<p>Water is an important part of sustaining life, and a large part comes from rainfall, which supplies rivers, reservoirs, fauna, and flora, with part of this water being stored in the soil. Therefore, the objective of this study is to analyze the variability, the trend, the variables that most influenced the water surplus and deficit, and which mesoregions were most affected. The study was carried out for the State of Paraíba, which is divided into four mesoregions (Mata Paraibana, Agreste, Borborema, and Sertão Paraibano) that vary according to the rainfall regime, with 90% of the State being in a semi-arid region. The amount of water stored in the soil was calculated using the water balance proposed by Thornthwaite and Mather method. A series of 43 years of monthly data on temperature, precipitation, radiation, relative humidity, and wind speed were used to determine water surplus and deficit and analyze these variables’ influence on surplus and deficit. The results show a large variability in surplus and deficit, mainly influenced by precipitation. The surplus series shows no trend, but 50% of the cities analyzed show an increasing/decreasing trend for the deficit. The water balance shows that the mesoregions of Borborema and Sertão Paraibano are the most affected, with a deficit greater than 1000&#xa0;mm. Projections up to 2100 also indicate impacts across all regions, including areas that previously showed no deficits. Therefore, mitigation policies will be required for these mesoregions.</p>