ASSESSMENT OF THE WATER VOLUME STORAGE IN RESERVOIRS FROM THE BRAZILIAN SEMIARID REGIONS

Resumo

Semiarid regions comprise a significant portion of the Earth and they are characterized by lack of water resources. Due to low water availability, surface water is commonly stored in small reservoirs that serve as a primary source of water supply and agriculture. The water volume stored in these reservoirs may be estimated by use of area-volume model,  which estimates the volume per  flooded area of the reservoir. The area of reservoirs can be easily estimated by computation of Normalized Difference Water Index (NDWI) using satellite imagery. Because of the vital importance of water availability estimation in small to medium reservoirs (0.1 to 15 Km²) of the  Brazilian semiarid region, the suitability of some previous area-volume models developed for semiarid was evaluated. Additionally, a new area-volume model valid for the Brazilian semiarid region was developed using non-linear regressions. The fitted model provides estimates close to the measured volumes, indicating the ability of these models to predict the volume of water in these reservoirs.  The proposed model was applied to evaluate the change of stored water in a watershed in the Brazilian semiarid region, allowing to verify a substantial reduction in the water volume during a prolonged drought. Consequently, this work points out useful strategies to monitor the water availability in the Brazilian semiarid region.