Relationship of Weather Types on the Seasonal and Spatial Variability of Rainfall, Runoff, and Sediment Yield in the Western Mediterranean Basin

Atmospheric circulation types and floods' occurrence; A thorough analysis over Greece

Floods have a direct impact on the society and the environment, causing human losses, affecting individual incomes and national economic activity including infrastructure damages. Atmospheric circulation is strongly related to both mean and extreme climate, with the latter being the driving force of adverse phenomena, such as inundations. The overarching goal of the research is the identification of those atmospheric circulation patterns that are associated with catastrophic flood events over Greece. An updated atmospheric classification scheme consisted of 12 circulation types (5 anticyclonic and 7 cyclonic) is implemented to detect and highlight the flood-dominant circulation types over the domain of interest. It is established that for a 7-year period (from 2012 to 2018), where reliable flood inventories are available as a derivative of the European Union (EU) Flood Directive implementation process, the dominant circulation type is the cyclonic type C with its center to be located over the Cyclades area. The study also reveals that during the most severe floods, the prevailing cyclonic types are substantially deeper than their mean anomaly field. Finally, out of the 14 River Basin Districts of Greece, Thrace (EL14) is the more flood prone area, while Eastern Macedonia (EL11) is far less flood affected. The introduced Floods' Frequency Vulnerability index (FFVI) showed that in the case of significant floods, Western Peloponnese (EL01) and Epirus (EL05) are the most vulnerable River Basin Districts. The proposed methodology of coupling circulation types with flood occurrences can be applied in all EU Member-States and set the base of effective floods' prediction mechanisms at River Basin Districts scales.

An improved vegetation cover and management factor for RUSLE model in prediction of soil erosion

Soil erosion and runoff of cultivated land will cause farmland to be degraded and the downstream to be contaminated, which has aroused extensive attention worldwide. The conventional soil loss prediction model revised universal soil loss equation (RUSLE) is capable of more significantly simulating and predicting the amount of soil loss, but this model often cannot achieve the satisfied prediction accuracy when the rainfall distribution of 1 year is significantly inconsistent with the annual distribution law. In this study, the 3-year field experiments were performed in Jilin, China. Besides, an improved revised universal soil loss equation (IRUSLE) was provided with a novel vegetation cover and management factor (C). It considered the interaction between rainfall distribution and normalized difference vegetation index (NDVI) by theoretical analysis and the genetic algorithm. It was reported that IRUSLE model can achieve more effective simulation result than RULSE model, as well as laying a theoretical basis for soil loss prediction.

Combining Geostatistics and Remote Sensing Data to Improve Spatiotemporal Analysis of Precipitation

The wide availability of satellite data from many distributors in different domains of science has provided the opportunity for the development of new and improved methodologies to aid the analysis of environmental problems and to support more reliable estimations and forecasts. Moreover, the rapid development of specialized technologies in satellite instruments provides the opportunity to obtain a wide spectrum of various measurements. The purpose of this research is to use publicly available remote sensing product data computed from geostationary, polar and near-polar satellites and radar to improve space–time modeling and prediction of precipitation on Crete island in Greece. The proposed space–time kriging method carries out the fusion of remote sensing data with data from ground stations that monitor precipitation during the hydrological period 2009/10–2017/18. Precipitation observations are useful for water resources, flood and drought management studies. However, monitoring stations are usually sparse in regions with complex terrain, are clustered in valleys, and often have missing data. Satellite precipitation data are an attractive alternative to observations. The fusion of the datasets in terms of the space–time residual kriging method exploits the auxiliary satellite information and aids in the accurate and reliable estimation of precipitation rates at ungauged locations. In addition, it represents an alternative option for the improved modeling of precipitation variations in space and time. The obtained results were compared with the outcomes of similar works in the study area.

An Enhanced Innovative Triangular Trend Analysis of Rainfall Based on a Spectral Approach

The world is currently witnessing high rainfall variability at the spatiotemporal level. In this paper, data from three representative rain gauges in northern Algeria, from 1920 to 2011, at an annual scale, were used to assess a relatively new hybrid method, which combines the innovative triangular trend analysis (ITTA) with the orthogonal discrete wavelet transform (DWT) for partial trend identification. The analysis revealed that the period from 1950 to 1975 transported the wettest periods, followed by a long-term dry period beginning in 1973. The analysis also revealed a rainfall increase during the latter decade. The combined method (ITTA–DWT) showed a good efficiency for extreme rainfall event detection. In addition, the analysis indicated the inter- to multiannual phenomena that explained the short to medium processes that dominated the high rainfall variability, masking the partial trend components existing in the rainfall time series and making the identification of such trends a challenging task. The results indicate that the approaches—combining ITTA and selected input combination models resulting from the DWT—are auspicious compared to those found using the original rainfall observations. This analysis revealed that the ITTA–DWT method outperformed the ITTA method for partial trend identification, which proved DWT’s efficiency as a coupling method.

Influence of weather types on the hydrosedimentary response in three small catchments on the Island of Mallorca, Spain

The influence of the sea and topography are vital factors in the atmospheric processes affecting any island, as they introduce peculiarities in the hydrosedimentary response of fluvial systems. In view of that, the relationship between the surface atmospheric conditions (weather types, WTs), rainfall, runoff and erosion dynamics in three small catchments located in Mallorca were analysed. The catchments are representative in terms of geomorphology and land use but also due to their location within the major rainfall areas previously identified in the island by (Sumner et al., 1993). Data of rainfall, runoff and sediment variables, coupled with calculated WTs were used for the 2013-2017 period. WTs frequency and distribution during this period were compared to the last climatic period reference (1981-2010) to test the climate validity of the study period. The results illustrated how hydrosedimentary response was mostly caused by eco-geographical patterns but also by differences in the response of each catchment to WTs, related to the intrinsic geographical position in the island and different exposures to humid winds. Anticyclonic WT was the most frequent, despite it being only involved in one flood event at the eastern catchment. Conversely, eastern and northeastern WTs generated more than 85% of the total runoff and sediment, representing only 39% of flood events. The understanding of the specific role of WTs on the island's hydrology was improved, considering that freshwater resources are scarce and eco-sociologically crucial.

Using UAV to Capture and Record Torrent Bed and Banks, Flood Debris, and Riparian Areas

Capturing and recording fluvio-geomorphological events is essential since these events can be very sudden and hazardous. Climate change is expected to increase flash floods intensity and frequency in the Mediterranean region, thus enhancing such events will also impact the adjacent riparian vegetation. The aim of this study was to capture and record the fluvial-geomorphological changes of the torrent bed and banks and flood debris events with the use of UAV images along a reach of Kallifytos torrent in northern Greece. In addition, a novel approach to detecting changes and assessing the conditions of the riparian vegetation was conducted by using UAV images that were validated with field data based on a visual protocol. Three flights were conducted using the DJI Spark UAV. Based on the images collected from these flights, orthomosaics were developed. The orthomosaics clearly identified changes in the torrent bed and detected debris flow events after major flood events. In addition, the results on the assessment of riparian vegetation conditions were satisfactory. Utilizing UAV images shows great potential to capture, record, and monitor fluvio-geomorphological events and riparian vegetation. Their utilization would help water managers to develop more sustainable management solutions based on actual field data.

Effectiveness of Nature-Based Solutions in Mitigating Flood Hazard in a Mediterranean Peri-Urban Catchment

Urbanization alters natural hydrological processes and enhances runoff, which affects flood hazard. Interest in nature-based solutions (NBS) for sustainable mitigation and adaptation to urban floods is growing, but the magnitudes of NBS effects are still poorly investigated. This study explores the potential of NBS for flood hazard mitigation in a small peri-urban catchment in central Portugal, prone to flash floods driven by urbanization and short but intense rainfall events typical of the Mediterranean region. Flood extent and flood depth are assessed by manually coupling the hydrologic HEC-HMS and hydraulic HEC-RAS models. The coupled model was run for single rainfall events with recurrence periods of 10–, 20–, 50–, and 100–years, considering four simulation scenarios: current conditions (without NBS), and with an upslope NBS, a downslope NBS, and a combination of both. The model-simulation approach provides good estimates of flood magnitude (NSE = 0.91, RMSE = 0.08, MAE = 0.07, R2 = 0.93), and shows that diverting streamflow into abandoned fields has positive impacts in mitigating downslope flood hazard. The implementation of an upslope NBS can decrease the water depth at the catchment outlet by 0.02 m, whereas a downslope NBS can reduce it from 0.10 m to 0.23 m for increasing return periods. Combined upslope and downslope NBS have a marginal additional impact in reducing water depth, ranging from 0.11 m to 0.24 m for 10– and 100–year floods. Decreases in water depth provided by NBS are useful in flood mitigation and adaptation within the peri-urban catchment. A network of NBS, rather than small isolated strategies, needs to be created for efficient flood-risk management at a larger scale.