The principal role of water and vegetation in the distribution of solar energy and in local and global climate is shown on basis of measured data. Poor knowledge of the function of plants in climate formation results in erroneous decision-making in landscape management. The principles of solar energy distribution in the landscape can be understood and verified by measurement at the level of basic physics and biology. Examples are given for measuring the radiation balance of sunny and cloudy days and spring frosts. The role of clouds in solar energy input and heat flux from the surface of the earth to the atmosphere (greenhouse effect) is emphasized. The thermographic images show the essential role of water evaporation (evapotranspiration) in the temperature regime. Vegetation supplied with water has lower surface temperatures than dry surfaces with higher albedo. Based on literature data and our long-term measurements, we have determined an average evapotranspiration value of 100 mg.m-2. s-1 which is equal to latent heat flux 240 W.m2. Drainage, urbanization, deforestation leads to a shift from latent heat of vaporization to sensible heat, and accelerated flow of heated air into the atmosphere. Per 1 km2 this represents a heat flux of 240 MW on a sunny day. The thermodynamic functions of water and vegetation are expressed in terms of ecosystem services. The history of human civilizations shows how deforestation, drainage, and urbanization lead to the drying up of the landscape. It is therefore necessary to recognize the role of plant physiological processes in the conversion of solar energy and the water cycle.
