Paired Watershed Research Articles

Treatment effects of conservation trenching on regulating and provisioning ecosystem services

United Nation Sustainable Development Goal 15.3 make a note of growing significance of management and restoration strategies for degraded land, and advocating globally for collaborative frameworks of innovative applied research and policy. Present study, quantified the impacts of the staggered contour trenching (SCT) technology in conjunction with silvi-pasture production system on regulating and provisioning ecosystem services of degraded mini-watersheds. Impacts of the SCT on hydrologic regulating ecosystem services were quantified by employing the paired watershed approach. Concept of watersheds with and without treatments was employed for computing non-hydrologic regulating and provisioning ecosystem services of the SCT in conjunction with silvi-pasture system. Results of analyses revealed that the SCT density of 505 trenches ha−1 had the highest reduction in the hydrologic regulating services namely, mean annual runoff event, runoff amount and soil loss, which were 35.5, 63.3, and 3.73%, respectively followed by 378, and 186 trenches ha−1. The highest improvement in the effective rainfall (9.9%) and effective rainfall efficiency (15.0%) was also with 505 trenches ha−1. The SCT density of 505 trenches ha−1 had retained silt 23.1 and 1.2 times higher than that of 378 and 186 trenches ha−1. The values of the post-treatment non-hydrologic regulating services of 505 trenches ha−1 were many folds higher compare to other trenching densities. Improvement in the non-hydrologic regulating services of the available -nitrogen, -potash and -potassium, and soil organic carbon values of the post-treatment of 505 trenches ha−1 were 36.7, 44.2, 25.8, and 25.0% than their pre-treatment values, respectively. Provisioning ecosystem services in term of the yields of the wood biomass of the Acacia nilotica and the Cenchrus ciliaris were the highest with 505 trenches ha−1 than the control (no trench) by 166.2 and 21.5%, respectively. Study indicated that 505 trenches ha−1 SCT density in the silvi-pasture production system was the best practices in conserving and maintaining the degraded land ecosystem services. These findings would be very supportive to the policy makers and degraded land managers for reclaiming and improving the sustainability and ecosystem functioning of the degraded land ecosystem for achieving the SDG 5.3 and maintaining the land degradation neutrality.

The selection of paired watersheds affects the assessment of wildfire hydrological impacts

Wildfires strongly alter hydrological processes and surface and groundwater quality in forested environments. The paired-watershed method, consisting of comparing a burnt (altered) watershed with an unburnt (control) watershed, is commonly adopted in studies addressing the hydrological effects of wildfires. This approach requires a calibration period to assess the pre-perturbation differences and relationships between the control and the altered watershed. Unfortunately, in many studies, the calibration phase is lacking due to the unpredictability of wildfires and the large number of processes that should be investigated. So far, no information is available on the possible bias induced by the lack of the calibration period in the paired-watershed method when assessing the hydrological impacts of wildfires. Through a literature review, the consequences of the lack of calibration on the assessment of wildfire hydrological changes were evaluated, along with the most used watershed pairing strategies. The literature analysis showed that if calibration is lacking, misestimation of wildfire impacts is likely, particularly when addressing low-severity or long-term wildfire effects. The Euclidean distance based on physical descriptors (geology, morphology, vegetation) was proposed as a metric of watersheds similarity and tested in mountain watersheds in Central Italy. The Euclidean distance proved to be an effective metric for selecting the most similar watershed pairs. This work raises awareness of biases exerted by lacking calibration in paired-watershed studies and proposes a rigorous and objective methodology for future studies on the hydrological effects of wildfires.

Hydrosedimentology of paired watersheds with clayey soils under cattle grazing and no-tillage cropping: LISEM calibration and validation

Hydrosedimentology of paired watersheds with clayey soils under cattle grazing and no-tillage cropping: LISEM calibration and validation

Validation of the MGB-IPH hydrological model for flows simulation in paired watershed in minas gerais, Brazil.

Simulating hydrological behavior makes it possible to analyze and predict water availability in river basins, anticipate potential events and carry out quantitative water balances using various scenarios. These scenarios arise from changes in land use and landscape over the years, the occurrence of extreme events and the effects of climate change. In this context, the aim of this study was to evaluate the effectiveness of the Large Basin Hydrological Model (MGB-IPH) for representing rainfall-runoff in the paired watershed of the Piracicaba River and Piranga River in the state of Minas Gerais, Brazil, using the usual calibration and validation procedures. The results of the average statistical performance indices NASH, NASH-Log, BIAS, R², D and Dr showed that the model was able to simulate the seasonality of the watersheds and presented good adjustments, with a tendency to overerestimate the flow, but within acceptable limits. It is concluded that the model performed satisfactorily in its ability to simulate the hydrological behaviour of the Piracicaba River and Piranga River watersheds, despite its limitations and the lack of input data, making it an applicable tool in local contexts.

Agricultural Land‐Use Increases Carbon Yields in Lowland Streams of the Congo Basin

AbstractAs the dominant mode of deforestation in the Congo Basin, shifting agriculture is expected to increase with the projected four‐fold population growth for the region by 2,100. To assess how this land‐use change will affect the export of carbon (C) to rivers in a typical lowland forest ecosystem, we studied paired watersheds near Kisangani, Democratic Republic of the Congo. Two streams, one draining an intact forest (Forest) and one draining an agricultural landscape (Ag), were gauged, equipped with sensors, and sampled fortnightly for one year. Annual average specific discharge was 1.4 mm d−1 (+76%) higher in the Ag compared to the Forest. Average annual dissolved organic C (DOC) and particulate organic C (POC) concentrations were 5.2 mg L−1 (+163%) and 1.3 mg L−1 (+81%) higher in the Ag stream, which, along with the higher discharge, resulted in 8.3 (+410%) and 2.4 g C m−2 yr−1 (+97%) larger C yields, respectively. Baseflow dissolved inorganic carbon, carbon dioxide, and methane yields were also higher in the Ag stream. Despite the higher yields of organic C (OC), the composition of OC did not differ significantly. Carbon to nitrogen ratios, along with isotopic signatures, revealed that both streams contained young, semi‐degraded organic matter derived from C3 vegetation. Correspondingly, biodegradable DOC (BDOC) proportions did not differ between the streams, although the Ag stream yielded more total BDOC. These results show that agricultural land‐use likely exports a greater proportion of Net Primary Productivity (NPP) to aquatic ecosystems, which may affect both C storage in soils and the proportion of gross PP that is ultimately respired.

Soil quality and vegetation cover characteristics as influenced by diverse grazing regimes and soil disturbance histories in a semi-arid rangeland (Iran)

This study investigates the soil functioning and regeneration processes in a semi-arid rangeland subject to an eleven-year conservation grazing (CG) program within the Gonbad paired watershed in Hamadan, Iran. Five distinct sites with varying rangeland vegetation cover were selected based on differences in grazing regimes and soil disturbance histories. These sites include: CG site with Astragalus-Artemisia vegetation (CG(A-A)); CG site with Astragalus-Bromus vegetation (CG(A-B)); CG site, easily accessible to grazing livestock, with Astragalus-Lactuca vegetation (CG(EA)); CG site with a history of past rainfed farming and Centaurea-Grasses vegetation (CG(PRF)); and free grazing (FG) site with Astragalus-Euphorbia vegetation. In addition, a long-term rainfed farming site (RF) was studied as the dominant land use. Rangeland management practices had a discernible impact on nearly all soil quality (SQ) indicators. However, due to their strong interdependence, only soil aggregate stability, carbohydrates, and phosphatase activity proved to be critical indicators representing soil functioning in the area. The general SQ index illustrated a decline in soil functioning at RF (58%), CG(PRF) (55%), FG (42%), and CG(EA) (22%) sites compared to sites classified as "good" (CG(A-A) and CG(A-B)). Total organic carbon and carbon stock were only recovered in well-restored sites, characterized by a predominance of shrubs and perennial grasses. Meanwhile, active carbon and carbohydrates revealed the positive effects of conservation grazing in moderately and poorly restored sites, characterized by a predominance of forbs and annual grasses. Our findings suggest that soil disturbance history and grazing accessibility are critical factors for successfully implementing conservation grazing management in the area.

Agroforestry on runoff nitrogen and phosphorus losses from three paired watersheds after 25 years of implementation

Agroforestry on runoff nitrogen and phosphorus losses from three paired watersheds after 25 years of implementation

Past and future roles of paired watersheds: a North American inventory and anecdotes from the Caspar Creek Experimental Watersheds

Given the high costs of constructing, maintaining, monitoring, and sampling paired watersheds, it is prudent to ask “Are paired watershed studies still worth the effort?” We present a compilation of 90 North American paired watershed studies and use examples from the Caspar Creek Experimental Watersheds to contend that paired watershed studies are still worth the effort and will continue to remain relevant in an era of big data and short funding cycles. We offer three reasons to justify this assertion. First, paired watersheds allow for watershed-scale experiments that have produced insights into hydrologic processes, water quality, and nutrient cycling for over 100 years. Paired watersheds remain an important guide to inform best management practices for timber harvesting and other land-management concerns. Second, paired watersheds can produce long climate, streamflow, and water quality records because sites are frequently maintained over the course of multiple experiments or long post-treatment periods. Long-term datasets can reveal ecological surprises, such as changes in climate-streamflow relationships driven by slow successional processes. Having multiple watershed records helps identify the cause of these changes. Third, paired watersheds produce data that are ideal for developing and testing hydrologic models. Ultimately, the fate of paired watersheds is up to the scientific community and funding agencies. We hope that their importance continues to be recognized.

Prolonged Drought in a Northern California Coastal Region Suppresses Wildfire Impacts on Hydrology

AbstractWildfires naturally occur in many landscapes, however they are undergoing rapid regime shifts. Despite the emphasis in the literature on the most severe hydrological responses to wildfire, there remains a knowledge gap on the thresholds of wildfire (i.e., burned area/drainage area ratio, BAR) required to initiate hydrological responses. We investigated hydrological changes in the Russian River Watershed (RRW) in California, a coastal, Mediterranean, drought‐prone, wildfire‐adapted ecosystem, following ten wildfires that burned 30% of the watershed. Our findings suggest that sub‐watersheds of the RRW have not burned beyond an intrinsic, unknown, threshold required to initiate change. Using paired watersheds, we examined spatiotemporal patterns of pre‐and‐post wildfire hydrology with a rainfall‐runoff hydrological model. Even though these successive wildfires burned 1%–50% of each sub‐watershed (1%–30% at moderate/high severity), we found little evidence of wildfire‐related shifts in hydrology. As a function of BAR, wildfire imposed limited effects on runoff ratios (runoff/precipitation) and runoff residuals (observations—model simulations). Our findings that post‐wildfire runoff enhancements asymptote beyond 30% burn indicate that when a watershed is burned beyond a certain threshold, the magnitude of the hydrologic response no longer increases. Drought and storm conditions explained much of the variability observed in streamflow, whereas wildfire explained only moderate variability in streamflow even when wildfire accounted for >45% BAR. While the BAR in the RRW was sufficiently beyond previously reported minimum disturbance thresholds (>20% burned forest), the lack of hydrological response is attributed to buffering effects of wildfire adaptation and drought factors that are unique to Mediterranean ecoregions.

Nonstationary stochastic paired watershed approach: Investigating forest harvesting effects on floods in two large, nested, and snow-dominated watersheds in British Columbia, Canada

Drawing on advances in nonstationary frequency analysis and the science of causation and attribution, this study employs a newly developed nonstationary stochastic paired watershed approach to determine the effect of forest harvesting on snowmelt-generated floods. Moreover, this study furthers the application of stochastic physics to evaluate the environmental controls and drivers of flood response. Physically-based climate and time-varying harvesting data are used as covariates to drive the nonstationary flood frequency distribution parameters to detect, attribute, and quantify the effect of harvesting on floods in the snow-dominated Deadman River (878 km2) and nested Joe Ross Creek (99 km2) watersheds. Harvesting only 21% of the watershed caused a 38% and 84% increase in the mean but no increase in variability around the mean of the frequency distribution in the Deadman River and Joe Ross Creek, respectively. Consequently, the 7-year, 20-year, 50-year, and 100-year flood events became approximately two, four, six, and ten times more frequent in both watersheds. An increase in the mean is posited to occur from an increase in moisture availability following harvest from suppressed snow interception and increased net radiation reaching the snowpack. Variability was not increased because snowmelt synchronization was inhibited by the buffering capacity of abundant lakes, evenly distributed aspects, and widespread spatial distribution of cutblocks in the watersheds, preventing any potential for harvesting to increase the efficiency of runoff delivery to the outlet. Consistent with similar recent studies, the effect of logging on floods is controlled not only by the harvest rate but most importantly the physiographic characteristics of the watershed and the spatial distribution of the cutblocks. Imposed by the probabilistic framework to understanding and predicting the relation between extremes and their environmental controls, commonly used in the general sciences but not forest hydrology, it is the inherent nature of snowmelt-driven flood regimes which cause even modest increases in magnitude, especially in the upper tail of the distribution, to translate into surprisingly large changes in frequency. Contrary to conventional wisdom, harvesting influenced small, medium, and very large flood events, and the sensitivity to harvest increased with increasing flood event size and watershed area.

Response of stream macroinvertebrate communities to forest harvesting in the Piedmont region of North Carolina

Forest disturbances have significant effects on water quality and quantity, river geomorphology, and the ecology of receiving waterbodies. Riparian forests provide numerous functions for aquatic communities including retaining fine sediments and nutrients, controlling water temperature, and providing food sources and habitat for aquatic organisms. Forestry Best Management Practices (BMPs) use riparian forests as buffers to mitigate potential sources of disturbance to aquatic ecosystems from forest management. The objective of this study was to quantify the impacts of timber harvest on stream macroinvertebrates in the Piedmont region. We assessed the changes in macroinvertebrate communities and identified their relationships with specific hydrologic and water quality parameters. We used a paired watershed approach to quantify the response of watershed hydrology and water quality to clearcut forest harvesting with the use of BMPs in the Hill Demonstration Forest and Umstead Research Farm in central North Carolina. We sampled macroinvertebrates and monitored water quality in the first-order streams, and surveyed vegetation within riparian zones one year preharvest (2010) and four years postharvest (2011–2014). We found more sensitive species (indicated by biotic index classifications), scrapers, and Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa from the harvested watershed than in the reference watershed at the Umstead Research Farm site. No differences were detected between the reference and treatment watersheds at the Hill Demonstration Forest site. More sensitive species were present in watersheds with the highest pine basal area and in-stream total organic carbon (TOC) loads. More scrapers were present in watersheds with low hardwood basal area, high stream flow, and more vines. EPT abundance was higher in watersheds with high stream flow, large pine trees, and thick leaf litter layer. EPT abundance was lower in watersheds with large hardwood trees and high TOC loads. Overall, sensitive species, scrapers, and EPT abundance were lower in the Umstead Research Farm reference watershed than in any other watershed. We conclude that, in contrast to similar studies in the region, clearcut harvesting with the use of BMPs did not cause detectable negative effects on macroinvertebrate communities. Moreover, water quality as determined by macroinvertebrates may even be improved in some cases following clearcutting. This study provides a better understanding of how macroinvertebrate communities in Piedmont streams change after harvesting and what watershed characteristics may be driving these changes. This information is useful in characterizing macroinvertebrates in headwaters in the Piedmont, and helps land managers protect aquatic resources across the region.

Evaluating hydrological and soil erosion processes in different time scales and land uses in southern Brazilian paired watersheds

ABSTRACT Land use is a driver for hydrological and soil erosion responses at the watershed scale. This study aimed to assess the hydrological and soil erosion processes in small watersheds under three different land uses, at three time scales. We investigated four small watersheds in southern Brazil: Agricultural North watershed (ANW), Agricultural South watershed (ASW), Eucalyptus watershed (EW), and Grassland watershed (GW). The SWAT (Soil and Water Assessment Tool) model was used to simulate streamflow (SF) and sediment yield (SY) at monthly, daily and hourly time scales. EW had the lowest SF and SY, whereas ANW showed the highest SY with an increase of 90% and ASW had the highest SF with an increase of 70%. The SWAT model had a satisfactory performance in all time scales and watersheds for SF and SY (NSE and R2 ≥ 0.3 and Pbias ≤ ± 39%). Overall, land use has a major impact on hydrological and soil erosion responses, and the magnitude of these processes depends on the time scale.

Modeling of Gully Erosion in Ethiopia as Influenced by Changes in Rainfall and Land Use Management Practices

Gully erosion is one of the most extreme land degradation processes that exhibit spatial and temporal variation depending on topography, soil, climate, and land use and management characteristics. This study investigated the impact of changes in rainfall, land use/land cover (LULC), and land use management (LUM) practices on gully erosion in two midland watersheds (treated Kecha and untreated Laguna) in the Upper Blue Nile basin of Ethiopia by using the LANDPLANER model in combination with intensive field measurements and remote sensing products. We simulated gully erosion under past (in 2005), present (in 2021), and three potential future curve number conditions, each time under four rainfall scenarios (10, 30, 60, and 100 mm) using the dynamic erosion index (e), static topographic (esp), and erosion channel (esp_channel) thresholds. Density plot analyses showed that gullies frequently occur in low-lying gentle slope areas with relatively higher curve number values. The best predictions of gullies identified through true positive rates (TPR) and true negative rates (TNR) were achieved considering the static esp_channel > 1 for Kecha (TPR = 0.667 and TNR = 0.544) and the dynamic e > 0.1 for 60 mm of rainfall in Laguna (TPR = 0.769 and TNR = 0.516). Despite the 10 mm rainfall having negligible erosion-triggering potential in both watersheds, the 60 and 100 mm rainfall scenarios were 4–5 and 10–17 times, respectively, higher than the 30 mm rainfall scenario. While the LULC change in the untreated Laguna watershed increased the impact of rainfall on gully initiation by only 0–2% between 2005 and 2021, the combination of LULC and LUM significantly reduced the impact of rainfall in the treated Kecha watershed by 64–79%. Similarly, the gully initiation area in Kecha was reduced by 28% (from 33% in 2005 to 5% in 2021) due to changes in LULC and LUM practices, whereas Laguna showed little increment by only 1% (from 42% in 2005 to 43% in 2021) due to LULC change. In addition, the future predicted alternative land use planning options showed that gully initiation areas in Laguna could be reduced by 1% with only LULC conversion; 39% when only LUM practices were implemented; and 37% when both were combined. These results indicate that LUM practices outweigh the impact of LULC on gully erosion in the studied paired watersheds. Overall, LANDPLANER successfully simulated the spatio-temporal variation of gully erosion with scenario-based analyses and hence can be used to predict gullies in the study area and other data-scarce regions with similar agro-ecological settings.

Effectiveness of side-inlet vegetated filter strips at trapping pesticides from agricultural runoff

Agriculture can be a contributor of pollutants, including pesticides and excess sediment, to aquatic environments. However, side-inlet vegetated filter strips (VFSs), which are planted around the upstream side of culverts draining agricultural fields, may provide reductions in pesticide and sediment losses from agricultural fields, and have the additional benefit of removing less land from production than traditional VFS. In this study, reductions of runoff, the soluble pesticide acetochlor, and total suspended solids were estimated using a paired watershed field study and coupled PRZM/VFSMOD modeling for two treatment watersheds with source to buffer area ratios (SBAR) of 80:1 (SI-A) and 481:1 (SI-B). Based on the paired watershed ANCOVA analysis, runoff and acetochlor load reductions were significant following the implementation of a VFS at SIA but not SI-B, indicating the potential for side-inlet VFS to reduce runoff and acetochlor load from a watershed with an area ratio of 80:1 but not a higher ratio of 481:1. VFSMOD simulations were consistent with the results of the paired watershed monitoring study, where simulated reductions of runoff, acetochlor loads, and TSS loads were substantially lower for SI-B than SI-A. VFSMOD simulations of SI-B with the SBAR ratio observed at SI-A (80:1) also show that VFSMOD can be used to capture variability in effectiveness of VFS based on multiple factors including SBAR. While this study focused on the effectiveness of side-inlet VFSs at the field scale, broader adoption of properly sized side-inlet VFSs could improve surface water quality at the watershed or larger scales. Additionally, modeling at the watershed scale could aid in locating, sizing, and assessing the impacts of side-inlet VFSs at this larger scale.

Eco-hydrological responses of the Black Dragon fire in three forested basins in the Daxing’an Mountains, northeast China

Understanding how bushfire affects basin-wide ecohydrological processes is critical for ecological restoration and water supply. However, the mechanisms responsible for post-fire streamflow remain poorly explored in forested basins of China due to complex scale-dependent relationships between fire-induced forest changes and ecohydrological processes, lack of reasonable design of paired watershed experiments, and especially data scarcity. Here, we re-examine ecohydrological responses of the Black Dragon fire (one of the largest and most damaging forest fires on record globally) on an annual scale in three forest basins (two fire-impacted basins, namely Emuer and Pangu, and a nearly unimpacted basin, Huma) in the Daxing’an Mountains using multiple most recent datasets and methods. We found that the Black Dragon fire decreased annual- and basin-averaged vegetation leaf area, evapotranspiration, interception loss, transpiration, soil moisture, runoff, and discharge capacity in 1987 in the two fire-impacted basins compared with the unimpacted basin. The annual- and basin-averaged evapotranspiration (runoff) did not reduce (increase) as much as that expected with decreased LAI given the precipitation amount in 1987 in the two fire-impacted basins, which properly linked to the quick postfire regrowth of vegetation in the growing season. Vegetation leaf area and productivity can quickly recover in the following two to three years postfire, but the hydrological systems need more than 10 years to adapt this disturbance. These findings improve the understanding of ecohydrological responses to bushfire disturbance and provide scientific evidence for ecological protection and water resources management under intensified natural and anthropogenic disturbances.

Rainfall event‐based surface runoff and erosion in small watersheds under dairy and direct‐seeding grain production

AbstractA 3‐year study on erosion and streamflow was conducted in two adjacent paired watersheds that flow into the Passo Real reservoir, one of the largest and most important reservoirs for human water supply and power generation in southern Brazil. The watersheds have similar land use and soil management, but different size and riparian vegetation. The first objective of the study was to monitor and evaluate hydrosedimentological dynamics and effects of riparian vegetation, over a range of rain events, in the two watersheds; the second was to assess the ability of the Limburg Soil Erosion Model (LISEM) to represent these small watersheds in hydrosedimentological terms (runoff and erosion) under individual rain events, in the context of better understanding the role of riparian vegetation and land cover. LISEM is a hydrological model structured on physically based equations that can be used for planning and conservation purposes. Studied rainfall events between 2016 and 2018 had a wide range in total rainfall (10–170 mm), rainfall intensity in 1 h (3–66 mm h−1), stream peak flows (4–5741 L s−1), runoff volume (0.02–40 mm), runoff coefficient (0.1–32%), maximum suspended sediment concentration (20–19 611 mg L−1), and sediment yield (0.002–33.790 Mg km−2). Both watersheds showed a rapid response to rain events with significant runoff generation. Abundance of unpaved roads (often parallel to the slope) promoted high runoff due to channelization effects. South Watershed has 59% more riparian vegetation than North Watershed, but this greater riparian vegetation was not effective in reducing surface runoff and erosion. Furthermore, local adoption of no‐tillage was insufficient to control runoff and sediment yield.

Hydrological response of a paired watershed to rainfall storm events in arid region: a study in Dehgin of Hormozgan province, Iran.

Influenced by global climate change, rainfall characteristics have changed in recent years, especially in arid regions. However, the actual response of the watersheds' hydrological indicators to erosive rainfalls has not been understood yet. Therefore, this study sought to investigate the changes in the watersheds' hydrological response due to the intra-rainfall indices of various events in the Dehgin paired watershed in Hormozgan, Iran, using the data collected from 2007 to 2019. To this end, first, all rainfall events which elicited the response of watersheds were identified concurrently based on the meteorological and flume data. Then, the qualitative and quantitative intra-storm variations associated with hydrological indicators (i.e., total runoff and discharge variables) were extracted for statistical analysis. The study's results revealed that (1) the increasing rates of the continuous discharge time of the control and treatment watershed's front position were about 2.25 and 4.76 times the rear position, respectively. (2) A strong linear relationship was found between total runoff volume and variables including precipitation of storm and time to storm peak in both control and treatment watersheds, with the R2 reported to be 67.7 and 63.6%, respectively. (3) It was also found that the watershed management operations reduced the variables' values including the maximum discharge, the discharge variation coefficient, continuity time of discharge, the peak of the time to discharge, the number of discharge peaks, and the total runoff volume by 3, 1.6, 2.25, 2.37, 2.42, and 3.27 times, respectively. Therefore, it could conceivably be argued that extreme rainfalls can be controlled by management practices in the watersheds.

Long‐term hydro‐meteorology and water quality data from low‐gradient catchments of varying scales on the Santee experimental Forest, South Carolina

AbstractThe forest landscape of the Southeastern Atlantic coastal plain of the United States is experiencing increased threats from extreme precipitation events, tropical storms, flooding, droughts, and growing urbanization impacting on vegetation, road infrastructure, water extraction and other related ecosystem processes (e.g., storm runoff, nutrient and carbon cycling) and functions (e.g., flood protection, aquatic habitat). We describe ongoing hydro‐meteorologic monitoring on two first—(1.6 km2 each), the second—(5 km2), and the third—(52.5 km2) order catchments. The catchments are located on the Santee Experimental Forest at the headwaters of the Cooper River that drains into Charleston Harbour, South Carolina. Monitoring started in 1946, with a gap between 1982 and 1989, includes precipitation, weather, streamflow, water table, and water quality (anions, cations, and physical parameters) at varying temporal scales. The catchments are forest ecosystems dominated by loblolly (Pinus taeda) and longleaf pine (Pinus palustris) (LLP) mixed hardwood stands on the uplands and bottomland hardwoods on well‐drained to poorly‐drained soils characteristic of the low‐gradient Atlantic Coastal Plain. These data support multiple field and modelling studies, ranging from water and carbon budgets to hydrologic and biogeochemical processes to effects of microtopography and extreme climate on hydrology and water quality of these coastal catchments withstands regenerated since Hurricane Hugo (1989). One significant finding from the long‐term data was a reversal of the pre‐Hugo flow pattern between the paired watersheds 3 years after Hugo. This reversal persisted for 10 years and was attributed to change in forest vegetation due to hurricane damage to older pine and larger hardwood stands followed by delayed regeneration before full forest recovery. These publicly available data serve as a reference within a rapidly developing landscape and also for addressing potential impacts of extreme climate and forest disturbance on ecohydrology, biogeochemistry, habitat, water supply and infrastructure using validated models and tools.

Streamflow Response to Wildfire Differs With Season and Elevation in Adjacent Headwaters of the Lower Colorado River Basin

AbstractFires increasingly impact forested watersheds, with uncertain water resources impacts. While research has revealed higher peak flows, longer‐term yields may increase or decrease following fire, and the mechanisms regulating post‐fire streamflow are little explored. Hydrologic response to disturbance is poorly understood in the Lower Colorado River Basin (LCRB), where snowmelt often occurs before the growing season. Here, we quantify annual streamflow changes following what have been, before 2020, two of the largest wildfires in the modern history of the contiguous United States. We evaluate nine nested watersheds with >50 years records within the Salt River Basin to evaluate fire impact over ranges of elevation, climate, vegetation, burned area, and spatial scale. We employ double‐mass comparison of paired watersheds, pre‐ and post‐fire runoff ratio comparison, multiple linear regression of climate and fire, and time‐trend analysis. Precipitation and streamflow are decoupled during dry periods; therefore we conduct separate change detection for wet and dry periods. Post‐fire summer streamflow increased by 24%–38% at all elevations. While winter/spring streamflow remained constant in the highest, coldest headwaters, winter flows declined in lower‐elevation headwaters. As a result, basin annual streamflow declined. These results support emerging understanding that warm semiarid watersheds respond differently to disturbance than well‐studied, colder watersheds. Asynchrony between winter snowmelt and summer evaporative demand is likely important when considering long‐term impacts of forest management and disturbance on water supply in the LCRB.

Analyzing the Effects of Land Cover Change on the Water Balance for Case Study Watersheds in Different Forested Ecosystems in the USA

We analyzed impacts of interannual disturbance on the water balance of watersheds in different forested ecosystem case studies across the United States from 1985 to 2016 using a remotely sensed long-term land cover monitoring record (U.S. Geological Survey Land Change Monitoring, Assessment, and Projection (LCMAP) Collection 1.0 Science products), gridded precipitation and evaporation data, and streamgaging data using paired watersheds (high and low disturbance). LCMAP products were used to quantify the timing and degree of interannual disturbance and to gain a better understanding of how land cover change affects the water balance of disturbed watersheds. In this paper, we present how LCMAP science products can be used to improve knowledge for hydrologic modeling, climate research, and forest management. Anthropogenic influences (e.g., dams and irrigation diversions) often minimize the impacts of land cover change on water balance dynamics when compared to interannual fluctuations of hydroclimatic events (e.g., drought and flooding). Our findings show that each watershed exhibits a complex suite of influences involving climate variables and other factors that affect each of their water balances differently when land cover change occurs. In this study, forests within arid to semi-arid climates experience greater water balance effects from land cover change than watersheds where water is less limited.