Because of the complexity and rapidly occurring changes in the dynamics of human demography and water demands, it is difficult to assess the future adequacy of limited freshwater resources. The planning of water resources largely depends on the meteorological variables (precipitation and evaporation) in terms of their distribution in space and time. Considering precipitation and evaporation as natural input and output without any human intervention for water-resources systems that can be perceived to represent the potential water-resources availability of an area, an uncertainty study was carried out for different water-resources regions in Texas. The entropy method was used for measuring the uncertainty in meteorological variables. It was observed that critical water-deficit regions based on meteorological variables are mostly located in the western part of Texas. The Mann-Kendall test was employed to understand the trend in precipitation, evaporation, and the meteorological excess index (MEI) in deficit and surplus water-resources zones. It was observed that increasing trends exist in both precipitation and evaporation at most of the grids, but the increasing trend of evaporation is more than precipitation in some of the water-resources zones, which is likely to make the deficit regions even more deficient and critical. DOI: 10.1061/(ASCE)HE.1943-5584.0000150. (C) 2011 American Society of Civil Engineers.