(1) Mediterranean Ecogeomorphological and Hydrological Connectivity Research Team (http://medhycon.uib.cat),
Department of Geography, University of the Balearic Islands, Carretera de Valldemossa Km 7.5 07122, Palma, Spain, (2)
Institute of Agro-Environmental and Water Economy Research –INAGEA, University of the Balearic Islands, (3) Institute of
Earth and Environmental Science, University of Potsdam, Karl-Liebknecht-Straße 24/25, 14476 Potsdam-Golm, Germany, (4)
Institute of Environmental Assessment and Water Research (IDAEA), Spanish Research Council (CSIC), Jordi Girona 18,
08034 Barcelona, Spain
Mediterranean catchments are characterized by high inter-intra annual precipitation variability and summer
drought. The hydrological regime is characterized by ephemeral behaviour due to the direct rainfall-runoff
relationship. Furthermore, extreme precipitations can generate an amount of rainfall higher than 200 mm in
24 hours with short response time. These events occurred normally under wet soil moisture conditions. The
Mediterranean catchment morphology is a favourable factor for flash floods: short catchments with a high gradient
slope. Others factor that condition the hydrological regime are the presence of limestone lithology and the impact
of human activities on fluvial systems as geomorphological changes in channels and flood plains.
The aim of this study is analyse the hydrological response of five hydrological years (2012-17) in an agricultural
headwater catchment (i.e. < 4 km2) at different time scales. Rainfall-runoff relationship was carried
out at annual and seasonal scale through the flow duration computation, the variability index, 30/70 ratio, quick
flow response ratio and base flow index. The rainfall-runoff relationship at event scale was carried out through
a Pearson correlation matrix using different variables extracted from the hyetograph and hydrograph. These
variables were placed into two groups: a) antecedent conditions and b) event conditions. The correlation results
determined the involved factors in the hydrological response.
At annual scale total flow was present for 42.8% of the time and quick flow was 1.4%. The Variability index value
(0.64) was higher than catchments with high dynamics storage (Vi < 0.5). At season scale, winter with 90.6%,
showed the highest discharge presence. This highest discharge percentage duration generated a sustained water
storage (Vi: 0.55) and increased the soil moisture from autumn getting favourable conditions for runoff generation.
Because of that, winter had the highest quick flow duration (3.1%) and also the 30/70 denotes an increase of
the flow variability. Autumn and spring had lower percentage of discharge duration than winter, 53% and 41%
respectively. Autumn is the season after the dry season when starts again the wet period getting favourable
conditions for runoff generation. Spring denotes the importance of the accumulated precipitation contribution of
the wet seasons, also indicated for the highest seasonal BFI (0.7). Summer presented flow and quick flow the
0.93% and 0.21% of time respectively.
At event scale, peak discharge, mean discharge, runoff and quick flow showed significant correlations (p<0.01)
with the total precipitation and correlated with antecedent precipitation of one and three days (p<0.05). Baseflow
variables correlated with antecedent precipitation until 15 days before flood date. Peak discharge was the unique
hydrological variable that correlated with maximum rainfall intensity 30’. That indicated that a shorter period
of rainfall intensity (15min) is not enough to generate a response. So, for peak discharge a combination of two mechanisms is needed to generate runoff: a) surface runoff occur when rainfall intensity exceeds infiltration capacity and b) surface runoff is produced by precipitation over the area where water table is at the surface.Peer reviewe
