Regional Hydrological Conditions Research Articles

Strong coupling between the East Asian summer monsoon and regional hydrological conditions as evidenced by multiproxy stalagmite records for the last deglaciation

Millennial-to centennial-scale abrupt climate events during the last glacial‒interglacial transition have significant relevance to modern-day extreme climate changes, which are occurring more frequently in the context of global warming. However, the regional expression of humidity conditions during the last deglaciation and their possible forcing mechanism in northern China are controversial. Here, combined with published δ18O data, we report 35-year-resolved δ13C and 76-year-resolved Mg/Ca and Sr/Ca records from a stalagmite from 15.3 to 10.9 ka BP from Lianhua Cave, northern China. The LH4 stalagmite δ18O record clearly records a weak monsoon event during the Younger Dryas (YD) from 12.8 to 11.6 ka BP and a strong monsoon event during the Bølling-Allerød (BA) from 14.6 to 12.8 ka BP. In addition, the δ13C and trace element ratio records, which represent local hydroclimatic changes, indicate wetter conditions during the BA and drier conditions during the YD, which appear to match well with the δ18O variations on the millennial timescale. A comparison of 28 records from 17 sites along the modern margin of the China summer monsoon revealed that the BA was characterized by wet conditions; inversely, the YD was characterized by dry conditions throughout northern China, which is obviously different from the consensus of the wet YD and the dry BA in northern northeastern China. The covariance in northern China suggests that the hydrological variation may be modulated by the advance and retreat of the large-scale East Asian summer monsoon (EASM) circulation. Further comparison revealed an anticorrelated relationship between millennial-scale precipitation changes in northern China and the middle‒lower reaches of the Yangtze River Valley during the last deglaciation. This correlation is analogous to the dipole precipitation mode at present, which is likely associated with the strength and position of the westerly jet and/or the western Pacific subtropical high, both of which play important roles in the spatial distribution of precipitation over eastern China.

A Highly Resolved Speleothem δ13C Record from Central China and Its Manifestation on Multiple Time Scales during the Last Glacial

Speleothem δ13C in monsoonal China differs from speleothem δ18O, which is widely used as a climatic proxy for several complex control reasons. Nevertheless, δ13C records have the potential to reveal the implications of hydroclimatic changes. This study reports a speleothem δ13C record from Didonghe (DDH) Cave in central China spanning 34 to 13 kyr BP. After we investigated the factors that influence speleothem δ13C, we found that the δ13C record showed that DDH Cave can prompt directional shifts via local hydroclimatic changes, such as in vegetation types, biomass, and rock–water interaction processes, suggesting that δ13C is mainly controlled by the local hydroclimate. Ensemble empirical mode decomposition (EEMD) results revealed a coupling relationship between δ18O and δ13C on multiple timescales, which suggested that changes in precipitation caused by large-scale monsoonal circulation are controlled by regional hydrological conditions to a great extent. However, the hydrological conditions of the cave were relatively mild and humid during the last glacial maximum (LGM), which revealed the impact of evaporation on changes in the region’s hydrological conditions. We also found that the δ18O and δ13C profiles decoupled when δ13C changed with a shift in the location of the westerly during HS1. The δ13C record correlates well with other paleoclimate records, suggesting that regional hydrological conditions are also modulated by the Earth’s internal and external driving factors.

Sources and transport of CO2 in the karst system of Jiguan Cave, Funiu Mountains, China

Conveyance and modification of carbon-isotope signals within the karst system remain difficult to constrain, due to the complexity of interactions between multiple components, including precipitation, bedrock, soil, atmosphere, and biota. Cave monitoring is thus critical to understanding both their transport in the karst system and dependence on local hydroclimatic conditions. Jiguan Cave, located in Funiu Mountain in central China, is representative of karst tourist caves with relatively thin epikarst zone. We conducted a comprehensive monitoring program of cave climate from 2018 to 2021 and measured δ13C during 2021 in monthly and heavy-rainfall samples of soil CO2, cave CO2, cave water (drip water and underground river), and underground river outlet. Our results demonstrate synchronous variations between CO2 concentration and δ13CCO2 in both soil and cave air on seasonal time scales. Cave pCO2 and carbon-isotope composition further exhibited a high sensitivity to human respiration with fluctuations of ~2000–3000 ppm within 4 days during the cave closure period in July 2021 without tourists. 13C-depleted isotopic signal of cave air in summer is the mixture of human respiration and soil CO2 which varies as a function of regional hydrological conditions of the summer monsoon during the rainy season with high temperatures and humidity. However, respired CO2 from the overlying soil was expected to be the only principal source of the cave CO2 when the anthropogenic CO2 source was removed. The high seasonal amplitude of cave air δ13CCO2 reflects ventilation dynamics, which leads to a prominent contribution from the external atmosphere during winter. Intriguingly, although the δ13C signal reflects complex vertical processes in the vertical karst profile, a heavy summer rainfall event was related to anomalously high δ13C values of cave water that can be utilized to interpret rainfall intensity and regional hydroclimate.

Response of mangrove development to paleoclimate variation over the past 3,550 years in Phang Nga Province, Thailand

High-resolution reconstruction of the development of mangrove forests in the late Holocene is the basis for scientifically predicting the fate of mangroves. In this paper, we analyze the contribution of mangrove-derived organic matter (CMOM) from sediment core G in Phang Nga Province, Thailand by using a ternary end-member mixing model based on stable organic carbon isotope (δ13C) and the molar ratio of total organic carbon to total nitrogen (C/N (molar)). The variations of the CMOM in Phang Nga Province over the past ∼3,550 cal yr BP indicate that mangrove forests underwent three periods of flourishing: ∼3,550–2,720 cal yr BP, ∼1,960–1,240 cal yr BP and ∼500–0 cal yr BP, and two periods of degradation: ∼2,720–1,960 cal yr BP and ∼1,240–500 cal yr BP. Of the potential factors that affect mangrove development, relative sea level (RSL) changes and regional hydrological conditions did not have notable effects on mangrove flourishing/degradation. However, paleoclimate variations, especially the air temperature and rainfall controlled by the Indian Summer Monsoon (ISM) were the primary factors. The mangrove development reconstructed by the CMOM in Phang Nga Province, Thailand was extremely synchronized with that in the Yingluo Bay and Qinzhou Bay of Southwest China and on the west coast of India Peninsula. This study provides evidence that mangrove development controlled by the Asian monsoon in tropical Asia has regional synchronism.

Deformation and failure characteristics of high-speed tunnels in complex karst areas: a case at the Qilinguan tunnel

The construction of expressway tunnels in karst areas faces many challenges under complex geological conditions. It is of great scientific and engineering significance to study the deformation and failure laws of tunnels and surfaces. Taking the Qilinguan tunnel of the Hubei Expressway as an example, the deformation and failure laws of the tunnel are analyzed when the tunnel passes through the complex karst area. The composition of karst water and surrounding rock was analyzed by inductively coupled plasma mass spectrometry and XRD, and the compression-shear failure model of tunnels in karst areas was proposed according to the regional hydrological and geological conditions. It was found that the thickness of the protective layer and the water pressure were the main factors affecting the deformation and failure of the surrounding rock in this area, and the treatment scheme of this project was put forward accordingly. The geological characteristics of karst areas were explored by advanced geological prediction and advanced geological drilling. The primary support is provided by a steel arch and advanced small pipe grouting. The composite lining is composed of shotcrete as the primary support and molded concrete as the secondary lining. The primary support structure of the flexible support system is adopted in the design to give full play to the bearing capacity of the surrounding rock. After the support measures were adopted, the trend of settlement change gradually slowed down, indicating that the support measures were effective.

Combined effects of climatic change and hydrological conditions on thermal regimes in a deep channel-type reservoir

The thermal regime in large reservoirs plays a significant role in the water quality and ecosystem succession; however, little is known about the impacts of regional climate changes and hydrological conditions on a sizeable stratified reservoir with strong inflow conditions, i.e., the Xiangjiaba Reservoir. Using measured data from 2014 to 2018, the monthly and seasonal variations of the water temperature, thermal stability, and their influencing factors were addressed by using empirical models. The results showed substantial variability and seasonality in the reservoir water temperature, which correlated highly with the air temperature, inflow water temperature, and discharge. Correspondingly, there was a seasonal varying thermal stratification in the reservoir's yearly cycle, with its duration being up to 4 ~ 5months, the maximum surface-bottom water temperature difference being up to 7 ~ 10°C. There were significant positive correlations between Schmidt's stability index of the thermal structure and inflow-reservoir temperature difference and the surface-bottom temperature differences, while negative correlations with large discharge. Moreover, the inflow tends to influence thermal stability by retaining hypolimnion cold water, with its maximum bottom hysteresis residence time being up to ~ 4months. Research findings indicated that climate warming in the recent 30years (1988 ~ 2017) would cause a 0.213°C/decade and 0.153kJ/m2/decade increase in reservoir surface water temperature and Schmidt's stability index, respectively. Among these variations, the inflow temperature increase caused by climate change accounted for the largest proportion, i.e., 0.16°C/decade and 0.115kJ/m2/decade. Therefore, climate warming significantly affected the thermal regimes in this large reservoir, and the inflow water temperature increase due to warm air was the main factor altering the reservoir's thermal structure. Findings from the present study provide a fresh perspective on how to best optimize the deep channel-type reservoirs' water quality in the face of anticipated climate change.

A generalized framework for drought monitoring across Central European grassland gradients with Sentinel-2 time series

Fractional cover time series of photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), and soil from remote sensing provide essential detail to understand how grasslands are affected by recent and future drought periods in the 21st century. In this regard, Sentinel-2A/B offer frequent large-area observations, which have not yet been fully exploited for a spatially continuous drought monitoring of highly dynamic Central European grasslands. In this study, we developed a generalized drought monitoring framework for Central European grasslands linking Sentinel-2 data, field survey information, and spectral unmixing. We first implemented a consistent and repeatable strategy to obtain a grassland spectral library supported by the Europe-wide Land Use/Cover Area frame statistical Survey (LUCAS) and multitemporal Sentinel-2 data. Our library captured the spectral variability of PV, NPV, and soil cover from 12 grassland areas distributed along typical environmental and land use gradients of Central Europe. We trained a generalized regression-based unmixing model with synthetic data generated from the spectral library and compared fractional cover estimates to a multitemporal reference dataset. PV, NPV, and soil were estimated with good accuracy, achieving MAEs of 6.54%, 13.7%, and 12.2%, respectively. Local unmixing models trained on area-specific library subsets were overall outperformed by the generalized model highlighting the value of a comprehensive grassland library for generalized spectral unmixing. Based on fractional cover time series from 2017 to 2021, we calculated time series of the grassland-specific Normalized Difference Fraction Index (NDFI) capturing proportions of NPV and soil relative to PV. Comparison of annual growing season drought metrics derived from the NDFI to annual meteorological drought statistics from the Standardized Precipitation Evapotranspiration Index (SPEI) as well as the Soil Moisture Index (SMI) revealed widespread drought impacts on grasslands during the persistent drought period in Central Europe from 2018 to 2020. While impacts on grasslands overall closely followed meteorological and soil drought conditions, regionally varying drought metrics underline that local to regional environmental and hydrological conditions shaped the drought response of Central European grasslands. Our study emphasizes the value of combining Sentinel-2 data, field survey information, and spectral unmixing to enable drought monitoring across grassland gradients of Central Europe with Sentinel-2 time series.

Impact of Palm Plantations In West Sulawesi Province: A Preliminary Study

Based on data from BPS-Statistics of West Sulawesi Province, vast oil palm plantations in West Sulawesi province continued to increase. This increase in the area of oil palm plantations had led to the conversion of land functions from cocoa plantations, rice fields, ponds and forests to oil palm plantations. This study This study aimed to explore the various impacts of land conversion into oil palm plantations. This study used secondary data and descriptive methods to describe the impacts that occurred when the land conversion was carried out. The results of this study indicated the occurrence of various impacts, for example, reduced rice farmers and reduced food agricultural land, changes from polyculture plantations to palm oil monocultures, changes in regional hydrological conditions and agrarian disputes.

Variations in Asian summer monsoon and hydroclimate during Heinrich stadials 4 revealed by stalagmite stable isotopes and trace elements

The iceberg melting-induced Heinrich events (HEs), which were first reported in 1988, caused a series of centennial-millennial global climate changes during the last glacial period. The patterns and details of low-latitude monsoons, oceans, and atmospheric circulation responses to HEs still need to be understood. Here, we report 11a resolved δ13C, δ18O and 36a resolved Mg/Ca, Sr/Ca and Ba/Ca multi-proxy stalagmite records during 42.29–37.14 ka BP from Yangkou cave, southwestern China. The Greenland ice cores and the δ18O of stalagmites from northern China recorded a rapid onset/termination of Heinrich stadials (HS) 4 (∼0.2 ka). However, the transition interval for the weakening/strengthening of the Asian summer monsoon (ASM) during HS4, as recorded by the southern Chinese stalagmite δ18O, is about 0.5 ka. Low latitude monsoons and hydrological variations are influenced by tropical oceans and interhemispheric thermal contrasts, which prolong the onset/termination transition process of HS4. Our findings highlight the importance of atmosphere-ocean interactions at low latitudes and in the Southern Hemisphere for ASM dynamics, which triggered the termination of millennial-scales abrupt climate events. During HS4, variations of the δ13C and trace elements ratios are inconsistent with δ18O, indicating that while the ASM is weakened, regional hydroclimate and local ecology are not significantly degraded, resulting in a relatively moderate hydrological environment. Prolonged southerly subtropical westerlies, super El Niño Southern Oscillation, western China autumn rains, and lower regional evaporation, may increase regional precipitation in different seasons and regulate hydrological conditions during HS4. As a result, while the ASM has weakened, regional hydrological conditions in the Yangtze River basin in southwest China maintain wet environmental conditions. The gradual northward shift of the Intertropical Convergence Zone and subtropical westerlies during the latter phase of HS4 will cause a limited northward shift of the rainfall bands. Although regional hydrological conditions deteriorate slightly in comparison to the early phase, it remains humid overall. We present new evidence that local hydrological conditions and ASM intensity were not fully coupled during the abrupt climate events on millennial scales in the last glacial period.

Climatic implication of stalagmite δ13C in the middle reaches of the Yangtze River since the Last Glacial Maximum and coupling with δ18O

The relationship between monsoon circulation and regional hydrology in the Yangtze River Basin since the Last Glacial Maximum (LGM) remains unclear. In this study, we present speleothem (LS46) δ18O and δ13C records over the past 23.5 kyr from the Luoshui Cave in Central China. Stalagmite LS46 δ13C displayed a good similarity with variations in δDwax-derived monsoon precipitation from Lake TengchongQinghai (TCQH) and the extreme precipitation events identified by the IRMsoft-flux from Heshang Cave, thus indicating that speleothem calcite δ13C reflects the changes in regional hydrology. The ensemble empirical mode decomposition (EEMD) and wavelet spectrum analyses revealed that the regional hydrology was paced by ∼2000-year periodicity during the LGM and last deglaciation and ∼ 1000-year periodicity during the Holocene, respectively. Our results further indicated that the El Niño-Southern Oscillation (ENSO) plays an important role in regulating changes in the frequency and magnitude of regional hydrology in the Yangtze River Basin under different climatic conditions. Moreover, our results demonstrated that δ18O and δ13C were coupled on multiple timescales, thus potentially indicating that local hydrological variations in the middle reaches of the Yangtze River are regulated by large-scale monsoonal circulation. However, we also found that the δ18O and δ13C profiles decoupled during the last deglaciation, likely due to a decrease in evapotranspiration in combination with a decrease in monsoon intensity and temperature during this period. Consequently, the regional hydrological conditions did not experience any dramatic changes.

Assessing butterfly diversity and their response to habitat condition in pristine peat bogs in Belarus

Peat bogs are valuable ecosystems because they support regional and local hydrological conditions, and store carbon and other greenhouse gases. Nevertheless, their area in Europe is extremely reduced due to human activities. As a result, the number of studies on biodiversity and the environmental factors affecting the distribution of insects, including butterflies, in large intact peatlands is limited. Such studies provide an important baseline for the subsequent analysis of changes during climate warming and for the assessment of succession in degraded peatlands. The results of such research have shown how butterfly assemblages react to local peat bog habitat conditions and contribute new information on the relations of consumers and the very specific environment of peat bogs. The presented research targets the relationship between characteristics of butterfly assemblages and key environmental variables in intact peat bog habitats. A total of 1427 individuals belonging to 23 butterfly species were recorded. In this study, I found that butterfly abundance, diversity and species composition varied significantly among three main habitat types, namely lagg zones, pine bogs and open bogs, although these habitats did not differ in species richness. The highest abundance was in the pine bogs which are characterized by higher plant community structural complexity and, as a result, higher butterfly food resources. The results confirmed positive responses of species richness and abundance of butterflies to nectariferous flower cover. On the other hand, open, sunny, but windy sites on the peat bogs contribute to a decrease of abundance.

Trophic state footprint index model and its application to Dianchi Lake, China

Given ongoing changes in regional climate and hydrologic conditions, a vast of studies have reported that under-prediction or over-prediction of the trophic status of a water body was widely existing by classic trophic state index method, it would create serious problems in management aspects such as allowing over-fertilization of the eutrophic water body. Each lake needs to establish its own trophic state evaluation method. Therefore, based on the concept of lake-specific and segmentation, a new assessment method for lake eutrophication is proposed: a Trophic State Footprint Index (TFI). This method constructed a concise response relationship between the response index (chlorophyll a) and the main cause index (such as total phosphorus and total nitrogen) with segmented data. This method is an improvement over the Modified Trophic State Index method and TFI is simpler, easier to conduct, and more accurate. It has been applied in Dianchi Lake of China and proved to be effective.

Failure Mechanism of Weak Rock Slopes considering Hydrological Conditions

Landslides frequently occur on cutting slopes with weak rock during the rainy season. An understanding of the failure mechanism is essential for designers to adopt effective measures to mitigate potential impacts caused by landslides. Based on an enormous number of highway slope practices in Guangdong Province, China, this paper presents a whole train of numerical investigations on the hydraulic response and stability of weak rock slopes subject to a subtropical climate where the average annual rainfall is approximately 1,800 – 2,000 mm. This study explored a different failure mechanism of three different types of weak rock slopes in a modeling approach. A physics-based slope model coupled with a hydrological model is used to simulate the factor of safety and porewater pressure development of unsaturated slopes with various rock masses under diverse rainfall scenarios. The input parameters were determined from the rainfall intensity–duration–frequency (IDF) curves of regional hydrological conditions to comprehensively consider the impact of rainfall. The general suction range of rock masses was acquired using three hydraulic characteristic curves associated with sandstone, siltstone, and mudstone. Furthermore, the failure models of weak rock slopes under different rainfall conditions were assessed. Based on the theory of regional hydrology, a unified rainfall and intensity-duration threshold for different weak rock slopes was established. The results indicate that both siltstone and mudstone slopes are more sensitive to long-term rainfall than short-term rainstorms. However, the sandstone slope appears to be unstable under regional rainfall conditions of 40-year return periods. This also proves that the instability mode of the siltstone slope exhibits a retrogressive type in which the sliding surface of the slope increases with an increase in rainfall duration. Translational shallow landslides occurred in the transient saturation zone of the sandstone slope, and the depth of the failure plane was independent of rainfall patterns and duration. This study revealed the instability mechanism and provided a robust early warning measure for weak rock slopes by fusing engineering geology and regional hydraulics, providing insightful information for mitigating potential landslide disasters. The proposed model can also be used to predict the possible infiltration depth of rainfall and the spatial location of the sliding surface, prior to construction to assess whether slope stabilization and reinforcement measures are needed.

Accelerating permafrost collapse on the eastern Tibetan Plateau

Permafrost collapse can rapidly change regional soil-thermal and hydrological conditions, potentially stimulating production of climate-warming gases. Here, we report on rate and extent of permafrost collapse on the extensive Tibetan Plateau, also known as the Asian Water Tower and the Third Pole. Combined data from in situ measurements, unmanned aerial vehicles (UAV), manned aerial photographs, and satellite images suggest that permafrost collapse was accelerating across the Eastern Tibetan Plateau. From 1969 to 2017, the area of collapsed permafrost has increased by approximately a factor of 40, with 70% of the collapsed area forming since 2004. These widespread perturbations to the Tibetan Plateau permafrost could trigger changes in local ecosystem state and amplify large-scale permafrost climate feedbacks.

Evaluation of Climate Change Impact on Streamflow (A Case Study of Dabus River,Abay Basin Ethiopia) Using CORDEX-RCP and SWAT Model

Climate change is becoming one of the most debating and threatening issues in terms of global context which alter regional hydrologic conditions and results in a variety of impacts on water resource systems. The aim of this study is to assess the impact of climate change on the stream flow of Dabus Sub-basin which located in upper Blue Nile Basin of Ethiopia. The CORDEX RCM downscaled and bias corrected were used for the climate projection. To estimate the level of impact of climate change, climate change scenarios of precipitation and temperature were divided into three time windows of 25 years as the whole from (2025-2099). Soil and water assessment Tool (SWAT) was calibrated and validated for stream flow simulation using SWAT-CUP with a method of SUFI2. The results showed that the value of calibration and validation reveals a good agreement with R 2 =0.84 during calibration and R 2 =0.82 during validation whereas NSE= 0.75 during calibration and NSE=0.72 during validation. The maximum and minimum temperatures increase for the three time horizons under both scenarios with largest increase under RCP8.5. The largest increase of mean annual maximum temperature under RCP4.5 is 1.31 o C while under RCP8.5 that increase by 3.097 o C in future periods of (2075-2099). Similarly, The largest increase of annual minimum temperature under RCP4.5 scenario by 1.28 o C while 1.42 o C under RCP8.5 in future periods of (2075-2099). Compared to the base line period the total annual precipitation decrease for the three time horizons under both scenarios. A decrease of mean annual precipitation under RCP4.5 are 12.8% , 18.26% and 21.27% while under RCP8.5, it show decrease by 13.76%, 14.87% and 13.6% in the future periods of (2025–2049), (2050-2074)and (2075-2099) respectively. The stream flow projections are made in the future with two emission scenarios of RCP4.5 and RCP8.5, the study show that an average annual decrease in the stream flow up to 11.97% for RCP4.5 and up to 13.37% for RCP8.5 in the next 75 years. Keywords: Dabus Sub basin; SWAT; RCP Scenario; CORDEX RCM ; Climate Change DOI: 10.7176/CER/12-12-02 Publication date: December 31 st 2020

Constraining the Water Cycle Model of an Important Karstic Catchment in Southeast Tibetan Plateau Using Isotopic Tracers (2H, 18O, 3H, 222Rn)

Understanding the connectivity between surface water and groundwater is key to sound geo-hazard prevention and mitigation in a waterscape such as the Jiuzhaigou Natural World Heritage Site in the southeast Tibetan Plateau, China. In this study, we used environmental isotope tracers (2H, 18O 3H, and 222Rn) to constrain a water cycle model including confirming hydrological pathways, connectivity, and water source identification in the Jiuzhaigou catchments. We established the local meteoric water line (LMWL) based on the weekly precipitation isotope sampling of a precipitation station. We systematically collected water samples from various water bodies in the study area to design the local water cycle model. The regional water level and discharge changes at one month after the earthquake indicated that there was a hydraulic connection underground across the local water divide between the Rize (RZ) river in the west and Zechawa (ZCW) lake in the east by the δ18O and δ2H measurements. We employed an end-member mixing model to identify and quantify Jiuzhaigou runoff-generating sources and their contributions, and we found that the average contributions of precipitation and groundwater to the surface runoff in the catchments are about 30% and 70%, respectively. The two branches of the Shuzheng (SZ) trunk were recharged by 62 ± 19% from the ZCW lake and 38 ± 19% from the RZ river, which was consistent with the fractions calculated by the actual discharge volume. 222Rn mass balance analyses were employed to estimate the water exchange between groundwater and river, which further confirmed this estimate. 222Rn concentrations and 3H contents showed that the groundwater had a short residence time and it was moderate precipitation, thought the contribution of groundwater to the river was 70%, according to the different tracers. A three-dimensional conceptual model of the water cycle that integrated the regional hydrological and geological conditions was established for the catchments.

Evaluation of Climate Change Impact on Streamflow (A Case Study of Dabus River,Abay Basin Ethiopia) Using CORDEX-RCP and SWAT Model

Climate change is becoming one of the most debating and threatening issues in terms of global context which alter regional hydrologic conditions and results in a variety of impacts on water resource systems. The aim of this study is to assess the impact of climate change on the stream flow of Dabus Sub-basin which located in upper Blue Nile Basin of Ethiopia. The CORDEX RCM downscaled and bias corrected were used for the climate projection. To estimate the level of impact of climate change, climate change scenarios of precipitation and temperature were divided into three time windows of 25 years as the whole from (2025-2099). Soil and water assessment Tool (SWAT) was calibrated and validated for stream flow simulation using SWAT-CUP with a method of SUFI2. The results showed that the value of calibration and validation reveals a good agreement with R 2 =0.84 during calibration and R 2 =0.82 during validation whereas NSE= 0.75 during calibration and NSE=0.72 during validation. The maximum and minimum temperatures increase for the three time horizons under both scenarios with largest increase under RCP8.5. The largest increase of mean annual maximum temperature under RCP4.5 is 1.31 o C while under RCP8.5 that increase by 3.097 o C in future periods of (2075-2099). Similarly, The largest increase of annual minimum temperature under RCP4.5 scenario by 1.28 o C while 1.42 o C under RCP8.5 in future periods of (2075-2099). Compared to the base line period the total annual precipitation decrease for the three time horizons under both scenarios. A decrease of mean annual precipitation under RCP4.5 are 12.8% , 18.26% and 21.27% while under RCP8.5, it show decrease by 13.76%, 14.87% and 13.6% in the future periods of (2025–2049), (2050-2074)and (2075-2099) respectively. The stream flow projections are made in the future with two emission scenarios of RCP4.5 and RCP8.5, the study show that an average annual decrease in the stream flow up to 11.97% for RCP4.5 and up to 13.37% for RCP8.5 in the next 75 years. Keywords : Dabus Sub basin; SWAT; RCP Scenario; CORDEX RCM ; Climate Change DOI: 10.7176/JEES/10-11-04 Publication date: November 30 th 2020

Contribution of nitrogen sources to streams in mixed-use catchments varies seasonally in a cold temperate region

Intensive agriculture and growing human populations are important nitrogen (N) sources thought to be associated with eutrophication. However, the contribution and seasonality of N delivery to streams from human activities is poorly understood and knowledge of the role of stream communities in the assimilation of N from human activities is limited. We used N and oxygen stable isotope ratios of dissolved inorganic N (DIN) and concentrations of artificial sweeteners to identify the relative contribution of key sources of anthropogenic N (i.e., fertilizers, human, and livestock waste) to tributaries of the Red River Valley (RRV), Manitoba, Canada. Water and algae were sampled in 14 RRV tributaries during snowmelt, spring, summer, and autumn; and water was sampled at three locations in the Red River in spring, summer, and autumn. δ15N values of DIN in tributary water differed seasonally and were greatest during snowmelt. Incorporation of ammonium δ15N provided evidence for the importance of manure N to tributaries during snowmelt. Fertilizer and municipal lagoons served as principal sources of N to streams in spring and summer. Human and livestock waste sources of N were the dominant contributor to algae at greater than 90% of sites and algae δ15N was greatest at sites downstream of municipal lagoons. We also showed that the tributaries contribute human and livestock waste N to the Red River, though much of the nitrate in the river originates outside of Manitoba. Overall, our study determined that the anthropogenic sources of N to RRV streams vary seasonally, likely due to regional hydrologic conditions. Our study also showed the potential of artificial sweeteners and ammonium δ15N as tools for identifying N sources to rivers. Moreover, we demonstrate the need for the management of N sources and the protection of stream function to control downstream transfer of N from landscapes to waterbodies.

Turning Water Pollution Sources Into Assets: Exploring Innovative Options Of Using Abandoned Mines For Generating And Storing Renewable Energy

Through moving large volumes of rock for decades or even centuries from geological underground to surface, industrial scale mining invariably alters the natural local and regional hydrological conditions. Consequences include irreversible changes of flow gradients and water quality in aquifers and streams effected through dewatering, ground subsidence, acid mine drainage, etc. During their lifetime mines spent significant resources and energy on maintaining an ever-increasing diversion from natural hydraulic equilibria through pumping rising volumes of ingress water from ever greater depths, especially if operating below water-rich formations (karst) or in humid climates. Associated pumping costs may even lead to premature mine closure. In cases where complete flooding of closed mines is not an option (e.g. to protect water resources or infrastructure) such costs remain well after mines closed for as long as flooding restrictions apply. In large and densely populated regions in South Africa or Germany, for example, where mining succeeded in triggering urbanisation and self-sustaining economic development it is (currently) assumed that pumping will be needed forever. Accordingly, postclosure water management is no longer only a long-term liability but indeed a perpetual burden placed on future generations that had little direct benefits from earlier mining. This paper focuses specifically on possible ways of reducing perpetual postclosure water management costs specifically of using abandoned mines for generating and storing renewable energy. It discusses successful examples already implemented, concepts investigated but not yet realised as well as technologies that received little, if any, attention to date. The latter range from using mines (included flooded ones) for the storage of electrical energy via different technologies, harvesting geothermal energy from mine water and voids to different ways of transforming chemical energy contained in mine water into electricity.

Improving precision in regional scale numerical simulations of groundwater flow into underground openings

Dewatering is a common engineering practice to secure the accessibility during the construction and operational phases of tunnels. It is thus important to accurately estimate the amount of groundwater flow into underground openings for the design and safe operation of tunnels. Numerical models need to be used to estimate groundwater flow into openings for given heterogeneity and regional hydrologic boundary conditions typically by assuming that the atmospheric pressure is maintained along open wall faces. As the scale of openings can be small as tens of centimeters, while models need to incorporate the regional hydrologic conditions, it is often practically impossible to explicitly represent the three-dimensional (3D) geometry of openings within numerical models. For the safety assessment of deep geological repositories of spent nuclear fuels, for example, complex configurations and geometry of various tunnels such as construction, access, ventilation, and deposition tunnels often need to be approximated as one-dimensional (1D) lines in 3D models. The application of a simple Dirichlet boundary condition along a set of tunnel nodes may yield inaccurate solutions due to geometric simplifications and coarse discretization. This study derives an appropriate boundary condition that can be applied to 1D tunnel segments to improve the accuracy when simulating inflow into openings. A third-type tunnel boundary condition is suggested to correct the difference between known wall pressure and the pressure simulated at tunnel nodes. Improvement in the precision of the solutions is demonstrated by comparing the numerical solutions using the new boundary condition with analytic solutions, and with numerical solutions when the 3D tunnel geometry is explicitly simulated. It is also shown that the formulation can be easily extended to incorporate the high permeability excavation damaged zone and the low permeability grouted zone in the tunnel vicinity. The applicability of the tunnel boundary condition is demonstrated using an example of a hypothetical deep geologic repository system consisting of various types of tunnels located in a hypothetical crystalline coastal aquifer.