Long‐term rainfall monthly shortage in Spain: spatial patterns, statistical models and time trends

Abstract

Several patterns of the monthly rainfall shortage in Spain are investigated by using long-term series of monthly rain amounts, which were recorded at 34 observatories and compiled by the Agencia Estatal de Meteorología, AEMET (Spanish Ministry of Environment). Owing to the strong variability of the pluviometric regime along the year, the median of the empirical monthly rain amounts is estimated for every month of the year. A monthly shortage is then defined as the difference between the corresponding monthly median and the monthly rain amount. A spell of monthly shortage is a set of consecutive months with amounts below the corresponding monthly medians. Five magnitudes are defined to characterize the rainfall shortage: (1) the spell length, L (months); (2) the average monthly shortage of a spell, <S > (mm); (3) the largest monthly shortage in a spell, S M (mm); (4) the total rainfall shortage for every spell, CS (mm) and (5) the rainfall amount for every shortage spell, CR. The whole number of spells, N, and the number of spells as a function of shortage lengths, N(L), are compared with those deduced from the distribution theory of runs (TR). Instead of a geometric distribution, a Markov chain of first order with two states becomes a better option for the probability density function of L. Although the empirical distributions of < S >, S M and CS are well fitted by a Pearson-type III model for most gauges, the generalized Pareto (GP) distribution is sometimes a better choice. The distribution of CR is well fitted by gamma and especially Poisson-gamma models. Besides these statistical analyses, an interpretation of the rainfall shortage is attempted by looking for links between the distributions of cumulative monthly shortage (CMS), and cumulative number of months (CNM) with rainfall deficit. Both distributions generate normalized shortage curves (NSC), which follow similar laws to the normalized rainfall curves (NRC), used, for instance, in the study of daily rainfall amounts. Finally, statistical significance of local and field time trends of < S >, S M and CS are evaluated.

Autoregressive process of monthly rainfall amounts in Catalonia (NE Spain) and improvements on predictability of length and intensity of drought episodes

“…Drought episodes in the Mediterranean region are quite usual, and sometimes characterized by long dry spells of several months depending on the threshold level assumed to define the dry spells (Kutiel, 1985; Kutiel and Maheras, 1992; Lana and Burgueño, 1998a, 1998b; Martín‐Vide and Gómez, 1999; Anagnostopoulou et al ., 2003; Lana et al ., 2006a; Serra et al ., 2006; Vicente‐Serrano, 2006; Diodato and Bellocchi, 2008; Nastos and Zerefos, 2009; Martínez et al ., 2010; Sergent et al ., 2014; Labuhn et al ., 2016, among others). In agreement with Alpert et al .…”

“…2003; Lana et al, 2006a;Serra et al, 2006;Vicente-Serrano, 2006;Diodato and Bellocchi, 2008;Nastos and Zerefos, 2009;Martínez et al, 2010;Sergent et al, 2014;Labuhn et al, 2016, among others). In agreement with Alpert et al (2002), it is worthy of mention at a global Mediterranean scale the paradoxical tendency to increase daily rainfall records and, at the same time, a decrease of monthly and annual amounts.…”

Intra‐annual rainfall variability in the Spanish hydrographic basins

“…In the Iberian Peninsula there are many studies showing the spatiotemporal variation of rainfall and the availability of water resources (García‐Barrón et al, ; Sánchez et al, ; Estrela et al, ; Guerreiro et al, ; Aguilar‐Alba, ). Other studies have analysed the rainfall variation at daily time scales (Martin‐Vide, ; Rodrigo and Trigo, ; Acero et al, ; Gallego et al, ; Ramis et al, ), or at monthly or seasonal time scales (García et al, ; Ninyerola et al, ; Martínez et al, ; Rodrigo, ; Del Rio et al, ; Costa et al, ; De Lima et al, ). Thus, De Luis et al .…”

“…In the Iberian Peninsula there are many studies showing the spatiotemporal variation of rainfall and the availability of water resources Sánchez et al, 2011;Estrela et al, 2012;Guerreiro et al, 2014;Aguilar-Alba, 2016). Other studies have analysed the rainfall variation at daily time scales (Martin-Vide, 2004;Rodrigo and Trigo, 2007;Acero et al, 2011;Gallego et al, 2011;Ramis et al, 2013), or at monthly or seasonal time scales (García et al, 2007;Ninyerola et al, 2007;Martínez et al, 2010;Rodrigo, 2010;Del Rio et al, 2011;Costa et al, 2012;De Lima et al, 2015). Thus, De showed that, from 1946 to 2005, there was a rainfall decrease in the Iberian Peninsula during the winter and spring months and an increase in the autumn.…”

Monthly rain amounts at Fabra Observatory (Barcelona, NE Spain): fractal structure, autoregressive processes and correlation with monthly Western Mediterranean Oscillation index

“…Along last two decades, the pluviometric regime at the Fabra Observatory (Barcelona, NE Spain) has been analysed at local scale as also at regional and European scales, including different points of view as statistical distributions of daily, monthly and annual amounts (Burgueño et al ., , , ), characterization of Standardized Precipitation Index (Lana et al ., ), periodicities, irregularities and time trends of several pluviometric parameters (Lana et al ., ; Martínez et al ., ; De Luis et al ., ; González‐Hidalgo et al ., ; Gallego et al ., ), extreme daily amounts (Lana et al ., ; Beguería et al ., ), monthly rainfall shortage (Martínez et al ., , ) and dry spell lengths (Lana et al ., , , , ; Serra et al ., , , ). The Fabra Observatory rainfall data have also taken part in fractal analyses of monthly rain amounts (MRA) and dry spell lengths for Iberian Peninsula and Europe by considering nonlinear processes, taking advantage of monofractal theory based on self‐invariance, self‐affine series and reconstruction theorem (Martínez et al ., ; Lana et al ., ).…”