José María Cuadrat

Water Resources and Precipitation Trends in Aragon

This work analyses the trend of annual precipitation in Aragon during the second half of the tentieth century, the spatial differences that this trend might entail in the Autonomous Community, both on an annual and a seasonal scale and the impact on water resources and their management. The regional series (1950–2000) presents drier and more humid phases and a slight negative trend which is not significant from the sixties onwards. The Zaragoza, Huesca and Teruel observatories follow a similar evolution. As regards to space, no significant trends can be observed in the annual totals of any Aragonese county; but instead on a seasonal scale there are some differences: winter shows a precipitation decreasing gradient from south-easat to north-west, opposite to the one produced in summer. Autumn has a clear north–south decreasing gradient, whereas spring does not offer clearly defined patterns. To be able to face the possible adverse effects coming from the rainfall decrease, efficient water policy actions are in need of a high degree of planning and rational water management.

Summer drought reconstruction in northeastern Spain inferred from a tree ring latewood network since 1734

Drought recurrence in the Mediterranean is regarded as a fundamental factor for socio-economic development and the resilience of natural systems in context of global change. However, knowledge of past droughts has been hampered by the absence of high-resolution proxies. We present a drought reconstruction for the northeast of the Iberian Peninsula based on a new dendrochronology network considering the Standardized Evapotranspiration Precipitation Index (SPEI). A total of 774 latewood width series from 387 trees of P. sylvestris and P. uncinata were combined in an inter-regional chronology. The new chronology, calibrated against gridded climate data, reveals a robust relationship with the SPEI representing drought conditions of July and August. We developed a summer drought reconstruction for the period 1734-2013 representative for the northeastern and central Iberian Peninsula. We identified 16 extremely dry and 17 extremely wet summers, and four decadal scale dry and wet periods, including 2003-2013 as the driest episode of the reconstruction.

Oaks Under Mediterranean-Type Climates: Functional Response to Summer Aridity

Mediterranean-type climates are characterized by warm or hot summers, mild or cold winters and, especially, by the existence of a summer drought period driven by the low or even nule precipitation during this season. Mediterranean-type climates are represented in different areas of the world, both in the Northern and the Southern Hemisphere. Specifically, regarding the existence of Quercus under these climatic conditions, two main geographical areas should be considered, namely the Mediterranean Basin in the Palearctic and California (USA) and Baja California (Mexico) in the Nearctic. Despite the relatively low geographical extension of the areas occupied by oaks under this type of climate, it has deserved its own phytoclimatical entity since the first geobotanical synthesis at a global scale. Although evergreen and sclerophyllous oak species are widely assumed as a prototype of mediterranean oaks, both palaeoecological evidences and present biogeographical analysis confirm the co-existence of this oak type with winter-deciduous species of the same genus. In this chapter, the different advantages and disadvantages of both phenological patterns (evergreeness and winter-deciduousness) are presented. Moreover, the strategies for saving water through the overall leaf size reduction, the stomatal control of water losses or some xeromorphic traits for a further reduction of transpiration are also shown. Finally, the development of a high resistance to drought-induced cavitation, as a way for coping with low water potential during dry periods, is discussed.

Influence of different factors on relative air humidity in Zaragoza, Spain

In this study, the spatial patterns of relative air humidity and its relation to urban, geographical and meteorological factors in the city of Zaragoza (Spain) is discussed. We created a relative humidity database by means of 32 urban transects. Data were taken on different days and with different weather types. This data set was used to map the mean spatial distribution of urban dry island (UDI). Using stepwise multiple regression analysis and Landsat ETM+ images the relationships between mean UDI and the main geographic-urban factors: topography, land cover and surface reflectivity, have been analyzed. Different spatial patterns of UDI were determined using Principal Component Analysis (Varimax rotation). The three components extracted accounted for 91% of the total variance. PC1 accounted for the most general patterns (similar to mean UDI); PC2 showed a shift of dry areas to the SE and PC3 a shift to NW. Using data on wind direction in Zaragoza, we have found that the displacement of dry areas to the SE (PC 2) was greater during NW winds while the shift to the NW (PC 3) was produced mainly by SE winds.