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The Niger Delta at the southernmost part of Nigeria, is a large and ecologically sensitive region. Natural and anthropogenic activities, such as subsidence, sea-level rise, upstream dams and reservoirs, dredging and overabstraction of groundwater, disturb this equilibrium, leading to adjustments in ecological conditions and boundaries. Ecological changes affecting large areas cannot be explained by local observation. Relating observed effects to causes of environmental behaviour therefore requires a regionalized data collection, that provides a broader perspective of the issues involved with resultant ease in the identification of common problems and formulation of effective solutions.

Groundwater is faced to seawater in the end of its flow system. The shape of the interface of the fresh groundwater and salt water is discussed by Ghyben-Herzberg Low, in the previous studies. However, the groundwater push out the interface to the off-shore side than the low expected and the fresh groundwater flows even in the marine bottom (beneath of the marine bottom). This study summarized the previous studies for the interface and review the data of recent works. Distribution of submarine groundwater discharge and the shape of the seawater / freshwater interface is related strongly each other. The understanding of the groundwater flow property in the bottom end of its flow system will be useful for the development of water resources and evaluation for the environments.

Copyright © 2013 John Wiley & Sons, Ltd. Introduction Tropical dry forests have lived in the shadow of their humid counterparts with respect to scientific research. Despite accounting for more than 42% of all tropical forest (Murphy and Lugo, 1995) and roughly 6% of the Earth’s land surface, less than 15% of the literature on all tropical forest research has focused on tropical dry forests with the remainder highlighting work in tropical wet forests (Sanchez-Azofeifa et al., 2005; Santos et al., 2011). Many of these tropical dry forest regions are currently water stressed, and additional pressures from population growth, land use and future climate change will have significant implications for the future functioning of their natural and socioeconomic systems. In spite of the recognized importance ofwater resources in the tropics, there have been remarkably few publications on the hydrological processes in this region as compared to the humid temperate zone (e.g. Bonell, 1993, 1998; Buttle et al., 2009;Ohte andTokuchi, 2011; Price, 2011). This is especially true for tropical dry forests, which is surprising given that surface runoff is often limited to a 3 – 5month period annually, with an intervening dry period with little to no precipitation (Ortiz-Jimenez et al., 2005; Love et al., 2010). Hence, there is a critical need to understand the hydrology of tropical dry forests, particularly in light of current land use and future climate change issues facing these regions. In this, commentary we will highlight the

After several decades of interception studies, there are still considerable gaps in the understanding of wet-canopy evaporation. Model development is being obstructed by the lack of techniques for the measurement of state and rate variables which have to be quantified for model validation. The applicability of microwave attenuation measurements for the determination of canopy wetness is examined. The attenuation caused by a single spruce fir in the laboratory and the vertical attenuation profiles of a Douglas fir stand were measured under dry and wet conditions. The results indicate an instant increase of the attenuation upon wetting and a decrease owing to drip and evaporation after rainfall ceased. From the results, conclusions have been drawn on the design of instrumentation for an optimized measuring system which is suitable for unattended automated scanning of canopy water storage. This system has been calibrated, using vertically integrated microwave attenuation profiles and canopy water budgets from precipitation and throughfall measurements. This system will be used for a forest hydrological study in the framework of the Dutch ACIFORN project, a research project on the effect of atmospheric deposition on Douglas fir vitality.

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In this study a 25-year (1976–2000) series of observed precipitation, temperature, runoff and further water-flows of a lysimeter balance within the pre-alpine research catchment Rietholzbach (Switzerland) is analyzed. The comparison of the precipitation volumes on this lysimeter to precipitation collected by a conventional rain gauge shows that conventional rain gauges provide strongly underestimated values for precipitation, especially in winter. The obtained monthly precipitation correction factors indicate that precipitation losses above 20% for rain and above 50% for snow are realistic. The observed hydrometeorological values allowed for improving the understanding of the model-based simulation of the hydrological processes with distributed hydrological models and for investigating both a conceptual and a physically based runoff-generation approach. The albedo, soil moisture and lysimeter water balance allowed for a simultaneous assessment of the performance of several model components, such as the soil moisture, runoff-generation and evapotranspiration modules and the module for the determination of snow cover accumulation and melt.

Three geophysical techniques have been applied within a complex man effected catchment (Vallcebre in Catalunya). The techniques explored included geoelectrical, seismies and some early attempts to apply a Ground Penetrating Radar (GPR) methodology. This area has a complex hydrology and the system is dominated by abandoned agricultural terraces and man made ditches. The work shows the possibility to acquire key hydrological parameters used in the construction of models and to demonstrate how the shallow geophysical methods can be used within experiments to visualize 3D hydrological flow processes.

The role and relative importance of experimental and representative basins in pre-dieting anthropogenic effects on water resources and the environment was the goal of the International Conference on Hydrological Research Basins and the Environment, held in Wageningen, the Netherlands, September 24–28, 1990. About 70 persons, almost exclusively from Europe, attended the meeting, which was organized by the Committee of the European Network of Experimental and Representative Basins and the National Committee of the Netherlands for the International Hydrological Program of Unesco. During the conference, the 3rd General Meeting of the European Network of Experimental and Representative Basins was held. This network of basins, covering nine countries in Europe, organizes periodic meetings and tries to enhance the compatibility of observations and methods of analysis, and to implement research projects of common interest.

In the past, land consolidation projects in the Netherlands were aimed almost exclusively at increase of crop yields and farm income. Also the improvement of the water management system served agricultural purposes. Hydrological research, therefore, was directed to find optimal agrohydrological conditions. The results were translated into criteria for hydrological variables (like groundwater and surface water levels, discharge coefficients) and design rules for subsurface drainage systems. Initially the need to reduce excessive wetness was emphasized, later yield reduction due to water shortages in summer also became important. Lately the land consolidation projects have been renamed as “land development projects”. This is a result of recent developments in the rural areas, where aspects of nature conservation and outdoor recreation have become important items. Because water management measures in favour of one function often interfere with another, fixed design rules are no longer sufficient. The hydrological consequences for different interests have to be known beforehand. For the calculations of groundwater flow, analytical solutions are being replaced by numerical methods in order to cope with increasingly complex situations. Aspects of water quality are becoming more important. In addition to analyses of water samples, attention is paid to flow paths and stream velocities of groundwater, which give insight into the relation between quality and quantity. In this work, a close cooperation with agronomists and biologists has been established. A review is given of the hydrological models used for this purpose, at present and in the near future.

SUMMARY This paper was presented to the Fifth British Empire Forestry Conference in London, 1947, and is reprinted here with the kind permission of the Director of Forestry. Progress made at the Jonkershoek Forest Influences Research Station in the Cape Province, the establishment of which was recommended by the Empire Forestry Conference in 1935, is described. A second research station, being established at Cathedral Peak in Natal, is briefly referred to. Surveys of site factors, technique of observations on rainfall, streamflow, net rainfall under forest canopies, infiltration, evaporation and transpiration, treatments being investigated, and design and interpretation of streamflow experiments, are discussed. The importance of streamflow investigations is specially stressed, and it is recommended that such research should be greatly extended, not only to test the effects of various forms of land management, but also to provide essential data on water supplies.

Observations in the Nabebuta and Kaioku districts show that the deep artesian water is not contaminated by the sea water, despite of the saline damage in the ground surface owing to the saline water percolation through the earth dam. The artesian heads in those areas are measured to be always lower than the sea level. These results suggest the existence of the impermeable layer between the aquifer and the sea water. Tidal changes in the water levels of four artesian wells are observed and are found the results corresponding with theoretically presented by the author under the assumption that the tidal effect on the artesian head is only due to the fluctuations in the loading weight upon the submarine aquifer. Some of the values which represent the characteristics of the aquifer are computed in using the analytical treatment from the observed results.

Summary The Cathedral Peak Forest Influences Research Station was established in Natal in 1938 to determine the effect of exotic conifer plantations on water supplies. The major investigation is the planting to within one chain of any streams, of six catchments with Pinus patula at eight year intervals. One catchment is to be protected from burning and grazing for an indefinite period to determine the trend of plant succession and the effect on water supplies of the various stages of the succession. An eighth catchment is to be grazed intermittently for five years followed by complete aforestation. The ninth catchment is to be completely planted to Pinus patula and no margins will be left open next to streams. Discharge from all experimental catchments is continuously recorded by means of clockwork instruments. The situation, topography, geology, soils, vegetation and climate of the area are described and mention is made of the nature of the streams and the more important characteristics of the catchments...

Intercepted rainfall may be evaporated during or after the rain event. Intercepted rain is generally determined as the difference between rainfall measurements outside and inside the forest. Such measurements are often used to discriminate between water storage and evaporation during rain as well. Two well-accepted methods underestimate water storage by a factor two as compared to direct observations. The underestimation of storage is compensated by an overestimation of evaporation during rain by a factor of three. The direct observations of water storage and evaporation appear to agree with previous direct observations. Thus, it is concluded that these observations are representative Also, our results based on methods using only rainfall measurements inside and outside the forest appear to agree with previous results, This would result in the conclusion that the common methods systematically underestimate water storage and overestimate evaporation during rain. Indeed, the systematic errors can be explained by the neglect of drainage before saturation. Water storage is better simulated assuming an exponential saturation of a larger storage capacity. A smaller evaporation can be simulated using an appropriate resistance to vapour transport. The observations in dense coniferous forest showed water storage to be the dominant process in rainfall interception, but this conclusion should not be generalized to other forests and climates. Direct observations of water storage and evaporation are recommended to build a realistic set of parameters for rainfall interception studies of the main vegetation types. (C) 1998 Elsevier Science B.V. All rights reserved.

This paper reports the effects of altering an aspen forest cover in Utah on evapotranspiration losses, overland flow, erosion, and mantle storage deficits during three successive growing seasons. These data, together with supplemental measures of winter precipitation and estimates of evaporation from snow, provided a basis for estimating amounts of water available for stream flow. Removal of aspen trees, leaving the herbaceous understory and litter undisturbed, reduced evapotranspiration losses and increased the amount of water available for stream flow by about four inches without seriously increasing overland flow or soil erosion during summer rains. Removal of the remaining herbaceous cover further reduced evapotranspiration losses and increased the amount of water available to streams by an additional four inches but resulted in an undesirable increase in summer rainfall runoff and soil loss.

Currently, the direction of hydrological research, highlighting certain aspects of the influenceof climatic factors on the average annual water discharge of river basins, is changing due to climate change,which is a function of annual atmospheric precipitation and average annual air temperature that characterizeevaporation, that is, hydrometeorological components of the geographical landscape reflecting that is theratio of heat and moisture, which is characteristic of the geographical area. One of the most importanttasks in the field of hydrological research is to study the genesis of long-term fluctuations in the averageannual water discharge and climatic indicators of the catchment area of river basins, and to identify theirregional patterns, modern geographic information systems and algorithms have been developed that makeit possible to quickly and efficiently solve this problem. On the basis of them, a research base was formedcovering the period 1934-2020, which is based on information and analytical materials of the reference andinformation portal «Weather and Climate», the RSE «Kazhydromet», the World Meteorological Organization(WMO) and the RSU «Tobol-Torgay Basin Inspection on the regulation of the use and protection of waterresources». The cyclical nature of the average annual water discharge, average annual air temperatures andannual atmospheric precipitation for the catchment area of the Tobol River basin manifests itself unequallyin separate periods at a particular phase of development, i.e. modeling linear trends and differential integralcurves. To assess the degree of synchronicity of average annual water discharge and average annual air temperatures and atmospheric precipitation, methodological support was developed, implemented in thecatchments of the Tobol River basin, which showed that in the steppe zone of Northern Kazakhstan, theirdegree of synchronicity is low, since the main source of runoff formation in the considered territory the snowcover of the previous year accumulated over the winter, that is, atmospheric precipitation at the end of theautumn and the beginning of the winter period, which are not taken into account when determining the degreeof synchronicity of a real year, which requires the need to clarify the structure of the calculated year, takinginto account the determining conditions for the formation of river flow.

Over the past decades, a number of water sciences and management programs have been developed to better understand and manage the water cycles at multiple temporal and spatial scales for various purposes, such as ecohydrology, global hydrology, sociohydrology, supply management, demand management, and integrated water resources management (IWRM). At the same time, rapid advancements have also been taking place in tracing, mapping, remote sensing, machine learning, and modelling technologies in hydrological research. Despite those programs and advancements, a water crisis is intensifying globally. The missing link is effective interactions between the hydrological research and water resource management to support implementation of the UN Sustainable Development Goals (SDGs) at multiple spatial scales. Since the watershed is the natural unit for water resources management, watershed science offers the potential to bridge this missing link. This study first reviews the advances in hydrological research and water resources management, and then discusses issues and challenges facing the global water community. Subsequently, it describes the core components of watershed science: (1) hydrological analysis; (2) water-operation policies; (3) governance; (4) management and feedback. The framework takes into account water availability, water uses, and water quality; explicitly focuses on the storage, fluxes, and quality of the hydrological cycle; defines appropriate local water resource thresholds through incorporating the planetary boundary framework; and identifies specific actionable measures for water resources management. It provides a complementary approach to the existing water management programs in addressing the current global water crisis and achieving the UN SDGs.

Over time, the content, scope and objectives of hydrological research in the Romanian Black Sea coastal area varied according to the state of society development, technology development and financial resources. Along with the activities of capitalizing on natural resources, water use, river and sea navigation, there have been demands for knowledge of the water regime and the interaction between the resource potential and the characteristics of the hydrological regime. As a result, hydrographic and hydrological research was started and developed in the Black Sea coastal zone. These researches developed in the first half of the nineteenth century, and then continued throughout this century and later in the twentieth century, with interruptions caused by the two world wars. Among the important activities that have taken place over time, there have been hydro-technical works. The design and elaboration of the projects of these works were based on the knowledge of the hydrographic and hydrological characteristics of the Black Sea coastal zone. This knowledge has evolved over time so that there is currently an important pool of data and information related to the hydrological, morphological, hydrochemical, hydrobiological characteristics of the water bodies mentioned. The paper presents briefly the most important moments of the history of the monitoring activity carried out over time in the Black Sea coastal zone, the types of coastal and transitional waters in Romania, coastal rehabilitation projects of the Black Sea, hydrological features, the structure of the marine complex model pom / ersem III) BREG / BSHELF.

Snow depth mirrors regional climate change and is a vital parameter for medium- and long-term numerical climate prediction, numerical simulation of land-surface hydrological process, and water resource assessment. However, the quality of the available snow depth products retrieved from remote sensing is inevitably affected by cloud and mountain shadow, and the spatiotemporal resolution of the snow depth data cannot meet the need of hydrological research and decision-making assistance. Therefore, a method to enhance the accuracy of snow depth data is urgently required. In the present study, three kinds of snow depth data which included the D-InSAR data retrieved from the remote sensing images of Sentinel-1 synthetic aperture radar, the automatically measured data using ultrasonic snow depth detectors, and the manually measured data were assimilated based on ensemble Kalman filter. The assimilated snow depth data were spatiotemporally consecutive and integrated. Under the constraint of the measured data, the accuracy of the assimilated snow depth data was higher and met the need of subsequent research. The development of ultrasonic snow depth detector and the application of D-InSAR technology in snow depth inversion had greatly alleviated the insufficiency of snow depth data in types and quantity. At the same time, the assimilation of multi-source snow depth data by ensemble Kalman filter also provides high-precision data to support remote sensing hydrological research, water resource assessment, and snow disaster prevention and control program.

In this paper, we demonstrated a practical application of realistic river image generation using deep learning. Specifically, we explored a generative adversarial network (GAN) model capable of generating high-resolution and realistic river images that can be used to support modeling and analysis in surface water estimation, river meandering, wetland loss, and other hydrological research studies. First, we have created an extensive repository of overhead river images to be used in training. Second, we incorporated the Progressive Growing GAN (PGGAN), a network architecture that iteratively trains smaller-resolution GANs to gradually build up to a very high resolution to generate high quality (i.e., 1024x1024) synthetic river imagery. With simpler GAN architectures, difficulties arose in terms of exponential increase of training time and vanishing/exploding gradient issues, which the PGGAN implementation seemed to significantly reduce. The results presented in this study show great promise in generating high-quality images and capturing the details of river structure and flow to support hydrological research, which often requires extensive imagery for model performance.

High-elevation grasslands worldwide provide essential hydrological services including water provision, flow regulation, and erosion control. Despite their importance, hydrological research of grasslands in montane regions is usually scarce and disperse, limiting the capacity to improve water resource management. We present a systematic literature review of the hydrological function of high Andean grasslands under conserved, degraded, and restored conditions in ecosystems situated above the tree line in the tropical Andes (paramos, punas, and jalcas). Most hydrological research on these grasslands has been developed in paramos (92%), especially in Ecuador, while research in punas is scarce (6%) despite being the largest grassland extent in the region. For paramos, published literature highlights the importance of conserving grasslands to facilitate water infiltration to soils, which in turn reduces erosive processes. Water-vegetation relations for conserved paramos are well understood, indicating that about 50% of water inputs return to the atmosphere via evapotranspiration, but knowledge about hydrological functions of conserved punas and jalcas is virtually non-existent. Under changing land use, afforestation of grassland ecosystems with exotic tree species, especially pines, reduces soil water storage as well as water yield and flow regulation capacity. Impacts of grazing and agriculture on the hydrological function of paramo grasslands strongly depend on historical land management and current land use practices and are not generalizable. Short-term restoration studies indicate that more than two years are necessary to recover the hydrological function of degraded grasslands, therefore medium and long-term studies are required to determine efficient restoration periods. These knowledge gaps limit the ability to extrapolate and regionalize findings. Future directions aimed to fill them are proposed, and methods successfully used to investigate the hydrology of high Andean grasslands are highlighted. This research not only enlightens what is known about the hydrology of high Andean grasslands, but also seeks to guide future hydrological evaluations to fill identified geographical and topical knowledge gaps precluding improved management of water resources in the tropical Andes.

Many small-scale water development initiatives are accompanied by hydrological research to study either the form of the intervention or its impacts. Humans influence both the development of intervention and research, and thus one needs to take human agency into account. This paper focuses on the effects of human actions in the development of the intervention and its associated hydrological research, as hydrological research is often designed without adequate consideration of how to account for human agency and that these effects have not yet been discussed explicitly in a systematic way. In this paper, we propose a systematic planning for hydrological research, based on evaluating three hydrological research efforts targeting small-scale water development initiatives in Vietnam, Kenya, and Indonesia. The main purpose of the three cases was to understand the functioning of interventions in their hydrological contexts. Aiming for better decision-making on hydrological research in small-scale water intervention initiatives, we propose two analysis steps, including (1) consideration of possible surprises and possible actions and (2) cost–benefit analysis. By performing the two analyses continuously throughout small-scale hydrological intervention-based initiatives, effective hydrological research can be achieved.