Long-term climate change and increased frequency and intensity of hydroclimatic extremes (e.g. droughts, heatwaves, floods) pose serious challenges for water management, not only in terms of water quantity, but also for securing suitable water quality for human use and ecosystems. Recent droughts, heatwaves and floods have been illustrative in showing major challenges due to exceeded water quality thresholds for sectoral use (e.g. inlet stops for drinking water production, irrigation). However, compared to water quantity, a limited number of studies have focused on water quality impacts, which are prevalent in many river basins of the world.

This presentation provides a synthesis of the potential impacts of climate change and extremes (droughts, heatwaves and floods) on global river water quality considering various water quality constituents relevant for different sectoral uses and ecosystems. This synthesis is based on: 1) an extensive literature review of local, regional to global river water quality studies; 2) statistical analyses of water quality monitoring data in various river basins over the last 40 years; and 3) global river water quality projections generated by process-based global water quality models forced with bias-corrected climate change scenarios. Comparison of results over various river basins show overall consistent responses for some general water quality constituents (e.g. water temperature, dissolved oxygen, salinity) due to the predominance of generic mechanisms (e.g. lower dissolved oxygen solubility under warming). However, mixed responses are overall found for nutrients, pathogens and pharmaceuticals due to different counterbalancing mechanisms. In addition, water quality responses vary due to differences in constituent forms (e.g. dissolved vs. particulate nutrient forms) and persistence in surface waters (e.g. for pharmaceuticals). Furthermore, geographic, environmental and socio-economic (e.g. pollution management and infrastructure) conditions conspire, showing substantial impacts on the magnitude of water quality responses under climatic change and extreme events.

How to cite: van Vliet, M. T. H.: River water quality under climate change and extremes: a synthesis of impacts for river basins globally (Invited), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2361, https://doi.org/10.5194/egusphere-egu23-2361, 2023.

The European Union has adopted an ambitious long-term, zero pollution vision for 2050  aiming for EU’s  “air, water and soil pollution to be reduced to levels no longer considered harmful to health and natural ecosystems …” [1]. However, the extent to which such a goal can be realistically realized for legacy contaminants like nitrogen (N) is not yet properly understood. Herein, we provide a comprehensive assessment of nitrogen retention and export across the European landscapes to receiving waterbodies using a suite of climate, hydrology, and future socioeconomic scenarios. We establish a chain of hydroclimate and nitrogen export scenarios, comprising climate simulations from global climate models (CMIP) under different emission pathways (RCPs) and shared socioeconomic pathways (SSPs) to force a coupled hydrology and water quality model (mHM-N [2]) that characterizes the N retention and export dynamics over the period 1971-2070. SSPs consider balancing options for agricultural land management and technical innovations, taking into account future food, economic growth, and environmental demands; and provide N input trajectories from both diffuse (agricultural) and point (wastewater) sources. Our analysis shows a higher degree of improvement with substantially lower N levels in all European surface water bodies by the 2050s, compared to current levels (2010s). Eastern European rivers may benefit from technological improvements by reducing point source inputs, while in the Western European region, lower N levels can be noticed due to a reduction in diffuse N inputs. Despite these improvements, there are areas of concern where some European water bodies may still suffer from N levels exceeding critical thresholds (e.g., 2-3 mg N/l) in 2050. This may be related to continued N exports that slowly deplete legacy storages (e.g., soil and groundwater). Overall, this requires more proactive measures, particularly aiming at reducing N inputs while harvesting/utilizing and attenuating the built-up storage, to achieve the zero-pollution goal.

References

[1] https://environment.ec.europa.eu/strategy/zero-pollution-action-plan_en

[2] https://doi.org/10.1029/2008WR007327; https://doi.org/10.1029/2022GL100278

How to cite: Kumar, R., V. Nguyen, T., J. Sarrazin, F., Ebeling, P., Schmidt, C., Beusen, A., Bouwman, L., H. Fleckenstein, J., Attinger, S., and Musolff, A.: Towards realizing the EU 2050 Zero Pollution Vision for Nitrogen Export, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12024, https://doi.org/10.5194/egusphere-egu23-12024, 2023.

Deforestation is currently a widespread phenomenon and a growing environmental
concern in the era of rapid climate change. In temperate regions, it is challenging to
quantify the impacts of deforestation on the catchment dynamics and downstream
aquatic ecosystems such as reservoirs and disentangle these from direct climate
change impacts, let alone project future changes to inform management. Here, we
tackled this issue by investigating a unique catchment-reservoir system with two
reservoirs in distinct trophic states (meso- and eutrophic), both of which drain into the
largest drinking water reservoir in Germany. Due to the prolonged droughts in 2015-
2018, the catchment of the mesotrophic reservoir lost an unprecedented area of forest
(exponential increase since 2015 and ca. 17.1% loss in 2020 alone). We coupled
catchment nutrient exports (HYPE) and reservoir ecosystem dynamics (GOTM-WET)
models using a process-based modelling approach. The coupled model was validated
with datasets spanning periods of rapid deforestation, which makes our future
projections highly robust. Results show that in a short-term time scale (by 2035),
increasing nutrient flux from the catchment due to vast deforestation (80% loss) can
turn the mesotrophic reservoir into a eutrophic state as its counterpart. Our results
emphasize the more prominent impacts of deforestation than the direct impact of
climate warming in impairment of water quality and ecological services to downstream
aquatic ecosystems. Therefore, we propose to evaluate the impact of climate change
on temperate reservoirs by incorporating a time scale-dependent context, highlighting
the indirect impact of deforestation in the short-term scale. In the long-term scale (e.g.
to 2100), a guiding hypothesis for future research may be that indirect effects (e.g., as
mediated by catchment dynamics) are as important as the direct effects of climate
warming on aquatic ecosystems.

How to cite: Rode, M., Kong, X., Ghaffa, S., Determann, M., Friese, K., Jomaa, S., Mi, C., Shatwell, T., and Rinke, K.: Reservoir water quality deterioration due to deforestation emphasizes the indirect effects of global change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5239, https://doi.org/10.5194/egusphere-egu23-5239, 2023.

Both discharge (Q) and stream temperature (Tw) are the key factors affecting water quality and the suitability of instream habitats, which are expected to experience substantial evolutions due to climate change. However, the absence of continuous and long-term data of Tw at a large scale limits our understanding of the spatio-temporal variations of Tw and their control factors, like riparian vegetation, strahler order, hydroclimate.

The present study used a physically-based thermal model (T-NET), coupled with a semi-distributed hydrological model (EROS) using SAFRAN meteorological reanalysis data provided of Météo-France to reconstruct past daily Q and Tw over the 1963-2019 period for 52 000 hydrographic reaches of the Loire basin (100 000 km²), France. Three regionalized climate projections under several future emissions scenarios (available on the DRIAS portal: www.drias-climat.fr) were used to project future daily time series of these variables over the 2005-2100 period.

The results over the 1963-2019 period showed that the increase of the Tw was higher than those air temperature (Ta) in spring, summer and autumn for the majority of the reaches of the basin. Indeed, Tw increased for almost all reaches and all seasons (average = +0.38°C/decade) with the largest increase in the spring (Mar-May) (range=+0.11 to +0.76°C per decade) and in summer (Jun-Aug) (+0.08 to +1.02°C per decade). Highest spring and summer increases were generally found in the south of the basin (Massif Central and Limousin plateau) and in higher Strahler order where a larger increase in Ta (up to 0.67 °C/decade) and a larger decrease in Q (up to -16%/decade) occurred jointly.  

Depending on climate models, scenarios and seasons,future projections showed changes in seasonal flow and water temperature. Seasonal median flow over the basin would be between -40% and +35% for the middle of the 21st century (2040-2079) compared to the 1990-2019 period. For the end of the century (2070-2099), flow change would be between -53% and +73%. A clear increase in future Tw was also found with seasonal  median increases of +0.7 to +2.7°C in the middle (2040-2079) and of +0.8°C to +5.0°C,  at the end of the century (2070-2099).

These climate-induced changes in Q and Tw could help us to explain shifts in the phenology and geographical distribution of cold-water species. Moreover, they highlight that we should take vital actions for both adaptation and mitigation strategies. In this regard, we found that some of these climate change-induced impacts on Tw can be mitigated through the restoration and maintenance of riparian shading specially in small streams.

How to cite: Moatar, F., Seyedhashemi, H., Vidal, J.-P., Diamond, J., Thiery, D., Hendrickx, F., and Maire, A.: Evolution of discharge and stream temperature from past to future in a large European River basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7683, https://doi.org/10.5194/egusphere-egu23-7683, 2023.

Precipitation is one of the essential driving factors of natural processes influencing the structure and functioning of river catchment ecosystems. Changes in precipitation conditions have a significant impact on surface runoff and consequently the intensity of sediment transport, and its deposition especially in mountain catchments exposed to frequent rainfalls and prone to erosion. Therefore, insightful information about future precipitation regional projections seems to be crucial for ecosystem services management, including dammed reservoirs and fresh water resources.

In general, precipitation is projected to change its annual structure over Central Europe in relation to enhanced atmospheric moisture, moisture convergence and extratropical cyclone activity. Although new generations of climate models focus on improved simulation of water cycle, precipitation projections still become a challenge as key processes driving precipitation changes at local and hemispheric scale remain significantly sensitive to model resolution.

The aim of the study is to indicate the differences between particular precipitation projections for the exemplary Carpathian mountains catchment (Raba River, Poland) and their further evaluation   towards the impact of the chosen climate model on the environmental modelling results (sediment load variability). The outcomes of High Resolution Model Intercomparison Project (HighResMIP) - CMIP6 and higher-resolution regional data for Europe from the Coordinated Regional Climate Downscaling Experiment (EURO-CORDEX) will be taken into account. Absolute and relative changes in annual precipitation structure will be examined for the whole period of 2026-2100 with short-term (2026-2050) and long-term (2051-2100) perspectives.

The research conducted so far revealed that both sediment yields from the exemplary catchment and the sediment loads from the studied river could be greatly altered due to the predicted changes in precipitation and temperature. Since such changes can have a pronounced impact on vital ecological processes ongoing in the catchment the utmost attention should be paid to assessment of differences between climate change scenarios applied in such studies. 

How to cite: Wypych, A., Wilk, P., Szalińska, E., and Orlińska-Woźniak, P.: Precipitation driven river catchment changes - how the climate models determine the results (the example from Polish Carpathians), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14799, https://doi.org/10.5194/egusphere-egu23-14799, 2023.

This presentation reports on the results of simulating 17 regulatory SIMCAT water quality models for England based on using the CEH Future Flows dataset. The de-biased uplifts were generated across 140 flow gauges comparing 2060-2080 with 2000-2020 for 11 ensembles, and kriged across the country to capture the gradients and apply river reach-specific uplifts in headwater and along-reach flows (for mean and 95 percentile exceedance flows). The resulting uplifts were applied using a recently developed UKWIR workbook and the statistical water quality models were simulated for a range of sanitary and chemical determinands (BOD, ammonia, dissolved oxygen, total and soluble phosphorus, nitrate, PFOS, cadmium and cypermethrin) to assess the potential change to Sewage Treatment Work permits.

Failure of target EQS and 10% deterioration of quality are analysed, computing the necessary adjustment to water quality permits to meet the water quality standards in the future. Ensemble uplifts representative of upper, lower and mid flows were used (focussing on the low flows) and their predicted annual average reduction. The sensitivity of the results to travel time, seasonality and temperature are investigated, and outputs are compared with recent process-based modelling using the EA HYPE model of England.

How to cite: Hankin, B., Heaney, T., Eccleston, P., Simmons, P., Garratt, A., and Wang, C.: Stress testing the impacts of climate change on water quality permitting across England, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6793, https://doi.org/10.5194/egusphere-egu23-6793, 2023.

Human activities greatly impact surface water quality due to the emission of various pollutants associated with different water use sectors (e.g. irrigation, livestock, domestic, energy and manufacturing)^1,2. In-stream concentrations are also strongly dependent on the dilution capacity of receiving waters, which is related to both the hydrological regime and surface water abstractions. Pollutant emissions, hydrological regimes and surface water abstractions are all projected to change into the future as a result of both (uncertain) climate change and socio-economic developments. Yet, quantitative projections of future surface water quality are sparse, particularly at the global scale.

In this work, we apply a new high-resolution global surface water quality model (DynQual)³ to project water temperature (Tw) and total dissolved solids (TDS), biological oxygen demand (BOD) and fecal coliform (FC) concentrations for the time period 2005-2100, considering multiple scenarios that combine Representative Concentration Pathways (RCPs) with Shared-Socioeconomic Pathways (SSPs). Input from five general circulation models (GCMs) is used to force PCR-GLOBWB2, the hydrological model coupled to DynQual, to account for the large range of uncertainties inherent in the climatological projections.

The mechanisms that drive patterns in future surface water quality are a complex balance between changes in pollutant emissions, the dilution capacity of streams and in-stream decay processes, which are strongly driven by water temperature, under global change. Patterns of both water quality improvement and deterioration exist, which vary greatly across world regions. Reductions in pollutant emissions across most of Western Europe, North America and East Asia drive trends towards surface water quality improvements, irrespective of climate and socio-economic scenario. Conversely, developing countries are more sensitive to (uncertain) climate and socio-economic changes, with surface water quality typically improving under SSP1-RCP2.6, a mixed response under SSP5-RCP8.5 and strong degradation under SSP3-RCP7.0. Changes to the hydrological cycle are particularly important for surface water quality in the Amazon basin, with substantial reductions in discharge projected under SSP3-RCP7.0 and SSP5-RCP8.5. These changes result in reduced dilution capacities of rivers and thus higher in-stream concentrations, for instance of TDS.

Surface water quality deterioration occurs across Sub-Saharan Africa under all scenarios, albeit to different magnitudes, which substantially increases the number of people that are exposed to poor water quality. Under SSP3-RCP7.0, the “worst-case” scenario for all constituents considered in our study, 4.2 billion people will be exposed to surface water with unsafe levels of organic (BOD) pollution by 2100. With 1.5 billion (36%) of these people located in Sub-Saharan Africa, compared to 290 million (11%) in the historical reference period, we conclude that Sub-Saharan Africa will become the new hotspot of water quality issues.  

References

1. Jones, E. R. et al. Current wastewater treatment targets are insufficient to protect surface water quality. Communications Earth & Environment 3, 221, doi:10.1038/s43247-022-00554-y (2022).

2. van Vliet, M. T. H. et al. Global water scarcity including surface water quality and expansions of clean water technologies. Environmental Research Letters 16, 024020, doi:10.1088/1748-9326/abbfc3 (2021).

3. Jones, E. R. et al. DynQual v1.0: A high-resolution global surface water quality model. Geosci. Model Dev. Discuss. 2022, 1-24, doi:10.5194/gmd-2022-222 (2022).

How to cite: Jones, E. R., Bierkens, M. F. P., van Puijenbroek, P. J. T. M., and van Vliet, M. T. H.: Modelling global surface water quality under uncertain climate and socio-economic change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1161, https://doi.org/10.5194/egusphere-egu23-1161, 2023.

Current multi-stressor pressures on water quality in agricultural catchments will be exacerbated by the more frequent occurrence of extreme weather events resulting in multi-stressor environments. Managing surface water under future climatic conditions will require adaptations and targeted mitigation strategies that consider individual catchment characteristics. Assessing the impacts of recent extreme weather events can allow for the better understanding of, and insight into, the key drivers of elevated pollutant losses and point to the possible future challenges for water quality management.

As a part of the Irish EPA funded WaterFutures project, changes in the impact of climatic drivers on nutrient losses from field to small stream scale catchments of different typologies are being investigated using long-term and high-frequency water quality datasets. The trends of daily nitrate-N, and phosphorus (TP) concentrations and loads over 11 years were interrogated in two agriculturally-dominated catchments in Ireland, and in both a permanent pasture and arable field in the southwest UK (ca. 0.38– 12 km²). The trends in nutrient losses and the significance of discharge, precipitation, potential evapotranspiration (PET), soil moisture deficit, air temperature, and soil temperature, were investigated using Mann-Kendall Trend and Generalised Additive Model, respectively.

Significant inter-seasonal trends were identified in both countries and similar fluctuations of nutrient concentrations and loads in October and November 2018 were observed following an exceptional summer drought. All study sites responded to daily rainfall exceeding 10mm, although in different ways due to the different site characteristics. The soil and air temperature in the two geographically-close Irish catchments revealed a significant upward trend from June to September. During this period, these two drivers, along with discharge and PET, were key drivers of N-losses in the well-drained and arable dominated catchment. The increasing trend of monthly average N-concentrations were significant in April and November (from 5.6 in 2009 to 8.9 nitrate-N mg L^-1 in 2018, Kendall-tau= 0.424). On the other hand, a catchment dominated by poorly-drained grassland showed an increasing trend in TP concentrations during January, May, September, and October (from 0.79 in 2009 to 6.72 TP mg L^-1 in 2020, Kendall-tau= 0.455). Here, changes in air temperature, precipitation, and discharge were the key drivers for P losses.

Changing weather patterns, consequent changes in nutrient concentrations and load trends, and precipitation-discharge responses can be detected using long-term water quality records and should be considered for future climate smart mitigation strategies.

How to cite: Ezzati, G., Mellander, P.-E., Pulley, S., and Collins, A.: Drivers and inter-seasonal trends of nutrient losses from contrasting agricultural river catchments in Ireland and UK, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1994, https://doi.org/10.5194/egusphere-egu23-1994, 2023.

Lake chlorophyll-a (Chl-a) is one of the important components of the lake ecosystem. The Chl-a concentration of global water has generally increased in recent decades due to climate change and intensified anthropogenic activity. However, few researches have been done on the lake Chl-a variations in remote areas with less disturbance by human activities such as the Tibet Plateau (TP). Here, we combined 95 in situ measured lake Chl-a concentration data and Landsat reflection spectrum to establish an inversion model of Chl-a concentration through the backpropagation (BP) neural network prediction method, by which the mean annual Chl-a concentration in the past 35 years (1986–2021) of 318 lakes with an area of > 10 km² in the TP have been retrieved. Meteorological and hydrological data, measured water quality parameters and glacier change in the lake basin were used to elucidate the driving factors of the Chl-a concentration changes in the TP lakes, with the help of geographic information system (GIS) technology and by spatial statistical analysis. The results showed that the mean annual Chl-a in the 318 lakes performed overall decrease during 1986-2021, but 63%, 32% and 5% of the total number exhibited no significant change, significant decrease and significant increase, respectively. After a slight increase during 1986–1995 (0.05 μg/L/y), the mean annual lake Chl-a significantly decreased during 1995–2004 (–0.18 μg/L/y). Further, after a slight increase during 2004–2011 (0.07 μg/L/y), it decreased slightly during 2011–2021 (–0.04 μg/L/y). The mean annual lake Chl-a concentration was significantly negatively correlated with precipitation (R² = 0.48, P < 0.01), air temperature (R²= 0.31, P < 0.01), lake surface water temperature (LSWT) (R² = 0.51, P < 0.01), lake area (R²= 0.42, P < 0.01) and lake water volume change (R² = 0.77, P < 0.01). The decrease in mean annual Chl-a was in consistant to the decrease in that of salinity (R²= 0.69, P < 0.01) and increase in that of transparency (R²= 0.55, P < 0.01). The Chl-a concentrations of non-glacial meltwater-fed lakes were higher than those of glacial meltwater-fed lakes, except during higher precipitation period. Our result of lake Chl-a inversion and their variation reason analyses is able to further deeply understand the climate change impacts on Chl-a changes in the TP lakes.

How to cite: Zhu, L., Pang, S., Liu, C., and Ju, J.: The decreasing Chlorophyll-a in Tibet Plateau lakes during 1986–2021 based on Landsat image inversion and their impact causes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6888, https://doi.org/10.5194/egusphere-egu23-6888, 2023.