To evaluate the surface water balance in Gran Canaria, standard procedures were modified to fit local conditions, taking into account the availability and quality of data as well as the special features of the island. In a bookkeeping method the terms of the balance equation were calculated on a daily basis. The precipitation was based on data from a limited number of representative stations. Runoff data were extrapolated by quantifying the characteristics of the geological formations using the SCS curve number method. Potential evapotranspiration data based on Class A pan measurements or Penman calculations were extrapolated using the Blaney-Criddle method, and the real evapotranspiration was calculated using the Thornthwaite-Mather hypothesis. The results of this simplified procedure coincide well with results of an independent evaluation of the recharge.

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