Regional Hydro-Ecological Simulation System Research Articles

Assessing the effects of land cover change in runoff processes with RHESSys: a case study in the Waterford River Watershed, Newfoundland and Labrador, Canada

Evaluating the current state of hydrologic processes in urban and semi-urban areas is an essential part of ensuring the sustainable management of water and preventing emergencies of extreme events. This study evaluated the effects of land use and land cover (LULC) change on runoff processes in the Waterford River Watershed (WRW), located in the eastern part of the province of Newfoundland and Labrador (NL), Canada. The Regional Hydro – Ecological Simulation System (RHESSys), a GIS-based hydro-ecological model, was used in a new urbanistic approach to simulate the effects of increasing impervious land as well as reducing urban green areas. The increase in hypothetical peak flows had a direct relationship with the reduction of pervious areas in the watershed. The most sizeable flow increases were observed in the periods of April to May and October to December. This study emphasizes the importance of using a prominent network of green and pervious structures or water retention areas when allocation for residential and commercial land increase.

Evolution of the water–carbon relationship at basin scale under the background of a vegetation restoration program

AbstractVegetation restoration is an important means for regional climate change mitigation and terrestrial carbon sequestration. However, large‐scale vegetation restoration in arid and semiarid regions can excessively consume local water resources, thus threatening regional water supply safety. To explore the impact of vegetation restoration on the water–carbon relationship in the Loess Plateau in China before and after the implementation of the Grain‐for‐Green Program (GfGP), the regional hydro‐ecological simulation system (RHESSys) model was used to simulate the temporal and spatial evolution of key variables of the water cycle, including the actual evapotranspiration (ET) and the surface runoff (Rs), and that of the carbon cycle, including the net primary productivity (NPP) and the total carbon density (TC). In addition, statistical methods were applied to analyze the interaction between water and carbon cycles. Results show that the RHESSys model is capable of simulating the key ecohydrological elements. In the period of 1990–2019, ET and NPP both showed significant increasing trends at rates of 8.9 mm yr−1 and 6.9 g C m−2 yr−1, respectively. The TC also had a slightly increasing trend, with rates of 0.04 t C hm−2 yr−1 (land‐use in 1995), 0.07 t C hm−2 yr−1 (land‐use in 2005), and 0.08 t C hm−2 yr−1 (land‐use in 2015). In contrast, Rs decreased at the rate of 0.35 mm yr−1. As for spatial distribution, in the middle and southeastern parts of the Yanhe River basin with the vegetation well‐restored, ET, NPP, and TC showed significant increasing trends, while the Rs showed a decreasing trend. ET was also found to have a positive correlation with NPP and TC, while the Rs has a negative correlation with NPP and TC. Moreover, the correlation of Rs‐NPP and Rs‐TC was found to increase after the implementation of the GfGP, which indicates the reinforcing effect of vegetation restoration on the water–carbon trade‐off relationship. Therefore, it is critical to coordinate and regulate the interaction between water consumption and runoff in the context of vegetation restoration in the Yanhe River basin, as well as to promote the synergy between regional ecological restoration and social economic development for water security.

Subsurface Lateral Flows Buffer Riparian Water Stress Against Snow Drought

AbstractIn the Sierra Nevada, CA, the Mediterranean climate exposes montane forests to water stress during the summer drought. Normally, spring snowmelt alleviates summer water stress, especially in riparian ecosystems that receive subsurface lateral inputs from groundwater. However, snow drought could potentially eliminate these beneficial effects. This research investigates how subsurface lateral redistribution mediates hillslope‐scale vegetation responses to snow drought. We apply a spatially‐distributed ecohydrologic model (Regional Hydro‐Ecologic Simulation System (RHESSys)) to a snow‐dominated watershed in the Sierra Nevada. We incorporate observed sap flow data along a hillslope to estimate relative differences in water stress for upslope and riparian sites, and constrain RHESSys drainage parameter uncertainty. Our model results show that subsurface lateral inputs buffer riparian water stress against snow drought. For all drought types, both upslope and riparian sites experience substantial losses of net primary productivity (NPP), and on average upslope sites are more adversely affected (upslope loss of NPP = 45% vs. riparian = 28%). Dry droughts from a lack of rain or snow induce substantial loss of biomass for upslope and riparian trees because of low annual precipitation, but a small snowpack retained during cold, dry years slightly alleviates these effects and delays water stress by 2 weeks in riparian areas and 3 weeks upslope. While riparian forests are often buffered against drought stress, our study also shows that riparian forests can suffer from water stress. We found 21% of drought scenarios where riparian trees experience greater water stress than upslope trees that were mostly associated with wet and warm snow droughts.

Turning points in the impact of earlier green-up on evapotranspiration and gross primary productivity in a semi-arid grassland watershed

Warming-induced shifts in vegetation phenology affect ecosystem functions and the hydrological cycle. Research has so far focused on phenological trends, drivers and feedback across temperate and tropical forests, while their impacts on carbon assimilation and hydrological processes in temperate semi-arid grasslands remain poorly understood. Based on remote-sensing datasets from the Moderate Resolution Image Spectroradiometer (MODIS), we examined the trends in vegetation phenology, gross primary productivity (GPP) and evapotranspiration (ET) in the Chabagou watershed of the Loess Plateau, China, for 2001–2020. The results revealed that the start of the growing season (SOS) had advanced significantly between 2001 and 2020, at an average rate of –1.47 days yr−1 (p < 0.05), while the end of the growing season (EOS) had delayed non-significantly by about 0.04 days yr−1. SOS robustly regulated growing season length (GSL), which was extended by an average rate of 1.60 days yr−1. Regression analysis between phenology and two main climatic factors (temperature and precipitation) reveals that precipitation is the main climatic factor affecting SOS, while temperature plays a relatively important role in EOS delay in the study area. Consistent with the phenological trend, annual ET and GPP increased steadily from 2001 to 2020. Based on the Regional Hydro-Ecological Simulation System (RHESSys), we further investigated the net effects of phenological change on carbon and water fluxes. The simulation results indicated that, for our study site, the correlation between SOS and summer ET would transform from positive to negative once SOS had advanced to around 129 days of the year (DOY) (and 125 DOY for summer GPP). Summer ET and GPP increased as SOS advanced (and GSL extended) until the SOS reached the turning points, and decreased if the SOS (and GSL) advanced beyond the turning points. The mechanism of variations in water and carbon fluxes responding to phenology dynamics could be more complex than we acknowledged to date because the climate is now approaching turning points. We, therefore, suggest improving the dynamic phenologic models for better predicting trends of ecosystem carbon gain and water loss with ongoing climate change.

Seasonal differences in future climate and streamflow variation in a watershed of Northern China

Study regionThe Chaohe watershed is a meso-scale watershed in northern China, and the primary reservoir watershed for Beijing's drinking water supply. Study focusThis research aims to evaluate the effects of climate change on future seasonal streamflow regimes and understand the challenges to watershed management. The Regional Hydro-Ecological Simulation System (RHESSys) was applied to investigate the watershed's future hydrographic characteristics under the forcing of the downscaled precipitation and temperature projected by General Circulation Models (GCMs) under three emissions scenarios. New hydrological insights for the regionThe future climate exhibits a drier and warmer trend in the summer monsoon period contrasting with other seasons in the watershed. Precipitation will decrease by 47.5–57.2 mm during the summer monsoon period while increasing annually. Future summer streamflow will decrease accordingly, which is also driven by increased evapotranspiration due to rising temperature. An increased dispersion coefficient of streamflow also indicates more dramatic variations in summer. The annual streamflow magnitude with a 5-year return period increases significantly (p < 0.01), indicating a reduced risk for future water shortages. However, the magnitude of streamflow will decrease with the prolonged return periods (p < 0.01). This study emphasizes the critical significance of predicting the seasonal variability of streamflow and other hydrological property changes at the local scale to provide valuable information for developing adaptive resource management and hazard relief strategies.

Carbon sequestration and water yield tradeoffs following restoration of abandoned agricultural lands in Mediterranean mountains

Abandoned cropland areas have the potential to contribute to climate change mitigation through natural revegetation and afforestation programs. These programs increase above and belowground carbon sequestration by expanding forest cover. However, this potential to mitigate climate change often involves tradeoffs between carbon sequestration and water availability. Particularly in a water limited environments such as the Mediterranean region, any loss of recharge to groundwater or streamflow can have critical societal consequences. In this study, we used an ecohydrologic model, Regional Hydro-Ecological Simulation System (RHESSys), to quantify these tradeoffs for land management plans in abandoned cropland areas in Mediterranean mountains. Changes to Net Ecosystem Production (NEP), water yield and Water-Use Efficiency (WUE) under different land management and climate scenarios were estimated for Arnás, a catchment with similar geology, vegetation and climate to many of the locations targeted for land abandonment restoration in the Spanish Pyrenees. Results showed significant changes to both carbon and water fluxes related to land management, while changes related to a warming scenario were not significant. Afforestation scenarios showed the highest average annual carbon sequestration rates (112 g C·m−2·yr−1) but were also associated with the lowest water yield (runoff coefficient of 26%) and water use efficiency (1.4 g C·mm−1) compared to natural revegetation (−27 g C·m−2·yr−1, 50%, 1.7 g C·mm−1 respectively). Under both restoration scenarios, results showed that the catchment ecosystem is a carbon sink during mid-February to July, coinciding with peak monthly transpiration and WUE, while during the rest of the year the catchment ecosystem is a carbon source. These results contribute to understanding carbon and water tradeoffs in Mediterranean mountains and can help adapt restoration plans to address both carbon sequestration and water management objectives.

Interspecific Soil Water Partitioning as a Driver of Increased Productivity in a Diverse Mixed Mediterranean Forest

AbstractIt has been assumed that mixing of species with high physiological diversity reduces competition over water and light resources, compared to single‐species forests. Although several mechanisms to explain this observation have been proposed, quantification of these effects is lacking. Here we studied water‐use dynamics for five tree species in a mature, mixed, evergreen, and Mediterranean forest. We use empirical measurements of key tree structural attributes including root distribution, through DNA barcoding and soil cores, tree height and biomass along with measurements of species‐specific water use for two years. These measurements at the tree‐scale were used to parameterize an ecosystem model of coupled water, carbon and energy fluxes (Regional Hydro Ecologic Simulation System, RHESSys). Site‐scale empirical measurements showed contrasting diurnal and seasonal transpiration and sap flow curves across tree species, with year‐round activity in angiosperms, and mostly wet season‐activity in gymnosperms. Water‐use patterns matched the rooting depth patterns, with the deep‐ and shallow‐rooted Ceratonia and Cupressus, showing year‐round and seasonal behaviors, respectively. RHESSys estimates of species‐specific and stand‐scale transpiration, biomass and productivity across 20 years of climate variation showed substantial differences between mixed and monoculture scenarios. Stand‐scale annual net primary productivity and transpiration increased by 20–70 g C m−1 yr−1 and 40–80 mm yr−1, respectively, for mixed stands relative to average fluxes aggregated across monocultures. Model results, collaborated by field data provide evidence for niche partitioning of the soil water resource among co‐habiting tree species, and demonstrate that this mechanism can facilitate higher productivity and an enhanced forest carbon sink especially in semi‐arid regions.

Natural revegetation and afforestation in abandoned cropland areas: Hydrological trends and changes in Mediterranean mountains

AbstractWater resources availability is one of the main concerns for policy makers around the world in present and future management plans. In the Mediterranean basin, this concern is increased given the extreme variability in climate and the intrinsic aridity conditions. Water resources in the Mediterranean region depend mainly on surface and subsurface supply from mountain areas. Because evapotranspiration comprises a substantial portion of the water budget, recent land cover changes due to cropland abandonment may change transpiration (TRANS) and water supply. Therefore, land management plans must account for these potential hydrologic changes to guarantee water availability in the upcoming decades. Short‐term changes to water yield have been shown to follow afforestation or natural revegetation, the main management strategies in abandoned cropland areas. Studies comparing long‐term trends of these management practices, however, are scarce due to the lack of long‐term hydrological data. In this study, we use the regional hydro‐ecological simulation system (RHESSys), to analyse long‐term changes and annual and seasonal trends in streamflow (STR) and transpiration following management of abandoned cropland areas. Annual mean values show significant differences between the three management scenarios for both streamflow and transpiration, while differences between climate scenarios are not significant. The Mann Kendall trend analysis shows significant changes to water yield compared to the situation before management. Depending on the total afforested area, afforestation could significantly decrease annual streamflow between 2.3%·decade−1 and 5.9%·decade−1 and increase annual transpiration between 1.1%·decade−1 and 3.5%·decade−1. These trends are attributed to changes during the first 30 years after management, while during the fourth and fifth decade, changes to water yield tend to stabilize or decrease. These results are substantial to optimize land management plans, ensuring sustainable hydrological and ecological ecosystem services.

Effects of vegetation succession and shrub clearing after land abandonment on the hydrological dynamics in the Central Spanish Pyrenees

Cropland abandonment is a global problem that has affected countries worldwide since the 19th century. Abandoned lands usually undergo a process of plant succession. This process has been widely shown to have implications for ecosystem services, including water provision. Mediterranean mountains are currently in the middle of these land transformations: for example, in the Pyrenees, 80% of the agricultural lands have been abandoned. During the last decades, the management of these areas have become a target of environmental policy makers to ensure the sustainability of ecosystem services. Targeting available resources for land management, however, requires estimates of the effectiveness of different treatment options. This study address this need by relating the management of the abandoned lands to plant succession and hydrological dynamics. We used the Regional Hydro-Ecological Simulation System (RHESSys) to predict the changes to land cover and hydrological dynamics following land abandonment in the Estarrún watershed in the Central Spanish Pyrenees. Projections from passive management allowing vegetation succession, and active management via shrub clearing were defined and their effects on annual streamflow (STR) and annual evapotranspiration (ET) are compared. Results show a high increase in forest cover due to the conversion of all the currently existing shrubs to forest during the upcoming three decades. This conversion to forest cover, would decrease STR by 19%, increase ET by 34%, and reduce the target area for shrub clearing by 72% within 30 years of plant succession. However, shrub clearing would similarly increase STR and decrease ET by 6%, if 7.5% of the study area is cleared. For both STR and ET changes decline rapidly if the management is delayed and the vegetation succession process continues. This study confirms the need to take into account succession following land abandonment in designing land management strategies to preserve water resources in Mediterranean mountain areas.

Simulation of Dissolved Organic Carbon Flux in the Penobscot Watershed, Maine

Dissolved organic carbon (DOC) is an important component of the carbon cycle as a measure of the hydrological transport of carbon between terrestrial carbon pools into soil pools and eventually into streams. As a result, changes in DOC in rivers and streams may indicate alterations in the storage of terrestrial carbon. Exploring the complex interactions between biogeochemical cycling and hydrologic processes, as well as the micro-climate variabilities that impact the rate of DOC fluxes, are challenging because the information is not readily available from in-situ measurements or from empirical models alone. This is particularly true of large-scale watersheds. The Penobscot Watershed is the largest watershed of the Gulf of Maine and the second largest in New England. Its typical soils, with high organic matter and a large forested and wetland landscape, result in higher DOC fluxes than what has been observed previously for most rivers in the northern temperate or boreal zones (Hope et al., 1994; Mulholland, 1997; Aitkenhead and McDowell, 2000). In this study, we emphasized the simulation of streamflow and DOC fluxes from the Penobscot Watershed (and several tributaries within the Penobscot Watershed) using the spatially distributed process-based Regional Hydro-Ecological Simulation System (RHESSys) model. Simulated results were evaluated using field measurements (streamflow, DOC fluxes) and remotely sensed products (Net Primary Production (NPP) and Leaf Area Index (LAI) from Moderate Resolution Imaging Spectroradiometer (MODIS). The average DOC flux for the Penobscot Watershed during 2004-2012 using the RHESSys model was 69 kg C/ha/year. The RHESSys simulated DOC flux is shown to correlate well with observed values, as well as with results previously reported from the empirical Load Estimator (LOADEST) model (71 kg C/ha/year) for 2004-2007 ( Huntington and Aiken, 2013 ). Our simulated results also show a temporal variation in the amount of DOC flux, indicating that the antecedent DOC concentration from one year can impact the DOC export in following years. Thus, DOC concentration is positively correlated with streamflow and antecedent precipitation, in agreement with previous studies ( Ågren et al., 2010 ; Huntington and Aiken, 2013 ; Tian et al., 2013 ). The successful application of the rigorous RHESSys model in the Penobscot Watershed makes it a reasonable platform to test future scenarios impacting the hydrology and biogeochemistry within similar large complex watersheds.

Process-based eco-hydrological modeling in an Eastern Himalayan watershed using RHESSys

Hydro-ecological models are important tools used to estimate streamflow from mountainous watersheds as driven by precipitation and snowmelt under the influence of different spatially variable hydro-ecological response variables. These models enable us to gain insight into hydrological and ecological processes occurring in the watershed. In the present study, a hydro-ecological model, Regional Hydro-Ecological Simulation System (RHESSys) was set up for a small representative watershed in Eastern Himalayan region of Arunachal Pradesh to investigate spatial variation in saturation deficit during snow depletion period. RHESSys model is capable of estimating variations in evaporation, transpiration, streamflow, overland flow, saturation deficit, etc. from the landscape. Studies related to hydrological and ecological sustainability of the Eastern Himalayan Rivers are limited, although a major part of the region is covered with evergreen forests, where ecological parameters may have a great impact on watershed hydrology. Nuranang watershed, which is located in Tawang district of Arunachal Pradesh, India, was selected as the study area. The hydro-meteorological data from 2004 to 2008 were collected from Central Water Commission (CWC). Digital Elevation Model (DEM) with 30 m spatial resolution was downloaded from NASA website. Calibration of the RHESSys model was performed for the depletion period of 2004 (13th April–21st August) and 2005 (17th April–4th September) and the model was validated for the years 2008 (17th April–20th September) and 2009 (13th April–23rd September) using observed streamflow at the watershed outlet. Comparison plot of the actual and log values of observed and simulated daily discharges showed that the model captured the variations in total observed discharge and subsurface flows reasonably well for both the calibration and validation years. Daily time-series outputs of various hydrological variables, i.e., subsurface flow, overland flow, streamflow, saturation deficit, and percentage saturated area, were obtained for both calibration and validation simulation. For simulation years, overland flow dominated stream discharge in all the months, and contributed around 60% of the total streamflow, whereas subsurface flow contributed around 40% in all the months. Comparatively, saturation deficit was more in the month of April due to less precipitation and it was reduced in the month of May because of pre-monsoon rainfall. It increased again in the month of June as the precipitation in the month was less compared to May. Then, it decreased again in the subsequent months of July and August due to high rainfall during the monsoon season and increased in the month of September. Average saturation deficit was estimated to be 389.69 mm and average percentage saturated area was estimated as 9.52%. The number of saturated pixels was found to be minimum in the month of April, while a maximum number of saturated pixels were observed in the month of August indicating the existence of inverse relationship between precipitation and saturation deficit for the study area.

Understanding How Fuel Treatments Interact With Climate and Biophysical Setting to Affect Fire, Water, and Forest Health: A Process-Based Modeling Approach

Fuel treatments are a key forest management practice used to reduce fire severity, increase water yield, and mitigate drought vulnerability. Climate change exacerbates the need for fuel treatments, with larger and more frequent wildfires, increasing water demand, and more severe drought. The effects of fuel treatments can be inconsistent and uncertain and can be altered by a variety of factors including the type of treatment, the biophysical features of the landscape, and climate. Variation in fuel treatment effects can occur even within forest stands and small watershed management units. Quantifying the likely magnitude of variation in treatment effects and identifying the dominant controls on those effects is needed to support fuel treatment planning directed at achieving specific fire, water, and forest health goals. This research aims to quantify and better understand how local differences in treatment, landscape features, and climate alter those fuel treatment effects. We address these questions using a mechanistic coupled ecohydrologic model—the Regional Hydro-Ecological Simulation System (RHESSys). We ran 13,500 scenarios covering a range of fuel treatment, biophysical, and climate conditions, for the Southern Sierra Nevada of California. Across fuel treatment type, biophysical, and climate parameters, we find nontrivial variation in fuel treatment effects on stand carbon, net primary productivity, evapotranspiration, and fire-related canopy structure variables. Response variable estimates range substantially, from increases (1–48%) to decreases (−13 to −175%) compared to untreated scenarios. The relative importance of parameters differs by response variable; however, fuel treatment method and intensity, plant accessible water storage capacity (PAWSC), and vegetation type consistently demonstrate a large influence across response variables. These parameters interact to produce non-linear effects. Results show that projections of fuel treatment effects based on singular mean parameter values (such as mean PAWSC) provide a limited picture of potential responses. Our findings emphasize the need for a more complete perspective when assessing expected fuel treatment outcomes, both in their effects and in the interacting biophysical and climatic parameters that drive them. This research also serves as a demonstration of methodology to assess the likely variation in potential effects of fuel treatments for a given planning unit.

The Regional Hydro-Ecological Simulation System for 30 Years: A Systematic Review

As the Regional Hydro-Ecological Simulation System (RHESSys) is a tool to simulate the interactions between ecological and hydrological processes, many RHESSys-based studies have been implemented for sustainable watershed management. However, it is crucial to review a RHESSys updating history, pros, and cons for further improving the RHESSys and promoting ecohydrological studies. This paper reviewed the progress of ecohydrological studies employing RHESSys by a bibliometric analysis that quantitatively analyzed the characteristics of relevant studies. In addition, we addressed the main application progress, parameter calibration and validation methods, and uncertainty analysis. We found that since its release in 1993, RHESSys has been widely applied for basins (&lt;100 km2) within mainly seven biomes. The RHESSys model has been applied for evaluating the ecohydrological responses to climate change, land management, urbanization, and disturbances, as well as water quality and biogeochemical cycle. While most studies have paid their attention on climate change, the focus has shifted to the application for land management in recent years. This study also identified many challenges in RHESSys such as the inaccessible data and parameters, oversimplified calibration approach, few applications for large-scale watersheds, and limited application fields. Therefore, this study proposed a set of suggestions to overcome the limitations and challenges: (1) Developing a new approach for parameter acquisition and calibration from multi-source data, (2) improving the applicability for a large-scale basin, and (3) extending the scope of application fields. We believe RHESSys can improve the understandings of human–environment relationships and the promotion of sustainable watersheds development.

Stand density effects on carbon and water fluxes in a semi-arid forest, from leaf to stand-scale

Drought-induced productivity reductions and tree mortality have been increasing in recent decades in forests around the globe. Prescribed reduction in stand density, i.e. thinning, has been proposed as a management tool to improve forest sustainability in face of a warmer, drier future. Thinning should potentially reduce net stand water use and improve water-availability for remaining trees, thus reducing their subsequent drought vulnerability. However, few studies have directly measured these effects.In 2009 we established a large-scale thinning experiment in a semi-arid, 40-years-old pine afforestation. Study plots (70 × 70 m) were thinned to 100, 200, and 300 trees ha−1, and compared with unthinned control plots (210–400 trees ha−1), each at five replications. Stem and needle growth, and needle gas exchange were measured along 3–9 consecutive years at seasonal to annual temporal resolution. Measurements at the tree-scale were further up-scaled using both simple upscaling relationships and using an ecosystem model of coupled carbon, energy and hydrology (Regional Hydro Ecologic Simulation System, RHESSys).At the needle scale, photosynthesis was 70% higher at the 100 trees ha−1 than at 300 trees ha−1, whereas transpiration was merely 10% higher. Consequently, stem and needle growth increased by 100% and 20%, respectively. For most parameters, there was little change between 200 and 100 trees ha−1. Applying RHESSys at the stand-scale, these effects on tree physiology translated into 35% reduction in CO2 uptake and a 47% reduction in tree water-use, which was compensated for by increased evaporation from exposed soil.Our long-term measurements at the dry timberline highlight the role of thinning in enhancing the activity and growth of remaining trees, with increased water-use efficiency. Unexpectedly, this density reduction was associated with a relatively small decrease in forest carbon uptake. Light availability was a limiting factor in the higher density plots, even in our light-abundant forest.

A top–down soil moisture and sap flux sampling design of a rain–snow transition mountain watershed

AbstractThis paper presents a top–down approach for soil moisture and sap flux sampling design with the goal of understanding ecohydrologic response to interannual climate variation in the rain–snow transition watersheds. The design is based on a priori estimates of soil moisture and transpiration patterns using a physical distributed model, Regional Hydro‐Ecologic Simulation System (RHESSys). RHESSys was initially calibrated with existing snow depth and streamflow data. Calibrated model estimates of seasonal trajectories of snowmelt, root‐zone soil moisture storage, and transpiration were used to develop five hydrologic similarity indicators and map these at (30 m) patch scale across the study watershed. The partitioning around medoids‐clustering algorithm was then used to define six distinctive spatially explicit clusters based on the five hydrologic similarity indictors. A representative site within each cluster was identified for sampling. For each site, soil moisture sensors were installed at the 30‐ and 90‐cm depths and at the five soil pits and a sap flux sensor at the averaged‐size white fir tree for each site. The model‐based cluster analysis suggests that the elevation gradient and topographically driven flow drainage patterns are the dominant drivers of spatial patterns of soil moisture and transpiration. The comparison of model‐based calculated hydrological similarity indicators with measured‐data‐based values shows that spatial patterns of field‐sampled soil moisture data typically fell within uncertainty bounds of model‐based estimates for each cluster. There were however several notable exceptions. The model failed to capture the soil moisture and sap flux dynamics in a riparian zone site and in a site where lateral subsurface flow may not follow surface topography. Results highlight the utility of using a hypothesis driven sampling strategy, based on a physically based model, for efficiently providing new information that can drive both future measurements and strategic refinements to model inputs, parameters, or structure that might reduce these errors. Future research will focus on strategies for using of finer scale representations of microclimate, topography, vegetation, and soil properties to improve models.

Evaluation of the effects of climate change on forest watershed hydroecology using the RHESSys model: Seolmacheon catchment

This study examines the effects of future climate changes on watershed hydroecology, including runoff, evapotranspiration, soil moisture content, gross primary production (GPP), and photosynthetic productivity (PSNnet), by applying the Regional Hydroecological Simulation System model to the Seolmacheon catchment (8.5 km2). Based on the daily runoff, evapotranspiration, and soil moisture content in the watershed from 2007 to 2009, calibration (2007–2008) and validation (2009) of the model were conducted. By utilizing PSNnet and GPP data collected with the Moderate Resolution Imaging Spectroradiometer sensor onboard the Terra satellite, model calibration (2007) and validation (2008) were implemented. For future climate change data, the MIROC3.2 (hires) and the HadCM3 climate change scenarios (A1B and B1), which were provided by the IPCC, were used for reference. Compared to the baseline period, the future temperature increased by a maximum of + 4.9 °C in the MIROC3.2 A1B scenario, and precipitation increased substantially in spring and winter. In the hydrological evaluation, MIROC3.2 showed annual change rates from − 33.9 to 6.0%. Both the A1B and B1 scenarios showed 6.0% and 1.0% increases in the 2020s and − 33.9% and − 32.8% decreases in the 2080s, respectively. For HadCM3, the A1B (B1) scenario showed rates of − 9.9% (1.4%), − 48.6% (− 19.2%), and − 42.4% (− 32.1%), in the 2020s, 2050s, and 2080s, respectively. Because climate region movement is relatively slow for temperature ranges when plant movement increases, existing forests might survive in their minimum state or vanish under extreme conditions, such as heat stress, droughts, and fires. In the simulation, the evapotranspiration volume, which was closely related to vegetation, caused the average annual temperature to increase by 2.6–3.6 °C, which caused local vegetation to vanish.

The Influence of Climate and Land-Cover Scenarios on Dam Management Strategies in a High Water Pressure Catchment in Northeast Spain

This paper evaluates the response of streamflow in a Mediterranean medium-scaled basin under land-use and climate change scenarios and its plausible implication on the management of Boadella–Darnius reservoir (NE Spain). Land cover and climate change scenarios supposed over the next several decades were used to simulate reservoir inflow using the Regional Hydro-Ecologic Simulation System (RHESsys) and to analyze the future impacts on water management (2021–2050). Results reveal a clear decrease in dam inflow (−34%) since the dam was operational from 1971 to 2013. The simulations obtained with RHESsys show a similar decrease (−31%) from 2021 to 2050. Considering the ecological minimum flow outlined by water authorities and the projected decrease in reservoir’s inflows, different water management strategies are needed to mitigate the effects of the expected climate change.

Development of a participatory Green Infrastructure design, visualization and evaluation system in a cloud supported jupyter notebook computing environment

Land use planners, landscape architects, and water resource managers are using Green Infrastructure (GI) designs in urban environments to promote ecosystem services including mitigation of storm water flooding and water quality degradation. An expanded set of urban sustainability goals also includes increasing carbon sequestration, songbird habitat, reducing urban heat island effects, and improvement of landscape aesthetics. GI is conceptualized to improve water and ecosystem quality by reducing storm water runoff at the source, but when properly designed, may also benefit these expanded goals. With the increasing use of GI in urban contexts, there is an emerging need to facilitate participatory design and scenario evaluation to enable better communication between GI designers and groups impacted by these designs. Major barriers to this type of public participation is the complexity of both parameterizing, operating, visualizing and interpreting results of complex ecohydrological models at various watershed scales that are sufficient to address diverse ecosystem service goals. This paper demonstrates a set of workflows to facilitate rapid and repeatable creation of GI landscape designs which are incorporated into complex models using web applications and services. For this project, we use the RHESSys (Regional Hydro-Ecologic Simulation System) ecohydrologic model to evaluate participatory GI landscape designs generated by stakeholders and decision makers, but note that the workflow could be adapted to a set of other watershed models.

Simulated Sensitivity of Urban Green Infrastructure Practices to Climate Change.

Climate change is likely to alter the quantity and quality of urban stormwater, presenting a risk to water quality and public health. How might stormwater management practices need to change to address future climate? Answering requires understanding how management practices respond to climate forcing. Traditional "gray" stormwater design employs engineered structures, sized based on assumptions about future rainfall, which have limited flexibility once built. Green infrastructure (GI) uses vegetation, soil, and distributed structures to manage rainwater where it falls and may provide greater flexibility for adaptation. There is, however, uncertainty about how a warmer climate may affect performance of different types of GI. This study uses the hydrologic and biogeochemical watershed model, Regional Hydro-Ecologic Simulation System (RHESSys), to investigate sensitivity of different GI practices to climate. Simulations examine 36 urban "archetypes" representing different development patterns (at the city block scale) of typical U.S. cities, eleven regional climatic settings, and a range of mid-21st century scenarios based on downscaled climate model output. Results suggest regionally variable effects of climate change on the performance of GI practices for water quantity, water quality, and carbon sequestration. GI is able to mitigate most projected future increases in surface runoff, while bioretention can mitigate increased nitrogen yield at nine of eleven sites. Simulated changes in carbon balance are small, while local evaporative cooling can be substantial. Given uncertainty in the local expression of future climate, infrastructure design should emphasize flexibility and robustness to a range of future conditions.

Balancing uncertainty and complexity to incorporate fire spread in an eco-hydrological model

Wildfire affects the ecosystem services of watersheds, and climate change will modify fire regimes and watershed dynamics. In many eco-hydrological simulations, fire is included as an exogenous force. Rarely are the bidirectional feedbacks between watersheds and fire regimes integrated in a simulation system because the eco-hydrological model predicts variables that are incompatible with the requirements of fire models. WMFire is a fire-spread model of intermediate complexity designed to be integrated with the Regional Hydro-ecological Simulation System (RHESSys). Spread in WMFire is based on four variables that (i) represent known influences on fire spread: litter load, relative moisture deficit, wind direction and topographic slope, and (ii) are derived directly from RHESSys outputs. The probability that a fire spreads from pixel to pixel depends on these variables as predicted by RHESSys. We tested a partial integration between WMFire and RHESSys on the Santa Fe (New Mexico) and the HJ Andrews (Oregon State) watersheds. Model assessment showed correspondence between expected spatial patterns of spread and seasonality in both watersheds. These results demonstrate the efficacy of an approach to link eco-hydrologic model outputs with a fire spread model. Future work will develop a fire effects module in RHESSys for a fully coupled, bidirectional model.