What is a river regime?

Each river is characterized by a unique river regime that can be stable or variable, depending on factors such as catchment conditions, precipitation, temperature, and anthropogenic influences. Understanding and analyzing the river regime are essential for effective surface water management, predicting extreme hydrological events such as floods and droughts, and protecting river biodiversity. This makes it possible to develop strategies to minimize the risk of natural disasters and ensure the sustainable use of water resources.

Factors shaping the river regime

The river regime (river regime, river regime) is the result of a complex interaction between many factors, which can be divided into three main categories: climatic, geographic and hydrological, and anthropogenic.

1. Climatic factors: climate is one of the most important determinants of the river regime. The amount and distribution of precipitation, temperature, and seasonal climatic changes have a direct impact on river flows. In arid climates, flows can be sporadic and dependent on periods of heavy rainfall, while in temperate and humid climates they are more regular. For example, in tropical regions, where there is a clear division of the year into rainy and dry seasons, the river regime is characterized by large fluctuations in flow. An example is rivers in India, which experience large increases in flow during monsoons. In temperate climates, where precipitation is more evenly distributed throughout the year, rivers exhibit less dramatic flow changes, with a typical spring peak due to melting snow.
2. Geographical and hydrological factors: catchment morphology, soil type, vegetation cover and the presence of natural water bodies have a significant impact on shaping the river regime. For example, rivers flowing through mountainous areas tend to have sharp increases in flow after heavy rainfall, while lowland rivers are characterized by more even flows. The presence of lakes, marshes and artificial reservoirs can act as a buffer, stabilizing flows by storing water and releasing it gradually.
3. Anthropogenic factors: human activities, including dam construction, land reclamation, irrigation and rainwater drainage, significantly modify the natural river regime. Urbanization and changes in land use can lead to a decrease in infiltration and an increase in surface runoff, resulting in a faster rise in river levels.

Types of river regimes

River regimes can be classified in various ways, but of particular note is Maurice Pardé’s (1955) typology, based on patterns of annual flow changes. He distinguished three basic types: simple, complex primary and complex variable regimes.

1. simple system – is characterized by one period of high and one period of low flows, meaning that the supply comes from one dominant source. Pardé distinguished five subtypes here:
   • Glacial – rivers reach their highest flows in summer, when glaciers melt;
   • Snowy mountain – high states occur in summer, but earlier than in the glacial system, maximum flows are also lower than in the glacial system;
   • Snowy plain – high flows occur in spring, during snowmelt;
   • Rainy oceanic – rivers have high flows in winter, and the difference between high and low flows is not large;
   • Rainy intertropical – rivers have high flows in the rainy season and low flows in the dry season. The differences between the two are significant.
2. primary complex system – rivers fed from two sources, leading to two periods of maximum and two periods of minimum flows. Within this type, Pardé distinguished several subtypes:
   • Snowy transitional – rivers mainly fed by water from snowmelt, and the second maximum is caused by winter rainfall;
   • snow plain – the main surges are caused by spring snowmelt, and the second, smaller ones are caused by autumn rainfall;
   • snow and rain – the main surge comes from snowmelt, and the second, smaller surge comes from summer precipitation;
   • Rain-snow – the main surge is caused by rains, and the second, smaller surge is caused by snowmelt.
3. complex variable system – rivers fed from more than two sources, meaning that there are several periods of highs and lows throughout the year. Examples include rivers such as the Po, Mississippi and East Asian rivers [1].

The importance of the river regime in water resources management

The river regime plays a fundamental role in water resources management at various levels, from local to global. Its understanding and continuous monitoring are essential for the effective management of surface water, the design of hydraulic infrastructure and the protection of river ecosystems.

A key aspect of water resources management is knowledge of the river regime, especially in regions where periodic water shortages pose serious challenges. In agriculture, the river regime determines the availability of irrigation water, which has a direct impact on production efficiency. In regions with seasonal precipitation, precise water resources management requires a deep understanding of cyclical changes in river flow to supply water during periods of drought.

In addition, the river regime has a direct impact on the planning and management of hydrotechnical infrastructure, such as dams, reservoirs, irrigation channels and flood control systems. In regions where the river regime is characterized by irregular flows, it is necessary to take these seasonal and annual variations into account when designing hydrotechnical structures. Only in this way can potential damage to infrastructure be prevented and the risk of flooding and drought minimized.

Protection of river ecosystems is another aspect in which the river regime plays an important role. The natural rhythm of river flows is essential to the health of aquatic ecosystems, and any changes in these flows can lead to habitat degradation, a decline in biodiversity and negative impacts on water-dependent species. For example, the construction of dams and other artificial regulations can disrupt the natural river regime, which consequently risks reducing populations of migratory fish that depend on seasonal changes in water flow.

Challenges of monitoring river regimes

Today’s challenges in monitoring river regimes stem primarily from ongoing climate change and increasing anthropogenic pressure on resources. Rising temperatures, changes in precipitation patterns and more frequent extreme weather events are significantly affecting river dynamics, leading to more frequent and intense flooding. In addition, intensive urbanization and land use changes are modifying natural river regimes, increasing the risk of urban flooding and degradation of aquatic ecosystems. In response to these challenges, it is necessary to implement advanced monitoring techniques. Only such an approach will enable better understanding and adaptation to dynamically changing hydrological conditions.

[1] Elizabeth Bajkiewicz-Grabowska E. (2020), General hydrology (p. 294). PWN Scientific Publishing House.