Resumen de Hidrometeorología y balance térmico de la marisma de Doñana
Doñana marshes are a wetland of ecological relevance at an international level. They are located on the right bank of the final Guadalquivir River, in the regions of Huelva and Seville in SW Spain. They occupy an area of 27000 ha and present an extremely flat topography, a Mediterranean climate with influence from the Atlantic Ocean and annual flooding and drying out processes, which normally develop from mid autumn to mid summer and present maximum water depths of about one meter. As a consequence of past anthropic modifications in their natural behaviour, intensive research and monitoring efforts have been conducted since the 1990¿s in order to better understand the natural processes related to the surface hydrology associated to the Doñana marshes. Such activities have been oriented to define the measures and establish the management criteria that allow, as far as possible, the recovering of the natural functionality of the marshes. This thesis studies the hydrometeorology and heat balance of Doñana marshes from field data collected through a network of automated gauging stations, which have been gathering hydrometeorological information for a number of consecutive years. Most part of the work refers to the three hydrological years from September 2006 to August 2009. Special attention has been drawn to the flooding period of 2006/2007, being the product of the development of a most characteristic flooding event. The work essentially focused on the characterization, at different time scales (annual, monthly, daily), of the measured hydrometeorological context and the heat fluxes that define the water heat balance of the flooded marshes. Sensible and latent heat fluxes between water and atmosphere have been estimated by means of the Bowen Ratio ¿ Energy Balance (BREB) method. Moreover, water and sediment temperature regimes have been analyzed, and vertical mean water temperature has been modelled for un entire flooding period through the implementation of a single-layer heat balance model. General results show a fast response of the water temperature to the atmospheric forcing. Net solar radiation constitutes the main source of heat and predominantly determines the net balance of all-wave radiation over the water surface. At an hourly timescale, most of this heat is invested in water heating but, at a daily timescale, heat gains and looses compensate. It results in a reduced heat storage per unit area of marshland. Since water availability is not a limiting factor, available heat is mainly lost by evaporation, which constitutes the main water loss from the marshes and explains to a large extent the rate of water level decrease. Daily thermal stratification and mixing processes have been identified, mostly from March onwards, which modify the marshlands¿ thermal behaviour at a short timescale. As thermal stratification and water depth reduce the importance of flooded sediment in the global water heat balance, water-sediment heat flux appeared negligible during most of the time of the study. Finally, the modelling of Doñana marshes¿ water temperature pointed out the necessity to include the vertical dimension despite the limited water depths registered.
