Quantification of the hydrological consequences of climate change in a typical West African catchment using flow duration curves

The quantification of the consequences of climate change (CC) on the hydrology of the West Africa region was performed using a validated Hydrologiska Byrans Vattenbalansavdelning hydrological model and regional climate models which was driven by different general circulation models (GCMs) from the Coordinated Regional Downscaling Experiment (CORDEX) and the Regional Climate Division of the Institute of Meteorology and Climate Research at Karlsruhe Institute of Technology (IMK-IFU). The quantile mapping and linear-scaling bias adjustment methods were used to correct the inherent errors in the climate simulations. Flow duration curves (FDCs) and generic annual discharge cycles were used in determining the impacts of the change on hydrology (river flow) in the Black Volta catchment within the subregion. It was found out that, in the first segment of the FDCs representing high flows, there was a slight increase in the future flow characterizing a higher watershed water yield from high rainfall events in the future. The 10–40% exceedance probabilities of flow representing wet conditions; 40–60% relating to mid-range flows; 60–90% representing dry period conditions; and low flows (90–100%) all show a decrease in the future flows for four out of the five GCM driving models. Most worrying is the reduction in flows for the 90–100% exceedance probabilities in the future relating to the sustainability of streamflow in the long term. It was concluded that CC could negatively impact and decrease the hydrology of the subregion in the future with most of the rivers in the catchment running dry in most months of the annual discharge cycle.

Stream discharge depends more on the temporal distribution of water inputs than on yearly snowfall fractions for a headwater catchment at the rain-snow transition zone

Climate warming affects snowfall fractions and snowpack storage, displaces the rain-snow transition zone towards higher elevations, and impacts discharge timing and magnitude as well as low-flow patterns. However, it remains unknown how variations in the spatial and temporal distribution of precipitation at the rain-snow transition zone affect discharge. To investigate this, we used observations from eleven weather stations and snow depths measured in one aerial lidar survey to force a spatially distributed snowpack model (iSnobal/Automated Water Supply Model) in a semi-arid, 1.8 km2 headwater catchment at the rain-snow transition zone. We focused on surface water inputs (SWI; the summation of rainfall and snowmelt) for four years with contrasting climatological conditions (wet, dry, rainy and snowy) and compared simulated SWI to measured discharge. We obtained a strong spatial agreement between snow depth from the lidar survey and model (r2: 0.88), and a median Nash-Sutcliffe Efficiency (NSE) of 0.65 for simulated and measured snow depths for all modelled years (0.75 for normalized snow depths). The spatial pattern of SWI was consistent between the four years, with north-facing slopes producing 1.09 to 1.25 times more SWI than south-facing slopes, and snow drifts producing up to six times more SWI than the catchment average. We found that discharge in a snowy year was almost twice as high as in a rainy year, despite similar SWI. However, years with a lower snowfall fraction did not always have lower annual discharge nor earlier stream drying. Instead, we found that the dry-out date at the catchment outlet was positively correlated to the snowpack melt-out date. These results highlight the heterogeneity of SWI at the rain-snow transition zone and emphasize the need for spatially distributed modelling or monitoring of both the snowpack and rainfall.

SPECIFIC FEATURES OF FLOW FORMATION AND WATER USE IN THE CATCHMENT AREAS IN THE TOBOL RIVER BASIN

On the basis of long-term information and analytical materials of the RSU Tobyl-Torgai Basin Inspectorate for Regulation of the Use and Protection of Water Resources of the Water Resources Committee of the Ministry of Agriculture of the Republic of Kazakhstan, characterizing the use of water resources in the economic sectors of administrative districts and cities of the Kostanay region, the conditions for the formation of surface flow and regional features of water use in the catchments of the Tobol river basin were determined.To assess the change in the average annual discharge in the catchments of the Tobol River basin under the influence of natural and anthropogenic activities, integral curves of average annual discharge were determined for the hydrological stations of Akkarga, Grishenka, Kostanay, and Milyutinka, which showed that in the period under consideration from 1996 to 2005, there was a slight increase in the average annual discharge for all hydrological stations under consideration, and from 2006 to 2017 - their constant decline, which is a signal to ensure the safety of economic activities in the region. To assess the peculiarities of water use in the catchments of the Tobol River basin, the volumes of water consumption by housing and public services, industry and agriculture were used, which gradually decrease over the period of 1996-2016, since the industry is mainly located in the cities of Lisakovsk, Kostanay and Rudny. and agriculture in Kamystinsky, Zhitikarinsky, Denisovsky, Taranovsky, Kostanaysky, Karabalyksky, Fedorovsky and Mendikarinsky districts is developing within the dryland cultivation, which determines the type of linear trend, which is characterized by a polynomial equation of third order.

Long-Term Runoff Variability Analysis of Rivers in the Danube Basin

The long-term runoff variability is identified to consist of the selected large rivers with long-term data series in the Danube River Basin. The rivers were selected in different regions of the Danube River Basin and have a large basin area (Danube: Bratislava gauge with 131,338 km2; Tisza: Senta with 141,715 km2; and Sava: Sremska Mitrovica with 87,966 km2). We worked with the station Danube: Reni in the delta as well. A spectral analysis was used to identify the long-term variability of three different types of time series: (1) Average annual discharge time series, (2) Minimum annual discharge time series and (3) Maximum annual discharge time series. The results of the study can be used in a long-term forecast of the runoff regime in the future.

Glacio-Nival Regime Creates Complex Relationships between Discharge and Climatic Trends of Zackenberg River, Greenland (1996–2019)

Arctic environments experience rapid climatic changes as air temperatures are rising and precipitation is increasing. Rivers are key elements in these regions since they drain vast land areas and thereby reflect various climatic signals. Zackenberg River in northeast Greenland provides a unique opportunity to study climatic influences on discharge, as the river is not connected to the Greenland ice sheet. The study aims to explain discharge patterns between 1996 and 2019 and analyse the discharge for correlations to variations in air temperature and both solid and liquid precipitation. The results reveal no trend in the annual discharge. A lengthening of the discharge period is characterised by a later freeze-up and extreme discharge peaks are observed almost yearly between 2005 and 2017. A positive correlation exists between the length of the discharge period and the Thawing Degree Days (r=0.52,p<0.01), and between the total annual discharge and the annual maximum snow depth (r=0.48,p=0.02). Thereby, snowmelt provides the main source of discharge in the first part of the runoff season. However, the influence of precipitation on discharge could not be fully identified, because of uncertainties in the data and possible delays in the hydrological system. This calls for further studies on the relationship between discharge and precipitation. The discharge patterns are also influenced by meltwater from the A.P. Olsen ice cap and an adjacent glacier-dammed lake which releases outburst floods. Hence, this mixed hydrological regime causes different relationships between the discharge and climatic trends when compared to most Arctic rivers.

Alkalinization Scenarios in the Mediterranean Sea for Efficient Removal of Atmospheric CO2 and the Mitigation of Ocean Acidification

It is now widely recognized that in order to reach the target of limiting global warming to well below 2°C above pre-industrial levels (as the objective of the Paris agreement), cutting the carbon emissions even at an unprecedented pace will not be sufficient, but there is the need for development and implementation of active Carbon Dioxide Removal (CDR) strategies. Among the CDR strategies that currently exist, relatively few studies have assessed the mitigation capacity of ocean-based Negative Emission Technologies (NET) and the feasibility of their implementation on a larger scale to support efficient implementation strategies of CDR. This study investigates the case of ocean alkalinization, which has the additional potential of contrasting the ongoing acidification resulting from increased uptake of atmospheric CO2 by the seas. More specifically, we present an analysis of marine alkalinization applied to the Mediterranean Sea taking into consideration the regional characteristics of the basin. Rather than using idealized spatially homogenous scenarios of alkalinization as done in previous studies, which are practically hard to implement, we use a set of numerical simulations of alkalinization based on current shipping routes to quantitatively assess the alkalinization efficiency via a coupled physical-biogeochemical model (NEMO-BFM) for the Mediterranean Sea at 1/16° horizontal resolution (~6 km) under an RCP4.5 scenario over the next decades. Simulations suggest the potential of nearly doubling the carbon-dioxide uptake rate of the Mediterranean Sea after 30 years of alkalinization, and of neutralizing the mean surface acidification trend of the baseline scenario without alkalinization over the same time span. These levels are achieved via two different alkalinization strategies that are technically feasible using the current network of cargo and tanker ships: a first approach applying annual discharge of 200 Mt Ca(OH)2 constant over the alkalinization period and a second approach with gradually increasing discharge proportional to the surface pH trend of the baseline scenario, reaching similar amounts of annual discharge by the end of the alkalinization period. We demonstrate that the latter approach allows to stabilize the mean surface pH at present day values and substantially increase the potential to counteract acidification relative to the alkalinity added, while the carbon uptake efficiency (mole of CO2 absorbed by the ocean per mole of alkalinity added) is only marginally reduced. Nevertheless, significant local alterations of the surface pH persist, calling for an investigation of the physiological and ecological implications of the extent of these alterations to the carbonate system in the short to medium term in order to support a safe, sustainable application of this CDR implementation.

Estimating peak water in glaciated basins: the importance of scale, process, and terminology

&lt;p&gt;Peak water is a concept that is increasingly used to describe a tipping point in time for glaciated drainage basins, where annual discharge reaches a maximum and thereafter is in continual decline. Millions of people across the globe depend on glacial meltwater, especially in regions such as the Himalayas and the Andes, and therefore current and future changes in meltwater generated flow and downstream water availability are important for society and ecosystem services. Due to the long-term negative consequence of glacier retreat on freshwater resources, peak water in glaciated basins has received more attention in recent years. Using an example case study from the Peruvian Andes, we highlight crucial considerations around scale, process, and terminology when measuring, modelling, and communicating peak water in glaciated basins. Through the application of commonly used peak water calculation methods, we explore the influence of these considerations on the estimation of peak water timing. One such consideration is the processes affecting discharge aside from direct glacial melt, such as catchment storage (aquifers, wetlands, lakes), precipitation, and human activities. In our example case study of the Rio Santa basin in Peru, we find that these factors may all play a much larger role than originally assumed. Subsequently, some peak water estimates may not isolate glacial melt peak water, but instead represent &amp;#8220;basin peak water&amp;#8221;. Depending on the basin of interest, these aspects can play a significant role in water availability, and thus in peak water estimates. We believe that these nuisances are important for ensuring that the peak water concept is appropriately communicated to end-users, and to inform suitable water management. As a scientific community, we now have an opportunity to assess and find ways to move forward with a unified approach to the terminology and communication of peak water.&lt;/p&gt;

Seasonal variations in the origin of river sediments (Baker River, Chile): A pre-requisite for climate and hydrological reconstructions

&lt;p&gt;&lt;/p&gt;&lt;div&gt; &lt;div&gt; &lt;div&gt;&amp;#160;&lt;/div&gt; &lt;div&gt;&lt;img&gt;Fjord sediments are increasingly recognized as high-resolution recorders of past climate and hydrological variability. Using them as such, however, requires a comprehensive understanding of the variables that affect their properties and accumulation rates. Here, we conduct a spatial and temporal study of sediment samples collected at the head of Mart&amp;#237;nez Channel (Chilean Patagonia, 48&amp;#176;S), to understand how the fjord&amp;#8217;s sediments register changes in the hydrodynamics of Baker River, Chile's largest river in terms of mean annual discharge. We apply end-member modeling to particle-size distributions of: (i) river suspended sediments, (ii) surface sediments collected along a proximal-distal transect at the fjord head, and (iii) fjord sediments collected in a sequential sediment trap at 15-day resolution during two consecutive years. Results show that the river suspended sediments and fjord sediments are consistently composed of two grain-size subpopulations. The finest end member (EM&lt;sub&gt;1&lt;/sub&gt;; mode 4.03 &amp;#956;m) reflects the meltwater contribution, which dominates in all but the winter season. The coarser end member (EM&lt;sub&gt;2&lt;/sub&gt;; mode 18.7 &amp;#956;m) dominates in winter, when the meltwater contribution is reduced, and is associated to rainfall events. We propose that log(EM&lt;sub&gt;1&lt;/sub&gt;/EM&lt;sub&gt;2&lt;/sub&gt;) can be used to reconstruct temperature in the lower Baker River watershed (r = 0.81, p &lt; 0.001). We also show that the fluxes of EM&lt;sub&gt;1&lt;/sub&gt; and EM&lt;sub&gt;2&lt;/sub&gt; provide quantitative estimates of baseflow (r = 0.82, p &lt; 0.001) and quickflow (r = 0.90, p &lt; 0.001), respectively. These results support the use of fjord sediments for quantitative reconstructions of climate and hydrological changes in glacierized watersheds.&lt;/div&gt; &lt;/div&gt; &lt;/div&gt;

Stream Flow Generation for Simulating Yearly Bed Change at an Ungauged Stream in Monsoon Region

The stream flow generation method is necessary for predicting yearly bed change at an ungauged stream in Monsoon region where there is no hydrologic and hydraulic information. This study developed the stream flow generation method of daily mean flow for each month over a year for bed change simulation at an ungauged stream. The hydraulic geometries of cross-sections and the corresponding bankfull indicators of the Byeongseong river of 4 km reach were analyzed to estimate the bankfull discharge. The estimated bankfull discharge of the target reach was 77.50 m3/s, and the total annual discharge estimated 3720 m3/s through the correlation equation with the bankfull discharge. The measured total annual discharge of the Byeongseong river was 3887.30 m3/s, which is greater by 167.30 m3/s of 4.3% relative error. The volume and bed changes over a year by the Center for Computational Hydroscience and Engineering Two-Dimension (CCHE2D) model simulated using the measured discharge during 2013 and 2014 coincided with the surveyed in the same period. Estimated total annual discharge was used for the scenarios of stream flow generation. The generated stream flow using the flow apportioned to each month on the basis of the flow percentage in an adjacent stream simulated the river bed most appropriately. The generated stream flow using the flow based on the monthly rainfall percentage of the rainfall station in the target stream basin also simulated river bed well, which is confirmed as an alternative. Quantitatively, the root mean square error (RMSE), mean bias error (MBE), and mean absolute percentage error (MAPE) in-depth change of thalweg between the measured and the simulated were found to be 0.25 m, 0.04 m, and 0.44%, respectively. The result of the simulated cross-sectional river bed change for target reach coincided well with the surveyed. The proposed method is highly applicable to generate the stream flow for analyzing the yearly bed change at an ungauged stream in Monsoon region.