Recent advances in hydrology studies under changing permafrost on the Qinghai-Xizang Plateau

Due to the great influences of both climate warming and human activities,permafrost on the Qinghai-Xizang Plateau(QXP)has been undergoing considerable degradation.Continuous degradation of plateau permafrost dramatically modifies the regional water cycle and hydrological processes,affecting the hydrogeological conditions,and ground hydrothermal status in cold regions.Permafrost thawing impacts the ecological environment,engineering facilities,and carbon storage functions,releasing some major greenhouse gases and exacerbating climate change.Despite the utilization of advanced research methodologies to investigate the changing hydrological processes and the corresponding influencing factors in permafrost regions,there still exist knowledge gaps in multivariate data,quantitative analysis of permafrost degradation's impact on various water bodies,and systematic hydrological modeling on the QXP.This review summarizes the main research methods in permafrost hydrology and elaborates on the impacts of permafrost degradation on regional precipitation distribution patterns,changes in surface runoff,expansion of thermokarst lakes/ponds,and groundwater dynamics on the QXP.Then,we discuss the current inadequacies and future research priorities,including multiple methods,observation data,and spatial and temporal scales,to provide a reference for a comprehensive analysis of the hydrological and environmental effects of permafrost degradation on the QXP under a warming climate.

Analysing the Potential Impact of Climate Change on the Hydrological Regime of the Upper Benue River Basin (North Cameroon)

In this study, we analyse the climate variability in the Upper Benue basin and assess its potential impact on the hydrology regime under two different greenhouse gas emission scenarios. The hydrological regime of the basin is more vulnerable to climate variability, especially precipitation and temperature. Observed hydroclimatic data (1950-2015) was analysed using a statistical approach. The potential impact of future climate change on the hydrological regime is quantified using the GR2M model and two climate models: HadGEM2-ES and MIROC5 from CMIP5 under RCP 4.5 and RCP 8.5 greenhouse gas emission scenarios. The main result shows that precipitation varies significantly according to the geographical location and time in the Upper Benue basin. The trend analysis of climatic parameters shows a decrease in annual average precipitation across the study area at a rate of -0.568 mm/year which represents about 37 mm/year over the time 1950-2015 compared to the 1961-1990 reference period. An increase of 0.7°C in mean temperature and 14% of PET are also observed according to the same reference period. The two climate models predict a warming of the basin of about 2°C for both RCP 4.5 and 8.5 scenarios and an increase in precipitation between 1% and 10% between 2015 and 2100. Similarly, the average annual flow is projected to increase by about +2% to +10% in the future for both RCP 4.5 and 8.5 scenarios between 2015 and 2100. Therefore, it is primordial to develop adaptation and mitigation measures to manage efficiently the availability of water resources.

Integrated Hydrological Modeling of the Godavari River Basin in Maharashtra Using the SWAT Model: Streamflow Simulation and Analysis

Hydrological modeling plays a crucial role in efficiently managing water resources and understanding the hydrologic behavior of watersheds. This study aims to simulate daily streamflow in the Godavari River Basin in Maharashtra using the Soil and Water Assessment Tool (SWAT). SWAT is a process-based hydrological model used to predict water balance components, sediment levels, and nutrient contamination. In this research, we used integrated remote sensing and GIS data, including Digital Elevation Models (DEM), land use and land cover (LULC) maps, soil maps, and observed precipitation and temperature data, as input for developing the SWAT model to assess surface runoff in this large river basin. The Godavari River Basin under study was divided into 25 sub-basins, comprising 151 hydrological response units categorized by unique land cover, soil, and slope characteristics using the SWAT model. The model was calibrated and validated against observed runoff data for two time periods: 2003-2006 and 2007-2010 respectively. Model performance was assessed using the Nash-Sutcliffe efficiency (NSE) and the coefficient of determination (R2). The results show the effectiveness of the SWAT2012 model, with R2 value of 0.84 during calibration and 0.86 during validation. NSE values also ranged from 0.84 during calibration to 0.85 during validation. These findings enhance our understanding of surface runoff dynamics in the Godavari River Basin under study and highlight the suit-ability of the SWAT model for this region.

Changes in climatic conditions drive variations in arbuscular mycorrhizal fungi diversity and composition in semi-arid oak forests

Arbuscular mycorrhizal fungi(AMF)play a vital role in plant productivity and ecosystem functions.However,their responses to abiotic factors(i.e.,climate,physiography,and soil properties)are unknown,especially across climatic gradients and slope aspects in arid and semi-arid ecosys-tems.In this study,using 60 composite soil samples,direct and indirect effects of climate factors and slope aspects on AMF diversity,composition and spore density were studied.The findings indicate that climate has a more direct influ-ence on soil properties(P<0.001)in comparison to slope aspect(P=0.449).In contrast,climate significantly affected AMF diversity and composition,with the highest diversity in dryer areas.Soil pH had the highest correlation with different facets of AMF diversity.Structural equation modeling(SEM)indicated that only a small part of the variation in AMF diversity and spore density could be explained by climate characteristics,slope aspect and soil properties.Based on SEM results,climate was the most important determinant of AMF diversity and spore density;slope aspect had a less critical role.The outputs suggest that variations in AMF diversity are derived by the direct effects of climate and the indirect effect of soil chemical properties.In addition,with increasing dryness,sporulation and AMF diversity increased.

Scale dependence of forest fragmentation and its climate sensitivity in a semi-arid mountain:Comparing Landsat,Sentinel and Google Earth data

Landscape fragmentation is generally viewed as an indicator of environmental stresses or risks,but the fragmentation intensity assessment also depends on the scale of data and the definition of spatial unit.This study aimed to explore the scale-dependence of forest fragmentation intensity along a moisture gradient in Yinshan Mountain of North China,and to estimate environmental sensitivity of forest fragmentation in this semi-arid landscape.We developed an automatic classification algorithm using simple linear iterative clustering(SLIC)and Gaussian mixture model(GMM),and extracted tree canopy patches from Google Earth images(GEI),with an accuracy of 89.2%in the study area.Then we convert the tree canopy patches to forest category according to definition of forest that tree density greater than 10%,and compared it with forest categories from global land use datasets,FROM-GLC10 and GlobeLand30,with spatial resolutions of 10 m and 30 m,respectively.We found that the FROM-GLC10 and GlobeLand30 datasets underestimated the forest area in Yinshan Mountain by 16.88%and 21.06%,respectively;and the ratio of open forest(OF,10%<tree coverage<40%)to closed forest(CF,tree coverage>40%)areas in the underestimated part was 2:1.The underestimations concentrated in warmer and drier areas occupied mostly by large coverage of OFs with severely fragmented canopies.Fragmentation intensity of canopies positively correlated with spring temperature while negatively correlated with summer precipitation and terrain slope.When summer precipitation was less than 300 mm or spring temperature higher than 4℃,canopy fragmentation intensity rose drastically,while the forest area percentage kept stable.Our study suggested that the spatial configuration,e.g.,sparseness,is more sensitive to drought stress than area percentage.This highlights the importance of data resolution and proper fragmentation measurements for forest patterns and environmental interpretation,which is the base of reliable ecosystem predictions with regard to the future climate scenarios.

Estimating the Drought-Induced Yield Loss for Winter Wheat in a Semi-Arid Region of the Southern United States Using a Drought Index

The economy of most rural locations in the semi-arid region of Llano Estacado in the southern United States is predominantly based on agriculture, primarily beef and wheat (Triticum aestivum L.) production. This region is prone to drought and is projected to experience a drier climate. Droughts that coincide with the critical phenological phases of a crop can be remarkably costly. Although drought cannot be prevented, its losses can be minimized through mitigation measures if it is predicted in advance. Predicting yield loss from an imminent drought is an important need of stakeholders. One way to fulfill this need is using an agricultural drought index, such as the Agricultural Reference Index for Drought (ARID). Being plant physiology-based, ARID can represent drought-yield relationships accurately. This study developed an ARID-based yield model for predicting the drought-induced yield loss for winter wheat in this region by accounting for its phenological phase-specific sensitivity to water stress. The reasonable values of the drought sensitivity coefficients of the yield model indicated that it could reflect the phenomenon of water stress decreasing the winter wheat yields in this region reasonably. The values of the various metrics used to evaluate the model, including Willmott Index (0.86), Nash-Sutcliffe Index (0.61), and percentage error (26), indicated that the yield model performed fairly well at predicting the drought-induced yield loss for winter wheat. The yield model may be useful for predicting the drought-induced yield loss for winter wheat in the study region and scheduling irrigation allocation based on phenological phase-specific drought sensitivity.

Spatio-temporal variation of depth to groundwater level and its driving factors in arid and semi-arid regions of India

Climate change and increasing anthropogenic activities,such as over-exploitation of groundwater,are exerting unavoidable stress on groundwater resources.This study investigated the spatio-temporal variation of depth to groundwater level(DGWL)and the impacts of climatic(precipitation,maximum temperature,and minimum temperature)and anthropogenic(gross district product(GDP),population,and net irrigated area(NIA))variables on DGWL during 1994-2020.The study considered DGWL in 113 observation wells and piezometers located in arid western plains(Barmer and Jodhpur districts)and semi-arid eastern plains(Jaipur,Ajmer,Dausa,and Tonk districts)of Rajasthan State,India.Statistical methods were employed to examine the annual and seasonal patterns of DGWL,and the generalized additive model(GAM)was used to determine the impacts of climatic and anthropogenic variables on DGWL.During 1994-2020,except for Barmer District,where the mean annual DGWL was almost constant(around 26.50 m),all other districts exhibited increase in DGWL,with Ajmer District experiencing the most increase.The results also revealed that 36 observation wells and piezometers showed a statistically significant annual increasing trend in DGWL and 34 observation wells and piezometers exhibited a statistically significant decreasing trend in DGWL.Similarly,32 observation wells and piezometers showed an statistically significant increasing trend and 37 observation wells and piezometers showed a statistically significant decreasing trend in winter;33 observation wells and piezometers indicated a statistically significant increasing trend and 34 had a statistically significant decreasing trend in post-monsoon;35 observation wells and piezometers exhibited a statistically significant increasing trend and 32 observation wells and piezometers showed a statistically significant decreasing trend in pre-monsoon;and 36 observation wells and piezometers reflected a statistically significant increasing trend and 30 observation wells and piezometers reflected a statistically significant decreasing trend in monsoon.Interestingly,most of the observation wells and piezometers with increasing trends of DGWL were located in Dausa and Jaipur districts.Furthermore,the GAM analysis revealed that climatic variables,such as precipitation,significantly affected DGWL in Barmer District,and DGWL in all other districts was influenced by anthropogenic variables,including GDP,NIA,and population.As a result,stringent regulations should be implemented to curb excessive groundwater extraction,manage agricultural water demand,initiate proactive aquifer recharge programs,and strengthen sustainable management in these water-scarce regions.

Hydrologic Response to Future Climate Change in the Dulong-Irra-waddy River Basin Based on Coupled Model Intercomparison Project 6

Within the context of the Belt and Road Initiative(BRI)and the China-Myanmar Economic Corridor(CMEC),the Dulong-Ir-rawaddy(Ayeyarwady)River,an international river among China,India and Myanmar,plays a significant role as both a valuable hydro-power resource and an essential ecological passageway.However,the water resources and security exhibit a high degree of vulnerabil-ity to climate change impacts.This research evaluates climate impacts on the hydrology of the Dulong-Irrawaddy River Basin(DIRB)by using a physical-based hydrologic model.We crafted future climate scenarios using the three latest global climate models(GCMs)from Coupled Model Intercomparison Project 6(CMIP6)under two shared socioeconomic pathways(SSP2-4.5 and SSP5-8.5)for the near(2025-2049),mid(2050-2074),and far future(2075-2099).The regional model using MIKE SHE based on historical hydrologic processes was developed to further project future streamflow,demonstrating reliable performance in streamflow simulations with a val-idation Nash-Sutcliffe Efficiency(NSE)of 0.72.Results showed that climate change projections showed increases in the annual precip-itation and potential evapotranspiration(PET),with precipitation increasing by 11.3%and 26.1%,and PET increasing by 3.2%and 4.9%,respectively,by the end of the century under SSP2-4.5 and SSP5-8.5.These changes are projected to result in increased annual streamflow at all stations,notably at the basin’s outlet(Pyay station)compared to the baseline period(with an increase of 16.1%and 37.0%at the end of the 21st century under SSP2-4.5 and SSP5-8.5,respectively).Seasonal analysis for Pyay station forecasts an in-crease in dry-season streamflow by 31.3%-48.9%and 22.5%-76.3%under SSP2-4.5 and SSP5-8.5,respectively,and an increase in wet-season streamflow by 5.8%-12.6%and 2.8%-33.3%,respectively.Moreover,the magnitude and frequency of flood events are pre-dicted to escalate,potentially impacting hydropower production and food security significantly.This research outlines the hydrological response to future climate change during the 21st century and offers a scientific basis for the water resource management strategies by decision-makers.

基于Hydrology的山区1:1万DEM水系提取研究

利用重庆市万州区4幅比例尺为1∶1万,地面分辨率为5 m的DEM数据,根据地表径流模型原理,通过ArcGIS中的HydrologyTools模块进行D8算法提取流域水系,计算汇流累积量,并最终生成河网。结果表明:对1∶1万DEM进行水系提取,最小水道集水面积阈值设定为50 000个栅格较合理;对于山地地形,基于1∶1万DEM数据,利用ArcGIS Hydrology模块提取河网的方法,从提取的效率和结果的精度两方面看来都是切实可行的。

基于MCR模型与Hydrology扩展模块的建设用地适宜扩张路径研究

随着城市化进程的不断加快,建设用地扩张迅速,不合理的城市扩展模式会干扰区域经济与生态之间的协调发展,引发资源利用不合理、生态环境恶化等负面效应。利用移动窗口法、MCR模型、Hydrology扩展模块相结合,得到武汉市适宜扩张路径、生态安全路径,为未来城市规划提供了借鉴。结果表明:(1)适宜建设区(适宜扩张区、优化建设区)所占比例达60.59%,说明目前城市发展格局较为合理;(2)不同的适宜性分区对于建设活动的要求不同,适宜建设区域可引导进行建设开发活动,禁止建设区、生态恢复区应设立相关政策,严禁开发;(3)“山谷线”作为建设用地的适宜扩展路径,“山脊线”作为生态安全路径,可避免建设用地盲目扩张,为城市建设指明了方向;(4)生态关键点对于维护城市的生态安全至关重要,应制定相关措施,进行有效管理。

Primary Research on WSeveral Theorems,Laws and Corollaries of Hydrology

The conceptions of theorems, laws and corollaries of hydrology were put forward. Combining with hydrology practice, several theo- rems, laws as well as corollaries of hydrology were summarized. The study provided some references for accelerating the development of hydrology theory in these aspects and promoting the improvement of its production technology.

Present and future of hydrology

The complexities of hydrological phenomena, the causes that lead to these complexities, and the essences and defects of reductionism are analyzed. The driving forces for the development of hydrology and the formation of branch subjects of hydrology are discussed. The theoretical basis and limitations of existing hydrology are summarized. Existing misunderstandings in the development of the watershed hydrological model are put forward. Finally, the necessity of the expansion of hydrology from linear to nonlinear is discussed.

Hydrology and water resources variation and its response to regional climate change in Xinjiang

Based on the surface runoff, temperature and precipitation data over the last 50 years from eight representative rivers in Xinjiang, using Mann-Kendall trend and jump detection method, the paper investigated the long-term trend and jump point of time series, the surface runoff, mean annual temperature and annual precipitation. Meanwhile, the paper analyzed the relationship between runoff and temperature and precipitation, and the flood frequency and peak flow. Results showed that climate of all parts of Xinjiang conformably has experienced an increase in temperature and precipitation since the mid-1980s. Northern Xinjiang was the area that changed most significantly followed by southern and eastern Xinjiang. Affected by temperature and precipitation variation, river runoff had changed both inter-annually and intra-annually. The surface runoff of most rivers has increased significantly since the early 1990s, and some of them have even witnessed the earlier spring floods, later summer floods and increasing flood peaks. The variation characteristics were closely related with the replenishment types of rivers. Flood frequency and peak flow increased all over Xinjiang. Climate warming has had an effect on the regional hydrological cycle.

IMPORTANCE OF HYDROLOGY, SOIL AND VEGETATIONIN WETLAND RESEARCH

Wetlands, one of the most productive systems in the biosphere are a unique ecosystem. They occur in landscapes that favor the ponding or slow runoff of surface water, discharge of ground water, or both. Wetlands are not only important for maintaining plant and animal diversity, but also for balancing global carbon budget via sequestrating or releasing CO2 from/into atmosphere depending on their management. Therefore, it is imperative to understand how wetlands form and function, then we can better manage, utilize, and protect these unique ecosystems. Hydrie soils,hydrophytic vegetation, and wetland hydrology are the three main parameters of wetlands. These parameters are interrelated with each other which jointly influence the development and functions of wetland ecosystems. The objective of this paper was to report the current understanding of wetlands and provide future research directions. The paper will first focus on aspects of hydrology research in wetlands, and then shift to soil hydrosequence and wetland vegetation to better understand processes, structure, and function of wetlands, and conclude with some possible future research directions.

Application of Developed Grid-GA Distributed Hydrologic Model in Semi-Humid and Semi-Arid Basin

A grid and Green-Ampt based （Grid-GA）distributed hydrologic physical model was developed for flood simulation and forecasting in semi-humid and semi-arid basin. Based on topographical information of each grid cell extracted fi＇om the digital elevation model （DEM） and Green-Ampt infiltration method, the Grid-GA model takes into consideration the redistribution of water content, and consists of vegetation and root interception, evapotranspiration, runoff generation via the excess infiltration mechanism, runoff concentration, and flow routing. The downslope redis- tribution of soil moisture is explicitly calculated on a grid basis, and water exchange among grids within runoff routing along the river drainage networks is taken into consideration. The proposed model and Xin＇anjiang model were ap- plied to the upper Lushi basin in the Luohe River, a tributary of the Yellow River, with an area of 4 716 km2 for flood simulation. Results show that both models perform well in flood simulation and can be used for flood forecasting in semi-humid and semi-arid region.

Important progress on the use of isotope techniques and methods in catchment hydrology

The use of isotope techniques and methods in catchment hydrology in the last 50 years has generated two major types of progress: (1) Assessment of the temporal variations of the major stocks and flows of water in catchments, from which the estimation of wa-ter residence times is introduced in this paper. (2) Assessment of catchment hydrologic processes, in which the interactions be-tween different waters, hydrographical separation, and bio-geochemical process are described by using isotopes tracers. Future progress on isotope techniques and methods in hydrology is toward the understanding of the hydrological process in large river basins. Much potential also waits realization in terms of how isotope information may be used to calibrate and test distributed rainfall-runoff models and regarding aid in the quantification of sustainable water resources management.

Land Surface Hydrology Parameterization over Heterogeneous Surface for the Study of Regional Mean Runoff Ratio with Its Simulations

An analytical expression for subgrid–scale inhomogeneous runoff ratios generated by heterogeneous soil moisture content and climatic precipitation forcing is presented based on physical mechanisms for land surface hydrology and theory of statistical probability distribution. Thereby the commonly used mosaic parameterization of subgrid runoff ratio was integrated into a statistical–dynamic scheme with the bulk heterogeneity of a grid area included. Furthermore, a series of numerical experiments evaluating the reliability of the parameterization were conducted using the data generated by the emulated simulation method. All the experimental results demonstrate that the proposed scheme is feasible and practical.

Karst caves and hydrology between geodesy and archeology:Field trip notes

The Geodynamics-Earth-Tides-meeting-2016 was held in the Karst, the origin of geologic karst- formation. Surface-rivers are absent, and water flows in channels over distances of 30 km, forming subsurface caves. Geodetic observations allow detecting caves and sense hydrologic flow. The Karst water had been recognized before Romans as provision for man and livestock. Proto-historic remains near the mouth of the underground river suggest the water outpouring from the Karst was associated with deities to be worshiped. Here the geodetic and cultural aspects of the Karst are summarized, illustrating the field trip that had been offered to the participants.

Coupled modeling of land hydrology-regional climate including human carbon emission and water exploitation

Carbon emissions and water use are two major kinds of human activities. To reveal whether these two activities can modify the hydrological cycle and climate system in China, we conducted two sets of numerical experiments using regional climate model RegCM4. In the first experiment used to study the climatic responses to human carbon emissions, the model were configured over entire China because the impacts of carbon emissions can be detected across the whole country. Results from the first experiment revealed that near-surface air temperature may significantly increase from 2007 to 2059 at a rate exceeding 0.1 ~C per decade in most areas across the country; southwestern and southeastern China also showed increasing trends in summer precipitation, with rates exceeding 10 mm per decade over the same period. In summer, only northern China showed an increasing trend of evapotranspiration, with increase rates ranging from 1 to 5 mm per decade; in winter, increase rates ranging from 1 to 5 mm per decade were observed in most regions. These effects are believed to be caused by global warming from human carbon emissions. In the second experiment used to study the effects of human water use, the model were configured over a limited region-- Haihe River Basin in the northern China, because compared with the human carbon emissions, the effects of human water use are much more local and regional, and the Haihe River Basin is the most typical region in China that suffers from both intensive human groundwater exploitation and surface water diversion. We incorporated a scheme of human water regulation into RegCM4 and conducted the second experiment. Model outputs showed that the groundwater table severely declined by -10 m in 1971-2000 through human groundwater over- exploitation in the basin; in fact, current conditions are so extreme that even reducing the pumping rate by half cannot eliminate the ground- water depletion cones observed in the area. Other hydrological and climatic elements, such as soil moisture, runoff generation, air humidity, precipitation, wind field, and soil and air temperature, were also significantly affected by anthropogenic water withdrawal and consumption, although these effects could be mitigated by reducing the amount of water drawn for extraction and application.

Aspects of forest restoration and hydrology:the hydrological function of litter

Although forests play important roles in the hydrological cycle,there is little information that relates the water retention capacity of litter in areas under passive restoration,especially in Cerrado savannas.This study relates litter levels to water holding capacity and effective water retention among forest fragments under different passive restoration stages:46,11,and 8 years to better understand litter hydrological functions in the Cerrado.Water retention capacity and effective water retention capacity of litters(unstructured materials,branches and leaves)in the field were monitored on a monthly basis.Total litter accumulation at 46 years was significantly higher than that of the other succession stages.Unstructured litter mass was significantly higher than that of leaves and branches.The 46-year stage had the highest water holding capacity in the leaf fraction,followed by unstructured material and branches.Although the water holding capacity was lower in the oldest resto-ration,this site showed the highest efficiency under field conditions.The process was quickly reestablished,as the 11-year restoration showed results closer to that for the 46-year stage in comparison to the area at 8 years.Thus,passive restoration plays a key role in soil water mainte-nance due to the influence of litter in Cerrado savannas.Deforestation and the imminent need of restoring degraded sites,highlight the need for further studies focused on bet-ter understanding of the process of forest restoration and its temporal effect on soil water recovery dynamics.