In this work were determined and analyzed the anomalies of theDecadal Water Balance components of 1977-1986, 1987-1996 and 19972006in relation to Climatological Water Balance components 1977-2006.Air temperature and rainfall monthly data from 1977-2006, distributed in16 surface meteorological stations of the Rio Grande do Sul (RS) wereused to calculate the Water Balance (WB). The methods proposed byThornthwaite e Mather (1955) and Thornthwaite (1948) were used tocalculate the WB and the evapotranspiration, respectively. According tothe results obtained decades 1977-1986 and 1987-1996 were drier than the climatological normal for most of the RS, but there was not lack of waterbecause even the excess water being lower than the climatological normal,it was sufficient to restore the demand evaporative of these decades. The1987-2006 decade was wetter than the climatological normal studied, so inthis decade there was excess water in the RS.
