This paper analyzes the effect of forest canopy on snow water equivalent during two consecutive snow seasons in a mixed beech–fir stand in the Pyrenees. The results confirm that the forest canopy is ...a dominant influence on snowpack distribution during the accumulation and melting periods. In general, a noticeable decrease in snow water equivalent and an increase in variability among observations are detected with increasing density of the forest canopy. The influence of the forest canopy on melting rates is complex and highly dependent on the dominant climatic conditions. Similar conclusions are reached for both of the snow seasons for which measurements are available, but several differences are also recorded. This study highlights the important influence of climatic conditions observed during the snow season on the relationship between stand characteristics and snowpack dynamics.
Land cover mapping obtained from photointerpretation of aerial photographs and orthophotographs was used to quantify land cover changes between 1957 and 1996 in a Mediterranean middle mountain area. ...Expansion of forested area is clearly the main land cover change caused by the abandonment of traditional agricultural activities and by the use of other materials and energy sources instead of forest resources. As a result, about 64% of the area was covered by forest by 1996, whereas in 1957 forests accounted for only 40% of the land cover. Spontaneous afforestation of abandoned fields with Scots pine (Pinus sylvestris L.) in terraced areas and areas of sparse scrub vegetation, coupled with an increase in the density of forest canopies, has been responsible for this expansion of woodland. The influence of physiographic factors in land cover change processes in the terraced areas of the catchment was also considered. The results demonstrate that within the terraced areas, north-facing and more elevated steeper slopes are more intensely afforested. However, an accurate analysis of the role played by these factors in land cover change cannot be carried out because the pattern of land abandonment is not independent of these physiographic characteristics. Furthermore, field observations at the terrace scale are evidence of the relevant influence of local topography in afforestation dynamics.
The semi-distributed hydrological model TOPMODEL was tested with data from the Can Vila research basin (Vallcebre) in order to verify its adequacy for simulating runoff and the relative contributions ...from saturated overland flow and groundwater flow. After a test of the overall performance of the model, only data from a wet period were selected for this work. The test was performed using the GLUE method. The model was conditioned on continuous discharge and water table records. Furthermore, point measurements of recession flow simultaneous with water table depth and the extent of saturated areas were used to condition the distributions of the more relevant parameters, using new or updated evaluation measures. A wide range of parameter sets provided acceptable results for flow simulation when the model was conditioned on flow data alone, and the uncertainty of prediction of the contribution from groundwater was extremely large. However, conditioning on water table records and the distribution of parameters obtained from point observations strongly reduced the uncertainty of predictions for both stream flow and groundwater contribution.
The forms, rotational patterns and trends of hysteretic loops of dissolved organic carbon (DOC) and nitrate (NO₃) were investigated in three headwater Mediterranean streams during one autumn-winter ...period using two biogeochemical descriptors summarizing the changes in solute concentrations (ΔC) and the overall dynamics of each hysteretic loop (ΔR). The study had two aims: (1) to examine whether the variability of solute hysteretic loops monitored in different streams during cold seasons followed a consistent and recurring pattern, (2) to identify hydrological parameters which could potentially influence features of the DOC and NO₃ hysteresis. Relationships between hysteresis features and hydrological parameters in the studied streams were explored using multivariate redundancy analysis (RDA). Both DOC and NO₃ typically increased in concentration during storm events, although hysteretic loops did not obey any consistent pattern across the three streams. The rotational patterns of DOC and NO₃ hysteresis ranged widely, from clockwise to counterclockwise. Storm hydrographs and also the magnitude of antecedent storm events were explanatory of the DOC and NO₃ concentration changes across the study sites. However, the detailed hydrological information did not offer a satisfactory explanation of the entire DOC and NO₃ concentration dynamics during the storm events.
Monitoring (in 5 min steps) of precipitation, throughfall, stemflow and bulk canopy wetness, and also weather conditions and soil moisture, was carried out from July 1993 to December 1995, in a
Pinus ...sylvestris forest patch located in a Mediterranean mountainous former agricultural basin subject to spontaneous change from pasture to forest. Throughfall collectors were designed to obtain hydrologically representative data and they consist of nine troughs with a total catchment area of 9 m
2. The bulk interception rate measured after 30 months of monitoring was about 24%. Relative interception was irregular and decreased with the magnitude of the event; it was at least 15% for events of more than 20 mm.
Multivariate analysis of the events demonstrates that their characteristics can be simplified in two main factors which respectively represent the duration of the event and its magnitude. The magnitude of the event biases the characterization because of the non-linearity of the rainfall-interception relationship. Long events do not produce higher interception rates than shorter ones because of the occurrence of low vapour pressure deficits during the former. In atmospheric dry conditions the rainfall intensity provides the main control on interception rates.
The lower Araguás catchment, central Pyrenees, is characterized by extensive badlands (25% of the total catchment), whereas the upper catchment is covered by dense plantation forest. The catchment ...(45 ha) has been monitored since October 2005 with the aim of studying its hydrological response. The 44 floods recorded over this period were analysed to identify the factors that control the rainfall-runoff relationship. The first relevant feature of the catchment was its responsiveness. The catchment reacted to all rainfall events, but the irregular nature of the hydrological response was the most characteristic feature of the response. No single variable could explain the response of the Araguás catchment. It was found that stormflow coefficients mainly depend on the combination of rainfall volume and antecedent baseflow. A significant correlation was observed between maximum rainfall intensity and peak flow values. The shapes of the different hydrographs are very similar, regardless of the peak flow magnitude; they show a short time lag, relatively narrow peak flow, and steep recession limb. This indicates a large contribution by overland flow, resulting mainly from the generation of infiltration excess runoff in badland areas.
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