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The spatiotemporal precipitation patterns in Greece are influenced by several factors, including the complex topography and the multifaceted climatic regimes of the country. Rain gauges, albeit a reliable tool for the accurate quantification of precipitation, are scarce, sporadic, and not properly maintained. In these instances, gridded datasets may provide a solution by administering spatially and temporally continuous precipitation data. The products, however, reveal limitations in the realistic simulation of precipitation, primarily caused by the intrinsic flaws of the underlying methods used. The assessment of eight of the most spatially and temporally detailed precipitation datasets, namely ERA5-Land (ERA5L), AgERA5, CHELSA-W5E5 v1.1 (CHELSA), MSWEP V2.8, CHIRPS05, IMERG V06 (Final), and E -OBS, compared against field observations acquired from 304 gauging stations across Greece has not been previously attempted. The evaluation is conducted on a daily and a monthly timescale, over a 32-year period (1984–2016), assessing the performance of the gridded products by considering both the country as a whole and its individual regions. The ability of the datasets to correctly portray the occurrence of extreme events and precipitation patterns is examined by statistical metrics and further insights are provided by the application and statistical analysis of climate indices on ground observations. CHELSA, CERRAL and AgERA5 consistently yield acceptable results across statistical metrics, outperforming the other datasets, which exhibit inferior performance in both temporal scales. The statistical analysis reveals distinct patterns of heavier precipitation in northern and western regions, with strong seasonal variability in the West and South and a possible average decennial increase of over 110 mm in mean annual and over 30 mm in extreme precipitation, along the assessment period. Overall, the datasets fail to accurately depict precipitable extremes, but CHELSA and CERRAL stand out as more reliable options for describing the precipitation dynamics in Greece. • Systematic evaluation of eight precipitation datasets against 304 stations in Greece. • Orographic effects better captured by CHELSA, CERRAL, MSWEP. • Gridded datasets aid in drought and extreme event analysis. • Consistent emerging patterns in the occurrence of heavy rainfall. [ABSTRACT FROM AUTHOR]

Solar power is the third major renewable energy, constituting an increasingly important component of global future--low carbon--energy portfolio. Accurate climate information is essential for the conditions of solar energy production, maximization, and stable regulation and planning. Climate change impacts on energy output projections are thus of crucial importance. In this study the effect of projected changes in irradiance and temperature on the performance of photovoltaic systems in Greece is examined. Climate projections were obtained from 5 regional climate models (RCMs) under the A1B emissions scenario, for two future periods. The RCM data present systematic errors against observed values, resulting in the need of bias adjustment. The projected change in photovoltaic energy output was then estimated, considering changes in temperature and insolation. The spatiotemporal analysis indicates significant increase in mean annual temperature (up to 3.5°C) and mean total radiation (up to 5 W/m²) by 2100. The performance of photovoltaic systems exhibits a negative linear dependence on the projected temperature increase which is outweighed by the expected increase of total radiation resulting in an up to 4% increase in energy output. [ABSTRACT FROM AUTHOR]

Summary: An assessment of the impact of global climate change on the water resources status of the island of Crete, for a range of 24 different scenarios of projected hydro-climatological regime is presented. Three “state of the art” Global Climate Models (GCMs) and an ensemble of Regional Climate Models (RCMs) under emission scenarios B1, A2 and A1B provide future precipitation (P) and temperature (T) estimates that are bias adjusted against observations. The ensemble of RCMs for the A1B scenario project a higher P reduction compared to GCMs projections under A2 and B1 scenarios. Among GCMs model results, the ECHAM model projects a higher P reduction compared to IPSL and CNCM. Water availability for the whole island at basin scale until 2100 is estimated using the SAC-SMA rainfall–runoff model And a set of demand and infrastructure scenarios are adopted to simulate potential water use. While predicted reduction of water availability under the B1 emission scenario can be handled with water demand stabilized at present values and full implementation of planned infrastructure, other scenarios require additional measures and a robust signal of water insufficiency is projected. Despite inherent uncertainties, the quantitative impact of the projected changes on water availability indicates that climate change plays an important role to water use and management in controlling future water status in a Mediterranean island like Crete. The results of the study reinforce the necessity to improve and update local water management planning and adaptation strategies in order to attain future water security. [Copyright &y& Elsevier]

Climate change is expected to have a significant impact on the hydrologic cycle, creating changes in freshwater resources. The Intergovernmental Panel on Climate Change (IPCC) predicts that, as a result, floods and prolonged droughts will take place at increasingly frequent periods. The Mediterranean has been described as one of the main climate change 'hot-spots', with recent simulations showing a collective picture of substantial drying and warming. This effect appears more pronounced during warm periods, when the seasonal decrease of precipitation can exceed control climatology by 25-30%. Despite the decreasing annual rainfall trend, an increase in the amount and intensity of wintertime rainfall is evident. However, the scientific question on the quantitative impact of these signals to small scale coastal watersheds and Mediterranean islands has not been answered. The state-of-the-art Ensembles dataset was employed to assess the impact of the changing climate on the water availability of the island of Crete at basin scale. Here, the Ensembles precipitation and temperature data is used as input for a rainfall-runoff model previous calibrated for the whole island with the principle of regionalization. Data analysis for the period 1970-2100 reveals an overall decreasing precipitation trend which, combined with a temperature rise, leads to substantial reduction of water availability. Quantitative results of hydrological change provide the data required to improve knowledge and adaptation policy to water shortages. [ABSTRACT FROM AUTHOR]

A modified drought index, named the spatially normalized--standardized precipitation index (SN-SPI), has been developed for assessing meteorological droughts. The SN--SPI is a variant index to the standardized precipitation index and is based on the probability of precipitation at different time scales, but it is spatially normalized for improved assessment of drought severity. Results of this index incorporate the spatial distribution of precipitation and produce improved drought warnings. This index is applied in the island of Crete, Greece, and the drought results are compared to the ones of SPI. A 30-year-long average monthly precipitation dataset from 130 watersheds of the island is used by the above indices for drought classification in terms of its duration and intensity. Bias-adjusted monthly precipitation estimates from an ensemble of 10 regional climate models were used to quantify the influence of global warming to drought conditions over the period 2010--2100. Results based on both indices (calculated for three time scales of 12, 24, and 48 months) from 3 basins in west, central, and east parts of the island show that 1) the extreme drought periods are the same (reaching 7%% of time) but the intensities based on SN--SPI are lower; 2) the area covered by extreme droughts is 3%% (first time scale), 16%% (second time scale), and 25%% (third time scale), and 96%% (first time scale), 95%% (second time scale), and 80%% (third time scale) based on the SN--SPI and SPI, respectively; 3) concerning the longest time scale (48 months), more than half of the area of Crete is about to experience drought conditions during 28%%, 69%%, and 97%% for 2010--40, 2040--70, and 2070--2100, respectively; and 4) extremely dry conditions will cover 52%%, 33%%, and 25%% of the island for the future 90-year period using 12-, 24-, and 48-month SN--SPI, respectively. [ABSTRACT FROM AUTHOR]

Summary: The seasonality of the hydrometeorologic characteristics of floods that occurred in Crete during the period 1990–2007 is presented. Hydrological characteristics were analyzed using seasonality indices based on a dataset of 53 daily precipitation stations as well as 15 daily and 7 monthly recording flow stations. The atmospheric circulation conditions during the flood events were examined based on a joint subjective classification and meteorological analysis. The flood event-based seasonality was found to coincide with the seasonality of the daily precipitation maxima of November and December. The seasonality of the three largest long term daily precipitation maxima indicates that 50% of the maximum precipitation events occur from November to January (NDJ period). Analysis showed that the maximum annual stream flows in Crete are lagging by approximately 1month from annual maximum daily precipitation in the region. The circulation type classification of the flood events showed that most of the weather systems occurring in the Mediterranean and passing over Crete have SW, NW and W direction. For the majority of the events, a common mean sea level pressure gradient field was observed over Europe. This comparison of the seasonality of selected hydrometeorologic characteristics reveals valuable information within the context of flood occurrence. [ABSTRACT FROM AUTHOR]

Summary: A method for estimating flash flood peak discharge, hydrograph, and volume in poorly gauged basins, where the hydrological characteristics of the flood are partially known, due to stage gauge failure, is presented. An empirical index is used to generate missing hourly rainfall data and hydrologic and hydraulic models performs the basin delineation, flood simulation, and flood inundation. The peak discharge, hydrograph, and volume, derived from the analysis of measured hydrographs in a number of non-flood causing rainfall events with operating stage gauge, were used for calibration and verification of the simulated stage-discharge hydrographs. An empirical equation was developed in order to provide the peak discharge as a function of the total precipitation, its standard deviation, and storm duration. The peak discharge for a flash flood case based on the empirical equation was in close agreement with the results from a number of consolidated methods. These methods involved hydrological and hydraulic modeling and peak flow estimates based on Manning’s equation and post flash flood measurements of the maximum water level observed at the control cross-section, for the 13–14 January 1994 flash flood in the Giofiros basin on the island of Crete, Greece. This method can be applied to other poorly gauged basins for floods with a stage higher than that defined by the rating curve. [Copyright &y& Elsevier]

A new method called Arbor Crown Enumerator (ACE) was developed for tree crown detection from multispectral Very High-resolution (VHR) satellite imagery. ACE uses a combination of the Red band and Normalized Difference Vegetation Index (NDVI) thresholding, and the Laplacian of the Gaussian (LOG) blob detection method. This method minimizes the detection shortcomings of its individual components and provides a more accurate estimation of the number of tree crowns captured in an image sample. The ACE was applied successfully to sample images taken from a four-band QuickBird (0. 7m × 0. 7m) scene of Keritis watershed, in the Island of Crete. The method performs very well for different tree types, sizes and densities that may include non vegetation features such as roads and houses. Statistical analysis on the tree crown detection results from the sample images supports the agreement between the measurements and the simulations. The new method reduces considerably the effort of manual tree counting and can be used for environmental applications of fruit orchard, plantation and open forest population monitoring. [ABSTRACT FROM AUTHOR]

The eastern Mediterranean is a hotspot in terms of geomorphic hazards, but the activity of gravitational processes in mountainous areas is largely unexplored. We carried out dendrogeomorphic research in the Helmos Mountains (Northern Peloponnese, Greece) to determine the timing, spatial extent, and hydrometeorological triggers of debris flows and snow avalanches. Specifically, we sampled increment cores from 123 injured Greek firs (Abies cephalonica L.) growing on a debris flow cone and growing along a snow avalanche track. Tree rings were counted and cross-dated with the reference chronology using CooRecorder and CDendro software and the event years were determined on the basis of the location of scars and traumatic resin ducts. We compiled an 118-year chronology (1904-2021) with seven debris flow event years and only one severe debris flow occurring in the 1970/1971 dormant period (W It = 148.0), followed by spatially limited records for 1986/1987 (W It = 3.8) and 1993/1994 (W It = 2.5). Similarly, seven snow avalanche event years were identified in the period 1854-2021, with one major event in 1997/1998 (W It = 304.5) followed by the 1998/1999 event (W It = 6.3). Extremely wet conditions in February-March 1971 followed by rain-on-snow precipitation were considered as the most likely trigger of the analysed debris flow event using data from nearby meteorological stations and the ERA5 reanalysis. The snow avalanche event was deciphered in the spring of 1998, when heavy snowfall over three days (62 cm) was followed by rapid snowmelt due to high average temperatures (6-11 °C). We conclude that the abundance of snow is a crucial factor in the geomorphic activity in the study region and that the temperature fluctuations and rain-to-snow transitions are the leading factors for the debris flows or snow avalanches to occur. Furthermore, the dendrogeomorphic approach used can be useful to clearly identify large-scale geomorphic events and excludes potential geomorphic noise caused by other ecological stresses., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)