Editing IPCC:AR6/WGI/Chapter-12 (section)

==== 12.4.5.2 Wet and Dry ====

<div id="h3-56-siblings" class="h3-siblings"></div>

'''Mean precipitation:''' Precipitation has generally increased in northern Europe and decreased in southern Europe, especially in winter ( [[#Fischer--2016|Fischer and Knutti, 2016]] ; [[#Knutson--2018|Knutson and Zeng, 2018]] ) but in the latter, precipitation trends are strongly dependent on the examined period (Atlas.8). These trends in precipitation increases in the north and decreases in the south are also represented by global and regional climate simulations ( [[#Jacob--2014|Jacob et al., 2014]] ; [[#Rajczak--2017|Rajczak and Schär, 2017]] ; [[#Lionello--2018|Lionello and Scarascia, 2018]] ; [[#Coppola--2021a|Coppola et al., 2021a]] ; Atlas.8.2) and have been attributed to climate change (Sections 3.3.2, 8.3.1).

Studies since AR5, together with EURO-CORDEX and MED-CORDEX experiments and the latest CMIP6 ensemble, have increased confidence in regional projections of mean and extreme precipitation ( [[#Prein--2016|Prein et al., 2016]] ) despite their wet bias, and show that it is ''very likely'' that precipitation will increase in Northern Europe in DJF and decrease in the Mediterranean in JJA under all climate scenarios except RCP2.6/SSP1-2.6 and for both mid- and end-century periods ( [[#Coppola--2021a|Coppola et al., 2021a]] ; Atlas.8.5).

'''River flood:''' There is ''high confidence'' of an observed increasing trend of river floods in Western and Central Europe (WCE) and ''medium confidence'' of a decrease in Northern (NEU) and southern Europe (MED).

The SR1.5 shows evidence of an increase in reported floods in the UK over the period 1884–2013, and increasing trends in annual maximum daily streamflow data over 1966–2005 in parts of Europe. Although high flow does not show uniform trends for the entire region ( [[#Hall--2014|Hall et al., 2014]] ; [[#Mediero--2015|Mediero et al., 2015]] ) or specific regions ( [[#Mudersbach--2017|Mudersbach et al., 2017]] ; [[#Vicente-Serrano--2017|Vicente-Serrano et al., 2017]] ; [[#Tramblay--2019|Tramblay et al., 2019]] ), regional patterns of significant flood trends do exist. Based on the most extended river flow database spanning the period 1960–2010, an increase in floods frequency in north-western Europe, decreasing in medium and large catchments in southern Europe and decreasing floods in Eastern Europe has been detected ( [[#Blöschl--2019|Blöschl et al., 2019]] ) in line with [[#Mediero--2014|Mediero et al. (2014)]] , [[#Arheimer--2015|Arheimer and Lindström (2015)]] , [[#Gudmundsson--2017|Gudmundsson et al. (2017)]] , [[#Krysanova--2017|Krysanova et al. (2017)]] , [[#Kundzewicz--2018|Kundzewicz et al. (2018)]] and [[#Mangini--2018|Mangini et al. (2018)]] .

There is ''high confidence'' of river floods increasing in Western and Central Europe (WCE) and ''medium confidence'' of a decrease in Northern (NEU), Eastern (EEU) and southern Europe (MED) for mid- and end-century under RCP8.5 and ''low confidence'' under RCP2.6. The projected increase in WCE is roughly 10% (18% by end of century) and the projected decrease in NEU is 5% (11% by end of century) for the peak flow with a return period of 100 years for mid-century, under RCP8.5 ( [[#Di%20Sante--2021|Di Sante et al., 2021]] ; Figure 12.9a for mid-century (Q100) projections of flood discharges per unit catchment area ( [[#Blöschl--2019|Blöschl et al., 2019]] ) based on EURO-CORDEX models).

<div id="_idContainer077" class="Basic-Text-Frame"></div>

[[File:86f12b8af8261abcbf2a23eda4f3289c IPCC_AR6_WGI_Figure_12_9.png]]

'''Figure 12.9''' '''|''' '''Projected changes in selected climatic impact-driver indices for Europe. (a)''' Mean change in 1-in-100-year river discharge per unit catchment area (Q100, m <sup>3</sup> s <sup>–1</sup> km <sup>–2</sup> ), and '''(b)''' median change in the number of days with snow water equivalent (SWE) over 100 mm (from November to March), from EURO-CORDEX models for 2041–2060 relative to 1995–2014 and RCP8.5. Diagonal lines indicate where less than 80% of models agree on the sign (direction) of change. '''(c)''' Bar plots for Q100 (m <sup>3</sup> s <sup>–1</sup> km <sup>–2</sup> ) averaged over land areas for the AR6 WGI Reference Regions (defined in Chapter 1). The left-hand column within each panel (associated with the left-hand y-axis) shows the ‘recent past’ (1995–2014) Q100 absolute values in grey shades. The other columns (associated with the right-hand y-axis) show the Q100 changes relative to the recent past values for two time periods (‘mid’ 2041–2060 and ‘long’ 2081–2100) and for three global warming levels (defined relative to the pre-industrial period 1850–1900): 1.5°C (purple), 2°C (yellow) and 4°C (brown). The bars show the median (dots) and the 10–90th percentile range of model ensemble values across each model ensemble. CMIP6 is shown by the darkest colours, CMIP5 by medium, and CORDEX by light. SSP5-8.5/RCP8.5 is shown in red and SSP1-2.6/RCP2.6 in blue. '''(d)''' As for (c) but showing absolute values for number of days with SWE &gt; 100mm, masked to grid cells with at least 14 such days in the recent past. See Technical ( [[IPCC:Wg1:Chapter:Annex-vi|Annex VI]] for details of indices. Further details on data sources and processing are available in the chapter data table (Table 12.SM.1).

Using frequency analysis of extreme peak flow events above a 100-year return period as a threshold, which is the average protection level of the European river network ( [[#Rojas--2013|Rojas et al., 2013]] ), [[#Alfieri--2017|Alfieri et al. (2017)]] and [[#Alfieri--2015|Alfieri et al. (2015)]] show that Europe is one of the regions where the largest increases in flood risk may occur, with only few countries in Eastern Europe showing a decrease (Poland, Lithuania, Belarus) ( [[#Osuch--2017|Osuch et al., 2017]] ). They find a significant increase of events with peak discharge above 100-year return period (Q100) in most of Europe in line with [[#Rojas--2012|Rojas et al. (2012)]] , [[#Hirabayashi--2013|Hirabayashi et al. (2013)]] , [[#Dankers--2014|Dankers et al. (2014)]] , [[#Forzieri--2016|Forzieri et al. (2016)]] , [[#Roudier--2016|Roudier et al. (2016)]] , [[#Thober--2018|Thober et al. (2018)]] , and an increase in the magnitude of floods in southern Europe, although [[#Giuntoli--2015|Giuntoli et al. (2015)]] projects no change. A modest but significant decrease in the 100-year return period river flood is projected for southern (due to reduction of precipitation) and north-eastern European regions, the latter because of the strong reduction in snowmelt induced river floods ( [[#Thober--2018|Thober et al., 2018]] ; [[#Di%20Sante--2021|Di Sante et al., 2021]] ).

'''Heavy precipitation and pluvial flood:''' Heavy precipitation frequency trends have been detected in Europe with ''high confidence'' for the NEU and Alpine regions and with ''medium confidence'' in WCE, and also attributed to climate change with ''high'' ''confidence'' in NEU ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] ). [[#Guerreiro--2017|Guerreiro et al. (2017)]] , based on observations, showed that 20% of city areas in WCE and MED regions are affected by pluvial flooding and less than 10% of city areas in the northern and western coastal cities.

Projections based on multiple lines of evidence from global to convective permitting model scales show ''high confidence'' in extreme precipitation increase in the northern, central and eastern European regions (NEU, WCE, EEU) and in the Alpine area. Increases with ''medium confidence'' are projected for the Mediterranean basin (with a negative gradient towards the south) for mid- and end-century under RCP4.5, RCP8.5 and SSP5-8.5 and for 2°C GWL and higher ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] ; [[#MedECC--2020|MedECC, 2020]] ).

'''Landslide:''' Rainfall periods connected to landslides are projected to increase in central Europe by up to one more period per year in flat areas in low altitudes and by up to 14 more periods per year at higher altitudes by mid-century, becoming even more evident by the end of the century ( [[#Schlögl--2018|Schlögl and Matulla, 2018]] ). An increase of landslides by up to 45.7% and 21.2% is projected for southern Italy (Calabria region) by mid-century under both RCP4.5 and RCP8.5 ( [[#Gariano--2016|Gariano and Guzzetti, 2016]] ) and by up to 40% in central Italy (Umbria) during the winter season ( [[#Ciabatta--2016|Ciabatta et al., 2016]] ). A decrease of landslides is projected in the Peloritani mountains in southern Italy (RCP4.5 and 8.5) by mid-century ( [[#Peres--2018|Peres and Cancelliere, 2018]] ). A slight increase for a 10-year return period landslide is projected in the eastern Carpathians, the Moldavian Subcarpathians and the northern part of the Moldavian Tableland and a higher increase in the 100-year return period event is projected in the western hilly and plateau areas of Romania ( [[#Jurchescu--2017|Jurchescu et al., 2017]] ).

'''Aridity:''' The Mediterranean region shows evidence of large-scale decreasing precipitation trends over 1901–2010, which are at least partly attributable to anthropogenic forcing according to CMIP5 models ( [[#Knutson--2018|Knutson and Zeng, 2018]] ). Nevertheless, there is ''low agreement'' among studies on observed precipitation trend in the Mediterranean region ( [[IPCC:Wg1:Chapter:Chapter-11#11.9.4|Section 11.9.4]] and Atlas.8.2).

Precipitation is projected to decrease by mid- and end-century for the RCP8.5 and SSP5-8.5 with ''strong agreement'' among CMIP5, CMIP6 and CORDEX regional climate ensemble models on the direction of change. With both temperature increase and precipitation decrease there is ''high confidence'' on increased aridity in the MED region (Sections 8.4.1.6 and 11.9.4 and Atlas.8.2; [[#Coppola--2021a|Coppola et al., 2021a]] ). In NEU there is '''high confidence''' of decrease in aridity linked to mean precipitation increase ( [[IPCC:Wg1:Chapter:Chapter-8#8.4.1.6|Section 8.4.1.6]] , [[IPCC:Wg1:Chapter:Atlas|Atlas]] 8.2) and meteorological drought decrease based on indicators like Standardized Precipitation Index and consecutive dry days ( [[IPCC:Wg1:Chapter:Chapter-11#11.9.4|Section 11.9.4]] , Figure 12.4, Coppola et al,, 2021a).

'''Hydrological drought:''' There is ''high confidence'' that hydrological droughts have increased in the Mediterranean basin with ''medium confidence'' in anthropogenic attribution of the signal, and ''high confidence'' that they will continue to increase through the 21st century for 2°C GWL and higher and all scenarios except RCP2.6/SSP1-2.6. (Sections 8.3.1.6, 8,4.1.6, and 11.9.4). There is ''medium confidence'' in hydrological drought increase in WCE and ''low confidence'' in direction of change for EEU and NEU from mid-century onwards and for 2°C GWL and higher and all scenarios except RCP2.6/SSP1-2.6 ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] and Figure 12.4g–i).

Streamflow droughts are projected to become more severe and persistent in the Mediterranean and western Europe (current 100-year events could occur approximately every 2–5 years by 2080; [[#Forzieri--2016|Forzieri et al., 2016]] ).

The opposite tendency is projected in Northern, Eastern and central Europe where higher precipitation that outweighs the effects of increased evapotranspiration is expected to result in a decrease in streamflow drought frequency ( [[#Forzieri--2014|Forzieri et al., 2014]] ). For a 2°C GWL droughts will become more intense in the MED and in France and longer mainly due to less rainfall and higher evapotranspiration. A reduction of drought length and magnitude is projected for NEU and EEU ( [[#Roudier--2016|Roudier et al., 2016]] ). In the southern Alps, both winter and summer low flows are projected to be more severe, with a 25% decrease in the 2050s ( [[#Vidal--2016|Vidal et al., 2016]] ).

'''Agricultural and ecological drought:''' There is ''medium confidence'' that agricultural and ecological droughts have increased in Western and Central Europe and in the Mediterranean region, and ''medium confidence'' that anthropogenic drivers contributed to the Mediterranean increase (Sections 8.3.1.6 and 11.9).

( [[IPCC:Wg1:Chapter:Chapter-11|Chapter 11]] assesses that agricultural and ecological droughts will increase in the Mediterranean regions ( ''high confidence'' ) and Western and Central Europe ( ''medium confidence'' ) by mid-century and with ''high confidence'' by the end of the century for the MED for 2°C GWL and higher and all scenarios except RCP2.6/SSP1-2.6 ( [[IPCC:Wg1:Chapter:Chapter-11#11.9.4|Section 11.9.4]] ). ''Low confidence'' in direction of change is assessed for EEU and NEU under all scenarios and global warming levels (Figure 12.4k).

Recent local studies provide additional risk-relevant context to changes in European drought. Agricultural and ecological drought conditions are expected to intensify in southern Europe by end-of-century based on the 12-month rainfall Drought Severity Index (a soil moisture indicator), precipitation deficit SPI and SPEI indices. There will be regions in southern Europe where this type of drought could be up to 14 times worse than the worst drought in the historical period ( [[#Guerreiro--2018|Guerreiro et al., 2018]] ). One-in-10-year drought events are projected to happen every second year ( [[#Mora--2018|Mora et al., 2018]] ; [[#Ruosteenoja--2018|Ruosteenoja et al., 2018]] ). The Mediterranean region will have 100 additional stress years (years with three consecutive months of precipitation deficits greater than 25%; [[#Giorgi--2018|Giorgi et al., 2018]] ); an increase of both drought frequency (up to two events per decade) and severity ( [[#Spinoni--2014|Spinoni et al., 2014]] , 2020) and an increase of consecutive dry days in the southern part of the MED region ( [[#Lionello--2020|Lionello and Scarascia, 2020]] ). In contrast, droughts are expected to decrease in winter in Northern Europe ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] ; [[#Spinoni--2018a|Spinoni et al., 2018a]] ). These findings are confirmed by the EURO-CORDEX, CMIP5 and CMIP6 ensemble that show a change of frequency of drought events in the MED between 2–3 events per decade by mid-century for scenario RCP8.5 (Figure 12.SM.3; [[#Coppola--2021a|Coppola et al., 2021a]] ).

'''Fire weather:''' Fire weather conditions have been increasing since about 1980 over a few regions in Europe including Mediterranean areas ( ''low confidence'' ) ( [[#Venäläinen--2014|Venäläinen et al., 2014]] ; [[#Urbieta--2019|Urbieta et al., 2019]] ; [[#Barbero--2020|Barbero et al., 2020]] ; [[#Giannaros--2021|Giannaros et al., 2021]] ). However, beyond a few studies, evidence is largely missing on attribution of these trends to anthropogenic climate change ( [[#Forzieri--2016|Forzieri et al., 2016]] ). An increase in fire weather is projected for most of Europe, especially western, eastern and central regions, by 2080 (current 100-year events will occur every 5–50 years), with a progressive increase in confidence and model agreement along the 21st century ( ''medium confidence'' ) ( [[#Forzieri--2016|Forzieri et al., 2016]] ; [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ). With increased drying and heat combined, in Mediterranean areas, an increase in fire weather indices is projected under RCP4.5 and RCP8.5, or SRES A1B, as early as by mid-century ( ''high confidence'' ) ( [[#Bedia--2014|Bedia et al., 2014]] ; [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ; [[#Dupuy--2020|Dupuy et al., 2020]] ; [[#Fargeon--2020|Fargeon et al., 2020]] ; [[#Ruffault--2020|Ruffault et al., 2020]] ) and an increase in burned area of 40% and 100% for a 2°C and 3°C GWL, respectively ( [[#Turco--2018|Turco et al., 2018]] ).

'''In summary, there is''' high confidence '''that river floods will increase in central and Western Europe and''' medium confidence '''that they will decrease in Northern, Eastern and southern Europe, for mid- and end of century under RCP8.5 and with''' low confidence '''under RCP2.6. There is''' high confidence '''that aridity will increase by mid- and end-century under the RCP8.5 and SSP5-8.5, and''' high confidence '''that agricultural, ecological and hydrological droughts will increase in the Mediterranean region by mid- and far end of century under all RCPs except RCP2.6/SSP1-2.6 and''' '''also for 2°C and higher GWLs. There is''' high confidence '''in fire weather increase in the Mediterranean region.'''

<div id="12.4.5.3" class="h3-container"></div>

<span id="wind-5"></span>