Observations of the presence or absence of surface water in streams are useful for characterizing streamflow permanence, which includes the frequency, duration, and spatial extent of surface flow in streams and rivers. Such data are particularly valuable for headwater streams, which comprise the vast majority of channel length in stream networks, are often non-perennial, and are frequently the most data deficient. Datasets of surface water presence exist across multiple data collection groups in the United States but are not well aligned for easy integration. Given the value of these data, a unified approach for organizing information on surface water presence and absence collected by diverse surveys would facilitate more effective and broad application of these data and address the gap in streamflow data in headwaters. In this paper, we highlight the numerous existing datasets on surface water presence in headwater streams, including recently developed crowdsourcing approaches. We identify the challenges of integrating multiple surface water presence/absence datasets that include differences in the definitions and categories of streamflow status, data collection method, spatial and temporal resolution, and accuracy of geographic location. Finally, we provide a list of critical and useful components that could be used to integrate different streamflow permanence datasets.

Accurate mapping of streams that maintain surface flow during annual baseflow periods in mountain headwater streams is important for informing water availability for human consumption and is a fundamental determinant of in‐channel conditions for stream‐dwelling organisms. Yet accurate mapping that captures local spatial variability and associated local controls on surface flow presence is limited. An empirical random‐forest model was developed to predict streamflow permanence (late summer surface‐flow presence) for Mount Rainier National Park and the surrounding mountainous area in western Washington, USA. This model was developed to improve upon the existing multi‐state, regional‐scale probability of stream permanence developed for the greater Pacific Northwest Region (PROSPER_PNW). The model was trained on 544 wet/dry observations collected during the late summer, baseflow period from 2018 to 2020 using the crowd‐source mobile application, FLOwPER. Final model accuracy was 0.74 with drainage area and covariates describing geology, topography, and land cover as top predictors of streamflow permanence compared to coarser resolution climatic covariates. The prevalence of static covariates over climatic covariates as top ranked important covariates highlights the importance of scale when evaluating controls on streamflow permanence. Cross validation of the model indicates that streamflow permanence probabilities from this model is an improvement over the regional‐scale PROSPER_PNW model demonstrating the utility of relatively simple, crowd‐sourced data to address water resource needs, and that determination of important predictors of streamflow permanence is influenced by the spatial and temporal resolution of analysis.

The structure, function, and dynamics of Earth's terrestrial ecosystems are profoundly influenced by how often (frequency) and how long (duration) they are inundated with water. A diverse array of natural and human-engineered systems experience temporally variable inundation whereby they fluctuate between inundated and non-inundated states. Variable inundation spans extreme events to predictable sub-daily cycles. Variably inundated ecosystems (VIEs) include hillslopes, non-perennial streams, wetlands, floodplains, temporary ponds, tidal systems, storm-impacted coastal zones, and human-engineered systems. VIEs are diverse in terms of inundation regimes, water chemistry and flow velocity, soil and sediment properties, vegetation, and many other properties. The spatial and temporal scales of variable inundation are vast, ranging from sub-meter to whole landscapes and from sub-hourly to multi-decadal. The broad range of system types and scales makes it challenging to predict the hydrology, biogeochemistry, ecology, and physical evolution of VIEs. Despite all experiencing the loss and gain of an overlying water column, VIEs are rarely considered together in conceptual, theoretical, modeling, or measurement frameworks and approaches. Studying VIEs together has the potential to generate mechanistic understanding that is transferable across a much broader range of environmental conditions, relative to knowledge generated by studying any one VIE type. We postulate that enhanced transferability will be important for predicting changes in VIE function in response to global change. Here we aim to catalyze cross-VIE science that studies drivers and impacts of variable inundation across Earth's VIEs. To this end, we complement expert mini-reviews of eight major VIE systems with overviews of VIE-relevant methods and challenges associated with scale. We conclude with perspectives on how cross-VIE science can derive transferable understanding via unifying conceptual models in which the impacts of variable inundation are studied across multi-dimensional environmental space.

Human activities such as mining, agriculture, and urbanization have resulted in severe, large‐scale alteration to landform organization and associated geomorphic processes. The mountaintop mining (MTM) region of West Virginia, USA has experienced dramatic topographic alteration, by removing steep slopes and introducing plateau‐like areas at ridgelines and benches on valley fills. The resulting engineered landforms create synthetic landscapes, disconnected from previous geomorphic processes. Invoking the process domain concept, we compare differences in slope‐area relations, cumulative area distributions (CADs), elevation, slope, upslope accumulated area, and a slope*area product before and after mining to adjacent unmined sub‐catchments in five study basins. Differences in the slope‐area relation include a 42% slope reduction in low drainage areas, corresponding to hillslopes, unchanneled valleys, and debris flow dominated channels, which may fall below thresholds required for debris flow processes. The curved slope‐area relation that represents valley incision by debris flows is replaced by slope‐area relations that resemble basins where gullying and the stream power law dominate. Extremely high chemical weathering of unconsolidated valley fills materials may facilitate process domain shifts from debris flows to gullying and fluvial erosion. The characteristic power law scaling break in CADs that represents the headward limit of the channelized network is subdued in post‐mined sites and may reflect headward channelized network extension in mined basins. Slope‐area relations and CADs present a unique topographic signature of MTM activity, potentially providing an analytical approach to assess impacts on underlying geomorphic processes for other synthetic landscapes such as cities or large‐scale agricultural production.