Introduction

The role of forests in the hydrological cycle is currently a topic of great interest within the scientific community (Bren 2023; Requena-Mullor et al. 2023). Forests play a crucial role in the hydrological cycle, and thus, water is a vital resource for biodiversity including human development on Earth (Chang 2006). Forest hydrology combines two distinct scientific disciplines: hydrology and forestry (Hewlett 1982). Hydrology is the science that studies the circulation of continental water, changes in its distribution over time, the chemical and physical properties of water, as well as the relationship of water to other ecosystem properties and functions (Brutsaert 2005). Forestry is the science and practice of managing the natural resources contained in or associated with forests which underpin human tangible and non-tangible benefits (Dodev et al. 2020). Traditionally, forestry has been considered a large-scale agricultural practice to improve wood yields (Young and Giese 2003), but more recently, forestry has been considered an approach to ecological management, including other aspects such as biodiversity and water use (Nocentini et al. 2022). Modern forest management, therefore, requires an interdisciplinary approach encompassing silviculture, hydrology, soil science, ecology and land use planning (Kattel and Wu 2024; Sun et al. 2023).

It is well established that carbon sequestration and water conservation are critical ecosystem services provided by forests that support both human well-being and wildlife (Costanza et al. 1997; Farooqi et al. 2020). Although expanding forests helps improve terrestrial carbon sequestration and other ecosystem services, establishing large-scale plantation forests involves trade-offs, such as reduced local water availability (Doelman et al. 2020; Jackson et al. 2005) and reduced streamflow on the affected watershed (Zhang et al. 2017). This is an issue of significant importance in areas susceptible to water scarcity and recurrent droughts (Schwärzel et al. 2020). On the other hand, it has been argued that forest cover increases water supply at regional and global scales through an increase in evapotranspiration and rainfall (Ellison et al. 2012; Teuling et al. 2019). Furthermore, forests also play a buffering role in the local water cycle by temporarily holding onto rainwater, which results in an increase in water storage in the litter layer (Wu et al. 2020).

Given the importance of the different ecosystem services that forests provide, especially their role in carbon storage, as well as their critical role in the water cycle, integrative forest management strategies are key to the sustainable regulation of water resources (Jenkins and Schaap 2018). For this reason, techniques have been developed to measure the impact of different forest management approaches (e.g., afforestation, cutting, etc.) in nearby watersheds. One well-established technique used for this purpose is paired watershed studies (PWS), in which one watershed serves as a reference, whereas one or more adjacent watersheds of similar features are treated (Neary 2016; Ssegane et al. 2013). However, PWS outcomes show only the local consequences of forest management on streamflow, lacking reliability for predictions at larger geographic scales, as noted by (Evaristo and McDonnell 2019). The lack of predictive power undermines forest management strategies and has favored the use of predictive models during the last years (Evaristo and McDonnell 2019).

To comprehensively assess scientific knowledge and map the current state of development in a research field, it is crucial to employ techniques capable of measuring research impact and citation processes. This study aims to thoroughly review the topic of forest hydrology. Despite the growing interest in forest hydrology, there is a lack of recent, globally focused studies in this field, which distinguishes the novelty of this research. The objective of this study is to analyze current global research trends in forest hydrology, elucidate various aspects of this discipline, and propose future research directions based on existing knowledge gaps in forest hydrological literature. To achieve this, scientometric analysis techniques were utilized to: (1) trace the evolution of research in forest hydrology; (2) identify pertinent keywords and research categories; (3) discern the primary countries, authors, institutions, co-cited journals, and articles associated with this field. This study offers valuable insights into the research hotspots within forest hydrology and is poised to guide researchers toward promising future research areas.

Approaches and methods

Scientometric analysis

The scientometric analysis involves massive bibliometric processing and can overcome some limitations of traditional review methods, such as lack of rigor due to subjectivity (Markoulli et al. 2017). Scientometrics has used a variety of methods and technologies such as CiteSpace, VOSviewer, and dynamic topic modeling to study trends in the literature (Kim and Zhu 2018). Several scientometric techniques were employed in this study. The collaboration network of countries, institutions, and authors is dedicated to increasing research productivity and making important contributions to academic development in a particular field of study. Co-citation network analysis includes references and journals for the identification of core ideas and prominent journals in the field (Farooqi et al. 2022). The process of identifying research hotspots involves analyzing co-occurring keywords and co-cited references (Farooqi et al. 2022; Zhang et al. 2021). Cluster analysis was used to identify the research themes. Finally, knowledge mapping was used to visualize the structure and dynamics of scientific knowledge in this field (Fig. 1).

Fig. 1
figure 1

Conceptual framework showing scientometric analysis steps used in this study

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Data collection and processing

The dataset used for this study was collected from the Web of Science (WoS) Core Collection of Clarivate Analytics. This dataset contains bibliographic and citation information of research articles, required for bibliometric investigations (Van Leeuwen 2006). The retrieval formula consisted forest (Topic) AND hydrology (Topic) OR “forest hydrology” (Topic) OR forest (Topic) AND streamflow (Topic) OR forest (Topic) AND watershed (Topic) OR “forested watershed” (Topic) OR “forest management” (Topic) AND hydrology (Topic) OR forest (Topic) AND runoff (Topic) OR forest (Topic) AND ecohydrology (Topic) OR “forest eco-hydrology” (Topic) OR “forest hydrology” (Topic) AND “water quality” (Topic) OR “forest hydrology” (Topic) AND “blue water fluxes” (Topic) OR “forest hydrology” (Topic) AND “green water fluxes” (Topic) OR “Land use changes” (Topic) AND “forest hydrology” (Topic) OR “land cover changes” (Topic) AND “forest hydrology” (Topic) OR “forest hydrology” (Topic) AND “remote sensing” (Topic) OR “forest management” (Topic) AND “eddy flux” (Topic) OR hydrology (Topic) AND “forest management” (Topic) AND “climate change” (Topic) OR forest (Topic) AND “Hydrological Modeling” (Topic) AND “forest hydrology” (Topic) AND Biogeochemistry (Topic) AND forest (Topic) AND “hydrological processes” (Topic) AND catchment (Topic) AND forest (Topic) AND water (Topic). The analytic tool searches for the selected topic in the title, abstract, keywords, and keywords plus. The retrieval time ranged from January 2000 to December 2022. A total of 18,118 publications were initially collected, including research and review articles, proceedings and book chapters. Finally, only research articles and review articles were selected for analysis (N = 17,006, 93.03%), all of them are written in the English language.

Visualization tool

Bibliographic data were analyzed using VOSviewer 1.6.19. VOSviewer is a Java-based, open-access scientometric analysis software. This tool provides better visual representation than former tools when using large datasets, and it is employed for developing maps based on network data. Software is useful for analyzing a specific research field’s research hotspots through visualization and predicting evolution trends. It allows for identifying nodes for countries, institutions, authors, journals, articles and keywords (Liu et al. 2022; Mishra et al. 2021).

Results and insights from scientometric analysis

Temporal research trend, and the performance of co-cited journals and articles

Between 2000 and 2022, the scholarly literature concerning forest hydrology experienced a remarkable surge, as depicted in Fig. 2a, signaling a burgeoning global interest in this field. The temporal distribution reveals a compelling narrative of growth, delineated into three distinct stages. Initially, from 2000 to 2005, the publication rate exhibited a modest uptick, with only a handful of papers annually, yet still registering a 14% rise. Subsequently, the period spanning 2006–2013 witnessed substantial expansion, boasting a robust 30% annual growth rate. Finally, from 2014 to 2022, an accelerated growth trajectory of 56% was observed, culminating in the apex of publications in 2021. On average, an impressive 787 publications emerged each year, indicative of the heightened attention forest hydrology garnered within the scientific community.

Fig. 2
figure 2

Evidence showing temporal research trends, and the performance of co-citation journals and articles. a Annual research production in forest hydrological science during the last two decades (Jan. 2000–Dec. 2022); b visualization of co-citation journals; c co-cited frequency of the top 20 academic journals; d the distribution map of co-cited articles. The size of each node represents research productivity, while the thickness of each link represents the strength of the connection between nodes. *WOS stands for Web of Science

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Efforts to enhance the visualization of co-cited journals led us to establish a criterion encompassing top journals co-cited at least 100 times (Fig. 2b). We identified 751 leading academic journals that published articles in forest hydrological research with significant link strength. These co-cited papers, hosted within prestigious journals, serve as keystones embodying crucial research directions and developmental paradigms within the field. Notably, the “Journal of Hydrology” emerged as the most cited, boasting an impressive 38,324 citations, underscoring its authoritative standing and widespread acclaim within the scientific fraternity. Additionally, “Water Resources Research”, “Hydrological Processes”, “Forest Ecology and Management”, and “Science of the Total Environment” featured prominently among the top 20 co-cited journals, cited 31,457, 26,838, 15,300, and 12,213 times, respectively (Fig. 2c). Encompassing various disciplines such as forestry, ecology, hydrology, agriculture, and environmental science, these top journals collectively underscored the interdisciplinary nature of the field.

Among the top 20 co-cited journals, which contributed 35% to the dataset, eight hailed from the Netherlands and the USA, three from England, and one from Germany. Notably, 60% of these top co-citation journals originated from Europe, with the remaining 40% stemming from North America, highlighting the significant contributions from these regions to impactful international journals in forest hydrology. Moreover, while “Hydrology and Earth System Sciences” stands as the sole open-access journal among them, the rest are hybrid journals (Table S1).

The visual distribution of highly cited articles in forest hydrological research, depicted in Fig. 2d, sheds light on the pivotal contributions of authors, institutions, journals, and countries to the field’s evolution. The top five co-cited articles, predominantly emanating from developed nations, underscore their substantive role in propelling high-quality research in this promising domain (Table 1). Furthermore, the co-citation network of articles delineated into five major clusters elucidates diverse thematic emphases within forest hydrological research. Cluster 1 (red), comprising 19 publications, centers on water quality and aquatic biodiversity. Cluster 2 (green), encompassing 9 items, delves into the impacts of vegetation cover changes on water yield in paired catchment experiments. Cluster 3 (yellow), consisting of 7 items, elucidates hydrological and geomorphological changes arising from wildfire (fire-induced water repellency in soil). Lastly, Cluster 4 (blue), featuring 7 items, scrutinizes the accuracy of hydrological forecasting for large watershed areas.

Table 1 Top five co-citation articles in forest hydrological research
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Performance of countries, institutions, and authors

We established a criterion to encompass countries with a minimum of 5 research publications on forest hydrology, revealing the involvement of 112 countries in advancing knowledge exchange and international collaboration within this field. Notably, the United States of America (USA) stands out with the largest node size, indicating its prominence in research article frequency ranking (see Fig. 3a). Researchers from the USA lead the pack with 7805 publications, followed by the People’s Republic of China (2440), Canada (1756), Germany (1008), and Australia (893). The top 20 most productive countries collectively contribute 81% of the publications, with Europe and North America jointly accounting for 71% of this share. Specifically, North America boasts the highest total of 9561 articles, trailed by Europe (5270), Asia (4291), Oceania (893), and South America (842) (Table S2).

Fig. 3
figure 3

Evidence showing a the visualization of the cooperative network and publication productivity of each country in forest hydrological research; b the geographical contribution of research articles and percent forest cover (FCP) in each country. The green circles indicate the country-wise percentage of forest cover (FAO 2020). From 2000 to 2022, the size of each node represents the number of articles published in that country. The number of links or connections is an indication of the level of cooperation between different countries

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Moreover, the USA, China, Germany, England, and France exhibit higher link strength, underscoring their pivotal role in global research cooperation and advocacy. Conversely, countries like South Korea, Russia, Italy, Finland, and Portugal, while contributing substantially to the literature, exhibit relatively weaker influence in research promotion compared to the top countries (Table S2). This dichotomy suggests that developed and rapidly developing nations demonstrate higher research efficiency in this promising field, while many underdeveloped and developing countries with substantial forest cover display lower research productivity in this domain (Fig. 3b). This indicates significant potential for research growth in regions such as South America and Africa, where forest hydrology remains relatively underexplored.

For enhanced visualization, we focused on the top 50 institutions, revealing 692 links that signify effective collaboration and communication among international teams engaged in forest hydrological research (Fig. 4a). The Chinese Academy of Sciences emerges as the most productive institution, having 915 published articles on the topic. Notably, among the top 20 institutions, 16 are from North America, 3 from Asia, and 1 from Europe, highlighting the proactive engagement of institutions predominantly from the public sector (95%) in advancing forest hydrological research (Table S3), indicative of its status as a federal-level priority. Furthermore, the network map unveils five clusters representing the most productive research collaboration institutions. Notable entities include the US Forest Service, Chinese Academy of Science, Oregon State University, Duke University, University of Minnesota, University of Washington, University of Georgia, and the Spanish National Research Council (CSIC), among others, demonstrating extensive collaboration across geographical boundaries and institutional affiliations.

Fig. 4
figure 4

Evidence depicts the visualization of a the cooperative network of research institutions and b the cooperative network of co-authors

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Similarly, the analysis of co-authors, covering 48 individuals with at least 20 articles in collaboration, reveals nine clusters based on co-authorship frequency (Fig. 4b). Leading researchers such as Charles T. Driscoll, Ge Sun, Hjalmar Laudon, James B Shanley, and Peter M Groffman, among others (Table 2), underscore the concerted efforts of experts worldwide in advancing forest hydrological research. Notably, collaboration among these researchers spans across continents, with significant contributions from North America, Europe, Oceania, and Asia, indicating the expanding global footprint of forest hydrological research (Table S4).

Table 2 The collaborative frequency among the top 20 most productive authors
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Understanding global performance: insights into cooperative countries, authors and institutions

The analysis reveals the US as the foremost research-productive country in forest hydrology, with the top co-author also hailing from the US (Tables S2 & S4). Additionally, the Chinese Academy of Science, PR. China emerges as the most prolific research institution for fostering cooperation in forest hydrology (Table S3). The US boasts the fourth-largest forest cover globally, spanning approximately 36.21% of its land, totaling about 300 million ha (Jones et al. 2009; Tidwell 2016; Vogt and Smith 2016). This diverse forest ecosystem, encompassing various forest types across different climatic zones, serves as a fertile ground for researchers, offering abundant opportunities to delve into forest hydrological dynamics (Amatya et al. 2011). Notably, forests in the US play a pivotal role in freshwater provision, with around 80% of the nation’s scarce freshwater resources originating from these forests (Sedell 2000).

The US boasts a rich history spanning nearly a century in exploring the intricate relationship between forests and water. Pioneering experiments such as the Wagon Wheel Gap’s watershed (1910) paved the way for subsequent global generalizations regarding forest-water interactions throughout the twentieth century (Andréassian 2004). Legislative milestones like the Weeks Act of 1911 underscore the nation’s commitment to safeguarding watersheds, laying the foundation for operational responsibilities assumed by entities like the U.S. Forest Service over the ensuing century (Sedell 2000). The establishment of iconic research facilities such as the Coweeta Hydrological Laboratory, H. J. Andrews Experimental Forest, and Hubbard Brook Experimental Forest further solidifies the US’s leadership in the research domain of forest hydrology (Whitehead and Robinson 1993). Since the establishment of the first paired catchment experiments (Wagon Wheel Gap’s watershed (1910), a lot of the knowledge about the forested vegetation’s effects on the hydrologic cycle and man’s influences came from paired catchment studies, and it remains the reference for all future forest hydrology studies (including size, geology, morphology, climatic forcing, and land use) (Andréassian 2004; Chang 2006; Neary 2016). Moreover, in the US, several former experimental forests have been converted into Long Term Ecological Research (LTER) observatories (Andréassian 2004), playing their vital research contribution to forest hydrology at the National and Global level.

Institutionally, the US is supported by prominent organizations like the US Forest Service, National Science Foundation, and the US Geological Survey, which provide substantial funding for research endeavors in forest hydrology (Lindsey et al. 2023). These funding opportunities facilitate long-term studies and comprehensive data collection efforts, bolstering the nation’s research output in this field. Moreover, national and international research collaborations, facilitated by institutions like the US Geological Survey, contribute significantly to research productivity (Callegary et al. 2018). Similarly, the US Geological Survey (USGS) is among the world’s top prominent agencies working on landscape-level hydrologic monitoring (Council 2007; NRC 2007). Several of its monitoring stations have been collecting hydrologic and climatic data for over a century (Lins et al. 2010). It shows that, at present, the US, as a country, has a bulk of resources and its institutional maturity in forest hydrology is playing a vital role in the generation of novel research and dissemination of research findings worldwide. These technologies provide researchers with detailed information about forest ecosystems and their hydrological processes.

The rapid growth in forest hydrological research by Chinese institutions might be due to the current challenges they are facing in managing already established forests, particularly regarding the trade-off between carbon sequestration and water consumption, as well as in planning future afforestation projects based on lessons erudite from previous experiences. Because rapid population growth and economic development, have caused lasting pressure on forests and grasslands led to large-scale ecosystem degradation in China (Lu et al. 2018), resulting in a significant loss of biomass and carbon stocks (Fang et al. 2018). The restoration of these degraded ecosystems was of utmost importance to improve environmental conditions and mitigate the challenges of climate change. Therefore, to cater for these challenges, since the 1970s, China initiated six major forest planting and protection initiatives to protect the environment and restore the degraded ecosystem, costing billions of dollars (Lu et al. 2018). China has successfully developed the world’s biggest planted forests, accounting for around 23% of the total global forest plantation area (Peng et al. 2014; Zeng et al. 2015). However, massive afforestation efforts, while aimed at combating climate change, intensify water shortages in many water-limited areas of China (Yu et al. 2019), for instance, in semiarid areas of the Loess Plateau in China caused significant streamflow reduction that resulted in water limitation (Fu et al. 2017). Forthcoming climate change scenarios already predicted that warming may increase drought stress over water-limited regions of China, causing ecological deterioration and food shortage (Wang et al. 2023b; Xu et al. 2019).

Keyword co-occurrence network

This analysis delves into the intricate interplay of keywords extracted from abstracts, titles, authors, and keywords-plus fields to construct a co-occurring network. Among the 30 top keywords identified, each exhibiting at least 600 co-occurrences, the keyword “runoff” emerges as the most prominent, appearing a staggering 2234 times. Following closely behind is “climate change” (2021), “dynamics” (1484), “vegetation” (1321), “catchment” (1235), “nitrogen” (1203), “model” (1193), “land-use” (1183), “soil” (1161), “water” (1135), “impacts” (1008), “management” (998), and “climate” (975), as depicted in Fig. 5. With the help of clustering, we can collect related keywords and mimic their closer association (Ma and Zhang 2020). The top three significant clusters were identified from the cluster analysis of keyword co-occurrence; Cluster-1 (Climate Change Impacts) represented in red color with primary keywords “climate” “climate change” and “forest”, “Impact” and “model”. Cluster-2 (Management strategies) in green color with essential keywords “dynamics”, “carbon” and “land use”, “management” and “nitrogen”. Cluster-3 (run-off-erosion dynamics) in blue color shows prominent keywords “catchment” “erosion”, “forest”, “impact” and “run-off” (Fig. 5).

Fig. 5
figure 5

Distribution map of keyword co-occurrence. Each circle indicates a node, the size of the circle indicates node size and the color of the circle indicates cluster classification

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Current research knowledge, prospective and future challenges

Linking climate change and forest hydrology

The relationship between forest hydrology and climate change is complex and multifaceted. Temperature and precipitation patterns can alter forest ecosystem hydrological cycles (Barik et al. 2023). The amount and time of water available for infiltration, evapotranspiration, and groundwater recharge can be affected by changes in precipitation patterns (Raz-Yaseef et al. 2012; Wang et al. 2020) while changing temperatures can impact the rate of evapotranspiration and water availability for infiltration and groundwater recharge (Caltabellotta et al. 2022; Jiao et al. 2023). Climate change will probably intensify the hydrological cycle in the regions, where plants can’t use much water for energy, but in water shortage areas, it might lead to a net drying effect (Li et al. 2017). Thus, moisture deficit in various forested soils for a longer period results in a higher frequency of drought events (Szejner et al. 2020). Increased drought and heat-induced tree mortality is the most concerning effect of climate change on forests leading to significant losses of carbon and ecosystem function (Allen et al. 2010; Hartmann et al. 2015). Mainly, the mortality of big trees contributes significantly to these losses (Lindenmayer et al. 2012). Similarly, the stand’s properties may affect streamflow, like the thinner stand could help alleviate drought effects on tree growth and mortality (D’Amato et al. 2013) and enhance water supply (Hawthorne et al. 2013). The hydrological sensitivity of catchments to climate change is influenced by vegetation types, with mixed forests producing more stable water yields than monoculture (Creed et al. 2014). Many studies reported that global warming could directly influence species proportion, leading to potential changes in plant community diversity, composition and biomass production (Dieleman et al. 2015; Li et al. 2021). These changes could also alter the hydrological cycle in forest ecosystems (Wang et al. 2023a). Additionally, warm temperatures boost widespread insect outbreaks, for example, bark beetle (Bentz et al. 2010), which increases anthropogenic carbon emissions could intensify the forest fire (Overpeck et al. 1990), ultimately, leading to water repellency conditions, accelerating runoff and deteriorating water quality (Dahm et al. 2015; Caltabellotta et al. 2022). A recent comprehensive data analysis indicates that wildfires significantly increase annual streamflow in the semi-arid regions of the Western US with warm or humid climates. On the other hand, subtropical Southeastern US has limited effects on streamflow. This finding underscores the multifaceted influence of fire on water resources and its implications for climate change adaptation strategies (Hallema et al. 2018).

Impact of forest management on hydrological dynamics

Forest management practices (such as deforestation, afforestation, and thinning) can significantly alter the hydrological functions of forests (del Campo et al. 2022; Shah et al. 2022). Before initiating any afforestation project, it is imperative to ascertain specific objectives based on what, why and where to tree planting (Creed and van Noordwijk 2018). Because the trade-off between forest carbon sequestration and water loss can be considerably altered by changes in vegetation cover (Farooqi et al. 2021). A recent global synthesis study reported that the effect of forestation on annual streamflow varies; approximately 60% of watersheds observed decreases in annual water yield of 0.7–65.1% with 0.7–100% gain in forest cover, whereas 30% (predominantly small watersheds), showed upsurge of 7–167.7% with 0.7–100% gain in forest cover (Zhang et al. 2017; Zhang and Wei 2021). Zhang and Wei further explain that this variation in annual streamflow response surpasses that induced by deforestation, potentially because of site conditions before forestation and selection of tree species (Zhang and Wei 2021). The negative impacts of large-scale tree plantations on water yield (streamflow) may offset these impacts because of increased precipitation through improved atmospheric moisture (Hoek van Dijke et al. 2022). However, these impacts may be more prominent in energy-limited regions. Water-limited regions are more hydrologically sensitive to cover changes than energy-limited regions. For example., a modeling study conducted in China revealed that reforestation could reduce annual runoff by up to 50% in semi-arid areas, whereas this reduction was only 30% in humid regions (Sun et al. 2006). Similarly, a catchment experiment conducted in south-central Chile (Mediterranean regions) demonstrated that several decades of non-native Eucalyptus and Pinus species forest plantations decreased streamflow by an amount equal to 87% of the average annual precipitation (1381 mm) (Iroumé et al. 2021).

Timber harvesting operations can significantly affect streamflow mechanisms (Li et al. 2018). For instance, a 70-year research conducted in western Oregon, the US, revealed that the timing of road construction and clearcutting, past geomorphic events, and forest dynamics had a greater impact on the watershed’s response to floods than flood magnitude (Goodman et al. 2023). Forest harvesting also affects snow accumulation and snow melting processes, which ultimately increase the magnitude and frequency of snowmelt floods (Green and Alila 2012). Moreover, thinned forest stands can alter hydrological processes, but they are highly dependent on several variables such as climate, species, forest type, and management strategy (del Campo et al. 2022). According to a recent global meta-analysis, thinning generally enhances runoff and groundwater recharge but may have mixed effects on water use efficiency and water quality, depending on management practices and local conditions (del Campo et al. 2022). Therefore, it is important to adopt an appropriate and flexible management approach that can address the need to increase water yield and promote forest carbon sequestration. For this purpose, a detailed assessment of the diverse effects of forest management operations on ecohydrological processes is needed while considering spatiotemporal dynamics and balancing various ecosystem services.

Forested watershed, water quality and aquatic biodiversity

Forestry operations have both direct and indirect impacts on water quality and aquatic ecosystems. For instance, clear-cutting increases runoff and exposes soil to erosion, increases sedimentation and transfers contaminants due to fertilizer/pesticide applications on agriculture and forest lands (Shah et al. 2022). Recently, nearly a decade of monitoring in three catchments at Flanders Moss in Scotland revealed that clear felling of conifer stands for peatland restoration negatively impacted water quality by releasing more phosphate, dissolved organic carbon (DOC), suspended sediment and color whereas there is little increase in N concentration. The mechanisms driving these releases, including nutrient leaching from forest leftovers, soil disturbance, and other indirect effects of forest clearance, require further investigation (Shah and Nisbet 2019). Similarly, another long-term monitoring paired catchment experiment in Eastern Finland found that extensive clear-cutting (< 30%) significantly increased runoff and exports of phosphate, nitrate, total nitrogen, and total organic nitrogen (Palviainen et al. 2014). In contrast, a study conducted in the state forests of Latvia found no significant increase in dissolved nitrogen in the stream in the first two years after harvesting (Libiete et al. 2017). The reason might be vegetation recovery, a quantity of slash, soil properties, dilution and nutrient assimilation effects, and forested buffer between the harvested areas and the stream, which affect nitrogen leaching (Deval et al. 2021; Libiete et al. 2017). In a latest review researchers found that despite using Best Management Practices (BMPs), harvesting often results in significant increases in runoff and sediment release. The effect can persist for decades, particularly in cases of extensive clear-cutting (Picchio et al. 2021). This scenario could lead to damaging effects on sustaining ecological health and, ultimately, impacting aquatic biodiversity. For example, a study in the Acará-Capim basin found that sediment levels and forest cover changes influence ecological health. Certain fish species, especially strong swimmers and fitting to specific trophic guilds, thrived with greater forest cover and ecological health (Cantanhêde and de Assis Montag 2024). Another study indicated that logging in forest streams in Perak, Malaysia, has been shown to reduce the abundance and diversity of aquatic macroinvertebrate (Al-Shami et al. 2017). Thus, implementing advanced best management practices (BMPs) in forestry can accelerate the recovery of forested watersheds (Walsh et al. 2020), and ultimately safeguard aquatic species (Warrington et al. 2017).

Forest hydrological modeling

The growing demand for water services from forests in changing global climate highlighted the significance of developing robust hydrological modeling techniques. More recent models incorporate energy, vegetation, and ecohydrological processes for wider applications, whereas previous models can forecast hydrological responses to changes in climate and land cover (Sun et al. 2022). Despite the substantial progressions in forest hydrological simulations, there remain many challenges associated with uncertainty in estimations. For example, from the stand to the watershed scale, modeling forest hydrological processes depends on parameterization assumptions, these assumptions, can lead to uncertainties that are hard to measure (Ouyang et al. 2014). Empirical models of hydro-ecological interactions are usually not transferable beyond the original location of creation (Scoullar et al. 2010). Moreover, the lack of ground‐based observational data for validation itself is a big hurdle in accurate estimations and validations (Clark et al. 2011). Generally, physically based hydrological models (e.g., VIC, MIKE-SHE) are widely used in Large-scale watershed studies (Keller et al. 2023). Moreover, these models are greatly dependent on empirical data acquired from small watershed studies, which may be an issue when applying them to larger scales (Kirchner 2006). Complexity in operating these models also presents challenges for non-hydrology or non-computer science researchers due to a need for a skilled interdisciplinary team (Ma et al. 2016). However, recent studies have confirmed the potential of newly emerging computing methods such as machine learning algorithms are effective, quick and accurate in predicting forest parameters, which can be useful for accurate assessment of the complex interaction between forest ecosystems and hydrology (Li et al. 2020). Therefore, the development and upgradation of sophisticated, user-friendly simulation tools is crucial and can be applicable across large spatiotemporal scale monitoring and evaluation. To achieve this, an effective and appropriate integration of emerging computing techniques of big data along with other forest hydrological data sources such as modeling, field observation and spatial data, is paramount for mitigating uncertainty in our estimates with rapidly changing in climate.

Research outlook and practical challenges in forest hydrological research

In this final subsection, we outline a series of critical research and practical challenges within forest hydrology that necessitate resolution. While previous studies have predominantly focused on watershed-scale analyses, significantly advancing our comprehension of water quality, surface and sub-surface water pathways, carbon and nutrient cycling, sedimentation, and eco-hydrological modeling, they have stimulated watershed-scale processes such as soil moisture dynamics, runoff generation, and streamflow. However, further comprehensive investigations are required to address the following challenges in forest ecohydrological research. The challenges encompass examining the impacts of climate change, land use, and forest management practices, as well as understanding ecosystem services, employing cutting-edge monitoring techniques, fostering interdisciplinary collaboration, and integrating data from various tools and methodologies. These represent the primary areas of focus for future research endeavors. By addressing these challenges, we can bolster the sustainable management of water resources and bolster the resilience and health of forest ecosystems. Following an in-depth analysis and comprehensive understanding of the subject, we propose several emerging frontiers. These key questions will guide future research endeavors in the field of forest hydrology (see Box 1).

Box 1 Emerging frontiers and outstanding questions.

1. How will global changes, including climate change, land use alterations, and biodiversity loss, impact forest hydrology influencing factors such as water availability, snowmelt patterns, and groundwater recharge across diverse forest types and climate zones?

2. What strategies can we employ to deepen our understanding of the intricate relationship between ecohydrological processes and forest management practices within the context of global change, thereby facilitating the development of sustainable forest management strategies?

3. How can we effectively integrate hydrological data collected through diverse methodologies and approaches across different spatiotemporal scales, encompassing ground-based monitoring, statistical modeling, GIS, remote sensing, and advanced computer/machine learning techniques?

4. What methods can we utilize to assess and balance the trade-offs and synergies between ecosystem services provided by forests and their hydrological functions?

5. How do human-induced changes in land use and cover, alongside natural long-term variations, influence the dynamics of large watersheds, and what implications do these changes hold for long-term hydrological studies?

6. In what ways can the integration of adaptive management techniques and traditional ecological knowledge contribute to the development of effective strategies for sustainable integrated watershed management?

7. What role does forest canopy interception play in regulating water flow and distribution within forested ecosystems, and how might changing climate patterns impact this crucial process?

8. What are the impacts of forest disturbances, such as wildfires or deforestation, on hydrological processes, and what innovative approaches can be employed to mitigate their effects on water quality and quantity?

9. How can we accurately quantify the invaluable contribution of forests to downstream water resources, encompassing aspects such as the provision of clean drinking water and the regulation of streamflow variability?

10. In what ways can community-based participatory approaches be integrated into forest hydrology research to ensure inclusive stakeholder engagement and foster equitable water resource management practices?

Limitations and conclusions

Our study has several limitations that should be addressed in future research endeavors. Firstly, it is confined to the research period from 2000 to 2022 and relies solely on data sourced from the Web of Science Core Collection. Additionally, it only considers publications in the English language. Therefore, it would be beneficial for future studies to extend the research period and utilize alternative data sources such as Scopus and Google Scholar, while also incorporating scientific literature in languages other than English, such as Chinese and Korean. Nonetheless, this study encapsulates the most crucial time frame and research trends written in English on a global scale, mitigating some of these limitations.

The analysis of forest hydrological research reveals its interdisciplinary nature, involving various fields of study, yet it warrants further exploration. Despite the widespread research on forest hydrology worldwide, there is an urgent need to involve more underrepresented nations and regions in future investigations to comprehensively grasp how the interaction between forest ecosystems and water can impact the entire planet. Key research areas include climate change, forest management practices, ecosystem services, cutting-edge monitoring techniques, interdisciplinary collaboration, and the integration of data from diverse tools and methodologies. Addressing these areas will be essential in bridging the substantial knowledge gap in forest hydrological research.