Nature-based solutions efficiency evaluation against natural hazards: Modelling methods, advantages and limitations

Nature-based solutions (NBS) for hydro-meteorological risks (HMRs) reduction and management are becoming increasingly popular, but challenges such as the lack of well-recognised standard methodologies to evaluate their performance and upscale their implementation remain. We systematically evaluate the current state-of-the art on the models and tools that are utilised for the optimum allocation, design and efficiency evaluation of NBS for five HMRs (flooding, droughts, heatwaves, landslides, and storm surges and coastal erosion). We found that methods to assess the complex issue of NBS efficiency and cost-benefits analysis are still in the development stage and they have only been implemented through the methodologies developed for other purposes such as fluid dynamics models in micro and catchment scale contexts. Of the reviewed numerical models and tools MIKE-SHE, SWMM (for floods), ParFlow-TREES, ACRU, SIMGRO (for droughts), WRF, ENVI-met (for heatwaves), FUNWAVE-TVD, BROOK90 (for landslides), TELEMAC and ADCIRC (for storm surges) are more flexible to evaluate the performance and effectiveness of specific NBS such as wetlands, ponds, trees, parks, grass, green roof/walls, tree roots, vegetations, coral reefs, mangroves, sea grasses, oyster reefs, sea salt marshes, sandy beaches and dunes. We conclude that the models and tools that are capable of assessing the multiple benefits, particularly the performance and cost-effectiveness of NBS for HMR reduction and management are not readily available. Thus, our synthesis of modelling methods can facilitate their selection that can maximise opportunities and refute the current political hesitation of NBS deployment compared with grey solutions for HMR management but also for the provision of a wide range of social and economic co-benefits. However, there is still a need for bespoke modelling tools that can holistically assess the various components of NBS from an HMR reduction and management perspective. Such tools can facilitate impact assessment modelling under different NBS scenarios to build a solid evidence base for upscaling and replicating the implementation of NBS

Geomorphological analysis of Scopia catchment (Central Greece), using DEM data and GIS

In this study a geomorphological analysis of Scopia catchment was achieved, using digital elevation model (DEM) and GIS. The study area is a 7th order drainage catchment with total number and total length of streams 2, 303 and 1, 253.53 km, respectively. Mean bifurcation ratio value (3.57) is distinctive of runoff s predominance versus infiltration, while the 2th stream orders refrain from ideal development, as many of them contribute directly to 4th stream orders. The drainage density (2.86) and the stream frequency (5.25), relate to the dense vegetation and the limited permeability of the lithological formations. The area and perimeter are 438.79 km2 and 116.06 km, respectively, the circularity is 0.40 and the elongation ratio 0.59, indicating that Scopia is a large-sized and elongated in shape catchment, less efficient in runoff discharge. The relief of the study area is hilly; with a relatively large average slope of 10.64° that expresses the quantitative of the roughness relief. The greater proportion of slopes ranges from 0° to 5°. They represent the flat to slightly inclined relief covering the cultivated areas on the central and west part of the catchment. The hypsometric integral value (25.74%) indicates that Scopia is an area not in equilibrium status, that may present the form of maturity stage, but in fact is in a transition stage (monadnock phase)

Hydrologic processes simulation using the conceptual model Zygos: the example of Xynias drained Lake catchment (central Greece)

In the catchment of Xynias drained Lake, hydrologic processes simulation took place using a lumped approach with the conceptual model Zygos. The model implements a conceptual soil moisture accounting scheme extended with a groundwater tank and the input data were the monthly time series of rainfall and the potential evapotranspiration. The automatic optimization procedure of the model was implemented using the evolutionary annealing-simplex algorithm for maximum 11,000 iterations, inserting an 18-month observed runoff time series. It showed that hydrologic balance factors had non-physical significance for the study area. The model’s manual calibration for a Nash coefficient of 0.85 revealed that actual evapotranspiration constitutes 62.5 % (389.7 mm), runoff 22.7 % (141.8 mm) and infiltration 14.8 % (92.2 mm) of precipitation, showing optimal adaptation of simulated to observed runoff. The model estimated the initial reserve of soil moisture related to the presence of organic matter which increases water retention, a residue of the former lake. It confirmed zero runoff values during the summer months and connected the occurrence of springs and the outflows to other catchments (59.8 mm) with the karstification degree of the study area. The error on the annual rainfall is 4.9 % and is considered acceptable. © 2016, Springer-Verlag Berlin Heidelberg

A lumped conceptual approach for modeling hydrological processes: the case of Scopia catchment area, Central Greece

In the catchment area of Scopia, Central Greece, a lumped applied approach of water balance was accomplished, by applying the Zygos model, which delineates an essential water balance forms. The model is in view of Thornthwaite model, in its modified version. It can be adjusted automatically, with the evolutionary annealing-simplex technique for nonlinear optimization, or manually and the input data are precipitation and the potential evapotranspiration. In the present study, both programmed and manual calibration occurred. Programmed calibration took place, utilizing a specimen of measured runoff values from October 2009 to March 2011. Despite the fact that the Nash–Sutcliffe coefficient (NSC) value was high (0.87), the simulated parameters of water balance had abnormal significance for Scopia catchment area. On the contrary, manual calibration uncovered that the actual evapotranspiration constitutes 64.6% (450.1 mm) of the precipitation. Runoff and percolation represent 20.6% (143.6 mm) and 14.8% (102.9 mm) of the precipitation, respectively. The NSC (0.70) and the validation criteria exhibit an ideal adjustment of simulated to measured runoff, while the hydrological parameters appeared to have a physical significance for the study site. Zygos model connects the emergence of springs with the development of the karstification in the carbonate rocks of the region and affirms the predominance of runoff versus percolation due to the hydrolithological structure of the Scopia catchment. This is related to the presence of episodic floods in the area. The yearly precipitation values were found with an error of 0.2% and are viewed as insignificant. © 2017, Springer-Verlag GmbH Germany

Assessment of natural and anthropogenic impacts in groundwater, utilizing multivariate statistical analysis and inverse distance weighted interpolation modeling: the case of a Scopia basin (Central Greece)

In Scopia basin, central Greece, a hydrochemical investigation was completed. Groundwater samples from 41 sites were used to assess the natural and anthropogenic impacts in groundwater, utilizing the principal component analysis (PCA) involved with the inverse distance weighted (IDW) interpolation modeling and hierarchical cluster analysis (HCA). Best fit model to explain the spatial distribution of both hydrochemical parameters and PCA was chosen by optimizing the IDW interpolator’s parameters. Precision of the model was picked based on less root-mean-squared prediction error (RMSPE) amongst predicted and actual values measured at the same locations. Groundwater exhibit Ca–Mg–HCO3 as the dominant hydrochemical type and their greater part are mixed waters with non-dominant ion. Interpolation models demonstrate high estimations of nitrates in zones with agricultural activities and high estimations of nickel and chromium in regions with the strong presence of ultrabasic rocks. Dominant part of the groundwater samples surpasses in many cases the European Community (EC) drinking water permissible limits. Thus, they are unsuitable for human consumption. PCA illustrated four factors, which clarified 80.62% of the aggregate variance of data and HCA classified two statistically significant clusters of sampling sites. Results show natural procedures ascribed to the weathering of the minerals contained in the ultrabasic rocks and anthropogenic influences related to the use of fertilizers and wastewater leak. In light of FAO standards and Richards’s classification, the groundwaters are reasonable for irrigation purposes, featuring waters with low sodium hazard and moderate salinity hazard. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature

Monitoring, modeling, and assessment of water quality and quantity in River Pinios, using ARIMA models

The purpose of this study is to analyze surface water quality and discharge data samples from River Pinios at Region of Thessaly, Central Greece. The statistical samples of each one of the variables consisted of a maximum of 188 monthly observations over a period of 16 years. For these measurements stochastic modeling algorithms were used by ARIMA Models in order to assess water quality and quantity parameters and to compare the measurements with the legislation standards. By using ARIMA to prewhiten each time series, relationships between the parameters were demonstrated. Moreover, the time response between the fluctuations of water temperature (Tw) with the ones of (1) dissolved oxygen (DO), (2) ammonium (NH4 +), and (3) nitrates (NO3 –) and the fluctuations of discharge (Q) with that of water electrical conductivity (ECw) was assessed. Also, (1) an evaluation of the status of river water quality according to the Hellenic and International Legislation and (2) a comparison with other corresponding studies in the area of River Pinios watershed were performed. Finally, in this study the necessity of multivariate statistical assessment of extended databases in combination with reliable and real–time monitoring data is presented, in order to “extract” information about the quality and quantity parameters and to apply managerial strategies for pollution control. © 2018 Desalination Publications. All rights reserved

Morphometric analysis of the drainage network of Samos Island (northern Aegean Sea): Insights into tectonic control and flood hazards

The morphometric analysis of alluvial drainage provides insights into its dynamics, erosion capacity, susceptibility to floods and possible genetic relations to tectonic faulting. In this study, we analysed the drainage system of Samos Island, located in the northern Aegean Sea. The results indicate a vulnerability to erosion and flooding events, and these intense phenomena concentrate mostly on third-order catchments. Two dissimilar drainage network systems are shown: an older drainage network system with a main NW–SE direction, which includes fourth- and fifth-order branches, and a recent drainage network system, which includes new, smaller order branches with a main NE–SW direction. The major tectonic fault orientations are NNW–SSE. The branches of the hydrographic network and faults present different directions, which indicates that the hydrographic pattern is not affected by tectonics. © 201

Evaluating nature-based solution for flood reduction in spercheios river basin under current and future climate conditions

Nature-based solutions (NBS) are being deployed around the world in order to address hydrometeorological hazards, including flooding, droughts, landslides and many others. The term refers to techniques inspired, supported and copied from nature, avoiding large constructions and other harmful interventions. In this work the development and evaluation of an NBS applied to the Spercheios river basin in Central Greece is presented. The river is susceptible to heavy rainfall and bank overflow, therefore the intervention selected is a natural water retention measure that aims to moderate the impact of flooding and drought in the area. After the deployment of the NBS, we examine the benefits under current and future climate conditions, using various climate change scenarios. Even though the NBS deployed is small compared to the rest of the river, its presence leads to a decrease in the maximum depth of flooding, maximum velocity and smaller flooded areas. Regarding the subsurface/groundwater storage under current and future climate change and weather conditions, the NBS construction seems to favor long-term groundwater recharge. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

An overview of monitoring methods for assessing the performance of nature-based solutions against natural hazards

To bring to fruition the capability of nature-based solutions (NBS) in mitigating hydro-meteorological risks (HMRs) and facilitate their widespread uptake require a consolidated knowledge-base related to their monitoring methods, efficiency, functioning and the ecosystem services they provide. We attempt to fill this knowledge gap by reviewing and compiling the existing scientific literature on methods, including ground-based measurements (e.g. gauging stations, wireless sensor network) and remote sensing observations (e.g. from topographic LiDAR, multispectral and radar sensors) that have been used and/or can be relevant to monitor the performance of NBS against five HMRs: floods, droughts, heatwaves, landslides, and storm surges and coastal erosion. These can allow the mapping of the risks and impacts of the specific hydro-meteorological events. We found that the selection and application of monitoring methods mostly rely on the particular NBS being monitored, resource availability (e.g. time, budget, space) and type of HMRs. No standalone method currently exists that can allow monitoring the performance of NBS in its broadest view. However, equipments, tools and technologies developed for other purposes, such as for ground-based measurements and atmospheric observations, can be applied to accurately monitor the performance of NBS to mitigate HMRs. We also focused on the capabilities of passive and active remote sensing, pointing out their associated opportunities and difficulties for NBS monitoring application. We conclude that the advancement in airborne and satellite-based remote sensing technology has signified a leap in the systematic monitoring of NBS performance, as well as provided a robust way for the spatial and temporal comparison of NBS intervention versus its absence. This improved performance measurement can support the evaluation of existing uncertainty and scepticism in selecting NBS over the artificially built concrete structures or grey approaches by addressing the questions of performance precariousness. Remote sensing technical developments, however, take time to shift toward a state of operational readiness for monitoring the progress of NBS in place (e.g. green NBS growth rate, their changes and effectiveness through time). More research is required to develop a holistic approach, which could routinely and continually monitor the performance of NBS over a large scale of intervention. This performance evaluation could increase the ecological and socio-economic benefits of NBS, and also create high levels of their acceptance and confidence by overcoming potential scepticism of NBS implementations. © 2021 The Author(s