Multi-Spatial Resolution Rainfall-Runoff Modelling—A Case Study of Sabari River Basin, India

One of the challenges in rainfall-runoff modeling is the identification of an appropriate model spatial resolution that allows streamflow estimation at customized locations of the river basin. In lumped modeling, spatial resolution is not an issue as spatial variability is not accounted for, whereas in distributed modeling grid or cell resolution can be related to spatial resolution but its application is limited because of its large data requirements. Streamflow estimation at the data-poor customized locations is not possible in lumped modeling, whereas it is challenging in distributed modeling. In this context, semi-distributed modeling offers a solution including model resolution and estimation of streamflow at customized locations of a river basins with less data requirements. In this study, the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model is employed in semi-distribution mode on river basins of six different spatial resolutions. The model was calibrated and validated for fifteen and three selected flood events, respectively, of three types, i.e., single peak (SP), double peak (DP)-and multiple peaks (MP) at six different spatial resolution of the Sabari River Basin (SRB), a sub-basin of the Godavari basin, India. Calibrated parameters were analyzed to understand hydrologic parameter variability in the context of spatial resolution and flood event aspects. Streamflow hydrographs were developed, and various verification metrics and model scores were calculated for reference-and calibration-scenarios. During the calibration phase, the median of correlation coefficient and NSE for all 15 events of all six configurations was 0.90 and 0.69, respectively. The estimated streamflow hydrographs from six configurations suggest the model’s ability to simulate the processes efficiently. Parameters obtained from the calibration phase were used to generate an ensemble of streamflow at multiple locations including basin outlet as part of the validation. The estimated ensemble of streamflows appeared to be realistic, and both single-valued and ensemble verification metrics indicated the model’s good performance. The results suggested better performance of lumped modeling followed by the semi-distributed modeling with a finer spatial resolution. Thus, the study demonstrates a method that can be applied for real-time streamflow forecast at interior locations of a basin, which are not necessarily data rich. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Land-use changes and precipitation cycles to understand hydrodynamic responses in semiarid Mediterranean karstic watersheds

This research was funded partially by the Central University of Ecuador and by the projects RESERVOIR (PRIMA programme supported by the European Union under grant agreement no. 1924) and BBVA2021-Leonardo2 along with local companies (projects Comunidad Regantes 220-I and Comunidad Regantes 1-20T). Antonio Jodar-Abellan acknowledges financial support received from the project BBVA2021-Leonardo2. In the same way, this work has been conducted within the Catedra del Agua of the University of Alicante (catedradelaguaua.org). Moreover, authors acknowledge the reviewers of the manuscript whose comments contributed greatly to improve this paper.Non-planned agricultural land abandonment is affecting natural hydrological processes. This is especially relevant in vulnerable arid karstic watersheds, where water resources are scarce but vital for sustaining natural ecosystems and human settlements.However, studies assessing the spatiotemporal evolution of the hydrological responses considering land-use changes and precipitation cycles for long periods are rare in karstic environments. In this research, we selected a representative karstic watershed in a Mediterranean semiarid domain, since in this belt, karst environments are prone to land degradation processes due to human impacts. Geographic Information Systems-based tools and hydrological modeling considering daily time steps were combined with temporal analysis of climate variables (wavelet analysis) to demonstrate possible interactions and vulnerable responses. Observed daily flow data were used to calibrate/ validate these hydrological models by applying statistic indicators such as the NSE efficiency and a selfdeveloped index (the ANSE index). This new index could enhance goodness-of-fit measurements obtained with traditional statistics during the model optimization. We hypothesize that this is key to adding new inputs to this research line. Our results revealed that: i) changes in the type of sclerophyllous vegetation (Quercus calliprinos, ilex, rotundifolia, suber, etc.) from 81.5% during the initial stage (1990) to natural grasslands by 81.6% (2018); and, ii) decreases in agricultural areas (crops) by approximately 60% and their transformation into coniferous forests, rock outcrops, sparsely natural grasslands, etc. in the same period. Consequently, increases in the curve number (CN) rateswere identified as a result of land abandonment. As a result, an increase in peak flow events jointlywith a relevant decrease of the average flow rates (water scarcity) in the watershed was predicted by the HEC-HMS model and verified through the observed data. This research provides useful information about the effects of anthropogenic changes in the hydrodynamic behaviour of karstic watersheds andwater resource impacts, especially key in water-scarce areas that depict important hazards for the water supply of related populations and natural ecosystems.Central University of EcuadorEuropean Commission 1924Comunidad de Madrid 220-ICatedra del Agua of the University of Alicant

Impacts of land use land cover change and climate change on river hydro-morphology- a review of research studies in tropical regions

Tropical regions have experienced the fastest Land Use Land Cover Change (LULCC) in the last decades, coupled with climate change (CC) this has affected the hydrological and geomorphological processes of river systems. With the increased demand for land, the general trend has been the loss of forest land to agriculture and settlements. These changes have altered the water balance components through enhanced or reduced evaporation, peak flow, flooding, and river morphology. The aim of this review paper is to provide a meta-analysis on the effects of spatiotemporal changes in climate and LULC on river hydro-morphology in the tropics. Following a systematic search, 60 case studies were identified, of which the majority (68%) experienced forest loss due to agricultural and urban expansion, resulting in increased streamflow, surface flow, and total water yield and decreased ET and groundwater recharge. 12% of the case studies showed the impacts of LULCC on channel morphology features through sediment transport and riverbank erosion. Results from this study show limited correlation between LULCC and hydrological variables, indicating that there are likely other factors controlling hydrological processes. Catchment heterogeneity including soil and topography play an important role. Based on studies that project these changes into the future, similar trends are expected over the next decades, with differences based on LU and climate scenarios. There are still limited studies on river hydro-morphology responses to LULCC and CC in the tropics despite the major changes taking place there. In light of future changes, more studies are needed to improve our understanding

ANALYZING THE IMPACTS OF LAND COVER CHANGE TO THE HYDROLOGIC AND HYDRAULIC BEHAVIOURS OF THE PHILIPPINES' THIRD LARGEST RIVER BASIN

Changes in land cover can have negative impacts on the hydrological and hydraulic processes in river basins and watersheds such as increase in surface runoff and peak flows, and greater incidence, risk and vulnerability of flooding. In this study, the impacts of land-cover changes to the hydrologic and hydraulic behaviours of the Agusan River Basin (ARB), the third largest river basin in the Philippines, was analysed using an integrated approach involving Remote Sensing (RS), Geographic Information System (GIS), and hydrologic and hydraulic models. Different land-cover classes in the ARB for the years 1995 and 2017 were mapped using Landsat 5 TM and Landsat 8 OLI images. Using a post-classification change detection approach, changes in land-cover were then determined. The impacts of these changes in land-cover to the to the basin discharge were then estimated using a calibrated hydrologic model based on the Hydrologic Engineering Center - Hydrologic Modeling System (HEC-HMS) under different extreme rainfall conditions. The impact of the changes in land-cover to flood depth and extent was also determined using a hydraulic model based on the HEC-RAS (River Analysis System). Land cover classification results revealed that the ARB is 67.7% forest in 1995 but have decreased to 62.8% in 2017. Agricultural areas in the basin were also found to have increased from 12.2% to 15.5% in the same period. Other notable land cover changes detected include the increase in built-up lands and range lands, and decrease in barren lands. HEC HMS and HEC RAS model simulation results showed that there was an increase in discharge, flood depth, and flood extents between 1995 and 2017, implying that that the detected changes in land cover have negative impacts to hydrologic and hydraulic behaviours of the ARB

Two-Dimensional Flood Inundation Modeling in the Godavari River Basin, India—Insights on Model Output Uncertainty

Most flood inundation models do not come with an uncertainty analysis component chiefly because of the complexity associated with model calibration. Additionally, the fact that the models are both data-and compute-intensive, and since uncertainty results from multiple sources, adds another layer of complexity for model use. In the present study, flood inundation modeling was performed in the Godavari River Basin using the Hydrologic Engineering Center—River Analysis System 2D (HEC-RAS 2D) model. The model simulations were generated for six different scenarios that resulted from combinations of different geometric, hydraulic and hydrologic conditions. Thus, the resulted simulations account for multiple sources of uncertainty. The SRTM-30 m and MERIT90 m Digital elevation Model (DEM), two sets of Manning’s roughness coefficient (Manning’s n) and observed and estimated boundary conditions, were used to reflect geometric, hydraulic and hydrologic uncertainties, respectively. The HEC-RAS 2D model ran in an unsteady state mode for the abovementioned six scenarios for the selected three flood events that were observed in three different years, i.e., 1986, 2005 and 2015. The water surface elevation (H) was compared in all scenarios as well as with the observed values at selected locations. In addition, ‘H’ values were analyzed for two different structures of the computational model. The average correlation coefficient (r) between the observed and simulated H values is greater than 0.85, and the highest r, i.e., 0.95, was observed for the combination of MERIT-90 m DEM and optimized (obtained via trial and error) Manning’s n. The analysis shows uncertainty in the river geometry information, and the results highlight the varying role of geometric, hydraulic and hydrologic conditions in the water surface elevation estimates. In addition to the role of the abovementioned, the study recommends a systematic model calibration and river junction modeling to understand the hydrodynamics upstream and downstream of the junction. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Modelling the Hydrological Effects of Woodland Planting on Infiltration and Peak Discharge Using HEC-HMS

Woodland planting is gaining momentum as a potential method of natural flood management (NFM), due to its ability to break up soil and increase infiltration and water storage. In this study, a 2.2 km2 area in Warwickshire, England, planted with woodland every year from 2006 to 2012, was sampled using a Mini Disk infiltrometer (MDI). Infiltration measurements were taken from 10 and 200 cm away from the trees, from November 2019 to August 2021. Two individual hydrological models were built using the US Hydraulic Engineering Center Hydrological Modelling System (HEC-HMS), to model the effects of infiltration change on peak flows from the site throughout the summer and winter. The models were calibrated and validated using empirical data; the Nash and Sutcliffe Efficiency (NSE) was used as an indicator of accuracy. Results from this study show that woodland planting reduced peak flow intensity compared to impermeable land cover by an average of 6%, 2%, and 1% for 6-h, 24-h, and 96-h winter storms, respectively, and 48%, 18%, and 3% for 6-h, 24-h, and 96-h summer storms, respectively. However, grassland simulations show the greatest reduction in peak flows, being 32%, 21%, and 10%, lower than woodland for 6-, 24-, and 96-h winter storms, respectively, and 6%, 3%, and 0.5% lower than woodland for 6-, 24-, and 96-h summer storms, respectively

Water Resource Variability and Climate Change

Climate change affects global and regional water cycling, as well as surficial and subsurface water availability. These changes have increased the vulnerabilities of ecosystems and of human society. Understanding how climate change has affected water resource variability in the past and how climate change is leading to rapid changes in contemporary systems is of critical importance for sustainable development in different parts of the world. This Special Issue focuses on “Water Resource Variability and Climate Change” and aims to present a collection of articles addressing various aspects of water resource variability as well as how such variabilities are affected by changing climates. Potential topics include the reconstruction of historic moisture fluctuations, based on various proxies (such as tree rings, sediment cores, and landform features), the empirical monitoring of water variability based on field survey and remote sensing techniques, and the projection of future water cycling using numerical model simulations

Drought Characteristics in the Lower Mekong River Basin and Relationship to Land Cover Change

Drought can have devastating effects on regional water resources and agriculture, with an estimated US$96 billions of damages globally between 2005 and 2015. In the Lower Mekong Basin, the impacts of drought have been a major concern for local stakeholders as the region is the largest rice-producing area in the world. Few studies of long-term drought in the region have directly assessed the effects of land cover changes on both agricultural and hydrological drought. We used a suite of remote sensing data to assess drought characteristics in five countries of this region (Vietnam, Cambodia, Thailand, Laos, Myanmar) where traditional in-situ measurements are not generally available. In addition to satellite data, we used the Variable Infiltration Capacity (VIC) macroscale hydrologic model to simulate drought and evaluate its variability with land cover change. The simulations had a relatively high spatial resolution of 5 km, which facilitated the identification of local patterns of land cover change and their relationship with drought characteristics such as severity, duration, and onset. Our results confirmed that 25% of land cover has changed in the region over the last two decades (2001 to present) by using MODIS observation data. Furthermore, our simulations of drought from 1980 onwards, have allowed us to explore the link between land cover change and hydrological characteristics. and found that drought characteristics in the Mekong River basin do not appear to be significantly affected by land cover change

Surface water – groundwater interactions: A case of a shallow semi-closed lake catchment in northern Tanzania

A Dissertation Submitted in Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy in Water Resources Engineering of the Nelson Mandela African Institution of Science and TechnologyConjunctive use of surface water and groundwater is rapidly growing in many developing countries as an adaptation strategy to climate variability and change. However, the interactions between the groundwater and the surface water systems are not adequately understood, especially among the East African rift valley lakes, where data paucity has limited studies and reporting on the spatial influence of catchment heterogeneity. In its humble contribution to sustainable water development, this study aimed to present a platform for understanding the influence of climatic variation and anthropogenic activities on surface water–groundwater interactions. To be relevant locally, Lake Babati, a freshwater lake in Northern Tanzania that provides the community with fish, freshwater, and a habit for hippopotamus, was studied. The study applied hydrological simulation, grey relational analysis, and stepwise regression analysis to model the hydrological behaviour of the lake. Further, it used hydrogeochemistry and environmental isotopes to identify groundwater fluxes and draw the conceptual understanding of surface water – groundwater interaction and applied topography-based indices to spatially map groundwater potentials within the catchment. The results showed that Lake Babati level is significantly declining (p-value < 0.01) at a rate of 25 mm per annum. The lake level decline could not be explained by climatic variability since the decline occurred when both evaporation and rainfall showed no significant changes either seasonally or annually. Instead, the consistent decline of the lake level in all seasons could be due to the expansion of the spillway, which effectively lowered the lake reservoir level and increased the lake outflow in rainy seasons. The hydro-geochemistry and isotopes data showed that the lake water and groundwater interact and are in hydraulic connections. Further, using Height Above Nearest Drainage based and Topography Wetness Index based methods, the study developed two groundwater potential maps to predict groundwater spatial variability and guide groundwater prospecting efforts and subsequent development. Given that Lake Babati is in a hydraulic connection with the groundwater, its consistent decline will likely impact the groundwater system. Similarly, abstracting groundwater at unsustainable rates could lower the lake levels further. Therefore, integrated water resources management is required for sustainable water resources development and management in the catchment. Mandatory and continuous monitoring of the water resources (groundwater levels, river flows, and lake levels) is recommended to generate quality in situ data for future studies

An assessment of the hydrologic response of the Keiskamma catchment to land use/cover changes

The Keiskamma catchment has undergone significant land use/cover changes (LUCC) underpinned by land use policy reforms and climate change. However, the hydrological responses of the catchment to LUCC are not fully understood. This study sought to assess the hydrological response of the Keiskamma catchment to LUCC at catchment and hillslope scale using remote sensing, GIS, hydrological modelling and field experiments. Catchment scale assessments first involved LUCC mapping in IDRISI TerrSet software, using supervised image classification for two sets of multispectral imagery; namely Landsat Thematic Mapper (TM) of 1994 and Landsat 08 Operational Land Imager (OLI) of 2016. The LUCC maps provided an indication of LUCC over time and were prerequisite land use inputs for modelling the hydrologic response of the catchment. The Soil and Water Assessment Tool (SWAT) hydrologic model was used to model the hydrologic response of the catchment to LUCC. The Sequential Uncertainty Fitting (SUFI-2) in SWAT-CUP was used to assess model performance and uncertainty analysis. The influence of rainfall on the hydrologic response of the catchment was also assessed using linear regression. One of the prominent forms of LUCC in the Keiskamma catchment, particularly central Keiskamma is P. incana shrub encroachment. Field experiments were set up to investigate the hydrologic impacts of P. incana shrub invasion at hillslope scale, as well as to validate the results obtained by the SWAT hydrologic model. Field experiments included an assessment of the Landscape Organisation Index (LOI) of the invasion, as well as assessing of surface conditions, surface runoff (L), volumetric soil water content (cm³/cm³) and sediment loss (grams) under P. incana, grass and bare-eroded areas. High image classification accuracy assessment values of 87.2 % and 87.4 % for 1994 and 2016 respectively were obtained, with a Kappa coefficient of 0.84 for both sets of imagery. Results of the study revealed a significant increase in woody vegetation encroachment, specifically shrub invasion, forest expansion in the upper parts of the catchment, as well as an increase in exotic and invasive vegetation species within the riparian zone. The SWAT model showed a good (NSE=0.69, R²=0.69 and RSR =0.56) and unsatisfactory (NSE=0.4, R²=0.4 and RSR 0.79) model performance for calibration and validation respectively. However, for both the calibration (p-factor =0.77; r-factor 1.03) and validation (p-factor =0.92; r-factor 1.38) periods there was acceptable uncertainty as indicated by the p- and r-factor statistics. The mean annual streamflow (-71.4 %), surface runoff (-98.8 %), soil water content (-4.5 %), evapotranspiration (-5.3 %), groundwater (-79.5 %) and sediment loss (-99.9 %) decreased from 1994 to 2016. The impoundments in the catchment viz Cata, Mnyameni, Binfield, Sandile, Debe and Dimbaza dams, also contributed significantly to the streamflow reduction. A strong correlation (r= 0.61) between the declining streamflow (m3/s) and rainfall (mm) was observed. At hillslope scale, P. incana invasion was characterised by a low LOI, owing to large inter-shrub bare patches and poor soil surface conditions characterised by soil surface crusting, conducive to high runoff generation and connectivity. High surface runoff and soil losses were evident under P. incana and bare-eroded areas. Volumetric soil water content was high under grass and P. incana tussocks, intermediate in P. incana inter-patches and low in bare-eroded areas. The findings and analysis of this study conclude that the hydrologic response of the Keiskamma catchment was influenced significantly by LUCC in the form of extensive invader shrub encroachment, expansion of forestry using exotic tree species, impoundments, as well as the infestation of riparian zones by invasive vegetation. Management of woody shrub encroachment and alien invasive plants as well as indigenous forest species utilisation should be considered as amongst the key efforts towards restoring the ecohydrological integrity of the Keiskamma catchment