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Universidade Federal do Rio Grande do Norte (UFRN) 2020

Drought characterization in the Northeast Brazil : a multiscale watershed analysis and remote sensing monitoring

Mutti, Pedro Rodrigues

Titre : Drought characterization in the Northeast Brazil : a multiscale watershed analysis and remote sensing monitoring

Auteur : Mutti, Pedro Rodrigues

Université de soutenance : Universidade Federal do Rio Grande do Norte (UFRN)

Grade : Doutorado em Ciências Climáticas 2020

Résumé
Drought is a recurrent phenomenon in the Northeast Brazil (NEB) region, especially in its semiarid inlands, which are characterized by a remarkable climate variability, the expansion of desertification areas and persistent water-use conflicts. Furthermore, future climate change projections indicate that drought events will become more frequent and intense, exerting more pressure over the already vulnerable region. Although several drought studies have been carried out at the NEB, some important methodological aspects inherent to data quality and control, specificities of the used techniques, and spatial scale still need to be further discussed. Therefore, the objective of this thesis is to characterize different aspects of drought in the NEB considering different spatial scales, meteorological data characteristics, and remote sensing monitoring alternatives. This characterization was carried out in the São Francisco watershed (SFW), which presents a remarkable climate diversity, in the Piranhas-Açu watershed (PAW), which is mostly located in the semiarid NEB, and in desertification hotspots. In the first study, we thoroughly validated Climate Research Unit Time Series (CRU TS) gridded precipitation and potential evapotranspiration data over the SFW. CRU TS data presents overall good correlation with observed data. Then, we compared the applicability of the evaporation deficit and the Standardized Precipitation-Evapotranspiration Index as drought indices in the SFW. Results show that periods of water shortage are becoming more frequent and more intense in the coastal and middle zones of the basin, indicating an expansion of aridity. In the second study, we used gap-filled observed rainfall time series in order to propose a comprehensive climatological analysis in the PAW. A rainfall anomaly index was used to identify drought events, which are mostly associated with El Niño events and the anomalous warming of the Tropical North Atlantic Ocean. Finally, in the third study, different stochastic models were tested in order to forecast remotely sensed Normalized Difference Vegetation Index data (MOD13A2 product) over six desertification hotspots in the NEB. Results show that the tested models satisfactorily forecast short-term dry and degraded vegetation states. The results of this thesis contribute to the current general knowledge associated with drought assessment over semiarid regions, and the specific results of each study can be further explored by management agencies or local entities in the development of specific strategies to face and adapt to drought in the NEB.

Mots Clés  : Semiarid ;Water balance ;Climate extremes ;Data series gap-filling ;Desertification;NDVI ;SPEI

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