Abstract
The Iberian Peninsula (IP) is a drought-prone area located in the Mediterranean which presents a significant tendency towards dryness during the last decades, reinforcing the need for a continuous monitoring of drought. The long-term evolution of drought in the IP is analyzed, using the Standardized Precipitation Evaporation Index (SPEI) and the Standardized Precipitation Index (SPI), for the period of 1901–2012 and for three subperiods: 1901–1937, 1938–1974, and 1975–2012. SPI and SPEI were calculated with a 12-month time scale, using data from the Climatic Research Unit (CRU) database. Trends in the drought indices, precipitation, and reference evapotranspiration (ET0) were analysed and series of drought duration, drought magnitude, time between drought events, and mean intensity of the events were computed. SPI and SPEI significant trends show areas with opposite signals in the period 1901–2012, mainly associated with precipitation trends, which are significant and positive in the northwestern region and significant and negative in the southern areas. Additionally, SPEI identified dryer conditions and an increase in the area affected by droughts, which agrees with the increase in ET0. The same spatial differences were identified in the drought duration, magnitude, mean intensity, and time between drought events.
Highlights
In recent decades, changes in climate have affected the average in temperature and precipitation and the frequency of extreme events causing impacts on natural and human systems on all continents and across the oceans [1, 2]
The moving sums of the precipitation and ET0 estimated with the Hargreaves method over the Iberian Peninsula (IP) are presented in Figure 1, as well as the corresponding linear trends obtained for the entire period
A marked pattern of decreased precipitation spread over the IP, with the exception of the NW of the Peninsula, was identified by Merino et al [72], using the Global Precipitation Climatology Center database, and by Coll et al [26], which used data from meteorological stations during the period 1906–2010
Summary
Changes in climate have affected the average in temperature and precipitation and the frequency of extreme events causing impacts on natural and human systems on all continents and across the oceans [1, 2]. A quantitative assessment of drought characteristics is revealed to be very challenging, due to the existence of several definitions of drought [12], as well as of different criteria used to determine the onset, end, and duration of a dry event This challenge is further increased by the difficulty of quantification of drought by means of a specific observational dataset, together with the sparsity of the available historical records of soil moisture [13]. The analysis of droughts for distinct time scales is frequently performed using multiscalar drought indices, such as the SPI [20, 23], which uses precipitation data to identify dry/wet conditions, and more recently the Standardized Precipitation Evaporation Index (SPEI) [16], which uses a simple water balance, incorporating evapotranspiration and indirectly several related climate variables that play an important role in drought occurrence and characterization
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