A method is outlined to predict actual evapotranspiration and groundwater recharge considering climate, soil and depth to groundwater

Bohne, K.

Miegel, K.

Wessolek, G.

English

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Tagungsbeitrag zu: Workshop Komm. I der DBG, 16.-17.11.2012 LeipzigMessung, Monitoring und Modellierung von Wasser-,Energie- und Stoffflüssen im System Boden-Pflanze-AtmosphäreMiegel,K.1, Bohne, K.2, Wessolek, G.2Prediction of the Long-Term Groundwater Recharge by Hydropedotransfer FunctionsKey words: Evapotranspiration, groundwater recharge, hydropedotransfer functionsLong-term groundwater recharge R is given byR=P−Ea                                     (1)P    average annual precipitationEa  average annual average evapotranspirationTo estimate Ea, Bagrov has proposed the differential equationdEadP=1−( EaE p )b                        (2)where b is a coefficient related to the availability of soil water and Ep is potential evapotranspira-tion. The Bagrov equation restricts evapotranspi-ration to the availability of either water or energy.  Ea is accessible by   € P= 11− Ea / Ep( )b dE0Ea∫                         (3)     and was successfully used by Glugla al. (1971, 2003 ).To estimate b, a transfer function        b=c1 W ac2 +c3  exp (c4 qmax )+c5C sP s−E p,s     (4)is used that considers climatic conditions (P, Ep), maximum plant available soil water (Wa), water supply by capillary rise from groundwater table, and the simultaneity of water and energy supply. An attempt was made to consider the effect of anaerobiosis on actual evapotranspiration. 1 Universität Rostock, AUF2 klaus.bohne@uni-rostock.de2 TU Berlin, Inst.f. ÖkologieData basisThe simulation model SWAP was used to generate a data basis comprising 30year simulation periods of 3 different weather stations, 14 soil texture classes and 4 levels of groundwater depth, in total 4050 simulation years. The only crop considered here was grass of 12 cm height covering the soil surface completely over the entire year. Limitations of the Bagrov methodThere  are  two  different  conditions  where  the Bagrov method fails. (A)  Because  of  the  underlying  assumption  that infiltrated  soil  water  be  available  to evapotranspiration, the  method  requires  the residence time of infiltrated water  in soil  to  be sufficient  to  make  water  available  to evapotranspiration.  (B)  The  second  limitation holds  for  plains  under  dry  climatic  conditions where  the  aquifer  is  recharged by groundwater inflow  from  regions  with  precipitation  excess. Since Eq.  (3) restricts  actual  evapotranspiration to  precipitation,  it  should  not  be  used  for wetlands where  Ea is enhanced by capillary rise from the groundwater table so much that it might exceed  the  local  precipitation  leading  to groundwater depletion.  To cope with conditions (B), a statistic prediction equation was set up which is given by    EaE p=c10+c11 P s+c12 qmaxc 13 +c14 W a                (5)Eq. (10)  predicts  the  relation  Ea/Ep  using  the long-term average of summer precipitation (April to September),  Ps. The remaining variables keep their meaning as explained above. ResultsTo find the parameters of the transfer function, Eq. (4)  was  substituted  into  Eq. (3)  and  the standard  error  of  the  predicted  actual evapotranspitration  was  minimized.   Eq. (3) predicts  the  actual  evaporanspiration  with  a standard error of 1.55 cm. Eq. (5)  predicts  groundwater  recharge  with  a standard  error  of  RMSE = 2.58  cm.   The coefficient  of  correlation  between  SWAP-simulated and predicted groundwater recharge is r = 0.975. Calculations may be performed using a computer code available at http://www.small-scale-hydrology.deReferencesGlugla, G., Tiemer, K., 1971. Ein verbessertes Verfahren zur Berechnung der Grundwasserneubildung.- Wasserwirtschaft, Wassertechnik 20 (10) 349-353Glugla, G., Jankiewicz, P., Rachinow, C., Lojek, K., Richter, K., 2003. BAGLUVA - Wasserhaushalts-verfahren zur Berechnung vieljähriger Mittelwerte der tatsächlichen Verdunstung und des Gesamtabflusses.- Bundesanstalt für Gewässerkunde Koblenz

Prediction of the long-term groundwater recharge by hydropedotransfer functions

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Prediction of the long-term groundwater recharge by hydropedotransfer functions

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