Mean Summer Research Articles

North‐West Europe Hottest Days Are Warming Twice as Fast as Mean Summer Days

AbstractEurope has seen a rapid increase in the frequency and intensity of hot extremes in recent decades. In this study it is shown, using ERA5 reanalysis data 1960–2021, that the hottest summer days in North‐West Europe are warming approximately twice as fast as mean summer days. Moreover, this pattern stands out as relatively unusual across the Northern Hemisphere. It is also shown that comprehensive climate models fail to capture this difference in trends. A hypothesis is suggested to explain the differential rate of warming between the mean and hottest days, namely that the hottest days are often linked to warm advection from Iberia and North Africa, areas that are warming faster than North‐West Europe. This hypothesis can account for about 25% of the difference between ERA5 and a climate model ensemble and hence further research is needed to understand the drivers of the differing trends in mean and extreme temperature.

Agricultural development has not necessarily caused forest cover decline in semi-arid northern China over the past 12,000 years

Forest cover significantly affects the global carbon cycle, biodiversity, and human welfare, but is seriously threatened by human activities. Here we found that anthropogenic forces did not necessarily lead to forest cover decline in the marginal agricultural region of northern China based on a quantitative reconstruction of 12,000-years forest cover changes using modern analog technique and random forest. The forest cover was strongly affected by human activities in the core agricultural region, as indicated by the high independent effects of archeological sites (38.3%) and burning area (42.3%). In contrast, climate impacted the forest cover in the marginal agricultural region, where the annual precipitation and summer mean temperature contributed 52.4% and 27.4%, respectively. Agricultural development in the marginal agricultural region likely occurred in the river valley or sunny slopes, not overlapping with zonal forests growing on shady slopes. This study implies much less afforestation potential than previously expected in the marginal agricultural region.

The effects of environmental and biological factors on the length of Atlantic Salmon age‐1+ parr in three Maine drainages

AbstractObjectiveAtlantic Salmon Salmo salar in the United States have been the focus of recovery efforts for over 150 years, but long‐term analyses of juvenile demographics are limited. We examined how parr size (fork length [FL]) varied across three Maine drainages (East Machias, Narraguagus, and Sheepscot rivers) during 1980–2014 and was affected by habitat and biological variables using a long‐term electrofishing data set.MethodsWe fitted generalized additive mixed models (GAMMs) to determine how parr FL varied with explanatory variables, including mean summer air temperature, elevation, mean channel width, juvenile salmon density, age‐0 parr stocked, a metric for the number of effective fry stocked, and year. When examining model‐averaged GAMM results, we found that parr size varied throughout the 34‐year time period across the three drainages.ResultBetween 1980 and 2014, parr FL in the Sheepscot River drainage (mean = 143.9 mm) steadily increased (~5‐mm increase). Parr FL in the Narraguagus River drainage (mean = 124.4 mm) declined from 1980 to about 2005 and then increased from 2006 to 2014. Parr FL in the East Machias River drainage (mean = 127.7 mm) experienced a decrease of approximately 10 mm during the study period. Density dependence was evident across drainages, suggesting that habitats were at capacity or that parr were experiencing competition. Given that the production of parr in Maine is highly reliant on stock enhancement, localized high stocking densities may limit parr growth without further restoration or habitat improvements. Stocking intensities generally decreased in all three drainages after 2000, possibly relaxing density dependence and partially explaining the plateau or increase in FL during recent years in the Sheepscot and Narraguagus rivers. Relationships between FL and summer air temperature were drainage specific, while wide channels and lower elevations were consistently associated with larger parr.ConclusionGiven our results, management should continue to prioritize habitat improvements to improve local carrying capacity and potentially reduce density‐dependent growth so as to increase stock enhancement efficacy within an adaptive management framework at the southern edge of the Atlantic Salmon's range.

Constrained high-resolution projection of hot extremes in the Beijing–Tianjin–Hebei region of China

The Beijing–Tianjin–Hebei (BTH) region is the political center and one of the largest and most dynamic economic centers in China. Relative to other regions of China, it faces greater challenges from increasing hot extremes. However, future projections of regional changes in hot extremes based on multi-model ensembles carry huge uncertainty. To improve the reliability of regional projections, we used the latest high-resolution outputs from nine GCMs in CMIP6-HighResMIP and constrained the projection of hot extremes in this region. In the BTH, the historical scaling of the annual maximum temperature with the mean summer (June–August) temperatures (TXx scaling) showed a significant linear relationship with the future TXx scaling in the multi-model ensemble. By comparing the observed and simulated historical TXx scaling we identified an observational constraint that could reduce the uncertainty of TXx scaling. We believed that the simulations of EC-Earth3P, EC-Earth3P-HR, MPI-ESM1-2-HR and MPI-ESM1-2-XR show advantages in simulating surface air temperature and related hot extremes in this region. Verification demonstrated that surface air temperature projection in the BTH region constrained by observational constraint is more reliable. In constrained projections, by the 2040s, the increase in summer surface air temperatures is projected to exceed 1 °C compared to 2010s. Also, the estimated number of days of compound (sequential hot day-night) hot extremes (HND), independent hot nights (HNi) and independent hot days (HDi) was found to increase by 0.3, 0.3, and −0.03 d per year during 2015–2049, respectively. The growth in numbers of days of HND, HNi and HDi was slower after observational constraint. Furthermore, the estimated increase in surface air temperature variables after constraint also reduced. This study provides support for adaptation policy-making and as a reference for the use of observational constraint in other regions of China.

Skilful Forecasts of Summer Rainfall in the Yangtze River Basin from November

Variability in the East Asian summer monsoon (EASM) brings the risk of heavy flooding or drought to the Yangtze River basin, with potentially devastating impacts. Early forecasts of the likelihood of enhanced or reduced monsoon rainfall can enable better management of water and hydropower resources by decision-makers, supporting livelihoods and major economic and population centres across eastern China. This paper demonstrates that the EASM is predictable in a dynamical forecast model from the preceding November, and that this allows skilful forecasts of summer mean rainfall in the Yangtze River basin at a lead time of six months. The skill for May–June–July rainfall is of a similar magnitude to seasonal forecasts initialised in spring, although the skill in June–July–August is much weaker and not consistently significant. However, there is some evidence for enhanced skill following El Niño events. The potential for decadal-scale variability in forecast skill is also examined, although we find no evidence for significant variation.

East Asian summer precipitation in AWI‐CM3: Comparison with observations and CMIP6 models

AbstractOwing to the complicated spatial–temporal characteristics of East Asian precipitation (EAP), climate models have limited skills in simulating the modern Asian climate. This consequently leads to large uncertainties in simulations of the past EAP variation and future projections. Here, we explore the performance of the newly developed Alfred Wegener Institute Climate Model, version 3 (AWI‐CM3) in simulating the climatological summer EAP. To test whether the model's skill depends on its atmosphere resolution, we design two AWI‐CM3 simulations with different horizontal resolutions. The result shows that both simulations have acceptable performance in simulating the summer mean EAP, generally better than the majority of individual models participating in the Coupled Model Intercomparison Project (CMIP6). However, for the monthly EAP from June to August, AWI‐CM3 exhibits a decayed skill, which is due to the subseasonal movement of the western Pacific subtropical high bias. The higher‐resolution AWI‐CM3 simulation shows an overall improvement relative to the one performed at a relatively lower resolution in all aspects taken into account regarding the EAP. We conclude that AWI‐CM3 is a suitable tool for exploring the EAP for the observational period. Having verified the model's skill for modern climate, we suggest employing the AWI‐CM3, especially with high atmosphere resolution, both for applications in paleoclimate studies and future projections.

Anthropogenic heat release due to energy consumption exacerbates European summer extreme high temperature

Anthropogenic heat release (AHR) is the release of heat generated by anthropogenic energy consumption. The global mean flux of AHR is 0.03 W m−2, while AHR is geographically concentrated and fundamentally correlates with economic activity; furthermore, AHR can reach a level sufficient for impacting regional even large-scale climate. In this study, the impacts of AHR on the summer European heatwaves (EHWs) are examined by using the Community Earth System Model version 1 (CESM1). The results show that in Europe, AHR increases the summer mean 2-m temperature by 0.26 °C and the surface minimum and maximum temperatures by 0.14 °C and 0.41 °C, respectively. AHR exacerbates the extreme high temperatures in the summer in Europe, increasing EHW days by 1–2 days in central and eastern Europe in the summer annually from 1992 to 2013. AHR strengthens the surface wind that flows from the ocean to the land in Europe by increasing the land surface temperatures. AHR decreases the lower-troposphere stability (LTS) and reduces the low-cloud amounts in Europe, which leads to more solar shortwave radiation reaching the surface. AHR affects water vapor and the surface energy balance in Europe, which impacts on European summer heatwaves further. AHR acts as a non-negligible factor for summer extreme high temperature in Europe and a potential factor impacting EHW days.

Trends and Spatio-Temporal Variability of Summer Mean and Extreme Precipitation across South Korea for 1973-2022.

The online version contains supplementary material available at 10.1007/s13143-023-00323-7.

Long-term changes in autumn migration timing of Garden Warblers Sylvia borin at the southern Baltic coast in response to spring, summer and autumn temperatures

Many migrant European birds have been departing their breeding grounds earlier in recent decades in response to rising temperatures from climate change. We examined long-term changes in the autumn migration timing of immature Garden Warblers using data from ringing station Bukowo-Kopań on the Polish Baltic coast in 1967–2018. We calculated an Annual Anomaly (AA) of migration and the dates when 10%, 50% and 90% of migrating birds were caught at each station. We modelled AA and the dates of these percentiles of passage for each station against the year and bi-monthly spring, summer and autumn temperatures as explanatory variables in multiple linear regression models. The overall passage (AA) of immature Garden Warblers advanced by 7 days and the dates of the 50th and 90th passage percentiles advanced by 6–11 days. Overall passage, and dates for 50% of passage occurred later the higher summer temperatures rose in Finland. We suggest favourable foraging conditions in warm summers at these breeding grounds and at first stopover sites delayed the passage because these inexperienced birds took advantage of the conditions to accumulate fuel before migrating south. The overall passage, and the dates of 10%, 50% and 90% of autumn passage occurred the earlier the higher were spring temperatures on spring migration route in Italy, and the higher were mean summer temperatures at breeding grounds in southern Sweden and Norway. We suggest a trans-generation carry-over effect, as warm springs encourage early arrival and nesting of returning adults, thus earlier broods and hatching of juveniles, which also grow faster in warm summers. These effects enable immatures to migrate earlier in autumn after a warm breeding season. The long-term increase in Europe’s spring and summer temperatures thus help explain the shift in Garden Warblers’ migration timing.

Physical drivers of chlorophyll and nutrients variability in the Southern-Central Arabian Gulf

The southern-central Arabian Gulf demonstrates a poor understanding of nutrients and chlorophyll dynamics in physical-biogeochemical settings. Here, using data of chlorophyll, nutrients and hydrographic parameters collected in two cruises in summer 2019 and winter 2020, we examined variability in nutrients and chlorophyll concentrations, and the driving mechanisms. Summer thermal stratification enhanced by intrusion of fresher surface water plume from the Arabian Sea developed a hypoxic zone (DO < 2.0 mL/L) below the thermocline. Nitrate and ammonium summer concentrations (2.24 ± 0.36, 1.70 ± 0.17 μM) were about 3 times the winter concentrations. Nutrient stoichiometry showed a Redfield-like nitrogen/phosphorus (N:P) ratio in summer (15.9:1) and a nitrogen limitation in winter (N:P = 4:1). Chlorophyll-a content in summer (mean = 0.80 mg/m3) was about 1.4 times the winter concentration (mean = 0.58 mg/m3) (p > 0.05). Photo-protective carotenoids content in summer (0.59 mg/m3) was about 2.7 times their winter concentration. Winter cooling resulted in downwelling of dense water on the shallow coastal banks, which enhanced near bottom oxygen concentrations and swept away nutrient-rich water resulting in lower winter chlorophyll. This research features aspects of the physical and biogeochemical drivers underpinning the dynamics of nutrients and chlorophyll in the central Gulf.

Tropical influences on European summer climate variability

Numerous studies have established a link between tropical atmospheric conditions and northern midlatitude circulation mediated by Rossby wave propagation in winter. In recent years, research has also investigated tropical to midlatitude teleconnections in northern hemisphere summer. In this paper, we examine summer connections further by imposing observed tropical conditions in climate model simulations. We examine resulting changes in the representation of seasonal mean surface climate variables and mid-troposphere circulation in the northern hemisphere summer, identifying regions where model fidelity improves following the imposition of tropical conditions. We demonstrate robust connections between the tropics and mid-latitudes on the seasonal timescale, with these connections apparent in three mid-latitude regions, namely eastern North America, central Europe and northern Siberia. These regions are shown to be impacted by wave trains originating in specific regions of the subtropics associated with patterns of upper-level convergence. The results provide a clearer picture of tropical to extratropical teleconnections that affect summer mean climate in the northern midlatitudes.

Asymmetries of the lag between air temperature and insolation in gauge observations and reanalyses over China

The annual cycle of near-surface air temperature should receive more attention in climate studies because it is especially important to crop growth and to human comfort. The phase of the annual temperature cycle generally lags behind that of insolation due to the time required for the Earth's surface to absorb the energy from solar radiation and then warm the near-surface air. This study decomposes the daily maximum, minimum, and mean air temperatures using Fourier transforms and examines the lag in number of days between the phases of temperature and insolation. It was found that the lags between air temperature and insolation were asymmetrical during the summer and winter seasons. The mean summer lags were 30.8, 32.4, and 30.6 days from gauge observations over China, which were longer than the 21.0, 21.5, and 16.7 days of winter lags for daily maximum, minimum, and mean temperature respectively. Spatially, these lags showed wider climatological and interannual variability in southern than in northern areas because higher atmospheric water vapor content and greater cloud cover caused a longer response time of air temperature to solar radiation. Decreasing variations were derived for the winter lag, at about −1.11 days/decade, −0.68 days/decade, and − 0.78 days/decade for the maximum, minimum, and mean temperature respectively. Currently, reanalysis data can accurately simulate the climatological, long-term, and interannual variability of the summer and winter lags over most of the study area, except for southwestern China, although they have negative biases in characterizing the annual cycle.

Geology‐Climate Interactions are Key Determinants of Climate‐Change Refugia in Japanese Mountain Streams

Photo 1. Example of the confluence of a volcanic and nonvolcanic stream (left panel). The right panel is a thermal photograph of the confluence taken using a TVS-500 camera (Nippon Avionics Co., Ltd.) on September 17, 2019, where blue colors correspond to the cold water from the volcanic stream mixing with the warmer (orange) water from the nonvolcanic stream. Photo credit: Kenta Iwasaki. Photo 2. View of a volcanic stream, Ponnunobe stream, the Sorachi river, Hokkaido, Japan. The stream is located inside the University of Tokyo Hokkaido Forest. Many springs (top panels) occur in around the main channel (bottom panel). In this region, the mean summer water temperature of volcanic streams is 3°C colder than that of nonvolcanic streams on average. Photo credit: Yu Nagasaka. Photo 3. Wrinklehead sculpin (upper panel: Cottus nozawae) and Southern Asian Dolly Varden (lower panel: Salvelinus curilus) two major cold-water species in northern Japan. Their distribution is tightly restricted by summer water temperature. Photo credit: Yu Nagasaka (upper panel) and Chiharu Furusawa (lower panel). Photo 4. View of biotic and abiotic surveys in mountain streams, Japan. Macroinvertebrates (upper left panel) and fish (lower left panel) were collected once in each monitoring stream. Water loggers were installed with short sections of perforated PVC pipes to facilitate water exchange and shield them from sunlight (right panels). Photo credit: Jorge García Molinos. Photo 5. Dynamic changes in riverscapes at a monitoring site due to a large flood associated with Typhoon Hagibis, 2019 (before: upper panel, after: lower panel). Monitoring of water temperature in the Japanese archipelago is very challenging because of the many typhoons hitting the archipelago every summer season. Unfortunately, the temperature data of this site in 2019 was not available due to the loss of the logger. The yellow bridge at the upper-left corner of the picture offers a good visual reference to compare both pictures. Photo credit: Nobuo Ishiyama. These photographs illustrate the article “Underlying geology and climate interactively shape climate change refugia in mountain streams” by Ishiyama, N., Sueyoshi, M., García Molinos, J., Iwasaki, K., Negishi, J. N., Koizumi, I., Nagayama, S., Nagasaka, A., Nagasaka, Y. & Nakamura, F. published in Ecological Monographs. https://doi.org/10.1002/ecm.1566

Climate change impacts on native cutthroat trout habitat in Colorado streams

AbstractHeadwater streams support vital aquatic habitat yet are vulnerable to changing climate due to their high elevation and small size. Coldwater fish are especially sensitive to the altered streamflow and water temperature regimes during summer low flow periods. Though previous studies have provided insights on how changes in climate and alterations in stream discharge may affect habitat availability for various native cutthroat trout species, suitable physical habitats have not been evaluated under future climate projections for the threatened Greenback Cutthroat Trout (GBCT) native to headwater regions of Colorado, USA. Thus, this study used field data collected from selected headwater streams across the current distribution of GBCT to construct one‐dimensional hydraulic models to evaluate streamflow and physical habitat under four future climate projections. Results illustrate reductions in both predicted streamflow and physical habitat for all future climate projections across study sites. The projected mean summer streamflow shows greater decline (−52% on average) compared to the projected decline in mean August flow (−21% on average). Moreover, sites located at a relative higher elevation with larger substrate and steeper slope were projected to experience more reductions in physical habitat due to streamflow reductions. Specifically, streams with step‐pool morphologies may experience grater changes in available habitat compared to pool‐riffle streams. Future climate change studies related to coldwater fish that examine spatial variation in flow alteration could provide novel data to complement the existing literature on the thermal characteristics. Tailoring reintroduction and management efforts for GBCT to the individual headwater stream with adequate on‐site monitoring could provide a more holistic conservation approach.

Effect of summer temperature on prolonged diapause of Tettigoniidae (Orthoptera) under realistic field conditions

To face recurrent temperature changes, tettigoniids inhabiting temperate climates overwinter as eggs in a diapause stage, being able to postpone embryogenesis for one or more years. To date, it is unclear if species living in warm regions, especially under the Mediterranean climate, could exhibit a diapause for a single year or enter a prolonged diapause due to higher summer temperatures experienced by eggs immediately after oviposition. In this two-year study, we tested the effect of summer temperatures on diapause of six Mediterranean tettigoniid species under natural field conditions. We found that five species can exhibit a facultative diapause depending on mean summer temperatures. For two species, a substantial shift in egg development from 50 to 90% occurred over an interval of c. 1 °C after the first summer period. All the species increased considerably their development (nearly 90%) after the second summer period irrespective of temperatures. Overall, this study suggests that diapause strategy and the different thermal sensibility of embryonic development varies considerably across species potentially affecting their population dynamics.

Underlying geology and climate interactively shape climate change refugia in mountain streams

AbstractIdentifying climate‐change refugia is a key adaptation strategy for reducing global warming impacts. Knowledge of the effects of underlying geology on thermal regime along climate gradients and the ecological responses to the geology‐controlled thermal regime is essential to plan appropriate climate adaptation strategies. In the present study, the dominance of volcanic rocks in the watershed is used as a landscape‐scale surrogate for cold groundwater inputs to clarify the importance of underlying geology in stream ecosystems along climate gradients. First, using hundreds of monitoring stations distributed across multiple catchments, we explored the relationship between watershed geology and the mean summer water temperature of mountain streams along climate gradients in the Japanese archipelago. Mean summer water temperature was explained by the interaction between the watershed geology and climate in addition to independent effects. The cooling effect supported by volcanic rocks reached up to 3.3°C among study regions, which was more pronounced in streams with less summer precipitation or lower air temperatures. Next, we examined the function of volcanic streams as cold refugia under contemporary and future climatic conditions. Community composition analyses revealed that volcanic streams hosted distinct stream communities composed of more cold‐water species compared with nonvolcanic streams. Scenario analyses based on multiple global climate models and Representative Concentration Pathways (RCPs) revealed a geology‐related pattern of thermal habitat loss for cold‐water species. Nonvolcanic streams rapidly declined in thermally suitable habitats for lotic sculpins even under the lowest emission scenario (RCP 2.6). In contrast, most volcanic streams will be sustained below the thermal threshold, especially for low‐ and mid‐level emission scenarios (RCP 2.6, 4.5). However, the distinct stream community in volcanic streams and geology‐dependent habitat loss for lotic sculpins was not uniform and were more pronounced in streams with less summer precipitation or lower air temperatures. These findings highlight that underlying geology, climate variability, and their interaction should be considered simultaneously for the effective management of climate‐change refugia in mountain streams.

Long‐term change of summer mean and extreme precipitations in Korea and East Asia

AbstractThe change of the precipitation characteristics over South Korea is investigated using long‐term (60 years) hourly precipitation records from surface stations focusing on extended summer (June–September) and rainy season (Changma). The precipitation characteristics including extreme events (&gt;30 mm·h−1 or &gt;100 mm·day−1) are also compared for the past (1961–1990) and recent (1991–2020) climatology. The amount of summer precipitation shows a notable increase over South Korea (2.6 mm·day−1·century−1) during the last 60 years (1961–2020) although it is smaller than recent 48‐year trend measured in North Korea (9.7 mm·day−1·century−1). Precipitation amounts are significantly increased than past climatology particularly in 70–100 and 200 mm·day−1 intensity ranges. The frequency of extreme precipitation also exhibits an increasing trend (1.0 frequency·century−1) during the last 60 years over South Korea. The frequency of extreme precipitation has been doubled in the recent climatology compared to the past climatology. Daily precipitations in top 1 percentile present clear increasing trends during the extended summer and Changma season in South Korea. Further investigation using gridded precipitation reveals that the similar mean and extreme precipitation increases are observed over the wider regions in East Asia, including central China and southern Japan. This result implies that the long‐term precipitation change over South Korea is related to a large‐scale circulation change in the East Asian summer monsoon.

Assessment of Climate Indices over the Carpathian Basin Based on ALADIN5.2 and REMO2015 Regional Climate Model Simulations

The Hungarian Meteorological Service has been conducting climate model simulations in order to assess the effects of climate change in the Carpathian Basin and provide data for impact research and stakeholders. Two regional climate models are used: ALADIN-Climate 5.2 (hereafter ALADIN5.2) and REMO2015. They were tested for the past when the lateral boundary conditions were taken from two sources. ERA-Interim reanalysis was used in the evaluation experiment, while the CNRM-CM5 and the MPI-ESM-LR global climate models (GCM) provided the forcings in the control experiments. The model outputs were compared with the CarpatClim-HU observational dataset for the 1981–2000 period. Future projections were carried out with the RCP4.5 and RCP8.5 scenarios, and the results were analyzed for 2021–2050 and 2071–2100. The evaluation of the results focused mainly on climate indices calculated from temperature and precipitation. The validation results showed that REMO2015 assessed the mean temperature well, but the indices based on the minimum and maximum temperature had a significant bias which has to be taken into account when interpreting future changes. The model overestimated the minimum temperature in summer, which might affect the number of tropical nights. Moreover, the maximum temperature was underestimated; thus, the derived indices, such as the occurrence of summer days and hot days, were profoundly underestimated. In comparison, ALADIN5.2 had smaller biases for the high temperature indices; moreover, the number of hot days and extremely cold days was overestimated. Taking future projections into account, we can clearly see that the results of REMO2015 show a much more moderate increase in temperature than ALADIN5.2. The reasons are yet unknown and require further investigation. In spring and summer, the number of wet days was slightly overestimated, while the number of heavy precipitation days was marginally underestimated. The projections showed the highest uncertainty in the changes in mean summer precipitation and other precipitation indices. Although the REMO2015 model assessed a decrease in precipitation, ALADIN5.2 projected an increase in precipitation with a similar magnitude.

Climate Change Trends for the Urban Heat Island Intensities in Two Major Portuguese Cities

Urban Heat Island (UHI) intensities are analyzed for the metropolitan areas of the two major Portuguese cities, Lisbon and Porto, in the period 2008–2017. Projections for the UHI intensity averaged over 2008–2017 and a future period 2021–2050 are calculated under the Representative Concentration Pathway (RCP) 8.5. The spatiotemporal characteristics of the UHI intensity are assessed for daytime, nighttime, and average daily conditions. This analysis is carried out for the winter (Dec-Jan-Feb, DJF) and summer (Jun-Jul-Aug, JJA) meteorological seasons. Maximum UHI intensities of about 3.5 °C were reached in 2008–2017 in both metropolitan areas, but over a wider region during winter nighttime than during summer nighttime. Contrariwise, the most intense urban cool island effect reached −1.5 °C/−1 °C in Lisbon/Porto. These UHI intensities were depicted during summer daytime and in less urbanized areas. Overall, the UHI intensities were stronger during the winter than in the summer for both cities. Results show that the UHI intensity is closely related to underlying surfaces, as the strongest intensities are confined around the most urbanized areas in both cities. Until 2050, under RCP8.5, the highest statistically significant trends are projected for summer daytime, of about 0.25 °C (per year) for Lisbon and 0.3 °C (per year) for the UHI 99th percentile intensities in both metropolitan areas. Conversely, the lowest positive statistically significant trends (0.03 °C/0.02 °C per year) are found for the winter daytime UHI intensities in Lisbon and the winter nighttime and average UHI intensities in Porto, respectively. These statistically significant patterns (at a 5% significance level) are in line with the also statistically significant trends of summer mean and maximum temperatures in Portugal, under RCP8.5 until 2050. Scientists, urban planners, and policymakers face a significant challenge, as the contribution of urbanization and the forcing promoted by global warming should be duly understood to project more sustainable, go-green, carbon-neutral, and heat-resilient cities.

Climate Change Impacts on Irish River Flows: High Resolution Scenarios and Comparison with CORDEX and CMIP6 Ensembles

Climate change is likely to impact water quality, resource availability and riverine ecosystems. While large ensembles are available to assess future impacts (e.g., the Coupled Model Intercomparison Projects (CMIP) and/or CORDEX) many countries have developed their own high-resolution ensembles. This poses a selection problem with robust adaptation dependent on plausible ranges of change being adequately quantified. Therefore, it is important to compare projected changes from available ensembles. Here we assess future climate change impacts for 26 Irish catchments. Using a high-resolution national ensemble of climate models projected impacts in mean, low and high flows are assessed and uncertainties in future projections related to catchment size. We then compare future impacts from CORDEX and CMIP6 ensembles for a subset of catchments. Results suggest increases in winter flows (-3.29 to 59.63%), with wide ranges of change simulated for summer (-59.18 to 31.23%), low (-49.30 to 22.37%) and flood (-19.31 to 116.34%) flows across catchments under RCP8.5 by the 2080s. These changes would challenge water management without adaptation. Smaller catchments tend to show the most extreme impacts and widest ranges of change in summer, low and flood flow changes. Both the ensemble mean and range of changes from the national ensemble were more modest and narrower than the CMIP6 and CORDEX ensembles, especially for summer mean and low flows, highlighting the importance of evaluating impacts across ensembles to ensure adaptation decisions are informed by plausible ranges of change.