8
Evaporation
Massimo Menenti
The Winand Staring Centre, P.O.Box 125,6700 AC, Wageningen, The Netherlands.
8.1 Introduction
8.1.1 General
Evaporation, the phase transition of liquid water to vapour, has attracted a rather
considerable amount of attention and research work over the last two centuries
(see Brutsaert, 1982 for a historic overview). This interest is due to the role played
by evaporation in many processes in the earth-atmosphere system and the resulting
practical relevance of observing and understanding evaporation in the context of
hydrology, water management, meteorology, climatology, ecology and agriculture.
The global role of evaporative processes is well established (Shukla and Mintz,
1982). Kustas and Norman (1996) referred to Wetherald and Manabe (1988) and
Sato et ai. (1989) while mentioning the impact of changes in available moisture
released by evaporation on cloud formation, radiation budget and precipitation
fields at global and continental scales. Many studies have documented the impact
of evaporation on mesoscale atmospheric processes (e.g. Wang et aI., 1995; Beljaars and Viterbo, 1994; Segal and Arritt,1992). Evaporation determines depletion
of soil moisture and, therefore, crop water requirements of irrigated crops (e.g.
Jensen et aI., 1990) and partitioning of precipitation (Bruijnzeel, 1990).
The term evaporation is used in this chapter to mean the transition of water from
the liquid to the vapor phase. The term transpiration is used in literature to mean
that this process occurs in plant leaves. Evaporation may occur at or underneath
the soil surface. The term evapotranspiration is widely used to mean evaporation
from a mixture of vegetation and soil, such as from agricultural fields. Because of
the clearer meaning, the term evaporation is preferred here.
Today's interest in evaporation spans a wide range of scientific disciplines and
applications, although basic concepts and tools came to light in the context of agriculture and plant ecology. Thornthwaite (1948) proposed the concept of potential
evaporation (Eo) to explain the relation of vegetation types with climate in terms of
the difference between precipitation P and Eo. The equation proposed by Penman
(1948) was meant to establish a general physical relation of climate with maximum
water use by crops. The heritage of agricultural sciences was evident in the review
G. A. Schultz et al. (eds.), Remote Sensing in Hydrology and Water Management
© Springer-Verlag Berlin Heidelberg 2000
Evaporation
Massimo Menenti
The Winand Staring Centre, P.O.Box 125,6700 AC, Wageningen, The Netherlands.
8.1 Introduction
8.1.1 General
Evaporation, the phase transition of liquid water to vapour, has attracted a rather
considerable amount of attention and research work over the last two centuries
(see Brutsaert, 1982 for a historic overview). This interest is due to the role played
by evaporation in many processes in the earth-atmosphere system and the resulting
practical relevance of observing and understanding evaporation in the context of
hydrology, water management, meteorology, climatology, ecology and agriculture.
The global role of evaporative processes is well established (Shukla and Mintz,
1982). Kustas and Norman (1996) referred to Wetherald and Manabe (1988) and
Sato et ai. (1989) while mentioning the impact of changes in available moisture
released by evaporation on cloud formation, radiation budget and precipitation
fields at global and continental scales. Many studies have documented the impact
of evaporation on mesoscale atmospheric processes (e.g. Wang et aI., 1995; Beljaars and Viterbo, 1994; Segal and Arritt,1992). Evaporation determines depletion
of soil moisture and, therefore, crop water requirements of irrigated crops (e.g.
Jensen et aI., 1990) and partitioning of precipitation (Bruijnzeel, 1990).
The term evaporation is used in this chapter to mean the transition of water from
the liquid to the vapor phase. The term transpiration is used in literature to mean
that this process occurs in plant leaves. Evaporation may occur at or underneath
the soil surface. The term evapotranspiration is widely used to mean evaporation
from a mixture of vegetation and soil, such as from agricultural fields. Because of
the clearer meaning, the term evaporation is preferred here.
Today's interest in evaporation spans a wide range of scientific disciplines and
applications, although basic concepts and tools came to light in the context of agriculture and plant ecology. Thornthwaite (1948) proposed the concept of potential
evaporation (Eo) to explain the relation of vegetation types with climate in terms of
the difference between precipitation P and Eo. The equation proposed by Penman
(1948) was meant to establish a general physical relation of climate with maximum
water use by crops. The heritage of agricultural sciences was evident in the review
G. A. Schultz et al. (eds.), Remote Sensing in Hydrology and Water Management
© Springer-Verlag Berlin Heidelberg 2000