Beech forests have a balancing effect on the climate. On warm days, tree rots draw large amounts of water from the soil and evaporate them through the leaves. The thus produced evaporative heat loss and the shade provided by the trees make the forest a pleasantly cool place even on hot days.
Hainich is a densely wooded shell lime ridge on the western edge of the Thüringer Becken (Thuringian Basin). The highest elevation is the "Alte Berg" at 494 m above sea level southwest of Craula on the fringe of the national park, the lowest point is at 225 m above sea level near Mülverstedt.
The geological subsoil is determined by shell lime sediments (primarily from the period of the Upper Muschelkalk). In very small areas, Keuper, Early Trias and Upper Permian formations can be found. Today's surface was formed by weathering and erosion as well as loam accumulations.
The hillsides exposed to the East towards the Thüringer Becken are subdued and have only a slight to moderate gradient. The Hainich's flank to the West to the Werra valley is markedly steeper, with deeply cut transverse and latitudinal valleys whose southern flanks have steep inclinations.
Hainich is located in the transition zone from ocean to continental climate. The average rainfall per year is between 600 and 800 mm, with the western slope generally benefitting from more rain due to the barrier effect of the ridge. The mean annual temperature is between 7 and 8 °C.