Hydrological Response Of Catchment Research Articles

Assessment of land use/ land cover change derived catchment hydrologic response: An integrated parsimonious hydrological modeling and alteration analysis based approach

Land use/land cover (LULC) change, often a consequence of natural or anthropogenic drivers, plays a decisive role in governing global catchment dynamics, and subsequent impact on regional hydrology. Insight into the complex relationship between the drivers of LULC change and catchment hydrology is of utmost importance to decision makers. Contemplating the dynamic rainfall-runoff response of the Indian catchments, this study proposes an integrated modeling-based approach to identify the drivers and relative contribution to catchment hydrology. The proposed approach was evaluated in the tropical climate Nagavali River Basin (NRB) (9512 km2) of India. The Soil and Water Assessment Tool (SWAT) hydrological model, which uses daily-scale rainfall, temperature, wind speed, relative humidity, solar radiation, and streamflow information was integrated with the Indicators of Hydrologic Alteration (IHA) technique to characterize the plausible changes in the flow regime of the NRB. Subsequently, the Partial Least Squares Regression (PLSR) based modeling analysis was performed to quantify the relative contribution of individual LULC components on the catchment water balance. The outcomes of the study revealed that forest land has been significantly converted to agricultural land (45–59%) across the NRB resulting in mean annual streamflow increase of 3.57 m3/s during the monsoon season. The affinity between land use class and streamflow revealed that barren land (CN = 83–87) exhibits the maximum positive response to streamflow followed by the built-up land (CN = 89–91) and fallow land (CN = 88–93). The period 1985–1995 experienced an increased ET scenario (911–1050 mm), while the recent period (2005–2020) experienced reduced ET scenario owing to conversion of forest to agricultural land. Certainly, the study endorses adopting the developed methodology for understanding the complex land use and catchment-scale hydrologic interactions across global-scales for early watershed management planning.

From global glacier modeling to catchment hydrology: bridging the gap with the WaSiM-OGGM coupling scheme

Coupled glacio-hydrological models have recently become a valuable method for predicting the hydrological response of catchments in mountainous regions under a changing climate. While hydrological models focus mostly on processes of the non-glacierized part of the catchment with a relatively simple glacier representation, the latest generation of standalone (global) glacier models tend to describe glacier processes more accurately by using new global datasets and explicitly modeling ice-flow dynamics. Yet, to the authors' knowledge, existing catchment-scale coupled glacio-hydrological models either do not include these most recent advances in glacier modeling or are simply not available to other users. By making use of the capabilities of the free, distributed, physically-based Water Flow and Balance Simulation Model (WaSiM) and the Open Global Glacier Model (OGGM), a coupling scheme is developed to bridge the gap between global glacier representation and local catchment hydrology. The WaSiM-OGGM coupling scheme is used to further assess the impacts under future climates on the glaciological and hydrological processes in the Gepatschalm catchment (Austria), by considering a combination of three climate projections under the Representative Concentration Pathways (RCP) 2.6, 4.5, and 8.5. Additionally, the results are compared to the original WaSiM model with the integrated Volume-Area (VA) scaling approach for modeling glaciers. Although both models (WaSiM with VA scaling and WaSiM-OGGM coupling scheme) perform very similar during the historical simulations (1971–2010), large discrepancies arise when looking into the future (2011–2100). In terms of runoff, the VA scaling model suggests a reduction of the mean monthly peak between 10–19%, whereas a reduction of 26–41% is computed by the coupling scheme. Similarly, results suggest that glaciers will continuously retreat until 2100. By the end of the century, between 20–43% of the 2010 glacier area will remain according to the VA scaling model, but only 1–23% is expected to remain with the coupling scheme. The results from the WaSiM-OGGM coupling scheme raises awareness of including more sophisticated glacier evolution models when performing hydrological simulations at the catchment scale in the future. As the WaSiM-OGGM coupling scheme is released as open-source software, it is accessible to any interested modeler with limited or even no glacier knowledge.

Estimation of soil moisture using environmental covariates and machine learning algorithms in Cathedral Peak Catchment, South Africa

AbstractSoil moisture (SM) is a fundamental constituent of the terrestrial environment and the hydrological cycle. Owing to its significant influence on catchment hydrological responses, it can be utilized as an indicator of floods and droughts to aid early warning systems. This study aimed to develop a field‐scale method to estimate SM using parametric and machine learning‐based methods to compare whether advanced artificial intelligence methods can give similar results as traditional methods. Considering this, monthly observed SM data (from the top 10 cm), environmental covariates, and remotely sensed data from March 2019 to July 2021 for the Cathedral Peak Research Catchments VI and IX in South Africa were obtained. From the 241 observations obtained across 12 sites, 160 (∼66%) were used for model training, while the remaining 81 (∼34%) were used for model testing. Employing 10‐fold cross‐validation, the individual machine learning models (viz., support vector machine [SVM], random forest (RF), k‐nearest neighbor, classification and regression trees [Rpart], and generalized linear model) displayed a satisfactory performance (R2 = 0.52–0.79; root mean square error = 3.79–5.80). In the validation phase, the RF model displayed a superior performance, followed by the SVM. Subsequent SM estimation using the hybrid model produced satisfactory results in training (R2 = 0.90) and testing (R2 = 0.45). The results obtained from this study can aid in predicting SM variations in catchments with limited monitoring. Furthermore, this model can be applied in drought monitoring, forecasting, and informing agricultural management practices.

Feature importance measures to dissect the role of sub-basins in shaping the catchment hydrological response: a proof of concept

Understanding the response of a catchment is a crucial problem in hydrology, with a variety of practical and theoretical implications. Dissecting the role of sub-basins is helpful both for advancing current knowledge of physical processes and for improving the implementation of simulation or forecast models. In this context, recent advancements in sensitivity analysis tools could be worthwhile for bringing out hidden dynamics otherwise not easy to distinguish in complex data driven investigations. In the present work seven feature importance measures are described and tested in a specific and simplified proof of concept case study. In practice, simulated runoff time series are generated for a watershed and its inner 15 sub-basins. A machine learning tool is calibrated using the sub-basins time series for forecasting the watershed runoff. Importance measures are applied on such synthetic hydrological scenario with the aim to investigate the role of each sub-basin in shaping the overall catchment response. This proof of concept offers a simplified representation of the complex dynamics of catchment response. The interesting result is that the discharge at the catchment outlet depends mainly on 3 sub-basins that are consistently identified by alternative sensitivity measures. The proposed approach can be extended to real applications, providing useful insights on the role of each sub-basin also analyzing more complex scenarios.

Hysteresis in streamflow‐water table relation provides a new classification system of rainfall‐runoff events

AbstractRainfall‐runoff event types can be used to better understand the hydrological functioning of catchments. In this study, we propose a framework to characterize and classify runoff events relying on the hysteresis analysis of the relation between streamflow (independent variable) and depth to water table (dependent variable). We evaluated hysteresis for 112 rainfall‐runoff events occurred in the period 2012–2016 in a small forested catchment in the Italian Pre‐Alps. Three main groups of rainfall‐runoff events were identified, each associated with specific hydro‐meteorological characteristics of the events. A first group, identified by a faster response of streamflow compared to the groundwater level (which led to a clockwise hysteretic loop), was characterized by dry antecedent conditions, short rainfall events, low streamflow peaks and small runoff coefficients. A second group had characteristics similar to the first group, that is, faster response of streamflow compared to the groundwater level (clockwise hysteretic loop), but on average displayed a narrower hysteretic loop. A third group, identified by a faster response of the groundwater level compared to streamflow (which led to an anti‐clockwise loop), was characterized by wet antecedent conditions, long rainfall events, high streamflow peaks and large runoff coefficients. Results showed statistically significant differences among the groups, corroborated by an analysis based on environmental tracers (2H and electrical conductivity). This study shows how the analysis of the hysteretic relation between streamflow and depth to water table can be used for grouping rainfall‐runoff events and to better identify the catchment's hydrological response to rainfall inputs.

Identifying most relevant controls on catchment hydrological similarity using model transferability – A comprehensive study in Iran

• We evaluate two distinct types of hydrological similarity in this study: (i) the apparent similarity measured by similarity distance based on observable catchments descriptors (CDs) and (ii) behavioral similarity, which is determined by highest-performance of transferred model parameters between gauged donor catchment and ungauged target catchment (best-donor case). • More than 75% of our physically similar catchments have a hydrological similarity. • The climatic (aridity index), topographic (mean elevation), and physiographic (catchment area) properties exert a greater influence on parameter transfer to ungauged catchments than do other CDs. A key goal of hydrological science is to understand the climatic controls on catchment hydrological response behavior. Progress toward this goal would result in improved model transferability from gauged to gauged catchments. In this sense, the effectiveness of the model's transferability is contingent on the proper selection of donor and target catchment pairs. Thus, using a rainfall-runoff model, we evaluate two distinct types of hydrological similarity in this study: (i) the apparent similarity measured by similarity distance based on observable catchments descriptors (CDs) and a Euclidean distance based on physical similarity (PS) method and (ii) behavioral similarity, which is determined by highest-performance of transferred model parameters between gauged donor catchment and ungauged target catchment (best-donor case (BD)). It is believed that catchments that apparently to be similar in terms of CDs, have a similar hydrological behavior. We wish to see if that assumption is valid in this paper. Spatial proximity (SP) is also implemented to see if it might be used as an alternative for PS where there is no apparent physical similarity between catchments. To test the study's assumptions, the HBV conceptual rainfall-runoff model is used in 576 catchments across four climate regions in Iran. The results indicate that: (1) as expected, the best-donor (BD) case performs the best, and the more than 75 % of our physically similar catchments have a hydrological similarity (the overlap was ≥ 70 %), (2) the superiority of PS over SP demonstrates that the CDs exert a great influence on transferability within each climate region than geographical distance. However, we demonstrated that the SP is superior, when spatial distance between donor and target catchments is reduced (nearest neighbor ≤ 20 km), (3) consistent with CDs, when utilizing SP method, geographical distance has a varying effect on model transferability within wetter and drier regions, such that SP performs better in wetter regions than it does in dry interior regions, (4) throughout Iran, the dominant controls on model transferability differ by region. Thus, the climatic (aridity index or PET/P), topographic (mean elevation), and physiographic (catchment area) properties exert a greater influence on parameter transfer to ungauged catchments than do other CDs, and (5) the runoff ratio (streamflow signature) confirmed the superiority of the wetter regions over the drier regions in terms of control on the parameters transfer.

2D hydrodynamic approach supporting evaluations of hydrological response in small watersheds: Implications for lag time estimation

The use of integrated flood models represents an approach of growing interest in the literature, being the hydrological and hydrodynamic flood processes described entirely within the two-dimensional (2D) hydrodynamic unsteady flow equations. Due to its ability in simulating complex spatial–temporal dependence of both the hydrodynamic and hydrologic responses of a catchment to rainfall events, this kind of approach paves the way to the development of novel lines of research in catchment hydrology. With particular reference to the lag time estimation, the paper focuses on three interrelated issues: 1) the use of the 2D-SWEs model to provide evidence on the variability of the lag time in small basins, 2) the description of the hydrologic response of small catchments based on characteristic times influencing the hydrodynamic response to rainfall events and 3) the representativeness of hydrodynamic-based rainfall-runoff scenarios in the description of the hydrologic response observed in real events. To that purpose, synthetic rainfall-runoff scenarios for different return periods are firstly generated to analyze the hydrologic response time in three ungauged basins. Then regressive formulas, based on ad hoc variables representing characteristic times, are introduced to interpret the variability shown by the computed lag time. Finally, the physical soundness of the proposed approach is tested against observed rainfall-runoff data in four additional basins. Despite all the simplifications introduced in the proposed approach, the regressive formulas provided a reasonably good agreement with the estimations of the lag time of the observed events, showing errors of the order of 30%. The comparison with the predictions of empirical literature formulas further confirms the potential of the proposed approach. This study represents the basis for future research on basin response to rainfall events through the use of a 2D integrated hydrodynamic-hydrologic modeling.

Construction of 3D Design Model of Urban Public Space Based on ArcGIS Water System Terrain Visualization Data

On the premise of being familiar with ArcGIS Server technology, we build the architecture of the entire platform, including the basic support layer, data layer, service platform layer, and application layer, and build the entire environment of the platform. We make electronic maps through Arc Map, and collect, organize, and improve spatial data and attribute data, so as to achieve satisfactory accuracy and visual comfort. This study implements various map services under the Dojo framework, including basic map operations, information display and query, marker points, eagle eye diagrams, measurement, printing, and other functions, and uses JavaScript technology to improve user experience. We publish various services through ArcGIS Server, and realize fast and error-free invocation of each service. Based on the theory of runoff and runoff, ArcGIS software was used to study the hydrological information of the watershed, and to determine the catchment area threshold and hydrological response unit. Combined with the GIS spatial analysis method, the numerical simulation of rainfall and runoff in the study case area was carried out, and the variation of the annual rainfall-runoff coefficient was obtained. This study selects an area where stock planning was first proposed as the object of this research. Briefly, we introduce the construction of three-dimensional public space in a certain area, select thirteen typical three-dimensional public spaces as representatives for public evaluation, and explore their existing problems, mainly including the lack of adaptability of space functions and the lack of diversity in space design, privatization of operation management, low level of public perception, etc. Since then, in response to the public problems of the three-dimensional public space in a certain area, a targeted three-dimensional public space optimization strategy is proposed from the four levels of planning policy, urban design, management subject, and user subject.

Croplands decreased stability of streamflow with changing climate: An investigation of catchments in Illinois

Croplands can significantly influence the hydrologic response of catchments to climate change in a region but such influence has not been well investigated and quantified. In this study, we firstly use the conceptual hydrological model to investigate the annual water balance for croplands-altered catchments, and the “natural” state without croplands of the catchment can be traced back by setting a zero area of croplands in the calibrated model. The model results are then applied to a hydrologic sensitivity framework with the Budyko-type relationship between hydrologic ratios (i.e. evapotranspiration ratio and water storage change ratio) and the aridity index (Ep/P) to yield the hydrologic sensitivity coefficients for the croplands-altered and “natural” catchments. The method is applied to investigate three catchments that are rarely affected by inter-basin groundwater flow in Illinois. The results show that croplands significantly increase the actual evapotranspiration (E) and decrease the runoff (Q), while changes in water storage (C) are rarely affected by croplands at the annual time scale. The actual evapotranspiration at the annual timescale is much more sensitive to potential evapotranspiration when the croplands exist. Croplands in Illinois significantly increase the sensitivity of streamflow on the climate change, to at least twice of the sensitivity in the “natural” state. The effectiveness of inter-annual hydrologic sensitivity framework is also demonstrated by hydrological model. This study provides a new simple insight to quantify the inter-annual stability with varying climate and land use at the catchment scale.

Changing rate of urban creep and urban expansion over time and its impact upon the hydrologic response of a catchment.

Most previous quantitative research conducted on urban creep and urban expansion has focused on small areas, short time periods, case studies with fairly uniform housing stock and demographic makeup, and the characterisation of urban creep and expansion exclusively in terms of impervious area changes without quantification of the consequential hydrological impact, i.e., increase in surface runoff volume and peak flows in a catchment. This study, using satellite imagery, catchment characteristics data, geographic information system and hydrologic modelling, presents, for the first time, a long-term analysis of urban creep and expansion. The case study is the Ouseburn catchment in Newcastle upon Tyne, a wide-ranging catchment made up of rural, suburban and urban areas, over a period of seven decades. The rate of increase of impervious surfaces is found not to be constant in time; the significant impact of this variation on the catchment's hydrologic response is quantified. This has overall caused a substantial flow volume increase in the Ouseburn over the study period, e.g. 48% for a 1 in 5 years rainfall event. The conclusions obtained are likely representative of many large towns and cities across the United Kingdom and the methodology presented can be easily replicated in other study areas.

Comparisons of distributed and lumped rainfall-runoff model for soil moisture estimation

Soil moisture is an important parameter in landslides because of increased pore pressure and decreased shear strength. This research aims to derive soil moisture indicators from two hydrological models: the physically-based distributed hydrological model and the lumped model. Rainfall-Runoff-Inundation (RRI) Model is used to simulate the hydrological response of catchments to the rainfall-induced landslide in a distributed manner. Tank Model as a lumped hydrological model is also used in this study to simulate the dynamic of soil moisture. The study area is the upper Brantas River Basin, prone to landslides due to heavy rainfall and steep slope. Calibration of the model is conducted by tuning the model according to the river discharge data. The simulation indicates that acceptable performance is confirmed. Tank Model can provide the dynamic of the soil moisture. However, by using this approach, the spatial variation of the soil moisture cannot be presented. Regarding the quantitative amount of soil water content, RRI Model could make a reasonable simulation though the temporal variation is not adequately reproduced. Validation of this method with satellite soil moisture as well as ground measurement is also presented. The challenges of using these approaches to develop landslide hazard assessment are discussed.

Scaling properties of the turbidity and streamflow time series at two different locations of an intra-Apennine stream: Case study

The time scales of a catchment hydrologic response in a human impacted intra-Apennine basin, was assessed by a power spectral analysis. Turbidity and streamflow data, at high resolution (10 min) have been considered during four years. The turbidity and streamflow have heavy tails that follow approximately Pareto distributions. Both also display scaling Fourier power spectra of the form f-b, over different scaling ranges: from 10 min to one day for the turbidity and from 1 h to 20 days for the streamflow data. For both locations the slope for the streamflow is close to b = 1.7, whereas for turbidity the values b = 1.68 and 2.25 are found for the upstream and downstream locations, respectively. The turbidity dataset at the downstream station has a steeper slope than the upstream station, implying a higher persistence of the turbidity fluctuations: this change of slope shows that the effect of the river channel and catchment is similar to a fractional integration from the upstream to the downstream data. Furthermore, the delay times of the turbidity dataset, and hence of suspended sediment, were calculated using a co-spectrum between the series and indicating characteristic transit times of 25 days and 145 days.

The temporal variations in runoff-generation parameters of the Xinanjiang model due to human activities: A case study in the upper Yangtze River Basin, China

Study regionUpper Yangtze River Basin, China. Study focusThe intensification of climate change and human activities leads to non-stationarity of hydrological processes. Previous studies mainly focus on monthly hydrological or Budyko models. However, it is a challenge that catchment hydrological responses to human activities for daily hydrological models. This study aims to evaluate anthropogenic impacts on water yield of the upper Yangtze River Basin by representing the Xinanjiang model parameters as functions of socio-economic factors. New hydrological insightsThe hydrological parameters WM (soil water storage capacity) and KE (ratio of potential evaporation to pan evaporation) increased in 1976–2000, while the parameter B (non-homogeneity of the soil water storage capacity) declined. It is further demonstrated that the population and the drainage area of reservoirs have the greatest impact on B and WM, respectively. Their linear functional form is validated to be effective for improving streamflow simulation. These findings can help understand the non-stationarity of the rainfall-runoff relationship due to increasing human development and contribute to adaptive development strategies for future water resource management.

Investigating the Impact of drought on the base flow using Standardized base flow index,Case study: Kaka-Reza catchment

Understanding the interaction of drought phenomenon and hydrological response of catchments can lead to obtaining some information for optimal water resource management. The aim of this study is to investigate the temporal relationship between drought and groundwater contribution to stream flow, in Kaka –Reza sub catchment. In this study, the common period (1382-2017) was considered for the corresponding hydrometric and rain gauge stations. The standardized precipitation index (SPI) was then calculated at time scales of 3, 6, 9, 18, 12 and 24 months. Base flow and related index were calculated by B-flow-Line and Halick digital filter method in monthly, annual and total time bases. Then the standardized base flow index (SBFI), the base flow duration curve (BFDC) and the base flow duration curve shape index (SBFDC) was calculated. Changes in (BFDC) and the corresponding shape index and the relationships between (SPI) and (SBFI) were investigated and analyzed using the correlation method. The results showed that the average BFI during the research period was equal to 0.52 and its minimum and maximum were equal to 0.46 and 0.57, respectively. Also, the trend of bas flow changes is a decreasing trend with a low slope. The trend of changes SBFDC decreases over study period with a low slope. The rate of slope change is also from one to three percent, and close to the straight line, which indicates the tendency for base flow to be stable in the long time. The greatest impact of the drought phenomenon on the river base flow is in the time step of nine and twelve months. The correlation between SPI and SBFI with a coefficient of determination 0.87 confirms the increase in the groundwater contribution to base flow, with a delay of nine to twelve months.

Insights into storm direction effect on flood response

In this study, we investigate the directional influence of storm movement on catchment flood peak response using the synthetic circular basin. Due to the complexity in defining storm movements that require meteorological modeling, we adopt a novel approach of combining the basin rotation method (BRM) with a circular basin construct. A systematic basin rotation approach provides a proxy for the storm direction relative to the river network topology to study its hydrologic response. Using Stage-IV rainfall with 4-km by 1-hour resolution for 16 years period from 2003 to 2018 in Iowa, U.S., we systematically analyze consequent flood peak response due to storm directions (basin rotations) using a distributed hydrologic model called the Hillslope-Link Model (HLM). HLM has demonstrated the ability to reproduce observed streamflow for real river basins studied in Iowa. The hydrologic simulation results show that the BRM can quantify the relationship between the rainstorm direction and catchment hydrologic response. Also, the maximum flood peak response is strongly dependent on the interaction of the peak of the rainstorm with the peak of the width function. The results indicate significant differences in runoff volume and runoff peak and their interannual variability due to rainstorm direction. The study has important implications for flood frequency predictions and developing flood resilience and watershed management strategies, particularly due to changing storm tracks under a warming climate.

Effects of streamflow isotope sampling strategies on the calibration of a tracer‐aided rainfall‐runoff model

AbstractIsotopes are increasingly used in rainfall‐runoff models to constrain conceptualisations of internal catchment functioning and reduce model uncertainty. However, there is little guidance on how much tracer data is required to adequately do this, and different studies use data from different sampling strategies. Here, we used a 7‐year time series of daily stable water isotope samples of precipitation and streamflow to derive a range of typical stream sampling regimes and investigate how this impacts calibration of a semi‐distributed tracer‐aided model in terms of flow, deuterium and flux age simulations. Over the 7 years weekly sampling facilitated an almost identical model performance as daily, and there were only slight deteriorations in performance for fortnightly sampling. Monthly sampling resulted in poorer deuterium simulations and greater uncertainty in the derived parameter sets ability to accurately represent catchment functioning, evidenced by unrealistic reductions in the volumes of water available for mixing in the saturation area causing simulated water age decreases. Reducing sampling effort and restricting data collection to 3 years caused reductions in the accuracy of deuterium simulation, though the deterioration did not occur if sampling continued for 5 years. Analysis was also undertaken to consider the effects of reduced sampling effort over the driest and wettest hydrological years to evaluate effects of more extreme conditions. This showed that the model was particularly sensitive to changes in sampling during dry conditions, when the catchment hydrological response is most non‐linear. Across all dataset durations, sampling in relation to flow conditions, rather than time, revealed that samples collected at flows >Q50 could provide calibration results comparable to daily sampling. Targeting only extreme high flows resulted in poor deuterium and low flow simulations. This study suggests sufficient characterization of catchment functioning can be obtained through reduced sampling effort over longer timescales and the targeting of flows >Q50.

Digital soil maps can perform as well as large-scale conventional soil maps for the prediction of catchment baseflows

The rapid advance of digital soil mapping (DSM) has resulted in the generation of fine resolution soils spatial datasets with associated uncertainty that can be as accurate but more cost-effective and faster to produce than conventional soil maps. There is documented and increasing interest by policy makers and end-users in moving from conventional soil mapping to DSM; however, the wider operational use of DSM depends on demonstrating the effectiveness of DSM in fulfilling user needs and requirements along with providing DSM products that can be easily used by non-specialists. In this study we used the Hydrology of Soil Types (HOST) classification scheme, which was devised to predict flows in ungauged catchments and is used by both the research and policy maker communities in the UK, as the exemplar for comparing the efficiency of HOST class maps produced using both DSM and conventional soil map approaches for predicting catchment hydrological response. The performance for hydrological predictions of a detailed (1:25,000 scale) polygon HOST class map and a HOST-DSM class map produced via spatial disaggregation was assessed by comparing Base Flow Index (BFI) calculated using HOST class proportions from both maps with BFI calculated using flow data from gauges in 39 selected catchments. Results showed that the disaggregated HOST-DSM class map gave similar or even better BFI predictions than the conventional polygon-based HOST class map, while also providing a better insight on spatial soil variability within map units and its effect on hydrological predictions. This study demonstrates the potential of DSM to produce soil hydrological maps that provide comparable or better baseflow predictions than maps produced using detailed and intensive soil surveying. The study results also suggest that translating DSM of classes to more easily interpretable mapping datasets and incorporating prediction uncertainty in the final DSM product, as in the case of BFI maps based on HOST-DSM classes, could help with facilitating the transition towards a wider operational use of DSM.

Stormwater management for highly urbanized areas in the tropics: Life cycle assessment of low impact development practices

Within the contemporary view of stormwater management, introduced through integrated urban water management approaches (e.g., low impact development [LID]), there are several strategies that can be used in urban settlements to enhance sustainability. These strategies include the construction of runoff source controls and changes in development patterns. To understand the environmental trade-offs, the comparison of single LID devices using life cycle assessment (LCA) is spreading. However, assessing both LID practices and the urban catchment hydrological response is a less explored field — especially in regions under climate conditions other than the temperate urban areas where LID first emerged. In this context, this paper aims to assess the environmental impacts and the hydrological effects of applying LID practices in a highly urbanized area in the tropics. Using a settlement in Brazil as a case study, three projects were developed and assessed using a hybrid framework based on hydrological modeling and LCA. Even though the projects had different elements, their system function was the same: assure flood protection for rainfall events with a 2-year return period and for a 30-year service life. The business-as-usual scenario, entitled Scen.CONV, used a conventional urbanization and storm-sewer conventional drainage system (CDS), commonly known as gray infrastructure. The alternative scenario, entitled Scen.WELL, used a conventional urbanization and CDS associated with the use of the LID controls to disconnect the lots (infiltration wells). The last scenario, entitled Scen.LID, used LID controls to disconnect both lots and streets (infiltration swales and swale trenches, considered green infrastructure measures) integrated with changes in development patterns. The hydraulic-hydrologic results pointed out Scen.LID as the best alternative for flood protection (100% of runoff source control), followed by Scen.WELL (60% decrease in the peak flow compared to Scen.CONV). The LCA total results indicated Scen.LID as the scenario with lower life cycle impacts, and Scen.WELL as the most impactful. However, this capacity-based approach could not capture the hydrological benefits of Scen.WELL, which were addressed using a performance-based functional unit. Assessing potential impacts per managed stormwater volume, Scen.WELL’s life cycle impacts were 51–65% lower than Scen.CONV, and Scen.LID’s were 74–82% lower than Scen.CONV, both in all life cycle impact categories. This joint approach provides a new perspective to stormwater systems assessment, enhancing their hydrological benefits, without burden shifting.

The Multiscale TROPIcal CatchmentS critical zone observatory M‐TROPICS dataset II: Land use, hydrology and sediment production monitoring in Houay Pano, northern Lao PDR

AbstractMountain regions of the humid tropics are characterized by steep slopes and heavy rains. These regions are thus prone to both high surface runoff and soil erosion. In Southeast Asia, uplands are also subject to rapid land‐use change, predominantly as a result of increased population pressure and market forces. Since 1998, the Houay Pano site, located in northern Lao PDR (19.85°N 102.17°E) within the Mekong basin, aims at assessing the long‐term impact of the conversion of traditional slash‐and‐burn cultivation systems to commercial perennial monocultures such as teak tree plantations, on the catchment hydrological response and sediment yield. The instrumented site monitors hydro‐meteorological and soil loss parameters at both microplot (1 m2) and small catchment (0.6 km2) scales. The monitored catchment is part of the network of critical zone observatories named Multiscale TROPIcal CatchmentS (M‐TROPICS). The data shared by M‐TROPICS in Houay Pano are (1) rainfall, (2) air temperature, air relative humidity, wind speed, and global radiation, (3) catchment land use, (4) stream water level, suspended particulate matter, bed particulate matter and stones, (5) soil surface features, and (6) soil surface runoff and soil detachment. The dataset has already been used to interpret suspended particulate matter and bed particulate matter sources and dynamics, to assess the impact of land‐use change on catchment hydrology, soil erosion, and sediment yields, to understand bacteria fate and weed seed transport across the catchment, and to build catchment‐scale models focused on hydrology and water quality issues. The dataset may be further used to, for example, assess the role of headwater catchments in large tropical river basin hydrology, support the interpretation of new variables measured in the catchment (e.g., contaminants other than faecal bacteria), and assess the relative impacts of both climate and land‐use change on the catchment.

Stream Temperature Response to 50% Strip-Thinning in a Temperate Forested Headwater Catchment

Stream temperature is a critical parameter for understanding hydrological and biological processes in stream ecosystems. Although a large body of research has addressed the effects of forest harvesting on stream temperature, less is known about the responses of stream temperature to the practice of strip-thinning, which produces more coherent patches of shade and sunlight areas. In this study, we examined stream temperature response to 50% strip-thinning in a 17 ha headwater catchment. The thinning lines extended through the riparian zone. Paired-catchment analysis was applied to estimate changes in daily maximum, mean, and minimum stream temperatures for the first year following treatment. Significant effects on daily maximum stream temperature were found for April to August, ranging from 0.6 °C to 3.9 °C, similar to the magnitude of effect found in previous studies involving 50% random thinning. We conducted further analysis to identify the thermal response variability in relation to hydrometeorological drivers. Multiple regression analysis revealed that treatment effects for maximum daily stream temperature were positively related to solar radiation and negatively related to discharge. Frequent precipitation during the summer monsoon season produced moderate increases in discharge (from 1 to 5 mm day−1), mitigating stream temperature increases associated with solar radiation. Catchment hydrologic response to rain events can play an important role in controlling stream thermal response to forest management practices.