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Universidade de Lisboa (2013)

Avaliação da seca global num clima de mudança

Ramalho, Maria Inês Vieira Lopes

Titre : Avaliação da seca global num clima de mudança

Auteur : Ramalho, Maria Inês Vieira Lopes

Université de soutenance : Universidade de Lisboa

Grade : Mestrado em Ciências Geofísicas 2013

Droughts are phenomena which affect Humanity since the earliest times. The impact they have in the ecosystems grants them a natural disaster status. They also have huge global socioeconomic effects. Thus, since the seventies several indices have been developed to identify and quantify droughts in what concerns intensity, duration and spatial extension. A widely used index is the Standardized Precipitation Index (SPI), which is based on rainfall and is time and space invariant. Recently, a new index has been developed, the Standardized Precipitation Evapotranspiration Index (SPEI), which has into account not only the rainfall but also the effect of temperature and evaporation on droughts. Including temperature in the SPEI evaluation is intended to be an added value to understand droughts in the context of global warming. The index Normalized Soil Moisture (NSM), which is based on the soil water content, was also analyzed. In this study, the results of the historical (1961-2005) and the future simulations RCP8.5 (2005-2100) of the EC-Earth model were used in order to compute and analyse the referred 3 drought indices, being the main goal the evaluation of the global drought in a changing climate. This analysis allowed to typify drought globally in terms of frequency of occurrence, severity and spatial extension in a present and future climate, enabling the assessment of the impact of climate change in drought properties at a global level. The EC-Earth model reasonably represents the occurrence and severity of droughts in the current climate in several regions when comparing its results with local observations. Results show that, locally in the present climate and for a 40 year timeframe, the SPEI index does not add significant information to the SPI index. In the global analysis, there was a clear increase of the areas affected by droughts (15%), moderate droughts (10%) and severe droughts (8%), with increased occurrences in Africa, east and south of Europe, Americas, Asia and Australia in the second half of the XXI century, as a result of global warming. In the areas considered, i.e., globe, Mediterranean and Iberian Peninsula, there was a sharp increase of the areas affected by drought, moderate drought and severe drought as from 2030, notably the Iberian Peninsula which presents an increase of the areas affected by droughts in 300% which corresponds to 67% of the total area of the Iberian Peninsula in the latter half of the XXI century. There is also an increase in the area affected by severe drought in 75%, which corresponds to 85 % of the total area of the Iberian Peninsula, however this abrupt increase is distributed only for 17 months from the last 15 years of the series.

Mots clés  : Seca Alterações climáticas Aquecimento global Indice Standardizado de Precipitação-Evpotranspiração Indice Standardizado de Precipitação Humidade do solo normalizada


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