Regionalization of hydrological model parameters for the semi-arid region of the northeast Brazil

This work deals with the regionalization of parameters of hydrological models in semi-arid regions with data scarcity, focusing on part of the Brazilian semi-arid region that involves the States of Ceara, Rio Grande do Norte, Paraiba and Pernambuco. The hydrological model adopted was the MODHAC- Self-Calibrating Hydrological Model. A total of 45 fluviometric gauge stations were selected with a minimum of eight consecutive years after 2000, in addition to the records from previous years. The main regionalization criterion was the proximity between the available flow gauge stations, also evaluating the choice based on physical and climatic properties for some stations. An analysis was made of factors that affect the quality of the flow series, as well as the rainfall gauge station network. The influence of reservoirs on these data and the deactivation of many rainfall stations were the most frequent problems. Considering different performance indicators, such as the Nash Efficiency Coefficient for the flow square root that was satisfactory in 63% of the cases, according to reference values presented in the literature the procedure was reasonably successful in quantifying the higher and medium flow, but it did not present in general a sound adjustment of the lower flows.