No abstract

Este trabajo analiza la variabilidad espacial y temporal de la precipitación en la cuenca del río lsábena (Cuenca del Ebro, Prepirineo aragonés) durante los años 2000 y 2001. También estudia los errores en la estimación de la precipitación según la fuente de datos y el tipo de interpolación. El estudio se rea­lizó a partir de datos obtenidos mediante 26 pluviómetros totalizadores y 3 pluviógrafos registradores distribuidos en las distintas subcuencas. En la cabecera de la cuenca la precipitación anual fue mayor, pero en la parte media de la cuenca las tormentas fueron más intensas, y con un desfase temporal medio de -50 minutos. La precipitación por episodio siguió un gradiente positivo en sentido sur-norte ( 1,84% /km). Se presentan los polinomios derivados para estimar el valor integrado de precipitación para cada subcuenca a partir de un solo pluviómetro, con coeficientes de ajuste entre el 70% y el 90%. Asimismo se detectó una infraestimación media del 13% en la precipitación a partir de los pluvióme­tros de la red oficial I.N.M .. La estimación ele la precipitación por subcuencas mediante el método de polígonos de Thlessen indica también un error medio por defecto del -15%. Los distintos errores son importantes, especialmente si los datos de precipitación se utilizan en rutinas de modelización hidro­lógica. No obstante, se pueden subsanar mediante el uso de polinomios de ajuste y con la instalación estratégica de pluviógrafos registradores.

Streamflow in theEsera and Upper Cinca Rivers (South Central Pyrenees) experiences alterations in the form of rapid pulses, commonly referred to as hydropeaks, associated with highly variable on-demand hydropower production from flowing or stored water. A hydrological characterization of the hydropeaks in these two rivers was carried out to examine their distinct hydropeaking pattern during hydrologically contrasted years. The Esera demonstrated a hydropeaking regime characterized by a high frequency and magnitude, while the Upper Cinca presented a regime with higher frequency but of lesser magnitude. Additionally, this study classified hydropeaks following the shapes proposed in previous studies and assessed their temporal distribution (frequency), timing, and magnitude. Results indicated that hydropeaks were different in shape and magnitude in both rivers; a Front Step pulse shape dominated in the Esera whereas a Rectangle pulse shape was the most frequent in the Cinca.The Front Step shape had the highest ramping rates during the rising limb of the hydrograph and the shortest time to the maximum flow; whereas the Rectangle shape had higher duration and a larger volume of water released. Hydropeaks in the Esera were less frequent (one per day) than in the Cinca (two per day). The river Esera presented, in general, high-magnitude hydropeaks, with double volume and duration, and three times larger up-ramping rates and time between flow pulses. Overall, hydropeak shapes in the Esera varied depending on the hydrological year and the season, while in the Cinca, shape distribution followed the same temporal pattern regardless of year and season; thus, hydropeaking in the Esera appeared to be much more dependent on the annual hydrology (whether the year is wet or dry) than in the Cinca. Hydropeaking regimes were characterized based on three categories of variables: magnitude (flow-based or hydrological variables), timing (duration), and frequency (occurrence). According to the variability of these variables, a total of three statistically significant groups were obtained in the Esera, while two groups were identified in the Cinca. Hydropeaks can be statistically classified by their hydrological characteristics that in turn may have a direct effect on sediment entrainment and transport with implications to the ecological functioning of rivers. The different shape