Hidrología y Cambio Climático/

Hydrology and Climate Change


Current European flood-rich period exceptional compared with past 500 years

- For first time, it was found that the past three decades (1990–2016 ) were among the most flood-rich periods in Europe during the past 500 years, and that this period differs from others in terms of its extent, air temperatures and flood seasonality.
- Regarding the temperature of the air, from 1500 to 1900, floods used to take place with higher frequency during cold climate phases, while after 1990, floods increased within the context of global warming.
 - The data analysis identified nine periods of floods that were more abundant and the associated regions. The most notable are 1560-1580 (western and central Europe), 1760-1800 (most part of Europe), 1840-1870 (western and southern Europe), and 1990-2016 (western and central Europe).
 - Current flood-rich phase is the third most severe regarding floods. However, this data is at the expense of the duration of the current phase of abundant floods, to be concluded.
- A present floods cause annual damages accounting for more than 100,000 million euros, and the general tendency of abundant floods is increasing.
- Due to the change in flood generating mechanisms, this study recommends the use of tools to assess the risk of floods that capture the physical processes involved, and management strategies that can incorporate recent changes in the risk analysis. 

Günter Blösch, Andrea Kiss, Alberto Viglione et Al. Current flood-rich period exceptional compared to past 500 years in Europe. Nature. DOI: 10.1038/s41586-020-2478-3.




Upper left: Flood-produced damages near Murcia after the 1879 Santa Teresa flood. American card.  Juan Almagro Roca, 1879 (Archivo General de la Región de Murcia).

Upper right: Detailed description of the damage caused by the Almanzora River in September 1580 in the town of Albox and the city Cuevas del Almanzora (Almería). Source: Historical files of Vera. Volume of the years 1550-1600. Photo: Carlos Sánchez-García, PaleoRisk Research Group, UB.

Bottom: Flood seasonality within and outside flood-rich periods. a, Time series of smoothed frequency of floods in four seasons (green line, spring; red, summer; brown, autumn; blue, winter) and flood-rich periods indicated by coloured bars. b, Frequency of floods in four seasons. Left bars, interflood periods; middle bars, flood-rich periods of the past; right bars, flood-rich period IX (1990–2016). Error bars show 90% confidence bounds (after Blösch et al., 2020).

Extreme Floods in Small Mediterranean Catchments: Long-Term Response to Climate Variability and Change

-The influence of climate variability on flooding was evaluated by an analysis of a 500-year palaeoflood and documentary records at Montlleó River, eastern Spain.

- Five paleofloods exceeded 740–950 m3 s−1; vs. 129 m3s-1highest gauged flood s.1971.

- Flood occurred in cluster episodes (30-year duration) either during cooler than usual climate (about 0.3 °C and 0.2 °C), or during high climate variability (floods and droughts).

- Flood quantiles from palaeoflood data showed 30%–40% higher peak discharges than those using only instrumental records.

- These extended flood records can assist on low-regret actions for flood-risk adaptation.

Large ice-age megafloods have significantly altered Patagonian landscapes, acting as triggers of climate change.

We provide the first detailed reconstruction of catastrophic glacial lake outburst flooding (>110,000 m3s-1) from the Southern Hemisphere, focusing on the Río Baker catchment in central Patagonia.

Morphological changes and sediment connectivity evaluation during flooding using high resolution photogrametry

- We evaluate morphological changes, sediment tranfers and functional sediment connectivity caused by flood events.

- Quantification of morphological change and sediment budgets was provided by Photogrammetric flights.

- A sediment connectivity index is proposed.

Frequency of boulders transport during large floods in hyperarid areas using paleoflood analysis – An example from the Negev Desert, Israel

- The 2004 flood (470 m3 s−1) in the hyperarid, ungauged Nahal Hatzera ephemeral stream (45 km2), transported and deposited 0.85–2.1 m concrete boulders.

- A 600 years paleoflood record of 23 floods with peak discharges of 200–760 m3 s−1, indicates an average return period of 120 years for this event. 

-The shear stress and stream power indicate that the moderate-large floods are the most geomorphically effective floods rather than the largest floods in Nahal Hatzera.

Flood hydro-geomorphology and vegetation dynamics along the hyperarid Kuiseb River, Namibia and detecting large floods in remote deserts

- The Kuiseb River flash floods  travel ~280 km downstream, before recharging the aquifers that sustain a 130-km long green belt across the hyperarid Namib desert.

-  This study reveals the importance of flood properties on the oasis life cycle and emphasizes the impact of drought and wet years.

- The downstream aquifers are fed only by the largest flood discharge that allows the infrequent germination of vegetation.

-Variations in NDVI index was revelead as an effective tool in determining occurrences of large floods in these headwater-fed hyperarid regions. 

Impacts of sediment connectivity on Holocene alluvial records across a Mediterranean basin (Guadalentín River, SE-Spain)

- Alluvial chronologies in two contiguous valleys show out-of-phase sedimentation periods under low connectivity conditions (9-3 ka), and in-phase cut-and-fill cycles after valley re-connection (post-3.0 ka).

- Vertically stacked alluvial sequences were dominant during periods of low connectivity.

whereas stair-case fill terraces due to cut-and-fill cycles occurred on connected reaches

- During the late Holocene alluvial activity periods coincide with morpho-stratigraphic data from the lower Guadalentín, indicating that fluvial connectivity throughout the catchment was only completed in the late Holocene.