Climate Conditions and Classification
The climatic elements to be considered for open-air and protected cultivation of plants are (von Zabeltitz and Baudoin
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Climate Conditions and Classification
2.1
The Climate Elements
The climatic elements to be considered for open-air and protected cultivation of plants are (von Zabeltitz and Baudoin 1999): l l l l l l
Solar radiation Temperature Precipitation Humidity Evaporation and evapotranspiration Wind velocity
The relationship between precipitation and evapotranspiration plays an important role for open-field cultivation. Crops under protected cultivation receive all their water by irrigation systems. If rainwater storage for irrigation is planned, the relationship precipitation to evapotranspiration inside the greenhouse has to be taken into consideration.
2.1.1
Solar Radiation
The solar radiation at the edge of the earth’s atmosphere, called solar constant, is 1,349 kW/m2. Solar radiation is reduced in the earth’s atmosphere by reflection, absorption and scattering, so that only part of it reaches the earth’s surface. The solar radiation on the earth’s surface changes with latitude, season, and time of day, as well as by the various radiation losses in the earth’s atmosphere, e.g., clouds and haze. Figure 2.1 shows the annual mean of daily solar radiation energy (kWh/m2 day) at the earth’s surface in relation to the latitude (von Zabeltitz and Baudoin 1999). Average solar radiation increases from very low mean values at the poles up to 20 C. von Zabeltitz, Integrated Greenhouse Systems for Mild Climates, DOI 10.1007/978-3-642-14582-7_2, # Springer-Verlag Berlin Heidelberg 2011
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2 Climate Conditions and Classification
global radiation [kWh / m2d]
7 6 5 4 3 2 1 0
90° south
60°
30°
0° latitude
30°
60°
90° north
Fig. 2.1 Annual means of global radiation depending on the latitude 8000 June December
7000
global radiation [Wh / m2d]
Fig. 2.2 Mean daily sum of global radiation for different latitudes. (1) Equator zone, (2) 25 –30 north, (3) 35 –40 north, (4) 45 –55 north (von Zabeltitz and Baudoin 1999)
6000 5000 4000 3000 2000 1000 0
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3
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latitude. In the equatorial zone, the mean solar radiation remains almost constant. A high amount of vapor in the atmosphere results here in extremely high radiation losses. For the production of plants, it is important to know the monthly mean of daily solar radiation energy. Figure 2.2 shows the mean daily sum of solar radiation for different latitudes of the northern hemisphere in the months of June and December. The daily solar radiation in the equatorial zone (1) is the same in summer and in winter, while the other zones show considerable differences between summer and
2.1 The Climate Elements
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winter. Daily solar radiation decreases in summer and winter evenly with growing latitudes. The same is true for the southern hemisphere. Figure 2.3 indicates the annual course of the daily solar radiation for different locations. Variations are small in the equatorial zone in the course of the year. Some locations show maxima in March/April and in September/October (Mogadishu, Bongabo). Higher latitudes show strong annual amplitude. Solar radiation sum
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