CLIMATE CHANGE MONITORING SOUTH TYROL
+ 90 mm
more heavy precipitation per year since 1980
Heavy precipitation
ClimateThe indicator shows the annual sum of heavy precipitation, i.e. the annual sum of daily precipitation above a certain threshold in South Tyrol (spatial average). The knowledge of the temporal development of these phenomena is crucial for the assessment of possible impacts on different sectors; in particular, heavy precipitation can cause floods and landslides with consequent damage to transport and infrastructure.
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Spatial distribution of the annual trend in heavy precipitation in the period 1981 to 2002 The trend shows how heavy precipitation has changed in each decade compared to the 1981 to 2010 mean (in %). The only parts of the country shown are where the trend is statistically significant (p-value < 0.05). Source: Weather and avalanche service of the Autonomous Province of Bolzano; Processing and illustration: Eurac Research
Description of the results
Annual heavy precipitation has increased over the last 43 years (+90 mm per year since 1980). The increase in annual heavy precipitation is statistically significant. The total annual amount of intense precipitation has increased by about +21 mm per year, which corresponds to an increase of about +10% of the average over the 30-year period between 1981 to 2010.
With a value of 1.3, the year 2020 set a new record for heavy precipitation since 1980: three times higher than the average for the 30-year period between 1981 to 2010, followed by the year 2000. In contrast, the period between 2003 to 2006 was the least affected by intense precipitation events.
The trends calculated at the individual grid points are increasing throughout most of South Tyrol, although the increase in intense events is more pronounced in the southern and eastern parts of the province, where the trends are statistically significant and include increases of up to +25% per decade compared to the 30-year average 1981 to 2010.
Method
The graph is based on the daily meteorological observations of more than 80 of the Office for Meteorology and Avalanche Warning of the Autonomous Province of Bolzano‘s measuring points, supplemented by the observation data of some sites in Switzerland and Austria close to the national border. The collected series were interpolated to a regular grid with a resolution of 1 km for the whole national territory using a geostatistical method.
Before interpolation, all observation series were checked for measurement errors and temporal homogeneity. In addition, missing daily values were reconstructed using a statistical procedure to maximize the temporal continuity of the series.
Interpolation allows the determination of a regional mean that is more representative and stable than one based on individual stations.
The threshold for identifying heavy daily precipitation was calculated for each point at a resolution of 1 km as the 95th percentile of the distribution of rainy days (daily precipitation > 1 mm) over the 30-year reference period between 1981 to 2010. The threshold based on the percentile thus varies from area to area to take into account the different local climatic conditions: what is considered as particularly heavy rainfall in one area may not be the case in another location which is characterized by a different climatic regime. Trends are calculated using the Theil-Sen method and significance is determined using the Mann-Kendall test. The trend is considered significant if the resulting p-value is less than 0.05.
Sectors affected
Water management
Soil
Natural hazard
Infrastructure
Related indicators
Further research at Eurac Research
The climate projections considered predict an increase in annual precipitation due to intense precipitation in both the RCP 4.5 and RCP 8.5 emission scenarios, although the time series show considerable variability. Considering the median of the different available model simulations, the most pessimistic scenario predicts an average increase in intense precipitation of about 29% for the period between 2071 to 2100 compared to that of 1981 to 2010, while the intermediate scenario predicts an average increase of about 22%.
The spatial distribution of annual heavy precipitation in South Tyrol as a 30-year mean for the period 2041 to 2070 and for the period 2071 to 2100 shows an increase in annual values compared to the 30-year reference period 1981 to 2010 over the whole area and for both emission scenarios. In absolute terms, the RCP 8.5 scenario predicts the strongest increase in annual heavy precipitation in the northernmost areas of the province, in the upper Eisack/Isarco valley, with an average increase of almost 100 mm at the end of the century compared to 1981 to 2010, i.e. the percentage increases compared to the average values of the reference period are evenly distributed over the area, with slightly higher values in Pustertal/Val Pusteria, where the RCP 8.5 scenario predicts medium-term (2041 to 2070) and long-term (2071 to 2100) increases of about 40-50%.
Maps of the annual heavy precipitation values for South Tyrol, shown as 30-year averages for the historical period 1981 to 2010, 2041 to 2070 and 2071 to 2100 according to the emission scenarios RCP 4.5 and RCP 8.5 emission scenarios. In all cases, the maps show the median of the model simulations. Source: EURO-CORDEX; Processing and illustration: Eurac Research
Method
The climate scenarios for annual and seasonal precipitation for South Tyrol were derived from EURO-CORDEX climate simulations over Europe for the two emission scenarios RCP 4.5 and RCP 8.5. RCP stands for “Representative Concentration Pathways“, i.e. projections of how greenhouse gas emissions in the atmosphere will develop in the future.
RCP 4.5 represents an intermediate scenario in which greenhouse gas emissions are curbed, but atmospheric concentrations continue to rise over the next 50 years and the +2°C target is not met. RCP 8.5 is the most pessimistic scenario, in which greenhouse gas emissions continue to increase and no action is taken to combat climate change.
The daily precipitation projections from 1971 to 2100 provided by different climate models (ensembles) for the two scenarios (11 for RCP 4.5 and 17 for RCP 8.5) have been processed using a downscaling process that allows the simulated values to be transferred from the original spatial resolution (in this case about 12 km) to a finer resolution (in this case 1 km). This step makes it possible to reduce systematic errors that occur in the model simulations due to the limited spatial resolution of the available models, which do not provide an adequate representation of local features, especially in mountainous regions with complex orography.
The downscaling method used is based on the delta-quantile mapping method (QDM, Cannon et al., 2015), in which simulated values are compared with observations over a common reference period and corrected so that the probability distributions match. Furthermore, in the QDM method, the corrections are made in such a way that the long-term climate signal originally present in the simulations is not altered. In this case, the reference period is 1981 to 2010 and the correction was made on the basis of the 1 km gridded data set.
From the corrected simulations, the annual winter (December to February) and summer (June to August) totals from 1971 to 2100 were calculated for each ensemble model, for each year and for both scenarios. The ensemble indicator values were then aggregated by calculating the median of the 11 (RCP 4.5) and 17 (RCP 8.5) model simulations for each year and using the interquartile range, i.e. the range of values between the 25th and 75th percentiles, to provide an estimate of the variability of the model simulations.
Contact
Eurac Research: Alice Crespi, Center for Climate Change and Transformation
Data provided by: Weather and avalance service of the Autonomous Province of Bolzano