Challenges in The Assessment of Fresh Water Resources in the Semi-Arid North-East of Brazil Under Changing Conditions

Ensuring water security, in particular drinking water availability, and reaching sustainability of water resource management is still the central task of modern water sectors (Goal 6, UN 2018). Growing water demands due to demographic and development trends often compete with fading water resources influenced by climate change which leads to the complex task of first assessing and secondly balancing both components. This is especially challenging in the northeastern region of Brazil, which is increasingly affected by water shortages due to overuse of water resources, serious drought impacts and possible saline intrusion at the coast. This paper presents results of the German-Brazilian research project BRAMAR, funded by the German Federal Ministry of Education and Research (BMBF) and the Brazilian Ministry of Science, Technology and Innovation (MCTI). The project aimed to develop and apply water management strategies in order to use water resources efficiently and to guarantee a sustainable development of the region. Embedded in the new Brazilian water policy and institutional framework the project aimed to bridge and close gaps with regards to the chain monitoring-modelling-managing.

This paper presents a regional fresh water availability study focused on the federal state Paraíba. Highly complex hydro(geo)logical model systems were applied for regional quantification of all relevant water cycle components considering both surface water and groundwater issues. The deterministic and partly physically based hydrological water budget model (PANTA RHEI) was applied for a large scale river basin of about 20,500 km². For a coastal area of about 1,000 km² the rainfall-runoff model was coupled with the three-dimensional numerical groundwater flow model FEFLOW. At these large-scale catchments a variety of water cycle components (precipitation, evapotranspiration, groundwater recharge, outflow regime, reservoir storage) were simulated and evaluated under the influence of climate change using CORDEX data. The paper addresses the specific challenges during the modelling process and the solutions developed during the project: the complex quantification of the runoff regime due to high artificial impact of dams and land-use changes, the structural deficits of the hydrometeorological network and the rehabilitation of the monitoring system, the difficulties and uncertainties in climate change modelling using BIAS-correction methods and finally the evaluation and transfer of the modeling results for set-up of a management system on river basin level.