Streamflow trends of the Pyrenees using observations and multi-model approach (1980–2013)

The Pyrenees. The Pyrenees is sensitive to changes in climate (both natural and of anthropic origin) and changes in land use and cover (LULC). These changes can influence the water resources. The historical evolution (1980–2013) of the stream flows are studied using observed time series from non-influenced gauging stations and two models (SASER and SWAT). Their comparison helps to detect and analyze changes in flow rates and their trends (trends are computed using the Sen's slope estimator, the significance of which was evaluated using the Mann-Kendall test). Furthermore, it also allows to explore the question of attribution (these models do not simulate LULC change). A complex and diverse domain such as the Pyrenees gives large differences between modelled trends revealing a large uncertainty that has been observed thanks to the use of two models. For the study period, mostly there are no significant trends. When trends are present in the observations and are also simulated, they are attributed to the effects of climate (natural variability and human induced climate change). When the significant trends observed are not simulated by the models, they are mainly attributed to changes in LULC. In general, models have difficulties detecting observed trends, leading to their attribution to changes in LULCs rather than climate, but there are some notable exceptions. [Display omitted] •Historical evolution of Pyrenean streamflow trends are studied using observations, two hydrological models, and statistical tools.•The statistically significant trends have been attributed to climate variability and/or land use changes. Although most of the time series do not present statistically significant trends.•Autumn is the season more affected by climate variability, showing negative significant trends in the simulated and observed Pyrenean stream flows.•Positive significant trends are located in the western part of the Pyrenees at the end of winter and beginning of spring due to a higher proportion of precipitation in liquid form and the earlier melting period.•The use of two hydrological models allows us to verify the large uncertainty in the streamflow trends in the Pyrenees