Understanding how water resources vary in response to climate at different temporal and spatial scales is crucial to inform long-term management. Climate change impacts and induced trends may indeed be substantially modulated by low-frequency (multi-year) variations, whose strength varies in time and space, with large consequences on risk forecasting systems. In this study, we present a spatial classification of precipitation, temperature and discharge variability in France, based on a fuzzy clustering and 5 wavelet spectra of 152 near natural watersheds between 1958 and 2008. We also explore phase-phase and phase-amplitude causal interactions between time scales of each homogeneous region. Three significant time scales of variability are found in precipitation, temperature and discharge: 1 year, 2-4 years and 5-8 years. The magnitude of these time scales of variability is however not constant over the different regions. For instance, Southern regions are markedly different from other regions, with much lower 5-8 years variability 10 and much larger 2-4 years variability. Several temporal changes in precipitation, temperature and discharge variability are identified during the 1980s and 1990s. Notably, in the Southern regions of France, we note a decrease in annual temperature variability in the mid 1990s. Investigating cross-scale interactions, our study reveals causal and bi-directional relationships between higher and lower-frequency variability, which may feature interactions within the coupled land-ocean-atmosphere systems. Interestingly, however, even though 15 time-frequency patterns (occurrence and timing of time scales of variability) were similar between regions, cross-scale interactions are far much complex, differ between regions, and are not systematically transferred 1 from climate (precipitation and temperature) to hydrological variability (discharge). Phase-amplitude interactions are indeed absent in discharge variability, although significant phase-amplitude interactions are found in precipitation and temperature. This suggests that watershed characteristics cancel the negative feedback 20 systems found in precipitation and temperature. This study allows for a multi-time scale representation of hydro-climate variability in France, and provides unique insight into the complex non-linear dynamics of this variability, and its predictability.
Bibliographical noteFunding Information:
The authors would like to thank Nikola Jajcay, for his support with the adaptation of the Conditional Mutual Information algorithm (pyclits) to our context. The authors would also like to thank the Centre Regional Informatique et d'Applications Numeriques de Normandie (CRIANN), for providing the HPC environment needed for all computations. This research work is part of a contribution to the EURO-Friend group 2.
© 2021 Manuel Fossa et al.
ASJC Scopus subject areas
- Water Science and Technology
- Earth and Planetary Sciences (miscellaneous)