Isotope hydrogeochemical models for assessing the hydrological processes in a part of the largest continental flood basalts province of India

Continental Flood Basalts(CFB)occupy one fourth of the world’s land area.Hence,it is important to discern the hydrological processes in this complex hydrogeological setup for the sustainable water resources development.A model assisted isotope,geochemical,geospatial and geophysical study was conducted to understand the monsoonal characteristics,recharge processes,renewability and geochemical evolution in one of the largest continental flood basalt provinces of India.HYSPLIT modelling and stable isotopes were used to assess the monsoonal characteristics.Rayleigh distillation model were used to understand the climatic conditions at the time of groundwater recharge.Lumped parameter models(LPM)were employed to quantify the mean transit time(MTT)of groundwater.Statistical and geochemical models were adopted to understand the geochemical evolution along the groundwater flow path.A geophysical model was used to understand the geometry of the aquifer.The back trajectory analysis confirms the isotopic finding that precipitation in this region is caused by orographic uplifting of air masses originating from the Arabian Sea.Stable isotopic data of groundwater showed its meteoric origin and two recharge processes were discerned;(i)quick and direct recharge by precipitation through fractured and weathered basalt,(ii)low infiltration through the clayey black cotton soil and subjected to evaporation prior to the recharge.Tritium data showed that the groundwater is a renewable source and have shorter transit times(from present day to<30 years).The hydrogeochemical study indicated multiple sources/processes such as:the minerals dissolution,silicate weathering,ion exchange,anthropogenic influences etc.control the chemistry of the groundwater.Based on the geo-electrical resistivity survey,the potential zones(weathered and fractured)were delineated for the groundwater development.Thus,the study highlights the usefulness of model assisted isotopic hydrogeochemical techniques for understanding the recharge and geochemical processes in a basaltic aquifer system.

Changes in hydrological processes in the headwater area of Yellow River,China during 1956-2019 under the influences of climate change,permafrost thaw and dam

Discharge characteristics are crucial for detecting changes in hydrological processes.Recently,the river hydrology)in the Headwater Area of the Yellow River(HAYR)has exhibited erratic regimes(e.g.,monotonously declining/low/high hydrograph,even with normal precipitation)under the effects of climate change,permafrost thaw and changes in dam operation.This study integrates hydroclimatic variables(air temperature,precipitation,and potential evapotranspiration)with anthropogenic dam operation and permafrost degradation impact data to systematically examine the mechanisms of these hydrological process changes during 1956–2019.The results show the following:1)compared with the pre-dammed gauged flow,dam construction(January 1998–January 2000)and removal of dam(September 2018–August 2019)induced monotonously low(−17.2 m^(3) s^(−1);−61%)and high(+54.6 m^(3) s^(−1);+138%)hydrographs,respectively;2)hydroclimatic variables mainly controlled the summer–autumn hydrological processes in the HAYR;3)the monotonous decline of the hydrograph of Yellow River in the HAYR in some hydrological years(e.g.,1977,1979,1990 and 1995)was closely related with unusually high atmospheric demands of evaporation and low-intense rainfall during summer–autumn seasons;and 4)the lengthening of subsurface hydrological pathways and residence time,permafrost degradation reduced the recession coefficient(−0.002 per year)of winter flow and altered the hydrological regimes of seasonal rivers,which resulted in flattened hydrographs that reduced and delayed the peak flow(of 0.05 mm per year and 1.65 d per year,respectively)as well as boosted the winter baseflow(0.01 mm per year).This study can provide updated and systematic understanding of changing hydrological processes in typical alpine catchments on northeastern Qinghai–Tibet Plateau,China under a warming climate.

A numerical study of hydrodynamic characteristics and hydrological processes in the coastal wetlands during extreme events

Providing accurate predictions of extreme water levels through numerical simulation has become essential for disaster prevention and damage mitigation in coastal wetland areas.This study applies the FVCOM model to simulate storm surges caused by several typhoons in the Bohai Sea and the North Huanghai Sea.The vegetation drag force caused by salt marsh plants is inserted into the FVCOM model for model improvement with vegetation effect by integrating RS and GIS technologies.A parametric typhoon model is coupled with background wind fields derived to acquire the spatio-temporal variations of wind and pressure fields in the computational domain.The simulation results reproduce the extreme storm surges induced by typhoon events very well.The modeling results are compared by validating with literature results to examine the effect of vegetation on tidal waves in tidal mud flats.Moreover,the coupled model is also applied to explore storm surge attenuation and land intrusion during Typhoon Winnie in the wetlands of the Liao River Estuary.The simulation results indicate that salt marsh plants can reduce the flow current with little impact on tide flooding/ebbing in vegetated regions.Furthermore,the results show that typhoon presence increases the inundation depth and extendes the flood time in the tidal wetlands of the study region.The FVCOM model incorporating the method with vegetation drag force can provide new insights to understand the comprehensive impact of tidal wetland plants on hydrodynamic characteristics in the Bohai Sea and other waters,hence presents a more accurate quantification of the hydrological process of storm surge in the tidal wetlands.

Modeling of hydrological processes in arid agricultural regions

Understanding of hydrological processes,including consideration of interactions between vegetation growth and water transfer in the root zone,underpins efficient use of water resources in arid-zone agriculture.Water transfers take place in the soil-plant-atmosphere continuum,and include groundwater dynamics,unsaturated zone flow,evaporation/transpiration from vegetated/bare soil and surface water,agricultural canal/surface water flow and seepage,and well pumping.Models can be categorized into three classes:(1)regional distributed hydrological models with various land uses,(2)groundwater-soil-plant-atmosphere continuum models that neglect lateral water fluxes,and(3)coupled models with groundwater flow and unsaturated zone water dynamics.This review highlights,in addition,future research challenges in modeling arid-zone agricultural systems,e.g.,to effectively assimilate data from remote sensing,and to fully reflect climate change effects at various model scales.

Hydrological Characteristics of the Heihe River Basin in the Arid Inland Area of Northwest China

The hydrological characteristics of the Heihe River Basin in the arid inland area of northwest China were investigated.The spatial distribution of annual precipitation in the basin indicates that it decreases from east to west and from south to north,and increases with elevation by a gradient of 24.4 mm per hundred meters below 2,810 m a.s.l.,but decreases with elevation by that of 37.0 mm per hundred meters above 2,810 m a.s.l.For the last 50 years,the mountain runoff of the ba-sin has a tendency of increase.Except in the mountain area,the aridity is very high in the basin,and the aridity index ranges from 1.6 to 7.0 at the piedmont,to 9.0~20.0 in the midstream area and up to 40.0 in the downstream Ejin region.It is estimated for the last 50 years that a 1oC increment of annual temperature causes a 21.5 mm increase of evaporation in the mountain area,and the equivalent reduction of mountain runoff is 0.215×109 m3/yr at the Yingluoxia Hydrometric Sta-tion.The estimation shows also that a 1oC increment of annual temperature causes 1,842 mm increase of farmland evapotranspiration in the midstream area,an equivalent of 0.298×109 m3/yr more water consumption.The anthropogenic influence on the hydrological processes and water resources is then discussed.

Reconciliation of research on forest carbon sequestration and water conservation

Carbon sequestration and water conservation are two of the key ecosystem services that forests provide for societal need to address environmental issues.Optimization of the dual services is the ultimate goal in forest management for mitigating global climate change and safeguarding terrestrial water balance.However,there are some tradeoff s between gain in forest productivity and ecosystem water balance.We conducted literature review based on published articles for learned knowledge on forest carbon fi xation and hydrological regulations.Some knowledge gaps and research needs are identifi ed by examining the inter-connections between forest carbon sequestration and water conservation.Past researches have helped gain basic understanding of the mechanisms and controls of forest carbon fi xation and hydrological regulations as two separate issues.Tools and approaches are well established for quantifying and monitoring forest carbon and hydrological issues,operating at diff erent spatial and temporal scales.There are knowledge gaps on how to design aff orestation schemes facilitating enhanced ecosystem services in forest carbon sequestration and water conservation.For the top-down planning of aff orestation in regions where water availability is anticipated to be problematic,the questions of how much and where to plant for given land availability,known environmental implications,and sustained regional development and livelihood need to be addressed.For local management considerations,the questions of what and how to plant prevail.Eff orts are needed in joint studies of forest carbon sequestration and water conservation functionalities,specifi cally in relation to establishment and management of planted forests aiming for delivering regulatory ecosystem services in carbon sequestration,water conservation and other social values.We propose an integrated framework with dual consideration of carbon sequestration and water conservation in forest management for future research pursue.

Water resources response and prediction under climate change in Tao'er River Basin,Northeast China

Climate change has significantly affected hydrological processes and increased the frequency and severity of water shortage,droughts and floods in northeast China.A study has been conducted to quantify the influence of climate change on the hydrologic process in the Tao’er River Basin(TRB),one of the most prominent regions in northeast China for water contradiction.The Soil and Water Assessment Tool(SWAT)model was calibrated and validated with observed land use and hydro-climatic data and then employed for runoff simulations at upper,middle and lower reaches of the river basin for different climate change scenarios.The results showed that a gradual increase in temperature and decrease in annual precipitation in the basin was projected for the period 2020-2050 for both representative concentration pathways(RCP)4.5 and 8.5 scenarios.The climate changes would cause a decrease in annual average runoff at basin outlet by 12 and 23 million m^(3) for RCP4.5 and 8.5,respectively.The future runoff in the upstream and midstream of the basin during 2020-2050 would be-10.8% and-12.1% lower than the observed runoff compared to the base period for RCP4.5,while those would be-5.3% and-10.7%lower for RCP8.5.The future runoff will decrease at three hydrology stations for the assumed future climate scenarios.The results can help us understand the future temperature and precipitation trends and the hydrological cycle process under different climate change scenarios,and provide the basis for the rational allocation and management of water resources under the influence of future climate change in the TRB.

Potential risks and challenges of climate change in the arid region of northwestern China

In the arid region of northwestern China(ARNC),water resources are the most critical factor restricting socioeconomic development and influencing the stability of the area’s ecological systems.The region’s complex water system and unique hydrological cycle show distinctive characteristics.Moreover,the intensified hydrological cycle and extreme climatic and hydrological events resulting from global warming have led to increased uncertainty around water resources as well as heightened conflict between water supply and water demand.All of these factors are exerting growing pressures on the socioeconomic development and vulnerable ecological environment in the region.This research evaluates the impacts of climate change on water resources,hydrological processes,agricultural system,and desert ecosystems in the ARNC,and addresses some associated risks and challenges specific to this area.The temperature is rising at a rate of 0.31
C per decade during 1961–2017 and hydrological processes are being significantly influenced by changes in glaciers,snow cover,and precipitation form,especially in the rivers recharged primarily by melt water.Ecosystems are also largely influenced by climate change,with the Normalized Difference Vegetation Index(NDVI)of natural vegetation exhibited an increasing trend prior to 1998,and then reversed in Xinjiang while the Hexi Corridor of Gansu showed the opposite trends.Furthermore,the desert-oasis transition zone showed a reduction in area due to the warming trend and the recent rapid expansion of irrigated area.Both the warming and intensified drought are threatening agriculture security.The present study could shed light on sustainable development in this region under climate change and provides scientific basis to the construction of the“Silk Road Economic Belt”.

Xin'anjiang Nested Experimental Watershed(XAJ-NEW)for Understanding Multiscale Water Cycle:Scientific Objectives and Experimental Design

This paper presents the background,scientific objectives,experimental design,and preliminary achievements of the Xin’anjiang nested experimental watershed(XAJ-NEW),implemented in 2017 in eastern China,which has a subtropical humid monsoon climate and a total area of 2674 km2.The scientific objectives of the XAJ-NEW include building a comprehensive,multiscale,and nested hydrometeorological monitoring and experimental program,strengthening the observation of the water cycle,discovering the spatiotemporal scaling effects of hydrological processes,and revealing the mechanisms controlling runoff generation and partitioning in a typical humid,hilly area.After two years of operation,preliminary results indicated scale-dependent variability in key hydrometeorological processes and variables such as precipitation,runoff,groundwater,and soil moisture.The effects of canopy interception and runoff partitioning between the surface and subsurface were also identified.Continuous operation of this program can further reveal the mechanisms controlling runoff generation and partitioning,discover the spatiotemporal scaling effects of hydrological processes,and understand the impacts of climate change on hydrological processes.These findings provide new insights into understanding multi scale hydrological processes and their responses to meteorological forcings,improving model parameterization schemes,and enhancing weather and climate forecast skills.

Quantitative assessment on basin-scale hydrological services of wetlands

Despite recognizing the importance of hydrological function of wetlands, basin-scale wetlands services have rarely been investigated. The PHYSITEL/HYDROTEL modelling platform was used to quantitatively assess the impact of wetlands on quickflow and baseflow with paired simulation scenarios in Duobukuli River Basin, namely with wetlands and without wetlands.Simulation results showed that wetlands exert significant impact on basin hydrological processes by decreasing streamflow and altering streamflow regime(magnitude, frequency, duration and time of flow events). The intensity(significant or not) of wetlands influences on quickflow had daily, monthly and annual variation. Wetlands significantly attenuated quickflow during flood season while slightly support daily, monthly and annual baseflow. The average quickflow attenuation and baseflow support of wetlands were 5.89% and 0.83%, respectively. Although the intensity and effect(mitigation or augment) of wetlands on streamflow temporally varied at daily, monthly, seasonal and annual scales, wetland overall mitigated quickflow and augment baseflow in Duobukuli River Basin. Our results could provide insights for future decision-making for rehabilitation and conservation of wetlands as well as integrated basin water resources management.

Effects of land use change on hydrological cycle from forest to upland field in a catchment,Japan

Understanding the effects of land use change on the hydrological cycle is very important for development of sustainable water resource in an upland field catchment.In this study,soil and hydrological properties in an upland field catchment,which was reclaimed partially from a forest catchment,were compared with another forest catchment.The soil properties of surface and subsurface layers were investigated in the two catchments.The soil was compacted and waterholding capacity of soil in the upland field catchment became smaller after the reclamation from forest to upland field,which decreased infiltration rate and water storage in the soil layers.We found that peak discharge and direct runoff in the upland field catchment increased compared with the forest catchment.Annual evapotranspiration from the upland field catchment tended to be lower due to the change in vegetation type and soil properties.Furthermore,a semi-distributed hydrological model was applied in the upland field catchment to understand the integrated effects of reclamation on the hydrological cycle.The model parameters,which were determined using a nonlinear optimization technique—the Shuffled Complex Evolution method(SCE),were compared between the two catchments.The Nash and Sutcliffe coefficient was used to evaluate the model performance.The simulated results indicated that evapotranspiration was decreased and change in discharge was more obvious in the surface layer.We considered that declined infiltration and water storage and increased peak discharge and direct runoff have a negative impact on water resources in the upland field catchment.This study will provide information for forest managers in planning and making decisions for land and water resource management.

Surface storm flow prediction on hillslopes based on topography and hydrologic connectivity

Background:Hillslopes provide critical watershed ecosystem services such as soil erosion control and storm flow regulation through collecting,storing,and releasing rain water.During intense rainstorms,rainfall intensity and infiltration capacity on the hillslope control Hortonian runoff while the topographic attributes of the hillslope(e.g.,slope,aspect,curvature)and the channel network define the structural hydraulic connectivity that determines how rapidly excess water is transferred.This paper discusses literature on the link between topographic attributes and hydrologic connectivity and demonstrates how this link can be used to define a parsimonious model for predicting surface runoff during high intensity rainfall.Main text:First,we provide a topographic characterization of the hillslope necessary to determine the structural hydrologic connectivity of surface flow based on existing literature.Subsequently,we demonstrate a hydrologic surface response model that routes the geomorphologic unit hydrograph(GIUH)through a spatial domain of representative elementary hillslopes reflecting the structural hydrologic connectivity.Topographic attributes impact flow and travel time distributions by affecting gravitational acceleration of overland flow and channel,solar irradiance,flow deceleration by vegetation,and flow divergence/convergence.Conclusions:We show with an example where we apply the GIUH-based model to hypothetical hillslopes that the spatial organization of the channel network is critical in the flow and travel time distribution,and that topographic attributes are key in obtaining simple yet accurate representations of hydrologic connectivity.Parsimonious GIUH models of surface runoff that use this hydrologic connectivity have the advantage of low data requirements,being scalable and applicable regardless of the spatial complexity of the hillslope,and have the potential to fundamentally improve flood forecasting tools used in the assessment of ecosystem services.

Evaluation of the WEAP model in simulating subbasin hydrology in the Central Rift Valley basin, Ethiopia

Background:The subbasin hydrologic behaviors have been altered by many natural and anthropologic factors such as climate change and land development activities.Model-based assessment can be used to simulate both natural hydrological processes,human-induced effects,and management strategies on water resources.For the Ketar subbasin,the WEAP(water evaluation and planning)hydrologic model was developed that aimed at(1)evaluating the application of the WEAP model in the Ketar subbasin,(2)evaluating the demonstration of the WEAP model using model efficiency evaluation criteria,and(3)simulating hydrological processes of the subbasin using the WEAP model.Methods:WEAP-based soil moisture method(rainfall-runoff)hydrology routine is comprised of a lumped,onedimensional,two-layer soil water accounting that uses empirical functions to designate evapotranspiration,surface runoff,interflow,and deep percolation for a sub-unit at root zone.A catchment is considered as the smallest hydrologic response unit.The catchment’s surface hydrological balance is typically estimated by discretizing the catchment into multiple land uses for which water balance is estimated at root zone.Results:The monthly measured and simulated streamflow statistics showed a positive strong relationship with R^(2) of 0.82,NSE of 0.80,and IA of 0.95;and with R^(2) of 0.91,NSE of 0.91,and IA of 0.98 for calibration and validation periods respectively.Similarly,the mean monthly measured and simulated streamflow showed an agreement with R^(2) of 0.99,NSE of 0.97,and IA of 0.99,and R^(2) of 0.94,NSE of 0.93,and IA of 0.93 for the periods of calibration and validation respectively.Conclusion:The model has demonstrated the capability to represent the hydrologic dynamics of the subbasin both at monthly and mean monthly periods.In general,the overall model performance evaluation statistics show a very good agreement between measured and simulated streamflow at the outlet of the subbasin.