Tropical River Basin Research Articles

INFLUENCE OF INVASIVE PLANT SPECIES ON SOIL PROPERTIES IN TROPICAL RIPARIAN ZONES

Riparian zones are highly productive biodiversity-rich transition areas. However, the invasion of exotic plant species depletes diversity and productivity, a severe global environmental concern as they alter ecosystem services. The analysis of spatio-temporal variations of soil nutrients in an invasive plant-impacted riparian zone is significant. This study was conducted in the riparian zones of a tropical river basin, Vamanapuram river basin (VRB), Southern Western Ghats, India, to analyse soil samples (total n= 60) from invaded (VR) and uninvaded (Control) areas for pH, Electrical Conductivity (EC), Organic Carbon (OC), available nitrogen (AN), available phosphorus (AP), and available potassium (AK). In general, comparing the invaded and control sites, changes were noticed in almost all the above physico-chemical parameters (except OC) at a significant level with high values in invaded soil sites mainly due to invasion. However, more studies are needed to differentiate the impacts within the system for a better understanding of invasive plant-soil interactions.

Evaluation of the SWAT Model for the Simulation of Flow and Water Balance Based on Orbital Data in a Poorly Monitored Basin in the Brazilian Amazon

The Amazon basin, the world’s largest river basin, is a key global climate regulator. Due to the lack of an extensive network of gauging stations, this basin remains poorly monitored, hindering the management of its water resources. Due to the vast extension of the Amazon basin, hydrological modeling is the only viable approach to monitor its current status. Here, we used the Soil and Water Assessment Tool (SWAT), a process-based and time-continuous eco-hydrological model, to simulate streamflow and hydrologic water balance in an Amazonian watershed where only a few gauging stations (the Jari River Basin) are available. SWAT inputs consisted of reanalysis data based on orbital remote sensing. The calibration and validation of the SWAT model indicated a good agreement according to Nash-Sutcliffe (NS, 0.85 and 0.89), Standard Deviation Ratio (RSR, 0.39 and 0.33), and Percent Bias (PBIAS, −9.5 and −0.6) values. Overall, the model satisfactorily simulated water flow and balance characteristics, such as evapotranspiration, surface runoff, and groundwater. The SWAT model is suitable for tropical river basin management and scenario simulations of environmental changes.

Flood susceptibility assessment and mapping in a monsoon-dominated tropical river basin using GIS-based data-driven bivariate and multivariate statistical models and their ensemble techniques

Flood susceptibility assessment and mapping in a monsoon-dominated tropical river basin using GIS-based data-driven bivariate and multivariate statistical models and their ensemble techniques

Neotectonics assessment using geomorphic indices: A study from the passive continental margin of India

ABSTRACT The response of landforms to tectonic deformative processes can be effectively understood by using geomorphic indices. The objective of this study is to evaluate the extent of neotectonic activities in the fourth-order sub-basins of a tropical river basin (Kallada River basin) in the Southern Granulite TerrainIndia. The extend of neotectonism was analyzed using geomorphic indices such as asymmetry factor, transverse topographic symmetry factor, hypsometric integral, stream-length gradient index, drainage basin shape index, ratio of valley floor to valley height, and mountain front sinuosity, with values varying from 0.3 to 41.20, 0.12 to 0.54, 0.13 to 0.69, 12.76 to 1036.49, 0.63 to 3.81, 0.05 to 6.04, and from 1.02 to 3.08, respectively. Further, the relative active tectonics index (IRAT) was derived from the geomorphic indices using GIS and the values vary from 1.67 to 3.0. Based on the degree of relative tectonic activity, Kallada River basin was classified into class 1, 2, 3 and 4 corresponding to very high (1.0-1.5), high (1.5-2), moderate (2.0-2.5), and low (IRAT>2.5) values. The spatial distribution of different “IRAT” classes shows a gradational pattern from east to west, suggesting a gradual decrease in the neotectonic activity in the basin.

Understanding the anthropogenic development impacts on long-term flow regimes in a tropical river basin, Central Vietnam

ABSTRACT The Vu Gia Thu Bon (VGTB) basin constitutes the primary water supply in Central Vietnam. While climate change disturbs stream discharges and affects flood extremes, upstream dam development may intensify or mitigate such impacts. Therefore, this study provides a quantitative evaluation of long-term alterations in the flow regimes of the VGTB rivers from 1977 to 2020 resulting from the impacts of upstream anthropogenic developments. The datasets are divided into two periods, pre-2000 (1977–2000) and post-2000 (2001–2020), using different indices and analytical methods. The analyses show that since 2011, reservoir operations have reduced the maximum and high-flow discharges downstream in excess of climate change and land-use effects. However, due to the impact of water transfer by the Dak Mi 4 hydropower dam from the Vu Gia River to the Thu Bon River through a diversion channel, the minimum and low-flow discharges decreased in the pre-dam period and increased in the post-dam period.

Geomorphological analysis of tropical river basins in southern Kerala using hypsometric indices and neotectonic proxies

Geomorphological analysis of tropical river basins in southern Kerala using hypsometric indices and neotectonic proxies

Land use drivers of riverine methane dynamics in a tropical river basin, India

Rivers are globally significant natural sources of atmospheric methane (CH4). However, the effect of land use changes on riverine CH4 dynamics, particularly in tropical zones, remain ambiguous, yet important to predict and anticipate the present and future contribution of rivers to the global CH4 budget. The present study examines the magnitude and drivers of riverine CH4 concentration and emission in the tropical Krishna River (KR) basin, India. The large spatial variability of CH4 concentration (0.03 to 185.34 μmol L −1) and emissions (0.04 mmol m−2 d−1 to 1666.24 mmol m−2 d−1) in the KR basin was linked to the site-specific features of the catchments through which rivers are draining. Several fold higher CH4 concentration and emission was observed for the urban river sites (64.63 ± 53.17 µmol L−1 and 294.15 ± 371.52 mmol m2 d−1, respectively) than the agricultural (1.05 ± 2.22 µmol L−1 and 3.45 ± 9.72 mmol m2 d−1, respectively) and forested (0.49 ± 0.23 µmol L−1 and 1.26 ± 0.73 mmol m2 d−1, respectively) sites. The concentrations of dissolved oxygen, total phosphorus, and Chlorophyll-a were significant hydrochemical variables strongly coupled with the dissolved CH4 concentrations. On the other hand, percentage of built-up area emerged as the most important landscape-level driver indicating that urbanization has an overriding effect on riverine CH4 concentration in the agriculture dominated KR basin. Our study supports the growing notion that tropical urban rivers are hotspot of CH4 emission. Furthermore, we show that the pattern of increasing in riverine CH4 concentration with built-up area (%) is a general feature of Asian river basins. As the urban land cover and population following an exponential increase, Asian rivers might contribute substantially to the regional and global CH4 budget.

A GIS based Fuzzy-AHP for delineating groundwater potential zones in tropical river basin, southern part of India

Groundwater plays a vital role in the development of ecological niches, the durability of the environment, and the socio-economic growth of an area. To meet the demand for groundwater over the increasing population, the scientific community stresses the prospective of identifying groundwater potential zones (GWPZ), aiming at conservation, planning, and regulation for optimum utilization of this natural resource. The GWPZ evaluation of the Karuvannur River Basin (KRB) in the southern part of India was carried out through GIS-Fuzzy-Analytical Hierarchy Process (FAHP), by assigning weights to interdependent factors controlling groundwater potentials such as geomorphology (Gm), slope(S), geology(G), drainage density (Dd), lineament density (Ld) and Land Use Land Cover (Lu) with the aid of Geographical Information system (GIS). FAHP includes a pairwise comparison of criteria and sub-criteria elements expressed with Triangular Fuzzy Numbers (TFNs), which can avoid vagueness, imprecision, and uncertainty of the linguistic scale. The model result was validated with the depth to water level data of dug wells by plotting them on the GWPZ map. This study reveals that the FAHP method is efficient in delineating GWPZ in this region with an accuracy of 80.9%. Further, GWPZ are reliant on underlying lithology; very good (48.1%) aquifers occupy the coastal area; good (12.7%); moderate (18.3%) aquifers are provided by the secondary porosity provided by underlying structures while poor aquifers (20.9%) occupy the eastern hard rock areas of KRB. This type of cost-effective FAHP method is efficient in delineating GWPZ and can be used for sustainable groundwater policies and management.

Extreme Rainfall Variations Under Climate Change Scenarios. Case of Study in an Andean Tropical River Basin

Extreme Rainfall Variations Under Climate Change Scenarios. Case of Study in an Andean Tropical River Basin

Comparative Evaluation of Five Hydrological Models in a Large-Scale and Tropical River Basin

Hydrological modeling is an important tool for water resources management, providing a feasible solution to represent the main hydrological processes and predict future streamflow regimes. The literature presents a set of hydrological models commonly used to represent the rainfall-runoff process in watersheds with different meteorological and geomorphological characteristics. The response of such models could differ significantly for a single precipitation event, given the uncertainties associated with the input data, parameters, and model structure. In this way, a correct hydrological representation of a watershed should include the evaluation of different hydrological models. This study explores the use and performance of five hydrological models to represent daily streamflow regimes at six hydropower plants located in the Tocantins river basin (Brazil). The adopted models include the GR4J, HYMOD, HBV, SMAP, and MGB-IPH. The evaluation of each model was elaborated considering the calibration (2014–2019) and validation period (2005–2010) using observed data of precipitation and climatological variables. Deterministic metrics and statistical tests were used to measure the performance of each model. For the calibration stage, results show that all models achieved a satisfactory performance with NSE values greater than 0.6. For the validation stage, only the MGB-IPH model present a good performance with NSE values greater than 0.7. A bias correction procedure were applied to correct the simulated data of conceptual models. However, the statistical tests exposed that only the MGB-IPH model could preserve the main statistical properties of the observed data. Thus, this study discusses and presents some limitations of the lumped model to represent daily streamflows in large-scale river basins (>50,000 km2).

Characterizing floods and reviewing flood management strategies for better community resilience in a tropical river basin, India

Characterizing floods and reviewing flood management strategies for better community resilience in a tropical river basin, India

Climate and land management accelerate the Brazilian water cycle

Increasing floods and droughts are raising concerns of an accelerating water cycle, however, the relative contributions to streamflow changes from climate and land management have not been assessed at the continental scale. We analyze streamflow data in major South American tropical river basins and show that water use and deforestation have amplified climate change effects on streamflow extremes over the past four decades. Drying (fewer floods and more droughts) is aligned with decreasing rainfall and increasing water use in agricultural zones and occurs in 42% of the study area. Acceleration (both more severe floods and droughts) is related to more extreme rainfall and deforestation and occurs in 29% of the study area, including southern Amazonia. The regionally accelerating water cycle may have adverse global impacts on carbon sequestration and food security.

Detection of groundwater potential zones using analytical hierarchical process (AHP) for a tropical river basin in the Western Ghats of India

Detection of groundwater potential zones using analytical hierarchical process (AHP) for a tropical river basin in the Western Ghats of India

Furthering the precision of RUSLE soil erosion with PSInSAR data: an innovative model

Soil erosion is a severe environmental problem worldwide, especially in tropical regions. The Revised Universal Soil Loss Equation (RUSLE), one of the universally accepted empirical soil erosion models, is quite commonly used in tropical climatic conditions to estimate the magnitude and severity of soil erosion. This study, apart from identifying the role of individual parameters in influencing the results of the RUSLE, also aims at refining the RUSLE results by incorporating the state-of-the-art technique Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) in a GIS environment by utilizing its ability to measure minute surface changes in millimetre levels. Apart from this novel approach of prioritising soil erosion classes using PSInSAR, the eroding surface conditions were also studied using low coherence value (<0.75 in this study). The spatially and temporally averaged annual soil loss and net soil erosion (2015–2019), derived through RUSLE and transport limited sediment delivery (TLSD) approach, respectively, was improved by spatially integrating the PSInSAR velocity map. The integrated methodological framework is demonstrated for a tropical river basin in South India (Muvattupuzha River Basin [MRB]), which shows a mean rate of net soil loss of 6.8 ton/ha/yr, and nearly 8% of the area experiences deposition. Our approach to improve the accuracy of RUSLE-based soil erosion classes using PSInSAR techniques clearly demarcated the areas that call for utmost priority in implementing management practices. The corollary results show that the very severe soil erosion class is characterized by PSI velocity with higher negative values, followed by the successively lower classes. Results strongly suggest that RUSLE output can be improved as well as validated using a velocity map derived from radar data.

The Effect of Size Distribution on the Geochemistry and Mineralogy of Tropical River Sediments and Its Implications regarding Chemical Weathering and Fractionation of Alkali Elements

Abstract The mineralogical and geochemical compositions of the sediments deposited by rivers have been used extensively to evaluate past chemical weathering and the physical erosion history of drainage basins at different time scales. However, the role of sediment sorting in the mineralogical and geochemical compositions of river sediment needs to be better constrained because it could significantly modify proxies used to evaluate weathering intensity in the past. In this study, major and trace element concentrations and mineralogical compositions were determined on seven different grain-size fractions of riverbed samples taken from the Pahang and Kelantan Rivers in the Malay Peninsula. The main aims are to assess chemical weathering and the fractionation of alkali elements during sediment transportation under tropical climate conditions. Fine sediments (from &amp;lt;2 μm to 4-8 μm) were characterized by higher concentrations of Al2O3, P2O5, V, Sc, and Cs than coarse sediments (from 8-16 μm to 32-63 μm). The presence of heavy minerals, such as zircon and monazite, was found to have critical effects on the concentration of several elements (e.g., Zr and Th), leading to extremely high elemental concentrations in the coarse-sediment fractions. Variations in elemental concentrations with particle sizes are mainly attributed to changes in the mineralogical composition during mineral sorting and weathering. In both rivers, the intensity of chemical weathering increased with decreasing grain sizes. However, the relationship between grain size and chemical weathering trends in the Pahang and Kelantan River basins was different in each case due to differences in plagioclase and K-feldspar concentrations, especially in the coarse-sediment fractions (16-32 μm and 32-63 μm). Kaolinite percentage, illite chemistry index, and illite crystallinity were directly proportional to the chemical index of alteration (CIA), suggesting that these mineralogical parameters are suitable proxies for determining chemical weathering intensity in sediments that have undergone significant changes due to mineral sorting during transportation. The comparison of Rb/K and Cs/K ratios and the CIA suggested that K and Rb mainly derive from primary minerals during the process of chemical weathering, whereas Cs is mainly present in fine weathered particles due to the reabsorption of Cs on clay minerals. Overall, our results highlight the relationship of grain size and mineral assemblages to different states of chemical weathering (and alkali fractionation) in tropical river basin sediments. These relationships need to be considered when using mineralogical and geochemical compositions to reconstruct weathering history in a “source to sink” approach.

Annual Soil Loss Estimation in a Tropical River Basin of Southern India Using RUSLE Model and AHP Techniques

Remote sensing and geographic information system (GIS) techniques have been shown to be effective tools for geohazard mapping. The Western Ghats of southern India are a classic terrain with a variety of geohazards such as landslides and soil erosion. The current study employs RUSLE methodology in conjunction with remote sensing and GIS to estimate annual soil loss and identify zones of high erosion potential in one of southern India's major tropical river basins, the Chalakkudy River Basin. The resulting map elaborates on the area's annual soil erosion to the tune of 14.7008 t ha1 year1. The map also divides the terrain into zones based on the likelihood of soil erosion. According to the study, approximately 4.70 percent of the total area (67.13 km2) is prone to severe soil erosion, while the remaining 67.13 percent (972.32 km2) is prone to high erosion. Soil erosion prognosis analysis assists decision-makers in developing a proper conservation planning programme to reduce soil erosion. Analytical Hierarchy Process (AHP) was used to identify critical soil erosion- prone areas by integrating geo-environmental variables such as land use/land cover, geomorphology, lithology, drainage density, lineament density, slope, aspect, elevation, LS factor, rainfall, soil texture, and soil depth after determining their relative contribution in conditioning the terrain susceptible to soil erosion. Only 4.70% of the total area is highly prone to soil erosion. Keywords: Remote Sensing, GIS, RUSLE, Soil Erosion, AHP, Chalakkudy

Physically-based distributed modelling of the hydrology and soil erosion under changes in landuse and climate of a humid tropical river basin

The effects of landuse/landcover (LULC) and climate change on hydrology and soil erosion processes are of major concern, especially in the humid tropics. In this study, an evaluation of these changes is performed in a humid tropical catchment (Vamanapuram river basin, India) using a physically based distributed model, SHETRAN. The past landuse maps and climate data from six fine resolution NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) are used to force the SHETRAN model. A comparison of the change in the rate of soil erosion and hydrological responses during the future climate scenarios (near: 2021–2050 and far: 2071–2100) with respect to the historical period (1980–2005) is conducted.The isolated effects of landuse, climate variability and the combined effect caused change in streamflow (1.1%, 7.9%, 9.0% respectively) and sediment load (−10.4%, 1.7%, −10.5% respectively) in the past. An ensemble mean of general circulation model (GCM) projections showed that mean temperature and average annual precipitation under representative concentration pathway RCP 4.5 (8.5) scenarios for near and far futures increased from the historic period by 0.51 °C (1.6 °C), 0.6 °C (3.2 °C) and by 9% (6%), 15% (22.8%), respectively. Under RCP4.5(8.5), the average annual streamflow increased gradually from the near to far future, by 3.2% (−1.8%) and 13.6 % (22.1%) whereas, the projected sediment load a showed change of −21.05% (−26.63%) in near future while far future indicated change by −11% (4%). The SHETRAN model has been found to be effective in evaluating climate change impacts on hydrology and sediment yield and is useful for future river basin management.

Suspended sediment transport in a tropical river basin exhibiting combinations of land uses/land covers and hydroclimatic conditions: Case study of upper Athi Basin, Kenya

Study regionThe Upper Athi River Basin (Lat: 1°25′17.61°S and Long: 37°15′29.55°E) in Kenya, East Africa. Study focusThe effects of land use/land cover type on suspended sediment concentrations and yield were investigated in the upper Athi river basin in Kenya. The suspended sediment concentrations and yield, river discharges, water levels and flow velocities were monitored in stations established at the outlets of sub-basins and also at the outlet of the main basin in period 2012–2015. New hydrological insightsThe magnitude of river discharge in the upper Athi river basin is not only a function of the magnitude of rainfall, but combination of land uses/land covers determined the magnitude of sediment yield in the sub-basins. The highest sediment yield occurred in a semi-arid sub-basin dominated by savannah grassland and livestock grazing. The lowest occurred in the high rainfall sub-basins dominated by forest with mixed farming and settlements. Significant sediment transport commenced at an effective river discharge of 405 m3s−1 which is a frequent discharge event resulting in significant sediment load transport in most rainy seasons and years. The magnitude of suspended sediment discharge is a function of the magnitude of rainfall such that the greatest sediment transport occurs during the long rainy seasons (54%) as compared to 41% during the short rainy season. The total annual suspended sediment load in the basin ranged 2.11–3.77 × 106 tons.yr−1 and sediment production rate ranged 205–366 tons.km−2.year−1.

Tree-based ensemble model prediction for hydrological drought in a tropical river basin of India

Tree-based ensemble model prediction for hydrological drought in a tropical river basin of India

Frequency-intensity-distribution bias correction and trend analysis of high-resolution CMIP6 precipitation data over a tropical river basin

Frequency-intensity-distribution bias correction and trend analysis of high-resolution CMIP6 precipitation data over a tropical river basin