The relative impacts of climate change and urbanization on the hydrological response of a Korean urban watershed

We assessed the relative hydrological impacts of climate change and urbanization using an integrated approach that links the statistical downscaling model (SDSM), the Hydrological Simulation Program—Fortran (HSPF) and the impervious cover model (ICM). A case study of the Anyangcheon watershed, a representative urban region in Korea, illustrates how the proposed framework can be used to analyse the impacts of climate change and urbanization on water quantity and quality. The evaluation criteria were measurements of low flow (99, 95, and 90 percentile flow), high flow (10, 5, and 1 percentile value), pollutant concentration (30, 10, and 1 percentile value), and the numbers of days required to satisfy the target water quantity and quality for a sensitive comparison of subtle impacts of variations in these measures. Nine scenarios, including three climate scenarios (present conditions, A1B, and A2) and three land use change scenarios, were analysed using the HSPF model. The impacts of climate change on low flow (34·1–59·8% increase) and high flow (29·1–37·1% increase) were found to be much greater than those on the biochemical oxygen demand (BOD) (3·8–10·0% decrease). On the other hand, the impacts of urbanization on water quality (19·0–44·6% increase) are more significant than those on high (1·0–4·4% increase) and low flow (11·4–25·6% decrease). Furthermore, low flows are more sensitive to urbanization than high flows. The number of days required to satisfy the target water quantity and quality can be a sensitive criterion to compare the subtle impacts of climate and urbanization on human society, especially as they are much more sensitive than low flow and pollutant concentration. Finally, urbanization has a potent impact on BOD while climate change has a high impact on flow rate. Therefore, the impacts of both climate change and urbanization must be included in watershed management and water resources planning for sustainable development. Copyright © 2010 John Wiley & Sons, Ltd.     

Improving sustainability of urban drainage systems for climate change adaptation using best management practices: a case study of Tehran,Iran

Although the effectiveness of best management practices (BMPs) in reducing urban flooding is widely recognized, the improved sustainability achieved by implementing BMPs in upstream suburban areas, reducing downstream urban floods, is still debated. This study introduces a new definition of urban drainage system (UDS) sustainability, focusing on BMP usage to enhance system performance after adaptation to climate change. Three types of hydraulic reliability index (HRI) plus robustness and improvability indices were used to quantify the potential enhanced sustainability of the system in a changing climate, together with a climate change adaptability index (CCAI). The sustainability of UDS for the safe conveyance of storm-water runoff was investigated under different land-use scenarios: No BMP, BMP in urban areas, and BMP inside and upstream of urban areas, considering climate change impacts. Rainfall–runoff simulation alongside drainage network modelling was conducted using a storm-water management model (US EPA SWMM) to determine the inundation areas for both base-line and future climatic conditions. A new method for disaggregating daily rainfall to hourly, proposed to provide a finer resolution of input rainfall to SWMM, was applied to a semi-urbanized catchment whose upstream runoff from mountainous areas may contribute to the storm-water runoff in downstream urban parts. Our findings confirm an increase in the number of inundation points and reduction in sustainability indices of UDS due to climate change. The results present an increase in UDS reliability from 4% to 16% and improvements in other sustainability indicators using BMPs in upstream suburban areas compared to implementing them in urban areas.     

Effect of climate change on overland flow generation: a case study in central Germany

The impact of global climate change on runoff components, especially on the type of overland flow, is of utmost significance. High‐resolution temporal rainfall plays an important role in determining the hydrological response of quick runoff components. However, hydrological climate change scenario analyses with high temporal resolution are rare. This study investigates the impact of climate change on discharge peak events generated by rainfall, snowmelt, and soil‐frost induced runoff using high‐resolution hydrological modelling. The study area is Schäfertal catchment (1.44 km²) in the lower Harz Mountains in central Germany. The WaSiM‐ETH hydrological model is used to investigate the rainfall response of runoff components under near future (2021–2050) and far‐distant future (2071–2100) climatic conditions. Disaggregated daily climate variables of WETTREG2010 SRES scenario A1B are used on a temporal resolution of 10 min. Hydrological model parameter optimization and uncertainty analysis was conducted using the Differential Evolution Adaptive Metropolis (DREAM_(ZS)) uncertainty tool. The scenario results show that total runoff and interflow will increase by 3.8% and 3.5% in the near future and decrease by 32.85% and 31% in the far‐distant future compared to the baseline scenario. In contrast, overland flow and the number and size of peak runoff will decrease moderately for the near future and drastically for the far‐distant future compared to the baseline scenario. We found the strongest decrease for soil‐frost induced discharge peaks at 79.6% in the near future and at 98.2% in the far‐distant future scenario. It can be concluded that high‐resolution hydrological modelling can provide detailed predictions of future hydrological regimes and discharge peak events of the catchment. Copyright © 2014 John Wiley & Sons, Ltd.     

A clear and present danger: Ladakh's increasing vulnerability to flash floods and debris flows

This preliminary investigation of the recent spate of deadly flash floods and debris flows in Ladakh (India) over the last decade identifies uncontrolled development in hazardous locations as an important factor contributing to loss of life and property damage in this high mountain desert. The sediments exposed in the channel banks and on the alluvial fans of several mountain streams in the area indicate a long history of flash floods and debris flows resulting from intense storms, which appear to have increased in frequency within the last decade. The signposts of these recurrent hazards are being ignored as a growing economy, which is boosted by a well‐established tourism industry, is now driving development onto lands that are susceptible to floods and debris flow hazards. In this science briefing we argue that the increasing vulnerability in Ladakh should be addressed with sound disaster governance strategies that are proactive, rather than reactionary. Copyright © 2016 John Wiley & Sons, Ltd.     

Multi-decadal variations in annual maximum peak flows in semi-arid and temperate regions of Chile

Abstract

In determining the possible influence of climate change, it is important to understand the temporal and spatial variability in streamflow response for diverse climate zones. Thus, the aim of this study was to determine the presence of changes in annual maximum peak flow for two climate zones in Chile over the past few decades. A general analysis, a flood frequency analysis and a trend analysis were used to study such changes between 1975 and 2008 for a semi-arid (29°S–32°S) and a temperate (36°S–38°S) climatic zone. The historic annual maxima, minima and mean flows, as well as decadal mean peak flow, were compared over the period of record. The Gumbel distribution was selected to compare the 30-year flood values of two ±15-year intervals, which showed that streamflow decreased by an average of 19.5% in the semi-arid stations and increased by an average of 22.6% in the temperate stations. The Mann-Kendall test was used to investigate the temporal changes in streamflows, with negative trends being observed in 87% of the stations analysed in the semi-arid zone, and positive trends in 57% of those analysed in the temperate zone. These differences in streamflow response between climate zones could be related to recent documented increases in altitude of the zero-degree isotherm in the Andes Mountains of Chile, since most of the significant positive and negative changes were detected in first-order rivers located closer to this mountain range.

Editor D. Koutsoyiannis; Associate editor H. Lins

Citation Pizarro, R., Vera, M., Valdés, R., Helwig, B., and Olivares, C., 2013. Multi-decadal variations in annual maximum peak flows in semi-arid and temperate regions of Chile. Hydrological Sciences Journal, 59 (2), 300–311.     

Lake flooding sensitivity to the relative timing of peak flows between upstream and downstream waterways: A case study of Poyang Lake,China

The relative timing of peak flows (RTPF) from tributaries has significant influence on flood occurrence at their confluence. This study is aimed at (1) analysing the characteristics of the RTPF of the 5 recharging rivers in the Poyang Lake catchment and the Yangtze River during the period of 1960–2012, and (2) employing a physically‐based hydrodynamic model (MIKE 21) to quantify the effects of RTPF on flood behaviour in the Poyang Lake (the largest freshwater lake in China). The results show that short RTPF, or close occurrence of peak flows, triggers flood in the Poyang Lake more easily. More than 75% of total flood events in the study period occurred with RTPF less than 60 days, and more than 55% of the events occurred with RTPF less than 30 days. The hydrodynamic simulation revealed that the date of flood peak in the lake was postponed by 4–7 days and the flood stage raised by 0.69 m because of the delay of peak flows from the upstream rivers/tributaries. On the other hand, earlier start of the Yangtze River peak flow led to flood peak in the lake 6–13 days earlier. Additionally, the duration of high lake water levels was extended by 9–12 days when the RTPF shortened, and the flood hydrograph of the Poyang Lake changed from a flat to a flashy type. These results indicate that an enlarged RTPF between the upstream rivers and the Yangtze River could be an effective way to prevent flood disasters in the Poyang Lake, a method apparently being adopted in the operation of the Three Gorges Dam. The RTPF should be considered and integrated when developing flood prevention and management plans in the Poyang Lake, as well as in other similar regions in the world.     

The role of urban growth,climate change,and their interplay in altering runoff extremes

Changes in climate and urban growth are the most influential factors affecting hydrological characteristics in urban and extra‐urban contexts. The assessment of the impacts of these changes on the extreme rainfall–runoff events may have important implications on urban and extra‐urban management policies against severe events, such as floods, and on the design of hydraulic infrastructures. Understanding the effects of the interaction between climate change and urban growth on the generation of runoff extremes is the main aim of this paper. We carried out a synthetic experiment on a river catchment of 64 km² to generate hourly runoff time series under different hypothetical scenarios. We imposed a growth of the percentage of urban coverage within the basin (from 1.5% to 25%), a rise in mean temperature of 2.6 °C, and an alternatively increase/decrease in mean annual precipitation of 25%; changes in mean annual precipitation were imposed following different schemes, either changing rainstorm frequency or rainstorm intensity. The modelling framework consists of a physically based distributed hydrological model, which simulates fast and slow mechanisms of runoff generation directly connected with the impervious areas, a land‐use change model, and a weather generator. The results indicate that the peaks over threshold and the hourly annual peaks, used as hydrological indicators, are very sensitive to the rainstorm intensity. Moreover, the effects of climate changes dominate on those of urban growth determining an exacerbation of the fast runoff component in extreme events and a reduction of the slow and deep runoff component, thus limiting changes in the overall runoff.     

Assessing urban flood and drought risks under climate change,China

Risk analysis of urban flood and drought can provide useful guidance for urban rainwater management. Based on an analysis of urban climate characteristics in 2,264 Chinese cities from 1958 to 2017, this study evaluated urban flood and drought risks. The results demonstrated that the annual average values of precipitation, aridity index, frequency and intensity of extreme precipitation and extreme drought events differed significantly in these cities. The values of the above six climatic indicators in the cities ranged from 9.29–2639.30 mm, 0.47–54.73, 1.08–8.79 time, 7.82–107.25 mm, 0.76–2.99 time, and 10.30–131.19 days, respectively. The geographical patterns of urban precipitation, aridity index, intensity and frequency of extreme precipitation and drought events in China fit well to the Hu‐Huanyong Line that was created in 1940s to identify the pattern of population distribution. Extreme precipitation in most cities has upward trends, except for those around the Hu‐Huanyong Line. The extreme drought events had upward trends in the cities east of the Hu‐Huanyong Line, but there were downward trends in the cities west of the line. The risk assessment indicated that 3.80% cities were facing serious flood and 6.01% cities were facing serious drought risks, which are located in the coast of southern China and northwestern China, respectively, and other 90.19% cities were facing different types of drought and flood risks in terms of their intensity and frequency.     

On the correlation between precipitation and potential evapotranspiration climate change signals for hydrological impact analyses

State-of-the-art hydrological climate impact assessment involves ensemble approaches to address uncertainties. For precipitation, a wide range of climate model runs is available. However, for particular meteorological variables used for the calculation of potential evapotranspiration (ET_o), availability of climate model runs is limited. It is preferred that climate model runs are considered coupled when calculating changes in precipitation and ET_o amounts, in order to preserve the internal physical consistency. This results in constraints on the maximum ensemble size. In this paper, we investigate the correlation between climate change signals of precipitation and ET_o. It is found that, for two medium-sized catchments in Belgium, uncoupling climate model runs used for calculation of change signals of precipitation and ET_o amounts does not result in a significant bias for changes in extreme flow. With these results, future impact studies can be conducted with larger ensemble sizes, resulting in a more complete uncertainty estimation.     

PMP and PMF estimations in sparsely-gauged Andean basins and climate change projections

Abstract

Mixed-regime Andean basins present a complex scenario for flood analysis. In this study, we propose a methodology for incorporating orographic effects influenced by mountainous barriers in the Probable Maximum Precipitation (PMP) estimation method in sparsely-gauged basins. The proposed methodology is applied to the Puclaro Reservoir basin in Chile, which is affected by the Andes. The PMP estimations were calculated by applying statistical and hydrometeorological approaches to the baseline (1960–1999) and climate change scenarios (2045–2065) determined from projections of the ECHAM5 general circulation model. Temperature projections for the 2040–2065 period show that there would be a rise in the catchment contributing area that would lead to an increase in the average liquid precipitation over the basin. Temperature projections would also affect the maximization factors in the calculation of the PMP, as precipitable water content, raising it to 126.6% and 62.5% under scenarios A2 and B1, respectively; the probable maximum flood (PMF) would increase to +175.5% under the A2 scenario. These projections would affect the safety of dam design and would be generalizable to zones with similar mixed hydrology and climate change projections. We propose that the methodology presented could be also applied to basins with similar characteristics.

Editor Z.W. Kundzewicz; Associate editor A. Porporato     

Rain on snow induced urban floods in cold maritime climate: Risk,indicators and trends

Urban floods pose a societal and economical risk. This study evaluated the risk and hydro-meteorological conditions that cause pluvial flooding in coastal cities in a cold climate. Twenty years of insurance claims data and up to 97 years of meteorological data were analysed for Reykjavík, Iceland (64.15°N; <100 m above sea level). One third of the city's wastewater collection system is combined, and pipe grades vary from 0.5% to 10%. Results highlight semi-intensive rain (<7 mm/h; ≤3 year return period) in conjunction with snow and frozen ground as the main cause for urban flood risk in a climate which undergoes frequent snow and frost cycles (avg. 13 and 19 per season, respectively). Floods in winter were more common, more severe and affected a greater number of neighbourhoods than during summer. High runoff volumes together with debris remobilized with high winds challenged the capacity of wastewater systems regardless of their age or type (combined vs. separate). The two key determinants for the number of insurance claims were antecedent frost depth and total precipitation volume per event. Two pluvial regimes were particularly problematic: long duration (13–25 h), late peaking rain on snow (RoS), where snowmelt enhanced the runoff intensity, elongated and connected independent rainfall into a singular, more voluminous (20–76 mm) event; shorter duration (7–9 h), more intensive precipitation that evolved from snow to rain. Closely timed RoS and cooling were believed to trigger frost formation. A positive trend was detected in the average seasonal snow depth and volume of rain and snowmelt during RoS events. More emphasis, therefore, needs to be placed on designing and operating urban drainage infrastructure with regard to RoS co-acting with frozen ground. Furthermore, more detailed, routine monitoring of snow and soil conditions is important to predict RoS flood events.     

The impact of climate change on U. K. river flows: A preliminary comparison of two generations of probabilistic climate projections

The impacts of climate change on future river flows are a growing concern. Typically, impacts are simulated by driving hydrological models with climate model ensemble data. The U.K. Climate Projections 2009 (UKCP09) provided probabilistic projections, enabling a risk-based approach to decision-making under climate change. Recently, an update was released—UKCP18—so there is a need for information on how impacts may differ. The probabilistic projections from UKCP18 and UKCP09 are here applied using the change factor method with catchment-based hydrological modelling for 10 catchments across England. Projections of changes in median, mean, high, and low flows are made for the 2050s, using the A1B emissions scenario from UKCP09 and UKCP18 as well as the RCP4.5 and RCP8.5 emissions scenarios from UCKP18. The results show that, in all catchments for all flow measures, the central estimate of change under UKCP18 is similar to that from UKCP09 (A1B emissions). However, the probabilistic uncertainty ranges from UKCP18 are, in all cases, greater than from UKCP09, despite UKCP18 having a smaller ensemble size than UKCP09. Although there are differences between the central estimates of change using UKCP18 RCP4.5, RCP8.5 and A1B emissions, there is considerable overlap in the uncertainty ranges. The results suggest that existing assessments of hydrological impacts remain relevant, though it will be necessary to evaluate sensitive decisions using the latest projections. The analysis will aid development of advice to users of current guidance based on UKCP09 and help make decisions about the prioritization of further hydrological impacts work using UKCP18, which should also apply other products from UKCP18 like the 12-km regional data.     

Small forested watershed weathers effects of climate change better than a nearby urban watershed in Northern Virginia,USA

South Fork Quantico Creek (SFQ; 19.8 square kilometre (km²), forested) and Fourmile Run (4MR; 32.4-km², urban) are small watersheds in northern Virginia, United States. Precipitation and streamflow data for both watersheds were examined from water year (WY) 1952 through 2022. Temporal changes in hydrologic metrics were identified by calculating trends in annual precipitation, annual peak flow, mean daily flow, minimum daily flow, stream flashiness, and the runoff ratio. The impact of climate and urbanization on watershed hydrology was assessed by computing trends on both raw and precipitation-adjusted data. Despite increasing precipitation in both watersheds, increasing monotonic trends in most hydrologic metrics were observed only in 4MR. At 4MR, the long-term trend in annual peak flow was non-linear, thus trends were calculated on separate periods. Annual peak flow increased from WY 1952 through 1968, coinciding with a period of rapid urbanization. During WY 1969 through 1981, annual peak flows decreased, coinciding with construction of a flood channelization project. Trends for both periods were robust to precipitation adjustment. From WY 1982 through 2022, no change in the precipitation-adjusted annual peak flows occurred, suggesting annual peak flows increased due to climate factors during this period. Comparison of area-normalized hydrologic metrics between the two watersheds revealed higher flows in 4MR than SFQ across all flows, not just high flows. Runoff ratio and stream flashiness also were higher in 4MR. Differences in hydrologic metrics between the two watersheds were driven primarily by differences in land use, land cover, and modifications to the water balance related to urbanization. Climate change has altered watershed hydrology at both sites, but extensive urbanization in 4MR has altered the hydrology more than that of SFQ. We conclude that urban watersheds are likely at greater risk of increased flooding than less developed areas as the climate intensifies.     

Impacts of climate change on water resources in the Mediterranean Basin: a case study in Catalonia,Spain

Abstract

Most climate change projections show important decreases in water availability in the Mediterranean region by the end of this century. We assess those main climate change impacts on water resources in three medium-sized catchments with varying climatic conditions in northeastern Spain. A combination of hydrological modelling and climate projections with B1 and A2 IPCC emission scenarios is performed to infer future streamflows. The largest reduction (34%) in mean streamflows (for 2076–2100) is expected in the headwaters of the two wettest catchments, while lower decreases (25% of mean value for 2076–2100) are expected in the drier one. In all three catchments, autumn and summer are the seasons with the most notable projected decreases in streamflow, of 50% and 30%, respectively. Thus, ecological flows in the study area might be noticeably influenced by climate change, especially in the headwaters of the wet catchments.     

The impact of climate change on extreme precipitation in Sicily,Italy

Increasing precipitation extremes are one of the possible consequences of a warmer climate. These may exceed the capacity of urban drainage systems, and thus impact the urban environment. Because short‐duration precipitation events are primarily responsible for flooding in urban systems, it is important to assess the response of extreme precipitation at hourly (or sub‐hourly) scales to a warming climate. This study aims to evaluate the projected changes in extreme rainfall events across the region of Sicily (Italy) and, for two urban areas, to assess possible changes in Depth‐Duration‐Frequency (DDF) curves. We used Regional Climate Model outputs from Coordinated Regional Climate Downscaling Experiment for Europe area ensemble simulations at a ~12 km spatial resolution, for the current period and 2 future horizons under the Representative Concentration Pathways 8.5 scenario. Extreme events at the daily scale were first investigated by comparing the quantiles estimated from rain gauge observations and Regional Climate Model outputs. Second, we implemented a temporal downscaling approach to estimate rainfall for sub‐daily durations from the modelled daily precipitation, and, lastly, we analysed future projections at daily and sub‐daily scales. A frequency distribution was fitted to annual maxima time series for the sub‐daily durations to derive the DDF curves for 2 future time horizons and the 2 urban areas. The overall results showed a raising of the growth curves for the future horizons, indicating an increase in the intensity of extreme precipitation, especially for the shortest durations. The DDF curves highlight a general increase of extreme quantiles for the 2 urban areas, thus underlining the risk of failure of the existing urban drainage systems under more severe events.     

A study on the impact of climate change on streamflow at the watershed scale in the humid tropics

Abstract

Climate change is recognized to be one of the most serious challenges facing mankind today. Driven by anthropogenic activities, it is known to be a direct threat to our food and water supplies and an indirect threat to world security. Increase in the concentration of carbon dioxide and other greenhouse gases in the atmosphere will certainly affect hydrological regimes. The consequent global warming is expected to have major implications on water resources management. The objective of this research is to present a general approach for evaluating the impacts of potential climate change on streamflow in a river basin in the humid tropical zone of India. Large-scale global climate models (GCMs) are the best available tools to provide estimates of the effect of rising greenhouse gases on rainfall and temperature. However the spatial resolution of these models (250 km?×?250 km) is not compatible with that of watershed hydrological models. Hence the outputs from GCMs have to be downscaled using regional climate models (RCMs), so as to project the output of a GCM to a finer resolution (50 km?×?50 km). In the present work, the projections of a GCM for two scenarios, A2 and B2 are downscaled by a RCM to project future climate in a watershed. Projections for two important climate variables, viz. rainfall and temperature are made. These are then used as inputs for a physically-based hydrological model, SWAT, in order to evaluate the effect of climate change on streamflow and vegetative growth in a humid tropical watershed.

Citation Raneesh, K. Y. & Santosh, G. T. (2011) A study on the impact of climate change on streamflow at the watershed scale in the humid tropics. Hydrol. Sci. J. 56(6), 946–965.     

The impact of climate change on water fluxes in a Macaronesian cloud forest

Fog phenomena and their associated meteorological variables were continuously monitored during 4 years in an evergreen laurisilva cloud forest of the Anaga Massif Biosphere Reserve (Tenerife, Canary Islands), in order to establish its current dynamics. Fog was more frequent during night through early morning and in the afternoon, and particularly from May until September, coincidental with a frequent immersion of the 1025 m a.s.l. experimental site in the cloud layer of wind‐driven stratocumulus. The concomitant meteorological conditions during different fog regimes, characterized according to visibility (Ω) ranges, were compared with those when fog was absent. The presence of fog was associated with a significant reduction in global solar radiation, R_g, increased wind speed, and lower and more stable ambient temperatures. The foggy versus fog‐free hourly medians of R_g were found to be linearly related, whereas the proportion of median R_g reduction due to fog varied logarithmically with Ω. However, foggy versus fog‐free extreme values of the hourly R_g distributions departed from such a linear trend. By contrast, hourly temperatures during foggy versus fog‐free periods behaved linearly for most of the Ω range, except for very dense fog, Ω ≤ 100 m. Transpiration of the canopy, intermittently wetted due to interception of both rain and fog water droplets, was determined by quantifying the water balance at leaf scale with a mathematical model for the two representative hypostomatous species present at the site: the arboreal shrub Erica platycodon, with needle‐like leaves, and the laurophyll tree Myrica faya. Both tree transpiration and evaporation of the intercepted fog water were predictively higher during summer. By contrast, transpiration was reduced during February, in agreement with a 1 year period of sap velocity measurements, and was not appreciably affected by soil moisture content. The consequences of an anticipated downward shift of the stratocumulus cloud layer and of various projected Representative Concentration Pathways (RCPs) scenarios in the Macaronesian area were simulated, yielding in all cases a significant rise in transpiration for both species. Particularly, the simulated RCPs scenarios implied 29%–73% increments in transpiration from the actual values. Because fog is concomitant with lower temperatures and vapour pressure deficit, the modification of its current distribution as a consequence of climate change may have a direct effect on such associated meteorological variables, and therefore a meaningful impact in the water relations of the laurel cloud forests.     

Impact of a CO2-induced climatic change on river flow variability in three rivers in Belgium

A hydrological conceptual model developed by the Royal Meteorological Institute of Belgium has been run to assess the potential hydrological impacts of an hypothetical doubling of the atmospheric CO₂ concentration. The simulated scenarios were derived from the predictions of climatic change currently provided by General Circulation Models (GCMs). Three typical drainage basins in Belgium have been selected for assessing their common responses and bringing out possible specific behaviours attributable to catchment characteristics. The study dealt essentially with modifications of the streamflow and with alterations of the flood and low-flow regimes. In catchments with prevailing surface flow the considered change in climate could induce:

• An increase in flood frequencies during the winter season together with a strengthening of the extreme river stages leading to greater flooding risks;
• A decrease in streamflow during the summer season and, as a corollary, increased risks of water pollution;
• Possible restraints, in summer and autumn, on water availability from local groundwater storages.

In catchments with high infiltration rate and with strong aquifer the impact could be:

• An increase in groundwater storage, bringing about an increase in the base flow throughout the year, which in turn involves increased flood risks;
• A reduction of the number of low-stage occurrences in summer, resulting in reduced river pollution;
• A possible increase in water availability from the aquifers.

     

Changes in low and high flows in the Vistula and the Odra basins: Model projections in the European‐scale context

A number of extensive droughts and destructive floods have occurred in Poland in the last 25 years; hence, projections of low and high river flows are of considerable interest and importance. In the first part of this paper, projections of low and high flows in the rivers of the Vistula and the Odra basins (VOB region), for two future time horizons, are presented. Projections are based on the Soil and Water Assessment Tool (SWAT) hydrological model simulations driven by results of the EURO‐CORDEX experiment under Representative Concentration Pathways 4.5 and 8.5. The VOB region covers most of Poland and parts of five neighboring countries, giving this study an international relevance. In the second part of the paper, a review of projections of low and high flows in rivers in Central and Eastern Europe is presented. Despite a substantial spread of flow projections, the main message of the modelling part is that increases of both low and high flows are dominating. The magnitude of increase of low flow is considerably higher than that of high flow. In other words, future streamflow droughts are projected to be less severe, whereas, in contrast, river floods are projected to increase, which is a challenge for flood risk reduction, water management, and climate change adaptation. There is an overall agreement of our findings for the VOB region with projections of hydrological extremes from large‐scale models forced by EURO‐CORDEX results in the European‐scale studies.