Editing Linear Trend Slope in River Discharge

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{| class="wikitable" style="float:right; clear:right; margin:0 0 1em 1em; width:320px;"
|+ SIGNAL Earth Structured Data
|-
! Object type
| Damage Signal
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! SIGNAL Earth ID
| DS-00673
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! Observable type
| River discharge (basin outlet)
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! Unit
| m³/s (cubic meters of water flowing per second)
|-
! Temporal structure
| Continuous/Periodic
|-
! Monitoring backbone
| National hydrometric networks / gauging stations
|}
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The {{SignalTerm|type=DS|id=DS-00673|label=Linear Trend Slope in River Discharge}} quantifies the rate of change in the volume of water flowing through a river basin outlet over time. This metric is essential for understanding long-term hydrological changes influenced by climatic variability, land use changes, and water management practices. It serves as an indicator of shifts in freshwater availability and river system dynamics at regional to global scales.

River discharge, typically measured in cubic meters per second (m³/s), reflects the integrated response of precipitation, evapotranspiration, groundwater contributions, and anthropogenic influences within a watershed. Assessing its linear trend slope helps identify persistent increases or decreases in flow that may affect ecosystems, water resources, and flood regimes.

Within the broader context of freshwater system monitoring, the linear trend slope in river discharge provides a state change signal that supports environmental assessment and resource management. This article describes the signal's definition, monitoring context, and its role within the SIGNAL environmental monitoring framework.

== Geographic / System Context ==
River discharge is a fundamental component of the global freshwater system, encompassing diverse geographic regions including mountainous headwaters, plains, and coastal zones. The signal applies globally, capturing trends in river flow across a wide range of climatic and hydrological regimes. Variability in river discharge trends is influenced by regional precipitation patterns, snowmelt dynamics, land cover changes, and human activities such as dam construction and water withdrawals. These factors vary spatially and temporally, making comprehensive geographic coverage critical for accurate trend assessment.

== Monitoring and Measurement ==
Monitoring of river discharge relies primarily on national hydrometric networks and gauging stations distributed worldwide. These stations measure the volume of water passing a specific point in a river channel, usually at basin outlets, using standardized hydrological methods. Data collection is typically continuous or periodic, providing time series records necessary for trend analysis. Advances in remote sensing and hydrological modeling complement in situ measurements by extending spatial coverage and filling data gaps. Scientific institutions and agencies such as [https://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administration NOAA] and [https://en.wikipedia.org/wiki/United_States_Geological_Survey USGS] contribute to data acquisition and quality control.

Within the SIGNAL system, this phenomenon is treated as a defined environmental signal whose boundaries and measurement conventions are described below.

== Signal Definition ==
The linear trend slope in river discharge is defined as the rate of change over time of the river discharge volume measured at a basin outlet. It is expressed in cubic meters per second per unit time (m³/s per year or another time unit), representing a continuous or periodic temporal structure. This signal captures the directional change in flow magnitude, indicating increasing or decreasing trends in river discharge that reflect alterations in watershed hydrology.

== Boundary Conditions ==
Boundary inclusions encompass river discharge measurements taken at the outlet of defined hydrological basins, representing integrated flow from the upstream catchment. The signal includes data from gauging stations with sufficient temporal coverage to calculate statistically meaningful trends. Boundary exclusions involve measurements from non-riverine water bodies such as lakes or reservoirs unless directly influencing river outlet flow. Short-term fluctuations and episodic events are excluded from the trend calculation, focusing instead on sustained directional changes over multi-year periods.

== Aggregation Semantics ==
Geographic aggregation of the linear trend slope in river discharge is performed at basin scales, allowing spatial integration of flow changes within hydrologically coherent units. Temporal aggregation involves analyzing continuous or periodic time series data over multi-year intervals to derive statistically robust trend estimates. Cross-signal aggregation may integrate this signal with related hydrological or climatic indicators to assess broader environmental system changes. Aggregation semantics ensure that the signal reflects meaningful hydrological state changes while accounting for spatial heterogeneity and temporal variability.

== Observational Status ==
Monitoring of river discharge trends is well established globally through extensive hydrometric networks, though data availability and quality vary regionally. Current datasets enable the detection of significant long-term trends in many river basins, informing scientific understanding of hydrological responses to environmental drivers. Future SIGNAL releases may incorporate enhanced spatial coverage, improved temporal resolution, and integration with complementary datasets to refine trend assessments and support environmental monitoring objectives.

== Related Signals ==
* None specified

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== Key Associated People ==
* '''L. Gudmundsson''' (ETH Zurich) [Lead author]
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== Sources ==
* [https://www.science.org/doi/10.1126/science.aba3996 Globally observed trends in mean and extreme river flow — 2021]
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