and delta deposits and considerable lagoon formations along the Ionian coast and their absence along the Aegean coast are, at least in part, an indirect consequence of these different climatic conditions.
Even the dry and arid landscape, especially characteristic of Attica and the small region around Athens, is what is usually considered typical Greek landscape. This aridity largely derives not only from climatic conditions, but also from the rocky constitution of the soil. This in fact, except in some restricted crystalline areas in the coastal mountains, is almost entirely made up of limestones: which determine an extraordinary development of karst morphology and hydrography, subtracting from the surface the scarce running waters that would be allowed by the scarce atmospheric precipitations. Thus there is the frequency of all the minor forms typical of karst regions, and also the frequency of real closed basins, more or less large, more or less complex, whose waters find a underground exit in the numerous sinkholes (καταβόϑραι), from which they run through complicated underground paths to rise again in nearby hydrographic basins or directly to the sea. Thus it is that many of the regional units are at the same time typical closed basins. Very frequent and extensive, these, throughout eastern Greece, much rarer in western Greece: because here the much more abundant rainfall is also accompanied by the presence of fairly extensive areas of schist soils, which allow an almost complete runoff to the waters of rain and therefore the formation and incision of real river basins.
Independently of these morphological differentiations of a more general nature, there are also more regional ones: for example, Greek Macedonia, that is the main part of the new territory added after the Balkan wars and the great world war. We are already here outside the region to which the name of Greece belongs geographically; indeed we are in a region that to a large extent continues, naturally, in the hinterland, beyond the political border. It includes the large and level alluvial plains, frequent of lakes and marshy areas, in which the main rivers of Macedonia flow in their extreme stretch: the Mesta, the Struma, maximum the Vardar. And between one and the other are areas of low mountains or hills; while a marked depression, also alluvial and with lakes, it almost connects the mouth of the Vardar to that of the Struma, separating the squat Peninsula Chalkidiki (1200 m.) from the mainland, which then extends into the Aegean the three long and thin appendages of Cassandra, Lóngos and Mount Santo (1935 m. in M. Athos). Only to the west of the great plain (Campania) of Vardar, a river, the Bistrítsa, falls entirely within the political boundary with its harshly mountainous basin (often over 2000 m.). The Bistrítsa was born in the north near the closed basin of the Albanian lake of Prespa and, receiving the waters of the small lake basin of Castoria, it flows for a long stretch towards the SE, then with a sharp turn to the NE. towards Campania: the snowy Olympus massif (2985 m.) separates it from the sea. The two trunks into which the course of the Bistrítsa divides enclose a massive triangle of mountains within which opens the large karst basin that sends its waters to Lake Ostrovo. The coasts, high and rocky along the sides of Olympus and along Chalkidiki, low and sandy with frequent delta formations in all the rest, describe two deep and safe gulfs: of Thessaloniki at the mouth of the Vardar, of Orfáni at that of the Struma ; just west of the mouth of the Mesta, is a third, of Cavala, in the shelter of the island of Thasos; and two others, again, are limited by the thin appendages into which Halkidiki breaks.
The mountainous right flank of the middle Bistrítsa forms the northern limit of Thessaly, a typical basin region. To the west the Pindus limits it, culminating here at 2124 m.; to the north one of its offshoots, which for the M. Chásia reaches as far as Olympus (2985 m.); at noon another offshoot of the Pindus, Mount Óthrys (1726 m.), which goes as far as the sea at the opening of the beautiful Golfo di Volo; and towards the east, towards the Aegean, a narrow but elevated coastal chain that culminates in Ossa (1987 m.) and in Pelio (1619 m.). Between this circle of mountains opens the low and level plain of Thessaly, which a low hilly area divides into two smaller plains: of Triccala to the west, of Larissa to the east. In the first, the Salambrias descends, which then comes out with the narrow and wild Tempe Valley, between Olympus and the Bones, towards the Aegean. A band of hills, which at times however fades to the point of almost disappearing, is all around the two plains; and in it, not far from Triccala, the meteoric decay and the erosion of the running waters have modeled the strange and characteristic ruiniform landscape of the Meteora. The Thessalian coast is united, straight, without gulfs, along the Aegean, but the coastal chain extends into the Magnesia peninsula, which with the extreme eastern part of M. Óthrys limits the Gulf of Volo, the natural outlet of Thessaly to the sea.