CRHyME (Climatic Rainfall Hydrogeological Model Experiment): a versatile geo-hydrological model for climatic scenario and extreme event simulation at basin scale

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).