The AdaptAlp Dataset: Description, guidance and analyses

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUDetecting climate-related trends in hydrological series is a notoriously challenging task, in particular due to (i) the strong natural variability of hydrologic regimes; (ii) the existence of non-climatic factors that may induce trends in hydrologic series (e.g., water withdrawal, land use); (iii) the existence of non-homogeneities in the runoff records due to measurement issues. Reliable and powerful statistical methods for trend detection are required to address point (i), while points (ii) and (iii) suggest that trend detection should be based on a reliable dataset of homogeneous hydrologic series representing undisturbed catchments. The study described in this report aims at detecting trends in the hydrologic regime of Alpine catchments. It is based on a dataset of 177 runoff time series collected over the Alpine space. These series cover at least forty years of daily record, are related to undisturbed catchments and have been quality-checked as thoroughly as possible by the partners of the project. The dataset covers the whole spectrum of hydrological regimes existing in the Alps (from glacier- to mixed rainfall/snowmelt regimes). In a second step, a set of hydrologic indices is defined to characterize the hydrologic regime in terms of low, medium and high flow. In particular, these indices describe the drought severity and seasonality, and the intensity and timing of snowmelt flows. At-site and regional statistical tests are applied for each hydrologic indice, and regional field significance is tested. Winter droughts tend to be less severe (in terms of volume and duration), while consistent trends affecting the timing of snowmelt flows are found. In particular, spring high flows due to snowmelt appear to start earlier in the season, and the duration of the snowmelt season is increasing