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Universidade Federal de Pernambuco (UFPE) 2017

Sazonalidade da chuva e dos fluxos de energia, água e carbono em áreas de caatinga e pastagem no semiárido pernambucano

SOUZA, Rodolfo Marcondes Silva

Titre : Sazonalidade da chuva e dos fluxos de energia, água e carbono em áreas de caatinga e pastagem no semiárido pernambucano

Auteur : SOUZA, Rodolfo Marcondes Silva

Université de soutenance : Universidade Federal de Pernambuco (UFPE)

Grade : Doutor em Ciências, Área de Concentração : Aplicações de Radioisótopos na Agricultura e Meio-Ambiente. 2017

Résumé
Climate change scenarios point to changes in the rainfall regime with a tendency for water scarcity in semi-arid regions. Projections of changes in seasonality and interannual rainfall variability indicate severe impacts on the vegetation of arid and semi-arid tropical regions. In addition, changes in land use can impact energy and carbon flows in these regions. In this sense, this research had two main objectives : i) evaluate the seasonal and interannual variability of flowsofenergyandcarbonindegradedpastureareaandinthesemi-aridcaatingaofPernambuco ; ii) assess the effects of seasonality and interannual variability of rain in caatinga and model the responses of the caatinga to future changes in rainfall regime. In order to meet the first objective, micrometeorological towers were installed for continuous measurements of meteorological variables, energy fluxes, carbon and soil water content in a degraded pasture (PA) and caatinga (CA) area in the municipality of Serra Talhada-PE. The energy and carbon fluxes were measured with a correlation system of turbulent vortices at 2.0 and 10 m height in PA and CA, respectively. Most of the available energy was converted into sensible heat flux in both PA and CA, however, latent heat and evapotranspiration in CA were higher than in PA. After the events of rain, especially at the beginning of the rainy season, have registered positive CO2 flows in both areas, which then started to have negative CO2 flux due to photosynthesis. During the rainy season, the respiration in CA was about 2.8 times higher than in PA. Despite the low rainfall regime, both areas acted as a carbon sink by an average of 3.9 and 3.4 Mg C ha−1 year−1 respectively to the PA and CA. In the second main objective, we calculated statistics of seasonality and interannual variability of rainfall and NDVI that describing the duration, timing, and intensity of wet and dry seasons for four sites in State of Pernambuco (São João, Araripina, Serra Talhada e Petrolina). The results showed that the caatinga tends to have a more stable response with the longest growing season (3.1±0.1 months) compared with the duration of the rainy season (2.0±0.5 months). The format and the size of the hysteresis loops of the rain-NDVI relations are linked to the buffering effects of soil moisture and plant growth dynamics. Finally, the simulations of the response of vegetation to different scenarios of rain have revealed the existence of a maximum productivity of the ecosystem at intermediate levels of seasonality of rain, which suggests a possible compensation effects of intensity (e.g. quantity) and the duration of the wet season in the growth of vegetation related to the dynamics of the water in the soil and the rate of transpiration.

Mots clés : Eddy covariance ; evapotranspiration ; Brazilian Semi-arid ; land use chagen ; ecohydrology modeling

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Page publiée le 14 septembre 2018