Many specific scientific problems or challenges related to hydrological study exist. These include assessing the impacts that growing populations have on water demand, land use change on groundwater reserves, and river discharges. Once successfully concluded, these assessments must be utilized as tools for predicting the extent of expected water stress in the coming decades due to potential changes in supply and demand of water resources. Scientists must strive to understand the extent to which increased evaporation and transpiration through increased withdrawal of groundwater and surface water will lead to changes in the local and global water cycle. There is a growing need for improved understanding of pollutant-related flows in groundwaters and the self-cleaning capacities of aquifers and rivers related to different pollutants. Work will need to be conducted that will describe the impacts of population growth and land use change on the quality of groundwater reserves, soils, and rivers and also what the effects may be to the natural ecosystems that depend on them.
Studies will need to be conducted to better understand landscape processes including hill slope forms, channel networks and the processes responsible for transportation of water, sediments, and pollutants. Hydrological research in past decades has focused attention mainly on modeling the dynamic response of channel networks. Progress in understanding catchment-scale flow processes will require that relevant hill slope flow processes also be carefully studied. This will require collaborative research approaches between hydrologists, geomorphologists, geologists, pedologists and other scientists to identify scaling relationships present in flow domain structures.
There remains a need for improved understanding of the interactions between climate change and the hydrologic cycle. Further understanding and documentation is required to predict apparent changes that have led to an intensification of the hydrological cycle due to climate change. Critical questions need to be asked concerning current changes observed in water availability and whether critical regions can be identified where the interactions between water availability and human demand becomes problematic. Conducting this type of research necessitates the need to better understand past climates and paleo-hydrological behavior. At present, the ability to predict changes in the fluxes of the water cycle under various scenarios of climate change is poor. It is therefore desirable to create improved methods of portraying the interactions between water systems and natural and human induced environments.
Due to the inherently complex nature of hydrological systems, the characterization and subsequent modeling of these systems is a continual challenge faced by scientists. There are a number of unresolved issues that continue to impede the ability of scientists to analyze and predict behavioral changes of hydrological systems. One of the most predominant features of hydrological systems is the spatial heterogeneities and temporal variability’s that occur perpetually and persistently at multiple scales. Modeling physical processes encumbered by such complexity is a constant challenge. It is for these reasons that theoretical upscaling and downscaling attempts to develop quantitative links among process descriptions at various hydrological scales has been such an arduous task. New or modified algorithms need to be devised, which will govern observed variabilities, and define constitutive relations for each system. In the past, many empirical observations made on simple systems have been often erroneously applied to more complicated systems. Since hydrologic systems are quite complex, and equations valid at one scale are not necessarily valid at higher scales, one may question the applicability of theories that are originally developed for a simple system and vise versa. Moreover, hydrological processes are nonlinear and there tend to be strong couplings among them. As a result, the effect of one process is influenced by the occurrence of other processes, and a negligible effect of one process can lead to significant impacts on another. Clearly, there is a need to develop rigorous physically-based theories, which describe the synergistic relationships of coupled nonlinear hydrologic systems at various scales. Intense study at the small scale is not leading to reliable working policy for addressing watershed processes critical to broad scale water management. As such, work needs to be undertaken designed specifically to improve our ability to model and predict water flows and movement. Finally, these models must also be appropriate and applicable to the modeling and accurate prediction of flows and outputs in ungauged basins.
Hydroelectric dams, while important for the generation of electricity, have transformed large fluvial systems into chained lakes. These large waterworks have generated a number of substantial environmental disruptions, including the erection of what are often unsurpassable obstacles for fish, explosive growth of floating aquatic plants, and eutrophication of dam reservoirs. The large development projects that connect watersheds and improve continental navigation networks, also affect wetlands. Timber harvest can likewise have negative effects on the production and regulation of water flows because increased soil erosion rates may increase the amount of suspended sediments, which can affect the quality of the water resources and the functioning of dams and reservoirs. On this basis, studies need to be implemented to clarify the most appropriate management practices for harvesting timber.
Water resource management faces many other problems. Academia needs to completely understand the current crisis to become innovative in producing new technologies and in advocating arrangements to satisfy demand. The sciences must be able to integrate and upscale. The field of Ecohydrology (Ecology and Hydrology) is a testimony to the potential success of integration science and should serve as a model for future interdisciplinary cooperatives. However, from a historical context, academia is easily drawn apart to the point that each discipline often fails to identify with statements of findings produced by other disciplines. The public is poorly served by a divided or polarized science. Hydrologists are not unique integrators amongst scientists, but interdisciplinary research is required in hydrology to solve the current water-related problems. The goal of strengthening the identity of hydrology as a discipline is commensurate with hydrology’s desire to better serve the needs of society. For example, the general public is much more aware of water problems (too much, too little, too dirty) than of the discipline of hydrology and how it relates to water problems. However, people agree that objectives intended to strengthen the hydrological sciences will result in hydrology being better equipped to serve well the needs of society. These are therefore compatible ideals, well suited to serve both coalitions.
Hydrological resources management has evolved through incremental refinements to its current point by using information on precipitation, stream flows, water demands, and other processes based largely on a measurement technology that is often archaic in design. Now, scientific advances offer technologies that can be used to add much more information and provide much greater detail. The academic community is often the source of new science and of new technology designed to better organize and disseminate information. Academia is also often the source of courses and literature intended to inform people and make them comfortable with information resources. The world has a fixed quantity of water to use to satisfy a widening diversity and deepening intensity of human and environmental needs. There must therefore be a concerted effort on the part of academia to inform the general public of the limitations to hydrological resources. A system for water resources management must also be sustainable to succeed. It is a major challenge to preserve options in a dynamic world where changes are caused by anthropogenic activities, environmental evolution, and geologic processes. These are the challenges that await educators, scientists, and water resource managers for the future. Ultimately, a management system that addresses periodic severe crises may be less sustainable than that which is designed to mitigate long-term contingencies. Perhaps the greatest difficulty lies in protecting future options as social preferences change. Regardless of origin, scientists, educators, politicians and lawmakers must all cooperate to meet these challenges.
Population growth and land use changes have resulted in sizeable impacts on surface water and groundwater resources. Increasing demands for fresh water has lead to water stress in many parts of the world. Increasing quantities of water are used for agriculture, and increasing water quantities withdrawn from subsurface water bodies and large rivers have had significant influences on the water cycle. Population growth and land use changes have led to polluting of surface waters and groundwater resources as well as soil deterioration through erosion, salinization, and of course pollution. The ability to meet challenges for increased demand and propose mitigating strategies will require intensive studies looking into the way that population growth and associated land use change and water demands influence the local, regional and global water cycle.