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GM10.2

EDI
From hydro-climatology to hydro-geomorphology under extreme climatic events

It becomes increasingly accepted that many regions all over the world are experiencing an increase in the frequency of extreme rainfall events and potentially in their properties. For predicting the impact of future climate change on the landscape, it is therefore vital to understand the dynamics of surface processes under extreme events. Furthermore, focusing on the conditions necessary for extreme events to occur can provide key insights into past changes in climate at different time scales. Extreme storms cause a multitude of hydrogeomorphic and natural hazards responses, including floods and respective fluvial responses, hillslope erosion and failures, and debris flows from slopes into fluvial systems. Measuring, evaluating, and predicting the impacts of extreme rainstorms, however, remains challenging due to the difficult-to-predict and complex nature of storms and rainfall-surface interactions.
This interdisciplinary session focuses on the causative chain which links the deterministic and mostly stochastic nature of the synoptic to meso/regional and watershed scales of extreme storms, to their respective transformation into watershed, slope, and stream hydrology, and to their geomorphic impact. We welcome studies from all the parts of this chain, from all climates, and at all temporal scales, that are focusing on the hydrological responses to extreme events and on their imprints on the landscape through erosion and sediment movement. We favor studies with emphasis on the final noticeable impact of extreme events on the landscape and/or on the integrated long-term consequences of extreme storm regime on landscape evolution. Especially, we encourage studies presenting new physical/stochastic modeling approaches that explicitly investigated the impact of extreme events on the landscape.

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Co-organized by CL3.1/HS13/NH1
Convener: Yuval Shmilovitz | Co-conveners: Francesco Marra, Efrat Morin, Yehouda Enzel, Roberta Paranunzio
Presentations
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Thu, 26 May, 11:05–11:40 (CEST)
 
Room G2

Thu, 26 May, 10:20–11:50

Chairpersons: Yuval Shmilovitz, Roberta Paranunzio

11:05–11:12
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EGU22-769
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ECS
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OSPP
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On-site presentation
Sediment supply affects uncertainties and memory in alpine geomorphic systems 
Jacob Hirschberg et al.

Geomorphic systems are affected by climate forcing and sediment supply. Due to non-linear relationships of forcings and sediment mobilization, it is debated whether environmental signals are preserved in such systems, or if they are rather dampened or shredded in the sediment output. Tracing the cause and effect in such systems is commonly impossible to do from observations alone. Therefore, numerical models are interesting to study geomorphic system behavior. We use a modeling chain consisting of the SedCas sediment cascade model (Bennett et al., 2014; Hirschberg et al., 2021) and the AWE-GEN stochastic weather generator (Fatichi et al., 2011), which has been calibrated for a debris-flow catchment in the Swiss Alps, the Illgraben, and used for climate change impact assessment (Hirschberg et al., 2021). Here we use this modeling setup to study the long-term behavior of such a system under consideration of different mean erosion rates and sediment production mechanisms. This numerical experiment is unique because we conducted simulations at high temporal resolution (hourly) while also spanning geological time scales (10k years).

We show that the analysis of short sediment records is characterized by high uncertainties and that especially supply-limited systems are at risk to have underestimated mean sediment. This is in concert with field observations on short- and long-term erosion rates from other basins, and can be attributed to transient hillslope sediment supply to the channel. Furthermore, we demonstrate how large hillslope landslides, or the absence of sediment supply, introduce long-term memory effects which can be quantified in the sediment yield. This long-term memory increases uncertainty and reduces interannual variability in annual sediment yields. Interestingly, details of the actual timing of sediment supply events are shredded and have no discernible impact on sediment yields at the outlet. The study highlights the need of characterizing variability in erosional events with regard to their stochastic nature. Furthermore, these results will corroborate the analysis of erosion rates, support decision making and decrease the risk of misinterpretation both in natural hazard and climate change impact assessment, especially if they are based on short records.

 

REFERENCES

Bennett, G. L., P. Molnar, B. W. McArdell, and P. Burlando (2014), A probabilistic sediment cascade model of sediment transfer in the Illgraben, Water Resour. Res., 50, 1225– 1244, doi:10.1002/2013WR013806.

Fatichi, S., Ivanov, V. Y., & Caporali, E. (2011). Simulation of future climate scenarios with a weather generator. Advances in Water Resources, 34(4), 448-467.

Hirschberg, J., Fatichi, S., Bennett, G. L., McArdell, B. W., Peleg, N., Lane, S. N., et al. (2021). Climate change impacts on sediment yield and debris- flow activity in an Alpine catchment. Journal of Geophysical Research: Earth Surface, 126, e2020JF005739. https:// doi.org/10.1029/2020JF005739

How to cite: Hirschberg, J., McArdell, B. W., Bennett, G. L., and Molnar, P.: Sediment supply affects uncertainties and memory in alpine geomorphic systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-769, https://doi.org/10.5194/egusphere-egu22-769, 2022.

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11:12–11:19
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EGU22-1717
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ECS
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Virtual presentation
Climate anomalies and geomorphic hazards in high-mountain regions in the Alps: new perspectives from the integrated use of observations and satellite-based products 
Roberta Paranunzio and Francesco Marra

High-elevation mountainous regions are experiencing an increase in the frequency of mass-wasting processes related to climate-change. Understanding the interplay between the climatic triggers (temperature and precipitation, in particular) and their effects on the dynamics of surface processes is crucial for developing reliable predictive models and for quantifying vulnerability and risk associated with these hazards.

In this work, we exploit a consolidated statistical-based approach in which triggering conditions are identified as climatic anomalies (i.e., non-exceedance probability below/above the 10th/90th percentile) in temperature and precipitation values at multiple temporal scales occurred in the lead-up of the events triggering. Specifically, we integrate the traditionally used in-situ information from daily weather stations with: (a) high-resolution (0.1°, 30-min) precipitation estimates from the Integrated Multi-Satellite Retrievals from GPM (IMERG) and (b) daily gridded temperature observations from ENSEMBLES OBServation (E-OBS). We investigate the use of these freely available gridded climatological datasets as an integration/surrogate for in-situ measurements.

Our analysis is based on a database of 358 geomorphic hazards occurred across the Italian Alps in the period 2000-2015, including landslides, rockfalls and debris flows. Preliminary results indicate that IMERG could significantly improve precipitation information by providing estimates directly on the initiation zones, which is particularly relevant in case of hazards triggered by small-scale convective storms. This advantage is evident and in particular for the case of debris flows: IMERG allows to detect precipitation in numerous cases (~60%) for which in-situ data showed no precipitation; in ~19% of these, climatic anomalies (exceedance of the 90th percentile) are detected.

Further results on the role of sub-daily precipitation processes, particularly relevant for hazards triggered by convective rainfall, such as debris and mud flows, and on the use of temperature data from E-OBS, as being evaluated and will be presented.

How to cite: Paranunzio, R. and Marra, F.: Climate anomalies and geomorphic hazards in high-mountain regions in the Alps: new perspectives from the integrated use of observations and satellite-based products, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1717, https://doi.org/10.5194/egusphere-egu22-1717, 2022.

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11:19–11:26
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EGU22-1854
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On-site presentation
A warming-induced rainfall heterogeneity accelerates landscape evolution 
Nadav Peleg et al.

The hydro-morphological response of a catchment is highly dependent on rainfall properties, including rainfall intensity, storm duration and frequency, and the timing of those events. Furthermore, rainfall spatial variability impacts streamflow, erosion, and sediment transport, and is explored primarily in the context of heavy rainfall triggering floods and rapid morphological changes on hillslopes and in channels. In order to examine the potential effects of warming on hydro-morphological responses, we first examined how changes in air temperature are affecting the spatial structure of rainfall. We observed that heterogeneity increases as temperatures rise. Then, we investigated the sensitivity of fast hydro-morphological responses to increasing temperatures and rainfall heterogeneity scenarios by simulating an extreme rainfall event that occurred in August 2005 in the Kleine Emme stream in Switzerland. The results show that rainfall heterogeneity has a greater impact on erosion processes than simply intensifying high rainfall intensities. We also looked at how changes in rainfall patterns affect landscape evolution over hundreds of years at the catchment scale. Multiple realizations of hourly rainfall fields, each with a different spatial distribution but identical in all other respects, were simulated using a stochastic weather generator, and the impact of the storm heterogeneity on catchment morphology was assessed using a landscape evolution model (CAESAR-Lisflood). We found that erosion and deposition rates increased and net erosion and deposition areas changed (increased and decreased, respectively) when the rain became less uniform in space. Increasing temperatures and rainfall heterogeneity resulted in longer, deeper, and more branched gullies. The results of these studies indicate that heterogeneity in rainfall spatial patterns accelerates landscape development even when rainfall volumes and temporal structures are identical.

How to cite: Peleg, N., Ramirez, J. A., Marra, F., Skinner, C., Fatichi, S., and Molnar, P.: A warming-induced rainfall heterogeneity accelerates landscape evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1854, https://doi.org/10.5194/egusphere-egu22-1854, 2022.

11:26–11:33
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EGU22-4061
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On-site presentation
The signature of extreme rainstorms properties on cliff morphology in arid areas  
Yuval Shmilovitz et al.

Climatic impact on landscape morphology was previously demonstrated under pronounced gradients in average climatic properties such as mean annual precipitation or temperature. However, in arid areas, where both meteorological observations and rainfall measurements are scarce and the latter is meager, short-term and highly variable in space and time, the determination of meaningful “average climatic” conditions and their variability is challenging. Although it is generally acknowledged that surface processes in arid landscapes should be effected by short-duration rainfall intensities and their extremes, the topographic sensitivity to storm-scale properties were rarely quantified. Here, we attempted to bridge this gap by documenting systematic precipitation variations along a 40 km arid escarpment (Ramon crater) in the central Negev desert (Israel) and their associated topographic signature.

We used 0.5 m pixel-1 LiDAR-derived topographic data coupled with field measurements to characterize the morphology of cliffs and slopes along the entire Ramon crater. Sub-hourly rainfall intensities were characterized using an 8-year record of high-resolution, convection-permitting, numerical weather model prediction (NWP). Frequency analyses of rainfall intensity and its spatial variation were conducted using a novel statistical method and used to determine runoff and sediment transport along sub-cliff slopes, through grid-based hydrological simulations of synthetic rainstorms with different frequencies.

Our results indicate that due to a pronounced decreasing gradient in the number of rain storms per year, the mean annual rainfall decreases from ~100 mm in the southwest (SW) cliff segment to ~40 mm in the northeast (NE) segment. However, in the drier NE cliff segment, extreme rainfall intensities such as the ones occurring during a storm with a 100-year return period are higher. Topographic cliff gradients and the percentage of exposed bedrock over the cliffs increase toward the drier NE cliff section. Sub-cliff slopes in the NE are systematically straighter, shorter, and associated with a smaller clast sizes relative to the wetter (SW) part of the escarpment. Hydrological simulations reveal that under extreme storms, sediment is mobilized by sheetwash on the NE slopes but is less mobile on the wetter SW slopes. In addition, incised gullies and disconnected talus-flatirons are more frequent in the NE and correlate with the higher erosion efficiency of extreme rainstorms in this zone. Our results indicate that significant morphologic differences can be imprinted in arid landforms due to spatial gradients in the properties of extreme rainstorms.  

How to cite: Shmilovitz, Y., Marra, F., Enzel, Y., Morin, E., Armon, M., Matmon, A., Mushkin, A., Levi, Y., Khain, P., and Haviv, I.: The signature of extreme rainstorms properties on cliff morphology in arid areas , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4061, https://doi.org/10.5194/egusphere-egu22-4061, 2022.

11:33–11:40
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EGU22-5929
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ECS
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OSPP
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Virtual presentation
CRHyME (Climatic Rainfall Hydrogeological Model Experiment): a versatile geo-hydrological model for climatic scenario and extreme event simulation at basin scale 
Andrea Abbate et al.

In this abstract is described the new model concept called CRHyME (Climatic Rainfall Hydrogeological Model Experiment). This model represents an extended version of the classical spatially distributed rainfall-runoff models. The main novelties are related to:

  • the possibility to have a direct integration with climatic scenario outputs, such as rainfall and temperature field data from NETCDF file format,
  • the physical description of some geo-hydrological hazards strongly related to rainfalls such as shallow landslide, debris flow, watershed erosion and solid transport,
  • the possibility to interact with other hydraulic/landslide models applied through the BMI (Basic Model Interface) approach at finer scale.

The CRHyME model is intended as a part of a hydrological modelling chain. The aim is to try to interpret the effect of future climate evolution on the local territory, giving a physical-based instrument to fill the gap between broader climatic scale and watershed scale. CRHyME model has been written in PYTHON language, using the PCRaster libraries. It has been inspired by the PCR-GLOWB2 model that was implemented at a global scale to study climate change effects on water resource availability. In this sense, the CRHyME model has been completely rewritten to work at a higher spatial resolution to let the assessment of geo-hydrological hazards using the available worldwide databases about morphology, land coverage, soil composition and hydrogeological properties.

The versatility of the CRHyME model permits to set also different timesteps of simulations, reproducing for example extreme rainfall events described with sub-hourly data. It is possible to set the model to reproduce watershed behaviour under critical rainfall using the information stored in local IDF (Intensity-Duration-Frequency) curves making CRHyME also suitable for the risks now-casting at the Civil Protection level.

CRHyME model is currently under development. Remarkable results have been obtained for the study case of the Valtellina catchment in the Alpine region (northern Lombardy, Italy) and three Apennine’s catchments (Emilia region, Italy). After calibration and validation for past occurred events, CRHyME was applied considering three different climatic models from the EUROCORDEX program. According to IPCC Fifth Assessment Report (AR5) indications, the reference period 1986-2005 and the future scenario 2006-2075 under RCP 8.5 were simulated. Several variables were investigated such as maximum daily precipitation, the mean temperature, the maximum daily water discharges, the annual sediment yield, the maximum daily number of triggered shallow landslide and debris flow movements. Statistical test on mean and variance was applied to data series to highlight possible future tendencies in comparison to the reference period. The results have shown a general intensity increase of the geo-hydrological cycle, especially across the Alpine region. Similar results were also assessed from the analysis of the outliers of the sample distributions. This evidence represents a confirmation of the studies carried out by IPCC scientists in respect to the latest updated report in the IPCC Sixth Assessment Report (AR6).

How to cite: Abbate, A., Longoni, L., Papini, M., Mancusi, L., and Frigerio, A.: CRHyME (Climatic Rainfall Hydrogeological Model Experiment): a versatile geo-hydrological model for climatic scenario and extreme event simulation at basin scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5929, https://doi.org/10.5194/egusphere-egu22-5929, 2022.

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