Revista Recursos Hdricos
Volume 33, Nmero 2, novembro 2012

DOI: 10.5894/rh33n2-1
O texto deste artigo foi submetido para reviso e possvel publicao em outubro de 2012, tendo sido aceite pela Comisso de Editores Cientficos Associados em novembro de 2012. Este artigo parte integrante da Revista Recursos Hdricos, Vol. 33, N 2, 5-23, novembro de 2012.

Superfcies de limiares de precipitao para identificao de secas em Portugal continental: uma aplicao complementar do ndice de Precipitao Padronizada, SPI

Surfaces of precipitation thresholds for drought recognition in mainland Portugal: a complementary use of the Standardized Precipitation Index, SPI

Maria Manuela Portela ¹, Joo Filipe Fragoso dos Santos ²,
Mauro Naghettini ³, Jos Pedro Matos ⁴, Artur Tiago Silva ⁵

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1 - IST; mps@civil.ist.utl.pt
2 - IPBeja; joaof.santos@estig.ipbeja.pt
3 - UFMG; mauronag@superig.com.br
4 - IST/EPFL; jose.matos@ist.utl.pt
5 - IST; artur.tiago.silva@ist.utl.pt

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RESUMO:De entre os ndices porventura mais amplamente utilizados na anlise de secas destaca-se o ndice de precipitao padronizada, SPI (Standardized Precipitation Index), que, mediante recurso a procedimentos de anlise estatstica, faz corresponder a precipitao num dado intervalo de tempo (ms ou grupos de meses) a valores numricos susceptveis de serem comparados entre regies com climas bastante distintos. No obstante a sua utilizao generalizada e as vantagens que apresenta na comparao de secas em diferentes contextos climticos, a interpretao dos valores associados ao SPI e a monitorizao das secas com base nesses valores no constituem tarefas triviais, fundamentalmente por se estar em presena de precipitaes padronizadas, obtidas mediante manipulao matemtica de registos daquela varivel hidrolgica e no perante registos propriamente ditos.
Por tal motivo, desenvolveu-se um clculo adicional que, respeitando o rigor do formalismo matemtico inerente ao SPI, devolve ao campo das precipitaes os valores desse ndice correspondentes a limiares de seca permitindo, de modo muito expedito e praticamente em tempo real, reconhecer as ocorrncias de seca e, assim, planear mais precocemente as aces subsequentes a tomar.
Aps um breve enquadramento , assim, efectuado o mapeamento de diferentes superfcies de precipitao que, para o territrio de Portugal Continental, fornecem ms a ms o que se designou de precipitaes limiares de seca entendendo-se, por tal, precipitaes abaixo das quais se considera estar perante uma seca com uma dada magnitude.

Palavras-chave:seca, ndice de precipitao padronizada, SPI, deteco e monitorizao de secas, limiares de precipitao conducentes identificao de secas.

ABSTRACT: Among the indices more often applied to characterize droughts, one of the most commonly, if not the most widely used, is the standardized precipitation index (SPI) which by means of statistical analysis procedures, assigns a numerical value to the monthly precipitation or to the cumulative precipitation in groups of consecutive months.
Despite the widespread use of the SPI, in part due to its great ability to compare droughts in different climatic contexts, the interpretation of the values associated to SPI and drought monitoring based on those values are by no means trivial tasks, particularly due to the fact that such values are standardized ones which can not be easily related with the precipitation records from which they derived.
For this very reason, an additional calculation method has been developed which returns back to the precipitation field the SPI values for any drought threshold. By assigning the drought thresholds directly to precipitation the meaning of the SPI results clearer and the identification and monitoring of the drought occurrences more expedite, thus allowing subsequent actions much more flexible and on the spot.
After a brief subject framework, this paper mentions some previous results of the application of the SPI to characterize droughts in mainland Portugal. Based on the new concept developed for the SPI, precipitation surfaces that provide precipitation thresholds for drought recognition on a monthly basis and across different timescales throughout the mainland Portuguese are presented. Finally the advantage of such complementary use of the SPI is discussed.

Keywords: drought, standardized precipitation index, SPI, detection and monitoring of droughts, precipitation thresholds for drought identification.

 

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