Heat balance and climatic water balance in vegetation period of spring wheat

Annals of Warsaw Agricultural University SGGW Land Reclamation No 37, 2006: 83 92 (Ann. Warsaw Agricult. Univ. SGGW, Land Reclam. 37, 2006) Heat balance and climatic water balance in vegetation period of spring wheat ELŻBIETA MUSIAŁ 1, JOANNA BUBNOWSKA 1, EDWARD GĄSIOREK 1, LESZEK ŁABĘDZKI 2, 1 Agricultural University of Wrocław, Departament of Mathematics 2 IMUZ Bydgoszcz Abstract: Heat balance and climatic water balance in vegetation period of spring wheat. This paper characterizes the changes of heat and climatic water balance structure during the growing season of spring wheat in four observatories: Wrocław- Swojec 1964 2000, Bydgoszcz 1946 2004, Gorzów Wielkopolski 1970 1995 and Łódź 1954 1995. Study of changes and trends contains the following elements of heat balance: net radiation, latent heat flux,sensible heat flux, soil heat flux and their contribution in net radiation. Climatic water balance is defined as a difference between precipitation and potential evapotranspiration reckoned by the Penmann method. Key words: heat balance, spring wheat, sensible heat flux, latent heat flux, climatic water balance. INTRODUCTION Energy and water relations in different ecosystems are best described by water and heat balance structure. Heat and water balance are connected through a streamvapour, that transports a huge quantity of energy to the atmosphere. Because of it any change in water balance influences heat balance and vice versa. Climate changes with their consequences are connected with heat exchange between active surface and atmosphere. Therefore, searching for climate variability concentrates on studying heat and water balance of different ecosystems. Different surfaces transform this energy in a particular way [Bubnowska, Gąsiorek, Łabędzki, Musiał 2005], [Bubnowska, Gąsiorek, Łabędzki, Musiał, Rojek 2005], [Kędziora, Olejnik, Kapuściński 1989], [Kapuściński 2000], [Olejnik 1996]. The knowledge of heat balance for various kinds of surface allows characterizing changes in flux distribution. METHODS The calculation of components of active surface heat balance was carried aut by using the BMC model, worked out by Olejnik and Kędziora [1991, 1999] The heat balance of ecosystems is described by the following equation [Kapuściński 2000; Kędziora 1989]: Rn + LE + H + G = 0 where: Rn net radiation [Wm 2 ] G soil heat flux [Wm 2 ] H sensible heat flux [Wm 2 ] LE latent heat flux [Wm 2 ] The exact description of applied calculation method could be found in a previous paper by the same authors [Musiał 2001; Bubnowska, Gąsiorek

84 E. Musiał et al. Łabędzki, Musiał, 2005] and in [Bowen 1926], [Karliński, Kędziora 1968], [Shuttleworth, Wallace 1985]. Water balance in this paper is defined as a difference between precipitation and potential evapotranspiration reckoned by Penmann method. Penman showed that the latent heat flux could be expressed as: Δ ( Rn + G) + Ea γ LE = Δ 1+ γ where: E a ability of air evapotranspiration [Wm s2 ], E a = 7,44(1 + 0,54v)d v wind speed at 2 m height [ms 1 ], d vapour pressure deficit [hpa], γ psychrometric constant γ = 0,655 [hpak 1 ], mean rate of change of saturated vapour pressure with temperature [hpak 1 ], LE, Rn, G like above. A simple relationship exists between evapotranspiration ETP expressed in [mm] and latent heat flux LE expressed in [Wm 2 ]: ETP = n LE 28,34 Where n number of days in decade, in month. RESULTS The study was carried out on data from the following meteorological observatories: Wrocław-Swojec (1964-2000), Bydgoszcz (1946-2003), Łódź (1954-1995) and Gorzów Wielkopolski (1975 1995). The variability of heat and water balance components was analyzed in given perennials. HEAT BALANCE IN VEGETATION PERIOD OF SPRING WHEAT Mean values of net radiation calculated for vegetation period of a spring wheat (IV VIII) in ssubsequent years in Gorzów Wielkopolski fluctuated between 94 and 112 Wm 2. The lowest value was obtained in 1962 when the sum of precipitation in vegetation period was also the lowest. Latent heat flux absorbed from 61 to 68% of net radiation, and sensible heat flux from 24 to 61%. The soil heat flux accounted for around 8% of net radiation. Values of heat balance components in other observatories had similar variability. Net radiation in Łódź changed from 90W/m 2 in 1960, when the precipitation was the highest (476.7 mm), to 115 W/m 2 in 1983, when the precipitation was the lowest (171.7 mm). In Wrocław and Bydgoszcz net radiation fluctuated from 89 to 112 [Wm 2 ] and from 89 to 109 [Wm 2 ] respectively. Latent heat flux absorbed from 58% in Bydgoszcz to 69% of net radiation in Łódź. The highest values of net radiation during the growing season were observed in Łódź and Gorzów Wielkopolski, whereas in Wrocław and Bydgoszcz the values of Rn were lower. Latent heat flux values were the highest in Łódź, where net radiation was the highest. This may be due to the fact that in Łódź more energy was supplied and therefore, more of it could be used for evapotranspiration.

Heat balance and climatic water balance... 85 TABLE.1. Components of heat balance during the growing season of spring wheat (IV VIII) in Gorzów Wielkopolski (1970 1995) Rok Rn -LE -G -H -LE/Rn -H/Rn -G/Rn P 1970 101 66 8 27 0,65 0,27 0,08 215,3 1971 105 64 8 33 0,61 0,31 0,08 256,4 1972 97 62 7 28 0,64 0,29 0,07 306,2 1973 105 66 8 31 0,63 0,30 0,07 273,7 1974 94 59 8 27 0,63 0,29 0,08 330,6 1975 110 71 8 31 0,65 0,28 0,07 233,0 1976 110 72 8 30 0,65 0,28 0,07 172,7 1977 98 65 8 25 0,66 0,26 0,08 460,0 1978 101 64 8 29 0,63 0,29 0,08 279,0 1979 102 65 8 29 0,63 0,29 0,08 225,5 1980 95 59 8 28 0,62 0,30 0,08 320,1 1981 104 63 9 32 0,61 0,31 0,08 306,9 1982 112 70 9 33 0,63 0,30 0,07 153,6 1983 109 71 8 30 0,65 0,28 0,07 214,4 1984 95 60 7 28 0,63 0,29 0,08 353,1 1985 103 65 8 30 0,63 0,29 0,08 229,6 1986 106 68 8 30 0,64 0,28 0,08 255,2 1987 94 62 7 25 0,66 0,27 0,07 365,3 1988 95 59 8 28 0,62 0,30 0,08 259,7 1989 107 70 8 29 0,65 0,27 0,08 190,9 1990 108 66 9 33 0,61 0,31 0,08 285,4 1991 102 69 8 25 0,68 0,24 0,08 221,0 1992 108 72 8 28 0,67 0,26 0,07 170,0 1993 100 64 8 28 0,64 0,28 0,08 268,0 1994 107 71 8 28 0,66 0,26 0,08 259,0 1995 108 69 8 31 0,64 0,29 0,07 320,0 Rn net radiation [Wm 2 ], LE latent heat flux [Wm 2 ], G soil heat flux [Wm 2 ], H sensible heat flux [Wm 2 ], P sum of precipitation in period IV VIII [mm] Regarding the Figure 3, the following conclusion could be drawn: in Łódź and Gorzów Wielkopolski more energy was transferred to the atmosphere from the active surface of spring wheat than in Wrocław and Bydgoszcz. In 1982 1995 perennial, common for all observatories, there was a distinct increasing tendency for sensible heat flux. Thus, the amount of energy used for heating atmosphere is growing. Due to the fact that the values of heat balance components depend on the net radiation value, it is worthy looking into contribution of each component to net radiation (Rn).

86 E. Musiał et al. FIGURE 1. Variation of mean ten-days values of net radiation (Rn) during the growing season of spring wheat in Wrocław Swojec, Bydgoszcz, Gorzów Wielkopolski and Łódź FIGURE 2. Variation of mean ten-days values of latent heat flux (LE) during the growing season of spring wheat in Wrocław Swojec, Bydgoszcz, Gorzów Wielkopolski and Łódź FIGURE 3. Variation of mean ten-days values of sensible heat flux (H) during the growing season of spring wheat in Wrocław Swojec, Bydgoszcz, Gorzów Wielkopolski and Łódź

Heat balance and climatic water balance... 87 FIGURE 4. Variation of mean ratios of latent heat flux and net radiation (LE/Rn) during the growing season of spring wheat in Wrocław Swojec, Bydgoszcz, Gorzów Wielkopolski and Łódź FIGURE 5. Variation of mean ratio values of sensible heat flux and net radiation (H/Rn) during the growing season of spring wheat in Wrocław Swojec, Bydgoszcz, Gorzów Wielkopolski and Łódź Looking at the course of mean values of latent heat flux contribution in net radiation, distinct decreasing tendency for this contribution in the last 20 years is seen. Therefore, less and less energy is used for evapotranspiration, especially in Wrocław and Bydgoszcz. Increasing share of sensible heat flux in net radiation in all observatories stress that more and more energy in all regions is used for heating atmosphere. The above mentioned results are concordant with those by Musiał [Musiał, Gąsiorek, Rojek 2004], Trepińska[1997], [Ryszkowski Kędziora, 1995] and [Kożuchowski 2004]. The temperature increase is a consequence of the growing contribution of latent heat flux to net radiation. Regression equations in Table 2 confirm this. CLIMATIC WATER BALANCE The net climatic water balance determines conditions of plant vegetation [Bac, Rojek, 1979, 1982]. This index may be the source of information on climate change effects.

88 E. Musiał et al. TABLE 2. Mean parennial air temperature values for periods IV VIII and IV IX with regression equations Obserwatory T weg [ C] T pc [ C] s sr [ C] Linear regression equation Tendency [ C/10 years] Bydgoszcz 15.22 15.0 0.92 y = 0.0176x + 14.7 0.18* Gorzów Wielkopolski 14.57 14.4 0.85 y = 0.0477x + 13.9 0.48* Łódź 14.32 14.1 0.88 y = 0.0129x + 14.0 0.13** Wrocław 14.93 14.7 0.83 y = 0.0347x + 14.3 0.35* T weg mean seasonal yearly air temperature (IV VIII), T pc mean seasonal, yearly air temperature (IV IX), s sr standard devation of temperature *) statistically significant for α = 0.05 **) statistically significant for α = 0.3 FIGURE 6. Variation of climatic water balance during the growing season of spring wheat (IV VIII) in Bydgoszcz (1946 2003) FIGURE 7. Variation of precipitation (P) and climatic water balance (CWB) during the growing season of spring wheat (IV VIII) in Wrocław (1964 2000)

Heat balance and climatic water balance... 89 In Bydgoszcz climatic water balance was positive in two years during the period 1946 2004. Those two years were chracterized by high sums of precipitation: 599,1 mm in 1980 and 506,6 mm in 1985. In years 1980 and 1985 the spring wheat vegetation period was characterized by rather low (390,56 and 419,35 mm, respectively) evapotranspiration values, whereas mean evapotranspiration value for years 1946 2004 was 456,5 mm. In Wrocław climatic water balance was positive in 1980 (11,3 mm) and in 1986 (9,2 mm). During the spring wheat vegetation period in 1980, the precipitation value was 438 mm and the potential evapotranspiration reached the level of 426,7 mm. The year 1997 is noteworthy due to the flood in Wrocław. During that spring wheat vegetation period the precipitation sum (494 mm) was 52% higher than the mean value. In spite of such high precipitation value, FIGURE 8. Variation of precipitation (P) and climatic water balance (CWB) during the growing season of spring wheat (IV VIII) in Łódź (1954 1995) FIGURE 9. Variation of precipitation (P) and climatic water balance (CWB) during the growing season of spring wheat (IV VIII) in Gorzów Wielkopolski (1970 1995)

90 E. Musiał et al. TABLE 3. Evapotranspiration tendencies in 4 examined regions Obserwatory P [mm] ETP [mm] Linear regression equation Tendency [ C/10 years] Bydgoszcz 281 457 y = 0.29x + 443.4 2,9 Gorzów Wielkopolski 266 477 y = 4.91x + 466.7 49,1* Łódź 312 505 y = 2.0x + 470.6 20** Wrocław 326 500 y = 2.0x + 468.2 20* P mean seasonal, yearly precipitation (IV VIII) ETP mean seasonal, yearly evapotranspiration (IV VIII), *) statistically significant for α = 0.05 **) - statistically significant for α = 0.01 the net climatic water balance in the 1997 growing season remained negative ( 31 mm). In Łódź, during the 1954 1995 perennial, there were 3 years with positive net climatic water balance: 1960 (precipitation 477 mm, climatic water balance 20 mm), 1980 (458 mm and 38,9 mm, respectively) and 1985 (464 mm and 17 mm, respectively). Mean precipitation sum in the growing season for spring wheat in Łódź was 312 mm. In Gorzów Wielkopolski, the climatic water balance was positive only once and reached the value of 48,2 mm in 1977, when the precipitation sum in vegetation period was the highest (460 mm). All analyzed regions were characterized by continuous water shortage in vegetation period. During the period 1970 1995 the worst water conditions were observed in Gorzów Wielkopolski (the highest water shortage sum 5474 mm), whereas the best terms were seen in Wrocław (water shortage sum of 4640 mm was 15% lower than that in Gorzów). During the wheat spring growing season the values of climatic water balance were positive only in years with the highest precipitation sums. CONCLUSIONS The enlargement of negative net climatic water balance, along with increasing potential evapotranspiration, confirms diminishing atmospheric precipitation. The increase of temperature during the spring wheat growing season in all discussed regions is a consequence of enlarging sensible heat flux, used for heating atmosphere. The growing temperature values enlarge the saturation deficiency, thus allowing more water to evapotranspirate (PET increase). Consequently, growing precipitation enlarge the negative net climatic water balance. The tendencies observed among heat balance components are concordant with changes seen among the components of climatic water balance. The research supported by KBN grant in years 2004 2007. REFERENCES BAC S., ROJEK M. 1979: Klimatyczny bilans wodny a odpływy w Polsce, Przegl. Geofiz. 24(3) 293 297.

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92 E. Musiał et al. MS. received November 2006 Authors addresses: E. Musiał, J. Bubnowska, E. Gąsiorek Agricultural University of Wrocław Departament of Mathematics ul. Grunwaldzka 53 50 357 Wrocław Poland (071)3205659 Leszek Łabędzki ul. Glinki 60 85 174 Bydgoszcz Poland musial@ozi.ar.wroc.pl