Assessment of flash floods taking into account climate change scenarios in the Llobregat River basin

Global change may imply important changes in the future occurrence and intensity of extreme events. Climate scenarios characterizing these plausible changes were previously obtained for the Llobregat River basin (NE Spain). This paper presents the implementation of these scenarios in the HBV (Hydrologiska Byråns Vattenbalansavdelning) hydrological model. Then, the expected changes in terms of flash flood occurrence and intensity are assessed for two different sub-basins: the Alt Llobregat and the Anoia (Llobregat River basin). The assessment of future flash floods has been done in terms of the intensity and occurrence of extreme events, using a peak over threshold (POT) analysis. For these two subbasins, most of the simulated scenarios present an increase of the intensity of the peak discharge values. On the other hand, the future occurrence follows different trends in the two sub-basins: an increase is observed in Alt Llobregat but a decrease occurs in Anoia. Despite the uncertainties that appear in the whole process, the results obtained can shed some light on how future flash floods events may occur.Postprint (publisher's version

Seasonal to yearly assessment of temperature and precipitation trends in the North Western Mediterranean Basin by dynamical downscaling of climate scenarios at high resolution (1971-2050)

The complex topography and high climatic variability of the North Western Mediterranean Basin (NWMB) require a detailed assessment of climate change projections at high resolution. ECHAM5/MPIOM global climate projections for mid-21st century and three different emission scenarios are downscaled at 10 km resolution over the NWMB, using the WRF-ARW regional model. High resolution improves the spatial distribution of temperature and precipitation climatologies, with Pearson's correlation against observation being higher for WRF-ARW (0.98 for temperature and 0.81 for precipitation) when compared to the ERA40 reanalysis (0.69 and 0.53, respectively). However, downscaled results slightly underestimate mean temperature (≈1.3 K) and overestimate the precipitation field (≈400 mm/year). Temperature is expected to raise in the NWMB in all considered scenarios (up to 1.4 K for the annualmean), and particularly during summertime and at high altitude areas. Annual mean precipitation is likely to decrease (around −5 % to −13 % for the most extreme scenarios). The climate signal for seasonal precipitation is not so clear, as it is highly influenced by the driving GCM simulation. All scenarios suggest statistically significant decreases of precipitation for mountain ranges in winter and autumn. High resolution simulations of regional climate are potentially useful to decision makers. Nevertheless, uncertainties related to seasonal precipitation projections still persist and have to be addressed.Peer ReviewedPostprint (published version

Projeccions climàtiques futures regionalitzades a Catalunya a alta resolució

Es presenten els principals resultats del projecte ESCAT desenvolupat entre el BSC-CNS i l’SMC sobre projeccions climàtiques al Mediterrani nord-occidental a 10 km de resolució (1971-2050) mitjançant el model mesoescalar WRF-ARW. Les simulacions desenvolupades reprodueixen els patrons generals espai-temporals de les observacions (1971-2000: temperatura i precipitació), però subestimant la temperatura i sobreestimant la precipitació. La temperatura s’espera que augmenti fins al 2050 independentment de l’escenari considerat (0,9-1,4ºC respecte 1971-2000), especialment a l’alta muntanya. En canvi, la precipitació disminuiria molt probablement (5-13% total anual respecte 1971-2000), però particularment a l’alta muntanya. També es projecten valors extrems més secs i càlids que els actuals, amb un augment significatiu en la durada de les sequeres i l’ocurrència de precipitacions extremes. Aquestes projeccions permeten definir les àrees més vulnerables (Pirineus i Vall de l’Ebre) i millorar l’avaluació dels futurs impactes en les activitats socioeconòmiques del territori.Postprint (author’s final draft

Intra-annual variability of the Western Mediterranean Oscillation (WeMO) and occurrence of extreme torrential precipitation in Catalonia (NE Iberia)

In previous studies the Western Mediterranean Oscillation index (WeMOi) at daily resolution has proven to constitute an effective tool for analysing the occurrence of episodes of torrential precipitation over eastern Spain. The western Mediterranean region is a very sensitive area, since climate change can enhance these weather extremes. In the present study we created a catalogue of the extreme torrential episodes (≥200 mm in 24 h) that took place in Catalonia (NE Iberia) during the 1951-2016 study period (66 years). We computed daily WeMOi values and constructed WeMOi calendars. Our principal result reveals the occurrence of 50 episodes (0.8 cases per year), mainly concentrated in the autumn. We confirmed a threshold of WeMOi ≤ −2 to define an extreme negative WeMO phase at daily resolution. Most of the 50 episodes (60 %) in the study area occurred on days presenting an extreme negative WeMOi value. Specifically, the most negative WeMOi values are detected in autumn, from 11 to 20 October, coinciding with the highest frequency of extreme torrential events. On comparing the subperiods, we observed a statistically significant decrease in WeMOi values in all months, particularly in late October and in November and December. No changes in the frequency of these extreme torrential episodes were observed between both subperiods. In contrast, a displacement of the extreme torrential episodes is detected from early to late autumn; this can be related to a statistically significant warming of sea temperature

Projeccions climàtiques i escenaris de futur

Aquest capítol tracta de la projecció dels impactes de climes futurs per a trams vulnerables de la costa catalana. Al començament, s’hi revisa la geodiversitat de la costa en termes meteorològics i geològics. El ventall d’impactes que en resulta (sota climes presents i futurs) presenta uns nivells d’incertesa que s’han de considerar per a poder prendre decisions. L’anàlisi es basa en les projeccions del nivell mitjà del mar i en les característiques de l’onatge per a les famílies d’escenaris RCP (trajectòries de concentracions representatives). La projecció dels impactes d’erosió i inundació per a platges i d’agitació i ultrapassament per a ports permet determinar quin és el domini costaner sotmès a aquests impactes, i també quins seran els nivells de risc que es poden esperar en platges i ports. Les conclusions del capítol s’estructuren com un seguit d’actuacions seqüencials per a afavorir la sostenibilitat de la costa. Aquest «camí d’adaptació» permetrà d’assolir uns nivells de riscs presents i futurs explícits, que han de ser considerats per a les activitats socioeconòmiques de la zona litoral.Peer ReviewedPostprint (published version

Assessment of flash floods taking into account climate change scenarios in the Llobregat River basin

Global change may imply important changes in the future occurrence and intensity of extreme events. Climate scenarios characterizing these plausible changes were previously obtained for the Llobregat River basin (NE Spain). This paper presents the implementation of these scenarios in the HBV (Hydrologiska Byråns Vattenbalansavdelning) hydrological model. Then, the expected changes in terms of flash flood occurrence and intensity are assessed for two different sub-basins: the Alt Llobregat and the Anoia (Llobregat River basin). The assessment of future flash floods has been done in terms of the intensity and occurrence of extreme events, using a peak over threshold (POT) analysis. For these two subbasins, most of the simulated scenarios present an increase of the intensity of the peak discharge values. On the other hand, the future occurrence follows different trends in the two sub-basins: an increase is observed in Alt Llobregat but a decrease occurs in Anoia. Despite the uncertainties that appear in the whole process, the results obtained can shed some light on how future flash floods events may occur.

Projeccions climàtiques futures regionalitzades a Catalunya a alta resolució

Es presenten els principals resultats del projecte ESCAT desenvolupat entre el BSC-CNS i l’SMC sobre projeccions climàtiques al Mediterrani nord-occidental a 10 km de resolució (1971-2050) mitjançant el model mesoescalar WRF-ARW. Les simulacions desenvolupades reprodueixen els patrons generals espai-temporals de les observacions (1971-2000: temperatura i precipitació), però subestimant la temperatura i sobreestimant la precipitació. La temperatura s’espera que augmenti fins al 2050 independentment de l’escenari considerat (0,9-1,4ºC respecte 1971-2000), especialment a l’alta muntanya. En canvi, la precipitació disminuiria molt probablement (5-13% total anual respecte 1971-2000), però particularment a l’alta muntanya. També es projecten valors extrems més secs i càlids que els actuals, amb un augment significatiu en la durada de les sequeres i l’ocurrència de precipitacions extremes. Aquestes projeccions permeten definir les àrees més vulnerables (Pirineus i Vall de l’Ebre) i millorar l’avaluació dels futurs impactes en les activitats socioeconòmiques del territori

Modelling wind resources in climate change scenarios in complex terrains

Wind farms have suffered a spectacular growth in Europe in the last few decades. However, future changes in climate could affect the availability of the wind resource in certain regions. This work assesses the capabilities of a Regional Climate Model (WRF) applied at medium-to-high resolution (10 km, 33 vertical layers) over a particularly complex and vulnerable terrain (North Eastern Iberian Peninsula) to derive mean wind speed and direction for 1981e2000. The model is able to reproduce geographical wind patterns, although it generally overemphasises surface wind intensity when compared to individual observations. Projections of mean wind speed changes for 2031e2050 suggest a decrease in surface wind intensity. Energy density estimations at 60 m agl (typical hub-height) show that the implications of the wind speed weakening could affect the preferential areas for the wind farm locations defined at present. Reductions up to 20% of wind energy density are found already in mid-21st century. Therefore, it is advisable to derive dynamic methodologies to assess the preferential areas for wind farm locations, not only considering past-time wind climatologies, but also considering future climate changes in geographical patterns. Regional Climate Models applied at medium-to-high resolution can be useful for this purpose.Peer Reviewe

Modelling wind resources in climate change scenarios in complex terrains

Wind farms have suffered a spectacular growth in Europe in the last few decades. However, future changes in climate could affect the availability of the wind resource in certain regions. This work assesses the capabilities of a Regional Climate Model (WRF) applied at medium-to-high resolution (10 km, 33 vertical layers) over a particularly complex and vulnerable terrain (North Eastern Iberian Peninsula) to derive mean wind speed and direction for 1981e2000. The model is able to reproduce geographical wind patterns, although it generally overemphasises surface wind intensity when compared to individual observations. Projections of mean wind speed changes for 2031e2050 suggest a decrease in surface wind intensity. Energy density estimations at 60 m agl (typical hub-height) show that the implications of the wind speed weakening could affect the preferential areas for the wind farm locations defined at present. Reductions up to 20% of wind energy density are found already in mid-21st century. Therefore, it is advisable to derive dynamic methodologies to assess the preferential areas for wind farm locations, not only considering past-time wind climatologies, but also considering future climate changes in geographical patterns. Regional Climate Models applied at medium-to-high resolution can be useful for this purpose.Peer Reviewe

Seasonal to yearly assessment of temperature and precipitation trends in the North Western Mediterranean Basin by dynamical downscaling of climate scenarios at high resolution (1971-2050)

The complex topography and high climatic variability of the North Western Mediterranean Basin (NWMB) require a detailed assessment of climate change projections at high resolution. ECHAM5/MPIOM global climate projections for mid-21st century and three different emission scenarios are downscaled at 10 km resolution over the NWMB, using the WRF-ARW regional model. High resolution improves the spatial distribution of temperature and precipitation climatologies, with Pearson's correlation against observation being higher for WRF-ARW (0.98 for temperature and 0.81 for precipitation) when compared to the ERA40 reanalysis (0.69 and 0.53, respectively). However, downscaled results slightly underestimate mean temperature (≈1.3 K) and overestimate the precipitation field (≈400 mm/year). Temperature is expected to raise in the NWMB in all considered scenarios (up to 1.4 K for the annualmean), and particularly during summertime and at high altitude areas. Annual mean precipitation is likely to decrease (around −5 % to −13 % for the most extreme scenarios). The climate signal for seasonal precipitation is not so clear, as it is highly influenced by the driving GCM simulation. All scenarios suggest statistically significant decreases of precipitation for mountain ranges in winter and autumn. High resolution simulations of regional climate are potentially useful to decision makers. Nevertheless, uncertainties related to seasonal precipitation projections still persist and have to be addressed.Peer Reviewe