Hydrology

Hydrology is the multidisciplinary science that investigates the occurrence, distribution, movement and storage of water within the Earth system. It encompasses the study of the hydrologic cycle—from precipitation and evapotranspiration to infiltration, surface runoff and groundwater recharge—and its interactions with atmospheric, terrestrial and oceanic processes. Advances in hydrology now integrate classical field measurements with remote sensing, numerical modelling and big data analytics to both elucidate natural variability and predict future water resource trends under the pressures of climate change and urbanisation. At its core, modern hydrology provides essential insights for water management, flood risk mitigation, ecological conservation and sustainable development.

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Groundwater sustainability has attracted broad attention, particularly regarding depletion trends and policy measures for aquifer recovery. A 2024 study synthesised data from 170,000 monitoring wells worldwide and demonstrated accelerated declines in many arid regions, while also highlighting specific success stories where depletion trends were reversed through interventions such as managed aquifer recharge [1]. Complementing this global synthesis is research showing a sharp decline in groundwater recharge in Iran, underscoring the role of local management practices and policy in preventing further deterioration [2].

Alongside groundwater issues, flood risk has emerged as a critical focus, driven by population growth in floodplains and shifts in climatic patterns. Investigations reveal that an increasingly large share of the global population—particularly in low- and middle-income nations—is exposed to severe flood hazards and associated poverty traps [3]. Satellite-based analyses further document a marked rise in flood occurrences, attributed to factors such as rapid urbanisation and insufficient flood defence infrastructures. These combined findings underscore the wider impacts of hydrological change on communities, livelihoods, and long-term economic development [4].

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Technical terms

Aquifer: An underground layer of permeable rock or sediments that holds groundwater.

Baseflow: Groundwater contribution to streamflow, providing steady flow in rivers between rain events.

Managed aquifer recharge: Purposely redirecting surface water to aquifers for storage and later use.

Floodplain: Low-lying ground adjacent to a river, prone to flooding.

References

1. Rapid groundwater decline and some cases of recovery in aquifers globally. Nature (2024).
2. Decline in Iran’s groundwater recharge. Nature Communications (2023).
3. Flood exposure and poverty in 188 countries. Nature Communications (2022).
4. Satellite imaging reveals increased proportion of population exposed to floods. Nature (2021).

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