Land Use and Cover or Precipitation? : Changes on Hydrological Response of the Upper Paraná River Basin
Abstract: The Upper Paraná River Basin (UPRB) has undergone extensive Land Use and Cover Changes (LUCC) in the latest decades, due to rapid population growth and economic development. Furthermore, variation in precipitation patterns was observed across the basin mainly after the 1970s Climate shift. Concurrently, the UPRB has presented significant changes in its hydrology. In this context, this thesis investigates the changes in precipitation and LUCC and their effects on the hydrological processes in the UPRB. The observed trends in the extreme precipitation events from 1977 to 2016 were evaluated using the Mann–Kendall test. Different numerical scenarios were simulated using the Soil and Water Assessment Tool (SWAT) model. The model was calibrated and validated with a satisfactory performance for the main rivers during the period 1984 – 2015 considering the Land Use and Cover (LUC) from 2015. The results revealed that the southern (northern) parts of the basin presented increasing (decreasing) trends in precipitation amounts. Besides, the southern regions of the UPRB presented an increase in the number of rainstorms > 50 mm/day and annual greatest 5-day total precipitation, while the northern part an increase in the number of consecutive dry days. The results also suggest that the basin is exposed to a longer rainy season. By comparing the LUC between 1985 and 2015, the numerical simulations showed that the natural vegetation suppression caused significant changes in basin hydrology. For instance, an increase (decrease) of surface runoff in the wet (dry) season at most UPRB subbasins, was observed. In addition, the simulations revealed a reduction in actual evapotranspiration and an increase in soil moisture in the annual and wet season. Consequently, the major rivers of the basin presented an increase (decrease) in their discharge in the wet (dry) period. This study also addressed the comparison between the LUC from a pristine period (around the year 1500), 1960 and 1985, and changes in precipitation before and after the 1970s Climate shift. In this case, the results showed that the 1970s Climate shift event has a higher effect on the changes in average annual discharge at the river mouth of the UPRB. This research improves the understanding of the effects of LUCC and changes in precipitation patterns on the hydrology across the UPRB. The results from this thesis will hopefully provide insights in improving sustainable management of water resources.
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