Dr Kitsara holds a PhD on Climate Change -Hydrological Cycle. Her field of study is the influences of climate change on the components of the hydrological cycle. Her work has been focused on the observed long term relationships between evapotranspiration and other various meteorological variables and their causes. Her main research interests are concerning the investigation of evaporation/evapotranspitation, solar radiation, precipitation and drought indices using ground observations, satellite products, statistical analysis of long time series and Geographic Information Systems to monitor the environmental changes.
Abstract: Reference evapotranspiration (ET) is an important component of the hydrological cycle a... more Abstract: Reference evapotranspiration (ET) is an important component of the hydrological cycle and its accurate quantification is crucial for designing and scheduling irrigation systems, preparing input data to hydrological water balance models and calculating potential evaporation for a land. Rainfall attributes are frequently available and thus an approach estimating ET using remote sensing-based surface temperature and local precipitation data could increase its spatial resolution in data-sparse areas. In the present study, in order to overcome low availability of meteorological data, MODIS surface temperature data are tested, as an alternative input for three ET models in Greece, during the growing season for the years 2002 and 2003. The air temperature range-based Hargreaves-Samani method and two methods depended upon precipitation besides air temperatures, such as the Droogers-Allen method and the improved Reference Evapotranspiration Model for Complex Terrains (REMCT) are considered. Daytime and night time land surface temperature (LST) data are used in replacement of maximum and minimum air temperature data in 22 ground stations. The obtained ET results are evaluated by comparisons with the corresponding ET estimates from the ground air temperature data and furthermore with Penman Monteith ET estimates based on ground data. The temperature-vegetation index method (TVX) is also used for improving the accuracy of the estimation of maximum air temperature and its results are tested in one selected station for investigating any improvement on the ET estimates obtained from the MODIS products. This study shows that in areas with lack of ground temperature data, rather similar results can be achieved using LST from the MODIS products in the selected minimum data-based ET methods, which were initially developed using ground air temperatures. The use of MODIS LST data in REMCT model can allow the spatial analysis of ET at higher spatial resolutions.
During the ongoing efforts for validating or invalidating the accelerating hydrological cycle, pa... more During the ongoing efforts for validating or invalidating the accelerating hydrological cycle, pan evaporation has come to the light, as an index of potential evaporation, often used together with precipitation measurements to obtain the surface moisture balance, and estimate its variability. Several studies have reported declines in pan evaporation rate throughout the Northern and Southern hemisphere for various periods since the 1950s. At individual sites, both increases and decreases in pan evaporation have also been reported. In this study, temporal analysis of daily pan evaporation measurements (Epan), Penman (ETp) and Penman-Monteith (ETp-m) evapotranspiration estimates, is presented for 16 stations in Greece, during the period 1979-1999. The high correlation between Epan and ETp-m on a yearly basis and the similarity in their annual time evolutions (in almost all stations of the study) indicate that pan evaporation can be used as an index of potential evapotranspiration in Greece, as has been reported in the literature for other regions. Furthermore, trends in Epan are examined, in order to investigate if they can represent the ETp-m trends as well. The decreasing Epan trend, reported widely in the literature, is confirmed in Greece for 10 stations, during the warm season only. In contrast, almost all stations indicate negative rainfall trends on annual, warm and cold season basis. When all stations are considered ‘as a whole’, annual, and cold season pan evaporation estimates show insignificant increases while rainfall trends are negative.
Water is the most significant factor for the agriculture. Soil moisture deficits are especially v... more Water is the most significant factor for the agriculture. Soil moisture deficits are especially valuable for estimating the consequences of climatic variability on crop growth and production. In this study, daily precipitation and pan evaporation measurements provided by the Institute of Land Reclamation of Crete for 11 sites, are utilized in a daily water balance model for estimating various hydrometeorological components. Trends in yearly, warm- and cold- season, precipitation, potential evapotranspiration, and soil moisture deficit are examined for the period 1974-2003. Averaged (for all sites) values for precipitation and pan evaporation are very slightly increasing or decreasing, respectively. Both trends are not significant (in the 90% level). The well documented decreasing of evaporation is apparent in only six of the pans (at 95% significant level). Precipitation and soil moisture deficit do not seem significantly increasing or decreasing in almost all stations.
To determine the influence of global changes on surface hydrological fluxes the feedback mechanis... more To determine the influence of global changes on surface hydrological fluxes the feedback mechanisms between the land surface and atmosphere within the framework of Bouchet’s complementary relationship between potential and actual evapotranspiration are investigated. Using meteorological observations and the advection-aridity model actual, potential and wet environment evapotranspiration are estimated for 28 or 16 stations in Greece for the period 1974 - 2001 or 1957 - 2001.Trends in actual and potential evapotranspiration are not increasing or decreasing uniformly over Greece. Directions of trends in actual and potential evapotranspiration (being in most cases opposite) are successfully used to offer observational evidence of the complementary relationship.
In this study daily pan evaporation measurements made at 13 sites in Greece are analyzed for evid... more In this study daily pan evaporation measurements made at 13 sites in Greece are analyzed for evidence of long-term changes. Furthermore, the similarities between magnitude and trends in observed pan evaporation (Epan) and daily estimated Penman-Monteith reference evapotranspiration (ETp-m) are examined within the same period (1979-2004), for investigating the use of ETp-m estimates as a guide for future changes in evaporation. The results show that ETp-m and Epan are well correlated on a yearly, seasonal, warm and cold period and monthly basis. Trends in Epan and ETp-m are found positive for most of the stations on a yearly or warm and cold period or during the seasons (except of autumn). When examining Epan or ETp-m trends for every month separately, increases are mainly concluded for most of the months. Median trends in yearly and seasonal ETp-m and Epan are similar in sign. ETp-m and Epan median trends for each month are in agreement (mostly positive) for 75% of the months. When all stations are considered ‘as a whole’, annual, seasonal, warm and cold period Epan and ETp-m estimates show insignificant increases, while rainfall trends are significantly negative.
Evidence of global dimming/brightening is mainly based upon few measurements of solar r... more Evidence of global dimming/brightening is mainly based upon few measurements of solar radiation. A need for more research supported and extended with the use of other climatic variables, such as sunshine duration (SD), recorded for a longer time period and successfully used as a proxy for solar radiation over the past 80 years, has already been urged. Thus, in this study, residual SD series computed after removal of the cloudiness-related variability, from daily sunshine duration and cloudiness data measured at the National Observatory of Athens are used for highlighting global dimming or brightening periods in Athens, during the period 1951-2001. Furthermore, the consistency of trends in radiation records and their implications for the hydrological cycle and especially the trends in reference evapotranspiration are examined, during the period 1951-2001. The analysis focuses on the seasonal decadal variations, determines and explains the causes of the seasonal trends from the inter-annual and decadal variability of the SD during the last half past century, with a special emphasis in detecting possible subperiods in Athens. The signs of trends in the modeled annual and seasonal reference evapotranspiration are estimated, according to the indicated global dimming/brightening periods.
<jats:p>&amp;lt;p&amp;gt;&amp;amp;#921;n the framework of two European Projects... more <jats:p>&amp;lt;p&amp;gt;&amp;amp;#921;n the framework of two European Projects, the LIFE URBANPROOF and LIFE TERRACESCAPE, a network of 24 meteorological stations has been installed for recording meteorological parameters and climate indices for the monitoring of impacts of climate change on urban and agricultural areas as well as for the assessment of respective adaptation measures.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Regarding the urban environment, the study aims to estimate the Urban Heat Island (UHI) effect in the Greater Athens&amp;amp;#8217; Municipality of Peristeri, Greece, by analysing data from the meteorological stations installed (since January 2020) in different urban surroundings and investigating relative changes in surface temperatures and perceived thermal discomfort (HUMIDEX) thus identifying hot and cool spots at the local scale. The UHI mapping in the Municipality of Peristeri was designed and implemented in such a way, as to provide accurate information about heat stress conditions across different parts of the city. Fully automated sensors of air temperature and relative humidity were installed at eleven (11) sites throughout the municipality, covering a wide range of urban characteristics, such as densely populated areas, open spaces, municipal parks etc., where local climatic conditions were expected to show a degree of variation.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;As regards the rural environment, the study intends to estimate the anticipated changes of the micro-climate in the Aegean island of Andros, Greece after land-use interventions, which are considering the use of drystone terraces as green infrastructures resilient to climate change impacts. To that end, a network of 13 meteorological stations has been installed in selected rural areas of Andros since June 2018 for monitoring purposes. The thirteen meteorological stations, 12 small autonomous stations and 1 automated, currently operating on Andros Island continue (till now days) to generate baseline (micro-) climatic data, providing basic meteorological parameters such as air temperature and relative humidity. In addition, the valuable information, based on observational data from installed network of the meteorological stations, located either at currently abandoned terrace sites (project plots) or cultivated sites of Andros will be used to provide a solid basis for comparisons with changes projected for the future climate, combined with climatic indices which directly or indirectly affect agriculture in the monitoring areas.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;</jats:p>
&lt;p&gt;To date, climate change has caused serious problems both in human societies and ... more &lt;p&gt;To date, climate change has caused serious problems both in human societies and in various ecosystems. Worldwide, the observed climate change hazards include increased droughts and floods, extreme heat waves, sea-level rise, storms and changes in natural land cover. Tourism, as an important pillar of the economy, is expected to be further affected until the end of the century by climate change hazards. An important factor in the selection of a tourist destination is the climatic conditions of the location.&lt;/p&gt;&lt;p&gt;This research aims to investigate the observed and projected heat stress conditions in a top world tourist destination, the island of Santorini, in Greece. The Mediterranean has been identified as a vulnerable region regarding the heat related risk. Simulations by Regional Climate Models downscaled over the island of Santorini were performed for the 1982&amp;#8211;2005 control period, the near future period 2035&amp;#8211;2058 and the distant future period 2075&amp;#8211;2098. The data for the future simulations are under the RCP4.5 and RCP8.5 future emissions scenarios. Thermal stress conditions were evaluated employing the Universal Thermal Climate Index (UTCI), which has a thermo-physiological basis and derived from the heat exchange theory between the thermal environment and the human body.&lt;/p&gt;&lt;p&gt;The analysis reveals that the thermal conditions in Santorini that cause moderate heat stress and strong heat stress are expected to increase in both RCPs scenarios in near and distant future. In particular, the exposure time under at least strong heat stress reaches 1.8% in the control period (1982&amp;#8211;2005), increasing to 5.3% in the near future (2035&amp;#8211;2058) and to 7.8% in the distant future (2075&amp;#8211;2098) under the RCP4.5 scenario. In the distant future (2075&amp;#8211;2098), under the RCP8.5 scenario, the exposure time under these conditions will exceed 12%.&lt;/p&gt;&lt;p&gt;The increasing heat related risk in one of the most popular tourist destinations in the world could be a wake-up call to the policy makers urging them to take prevention measures.&lt;/p&gt;
The paper presents the analysis of a sub-set of high-resolution bias-adjusted simulations from th... more The paper presents the analysis of a sub-set of high-resolution bias-adjusted simulations from the EURO-CORDEX initiative, in order to examine the changes in the mean climate and the extremes in three Mediterranean islands, namely, Sicily, Crete and Cyprus, in the near future (2031–2060) compared to the present climate (1971–2000), under two future scenarios, i.e. RCP4.5 and RCP8.5. The analysis entails commonly used climatic indices of interest related to the islands’ agricultural sector. The results indicate robust increases for both the mean maximum and minimum temperatures on a seasonal basis, as well as for the temperature related extremes under both climate scenarios. On the contrary, the changes in precipitation are less pronounced as the changes in the seasonal precipitation are not found statistically significant for the three islands under both scenarios. The projected warming combined with the projected unchanged precipitation pattern in the future, especially in spring a...
Euro-Mediterranean Journal for Environmental Integration, 2021
The Aegean islands, characterized by strong relief and low vegetation cover, are listed as a regi... more The Aegean islands, characterized by strong relief and low vegetation cover, are listed as a region of high desertification risk. Impacts of climate change are expected to affect significantly agricultural production and the local economy. In this paper, projections derived from seven regional climate models (RCMs) are used to examine future climate changes in the Aegean area to identify areas most vulnerable to climate change and to prioritize future interventions in the agricultural sector. Changes in climate indices, derived from the mean ensemble of the seven RCMs, are examined under the medium mitigation (RCP4.5) and the high emission scenario (RCP8.5) for the control (1971–2000), near (2031–2060) and distant (2071–2100) future periods. Ensemble results are calibrated against the long-term historical meteorological record of Naxos Island in the central Cyclades. Annual averaged maximum and minimum temperatures show increases of about 1.5 °C (RCP4.5) or 2.1 °C (RCP8.5) in the ne...
The Mediterranean area is one of the most visited tourist destinations of the world, but it has a... more The Mediterranean area is one of the most visited tourist destinations of the world, but it has also been recognized as one of the most vulnerable to climate change areas worldwide with respect to increased thermal risk. The study focuses on a top worldwide tourist destination of the Mediterranean, Santorini Island in Greece, and aims to assess the past, present and future thermal environment in the island based on the advanced Universal Thermal Climate Index (UTCI). The study utilizes historical observations capturing past (late 19th to early 20th century) and more recent (1982–2019) time periods, while future projections are realized based on four regional climate models (RCMs) under the weak mitigation scenario (RCP4.5) and the non-mitigation scenario with high emissions (RCP8.5). The frequency of cold stress conditions at midday decreases during winter and early spring months by up to 19.8% (January) in the recent period compared to the historical one, while heat stress conditio...
ABSTRACT Moderate Resolution Imaging Spectroradiometer (MODIS), land surface temperature data, du... more ABSTRACT Moderate Resolution Imaging Spectroradiometer (MODIS), land surface temperature data, during daytime (LSTday) or night-time (LSTnight), were employed for predicting maximum (Tmax) or minimum (Tmin) air temperature measured at ground stations, respectively, in order to be used as alternative inputs in minimum data-based reference evapotranspiration (ET) models in 28 stations in Greece during the growing season (May–October). The deviations between daily LSTnight and Tmin were found to be small, but they were greater between LSTday and Tmax. Furthermore, the temperature vegetation index (TVX) method was employed for achieving more accurate Tmax values from LSTday, after determining the normalized difference vegetation index of a full canopy (NDVImax). The TVX method was validated on ‘temporal’ basis, but when the method was tested spatially, the improvement on the Tmax estimates from LSTday was not encouraging, for being used operationally over Greece. Thus, LSTday or LSTnight MODIS data were used as inputs in three ET models [Hargreaves–Samani, Droogers–Allen, and Reference Evapotranspiration Model for Complex Terrains (REMCT)] and their estimations, as compared with ground-based Penman–Monteith estimates, indicated that the REMCT model achieved the most accurate ET predictions (r = 0.93, mean bias error = 0.44 mm day–1 and root mean square error = 0.74 mm day–1), which can allow the spatial analysis of ET at higher spatial resolutions in areas with lack of ground temperature data.
AbstractΤhis study evaluates the hourly actual evapotranspiration (AΕT), predicted either by the ... more AbstractΤhis study evaluates the hourly actual evapotranspiration (AΕT), predicted either by the two modified Penman-Monteith models (PM) which take into account the canopy resistance (rc) from the Katerji-Perrier (KP) or Todorovic (TD) models, or the simplified PM model with zero rc, as proposed by Priestley and Taylor (PT). The evaluation is based on comparisons with experimental measurements of AΕT applying the ‘Bowen ratio’ method. Hourly experimental data, of air temperature, humidity, wind speed and radiation balance measurements, taken at a 0.5 ha olive orchard in the rural area of Sparta (37° 04΄ N, 22°05΄ E), during the period from June 2010 up to July 2014, are used. The rc estimated by KP model is parameterized by a semi-empirical approach which requires a simple calibration procedure, while rc from TD model is parameterized using a theoretical approach. For estimating AET from minimum data (air temperature, humidity and radiation balance components) the PT model is also employed, since rc is not required and the aerodynamic term of PM is taken into account in the empirical parameter of the model. The results show that PT and KP models are the most appropriate [Refined Index of Agreement (RIA) equal to 0.89 or 0.88, respectively] followed by the TD model (RIA = 0.78). PT or KP models underestimate AET by 9.3% or 9.8%, respectively, while TD model overestimates AET by 15.0%, increased up to 25.8%, during warm period.
To determine the influence of global changes on surface hydrological fluxes the feedback mechanis... more To determine the influence of global changes on surface hydrological fluxes the feedback mechanisms between the land surface and atmosphere within the framework of Bouchet's complementary relationship between potential and actual evapotranspiration are investigated. Using meteorological observations and the advection-aridity model actual, potential and wet environment evapotranspiration are estimated for 28 or 16 stations in Greece for the period 1974 -2001 or 1957 -2001.Trends in actual and potential evapotranspiration are not increasing or decreasing uniformly over Greece. Directions of trends in actual and potential evapotranspiration (being in most cases opposite) are successfully used to offer observational evidence of the complementary relationship.
The water balance model underlying calculations of the Palmer Drought Severity index (PDSI) has b... more The water balance model underlying calculations of the Palmer Drought Severity index (PDSI) has been recently used on a worldwide long–term basis leading to the conclusion of continental drying during recent decades. In its traditional formulation potential evaporation (Ep) is estimated from Thornthwaite's empirical formula, based solely on air temperature (Tair). Consequently, as Tair steadily increases with global warming, the calculated value of Ep in the model also steadily increases. In contrast, calculations of reference evapotranspiration from Penman-Monteith method have been reported as declining in some regions of the world, in general agreement with declining pan evaporation records. Thus, assessing the hydrologic impacts of climate change, the conflicting estimates of declining evaporative demand must be taken into account. In this paper, the effects of three different parameterisations of potential evaporation on long-term trends in actual evaporative flux (AET) and ...
During the ongoing efforts for validating or invalidating the accelerating hydrological cycle, pa... more During the ongoing efforts for validating or invalidating the accelerating hydrological cycle, pan evaporation has come to the light, as an index of potential evaporation, often used together with precipitation measurements to obtain the surface moisture balance, and estimate its variability. Several studies have reported declines in pan evaporation rate throughout the Northern and Southern hemisphere for various periods since the 1950s. At individual sites, both increases and decreases in pan evaporation have also been reported. In this study, temporal analysis of daily pan evaporation measurements (Epan), Penman (ETp) and Penman-Monteith (ETp-m) evapotranspiration estimates, is presented for 16 stations in Greece, during the period 1979-1999. The high correlation between Epan and ETp-m on a yearly basis and the similarity in their annual time evolutions (in almost all stations of the study) indicate that pan evaporation can be used as an index of potential evapotranspiration in Gr...
In this study daily pan evaporation measurements made at 13 sites in Greece are analyzed for evid... more In this study daily pan evaporation measurements made at 13 sites in Greece are analyzed for evidence of long-term changes. Furthermore, the similarities between magnitude and trends in observed pan evaporation (Epan) and daily estimated Penman-Monteith reference evapotranspiration (ETp-m) are examined within the same period (1979–2004), for investigating the use of ETp-m estimates as a guide for future changes in evaporation. The results show that ETp-m and Epan are well correlated on a yearly, seasonal, warm and cold period and monthly basis. Trends in Epan and ETp-m are found positive for most of the stations on a yearly or warm and cold period or during the seasons (except of autumn). When examining Epan or ETp-m trends for every month separately, increases are mainly concluded for most of the months. Median trends in yearly and seasonal ETp-m and Epan are similar in sign. ETp-m and Epan median trends for each month are in agreement (mostly positive) for 75% of the months. When all stations are considered ‘as a whole’, annual, seasonal, warm and cold period Epan and ETp-m estimates show insignificant increases, while rainfall trends are significantly negative.
Abstract: Reference evapotranspiration (ET) is an important component of the hydrological cycle a... more Abstract: Reference evapotranspiration (ET) is an important component of the hydrological cycle and its accurate quantification is crucial for designing and scheduling irrigation systems, preparing input data to hydrological water balance models and calculating potential evaporation for a land. Rainfall attributes are frequently available and thus an approach estimating ET using remote sensing-based surface temperature and local precipitation data could increase its spatial resolution in data-sparse areas. In the present study, in order to overcome low availability of meteorological data, MODIS surface temperature data are tested, as an alternative input for three ET models in Greece, during the growing season for the years 2002 and 2003. The air temperature range-based Hargreaves-Samani method and two methods depended upon precipitation besides air temperatures, such as the Droogers-Allen method and the improved Reference Evapotranspiration Model for Complex Terrains (REMCT) are considered. Daytime and night time land surface temperature (LST) data are used in replacement of maximum and minimum air temperature data in 22 ground stations. The obtained ET results are evaluated by comparisons with the corresponding ET estimates from the ground air temperature data and furthermore with Penman Monteith ET estimates based on ground data. The temperature-vegetation index method (TVX) is also used for improving the accuracy of the estimation of maximum air temperature and its results are tested in one selected station for investigating any improvement on the ET estimates obtained from the MODIS products. This study shows that in areas with lack of ground temperature data, rather similar results can be achieved using LST from the MODIS products in the selected minimum data-based ET methods, which were initially developed using ground air temperatures. The use of MODIS LST data in REMCT model can allow the spatial analysis of ET at higher spatial resolutions.
During the ongoing efforts for validating or invalidating the accelerating hydrological cycle, pa... more During the ongoing efforts for validating or invalidating the accelerating hydrological cycle, pan evaporation has come to the light, as an index of potential evaporation, often used together with precipitation measurements to obtain the surface moisture balance, and estimate its variability. Several studies have reported declines in pan evaporation rate throughout the Northern and Southern hemisphere for various periods since the 1950s. At individual sites, both increases and decreases in pan evaporation have also been reported. In this study, temporal analysis of daily pan evaporation measurements (Epan), Penman (ETp) and Penman-Monteith (ETp-m) evapotranspiration estimates, is presented for 16 stations in Greece, during the period 1979-1999. The high correlation between Epan and ETp-m on a yearly basis and the similarity in their annual time evolutions (in almost all stations of the study) indicate that pan evaporation can be used as an index of potential evapotranspiration in Greece, as has been reported in the literature for other regions. Furthermore, trends in Epan are examined, in order to investigate if they can represent the ETp-m trends as well. The decreasing Epan trend, reported widely in the literature, is confirmed in Greece for 10 stations, during the warm season only. In contrast, almost all stations indicate negative rainfall trends on annual, warm and cold season basis. When all stations are considered ‘as a whole’, annual, and cold season pan evaporation estimates show insignificant increases while rainfall trends are negative.
Water is the most significant factor for the agriculture. Soil moisture deficits are especially v... more Water is the most significant factor for the agriculture. Soil moisture deficits are especially valuable for estimating the consequences of climatic variability on crop growth and production. In this study, daily precipitation and pan evaporation measurements provided by the Institute of Land Reclamation of Crete for 11 sites, are utilized in a daily water balance model for estimating various hydrometeorological components. Trends in yearly, warm- and cold- season, precipitation, potential evapotranspiration, and soil moisture deficit are examined for the period 1974-2003. Averaged (for all sites) values for precipitation and pan evaporation are very slightly increasing or decreasing, respectively. Both trends are not significant (in the 90% level). The well documented decreasing of evaporation is apparent in only six of the pans (at 95% significant level). Precipitation and soil moisture deficit do not seem significantly increasing or decreasing in almost all stations.
To determine the influence of global changes on surface hydrological fluxes the feedback mechanis... more To determine the influence of global changes on surface hydrological fluxes the feedback mechanisms between the land surface and atmosphere within the framework of Bouchet’s complementary relationship between potential and actual evapotranspiration are investigated. Using meteorological observations and the advection-aridity model actual, potential and wet environment evapotranspiration are estimated for 28 or 16 stations in Greece for the period 1974 - 2001 or 1957 - 2001.Trends in actual and potential evapotranspiration are not increasing or decreasing uniformly over Greece. Directions of trends in actual and potential evapotranspiration (being in most cases opposite) are successfully used to offer observational evidence of the complementary relationship.
In this study daily pan evaporation measurements made at 13 sites in Greece are analyzed for evid... more In this study daily pan evaporation measurements made at 13 sites in Greece are analyzed for evidence of long-term changes. Furthermore, the similarities between magnitude and trends in observed pan evaporation (Epan) and daily estimated Penman-Monteith reference evapotranspiration (ETp-m) are examined within the same period (1979-2004), for investigating the use of ETp-m estimates as a guide for future changes in evaporation. The results show that ETp-m and Epan are well correlated on a yearly, seasonal, warm and cold period and monthly basis. Trends in Epan and ETp-m are found positive for most of the stations on a yearly or warm and cold period or during the seasons (except of autumn). When examining Epan or ETp-m trends for every month separately, increases are mainly concluded for most of the months. Median trends in yearly and seasonal ETp-m and Epan are similar in sign. ETp-m and Epan median trends for each month are in agreement (mostly positive) for 75% of the months. When all stations are considered ‘as a whole’, annual, seasonal, warm and cold period Epan and ETp-m estimates show insignificant increases, while rainfall trends are significantly negative.
Evidence of global dimming/brightening is mainly based upon few measurements of solar r... more Evidence of global dimming/brightening is mainly based upon few measurements of solar radiation. A need for more research supported and extended with the use of other climatic variables, such as sunshine duration (SD), recorded for a longer time period and successfully used as a proxy for solar radiation over the past 80 years, has already been urged. Thus, in this study, residual SD series computed after removal of the cloudiness-related variability, from daily sunshine duration and cloudiness data measured at the National Observatory of Athens are used for highlighting global dimming or brightening periods in Athens, during the period 1951-2001. Furthermore, the consistency of trends in radiation records and their implications for the hydrological cycle and especially the trends in reference evapotranspiration are examined, during the period 1951-2001. The analysis focuses on the seasonal decadal variations, determines and explains the causes of the seasonal trends from the inter-annual and decadal variability of the SD during the last half past century, with a special emphasis in detecting possible subperiods in Athens. The signs of trends in the modeled annual and seasonal reference evapotranspiration are estimated, according to the indicated global dimming/brightening periods.
<jats:p>&amp;lt;p&amp;gt;&amp;amp;#921;n the framework of two European Projects... more <jats:p>&amp;lt;p&amp;gt;&amp;amp;#921;n the framework of two European Projects, the LIFE URBANPROOF and LIFE TERRACESCAPE, a network of 24 meteorological stations has been installed for recording meteorological parameters and climate indices for the monitoring of impacts of climate change on urban and agricultural areas as well as for the assessment of respective adaptation measures.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Regarding the urban environment, the study aims to estimate the Urban Heat Island (UHI) effect in the Greater Athens&amp;amp;#8217; Municipality of Peristeri, Greece, by analysing data from the meteorological stations installed (since January 2020) in different urban surroundings and investigating relative changes in surface temperatures and perceived thermal discomfort (HUMIDEX) thus identifying hot and cool spots at the local scale. The UHI mapping in the Municipality of Peristeri was designed and implemented in such a way, as to provide accurate information about heat stress conditions across different parts of the city. Fully automated sensors of air temperature and relative humidity were installed at eleven (11) sites throughout the municipality, covering a wide range of urban characteristics, such as densely populated areas, open spaces, municipal parks etc., where local climatic conditions were expected to show a degree of variation.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;As regards the rural environment, the study intends to estimate the anticipated changes of the micro-climate in the Aegean island of Andros, Greece after land-use interventions, which are considering the use of drystone terraces as green infrastructures resilient to climate change impacts. To that end, a network of 13 meteorological stations has been installed in selected rural areas of Andros since June 2018 for monitoring purposes. The thirteen meteorological stations, 12 small autonomous stations and 1 automated, currently operating on Andros Island continue (till now days) to generate baseline (micro-) climatic data, providing basic meteorological parameters such as air temperature and relative humidity. In addition, the valuable information, based on observational data from installed network of the meteorological stations, located either at currently abandoned terrace sites (project plots) or cultivated sites of Andros will be used to provide a solid basis for comparisons with changes projected for the future climate, combined with climatic indices which directly or indirectly affect agriculture in the monitoring areas.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;</jats:p>
&lt;p&gt;To date, climate change has caused serious problems both in human societies and ... more &lt;p&gt;To date, climate change has caused serious problems both in human societies and in various ecosystems. Worldwide, the observed climate change hazards include increased droughts and floods, extreme heat waves, sea-level rise, storms and changes in natural land cover. Tourism, as an important pillar of the economy, is expected to be further affected until the end of the century by climate change hazards. An important factor in the selection of a tourist destination is the climatic conditions of the location.&lt;/p&gt;&lt;p&gt;This research aims to investigate the observed and projected heat stress conditions in a top world tourist destination, the island of Santorini, in Greece. The Mediterranean has been identified as a vulnerable region regarding the heat related risk. Simulations by Regional Climate Models downscaled over the island of Santorini were performed for the 1982&amp;#8211;2005 control period, the near future period 2035&amp;#8211;2058 and the distant future period 2075&amp;#8211;2098. The data for the future simulations are under the RCP4.5 and RCP8.5 future emissions scenarios. Thermal stress conditions were evaluated employing the Universal Thermal Climate Index (UTCI), which has a thermo-physiological basis and derived from the heat exchange theory between the thermal environment and the human body.&lt;/p&gt;&lt;p&gt;The analysis reveals that the thermal conditions in Santorini that cause moderate heat stress and strong heat stress are expected to increase in both RCPs scenarios in near and distant future. In particular, the exposure time under at least strong heat stress reaches 1.8% in the control period (1982&amp;#8211;2005), increasing to 5.3% in the near future (2035&amp;#8211;2058) and to 7.8% in the distant future (2075&amp;#8211;2098) under the RCP4.5 scenario. In the distant future (2075&amp;#8211;2098), under the RCP8.5 scenario, the exposure time under these conditions will exceed 12%.&lt;/p&gt;&lt;p&gt;The increasing heat related risk in one of the most popular tourist destinations in the world could be a wake-up call to the policy makers urging them to take prevention measures.&lt;/p&gt;
The paper presents the analysis of a sub-set of high-resolution bias-adjusted simulations from th... more The paper presents the analysis of a sub-set of high-resolution bias-adjusted simulations from the EURO-CORDEX initiative, in order to examine the changes in the mean climate and the extremes in three Mediterranean islands, namely, Sicily, Crete and Cyprus, in the near future (2031–2060) compared to the present climate (1971–2000), under two future scenarios, i.e. RCP4.5 and RCP8.5. The analysis entails commonly used climatic indices of interest related to the islands’ agricultural sector. The results indicate robust increases for both the mean maximum and minimum temperatures on a seasonal basis, as well as for the temperature related extremes under both climate scenarios. On the contrary, the changes in precipitation are less pronounced as the changes in the seasonal precipitation are not found statistically significant for the three islands under both scenarios. The projected warming combined with the projected unchanged precipitation pattern in the future, especially in spring a...
Euro-Mediterranean Journal for Environmental Integration, 2021
The Aegean islands, characterized by strong relief and low vegetation cover, are listed as a regi... more The Aegean islands, characterized by strong relief and low vegetation cover, are listed as a region of high desertification risk. Impacts of climate change are expected to affect significantly agricultural production and the local economy. In this paper, projections derived from seven regional climate models (RCMs) are used to examine future climate changes in the Aegean area to identify areas most vulnerable to climate change and to prioritize future interventions in the agricultural sector. Changes in climate indices, derived from the mean ensemble of the seven RCMs, are examined under the medium mitigation (RCP4.5) and the high emission scenario (RCP8.5) for the control (1971–2000), near (2031–2060) and distant (2071–2100) future periods. Ensemble results are calibrated against the long-term historical meteorological record of Naxos Island in the central Cyclades. Annual averaged maximum and minimum temperatures show increases of about 1.5 °C (RCP4.5) or 2.1 °C (RCP8.5) in the ne...
The Mediterranean area is one of the most visited tourist destinations of the world, but it has a... more The Mediterranean area is one of the most visited tourist destinations of the world, but it has also been recognized as one of the most vulnerable to climate change areas worldwide with respect to increased thermal risk. The study focuses on a top worldwide tourist destination of the Mediterranean, Santorini Island in Greece, and aims to assess the past, present and future thermal environment in the island based on the advanced Universal Thermal Climate Index (UTCI). The study utilizes historical observations capturing past (late 19th to early 20th century) and more recent (1982–2019) time periods, while future projections are realized based on four regional climate models (RCMs) under the weak mitigation scenario (RCP4.5) and the non-mitigation scenario with high emissions (RCP8.5). The frequency of cold stress conditions at midday decreases during winter and early spring months by up to 19.8% (January) in the recent period compared to the historical one, while heat stress conditio...
ABSTRACT Moderate Resolution Imaging Spectroradiometer (MODIS), land surface temperature data, du... more ABSTRACT Moderate Resolution Imaging Spectroradiometer (MODIS), land surface temperature data, during daytime (LSTday) or night-time (LSTnight), were employed for predicting maximum (Tmax) or minimum (Tmin) air temperature measured at ground stations, respectively, in order to be used as alternative inputs in minimum data-based reference evapotranspiration (ET) models in 28 stations in Greece during the growing season (May–October). The deviations between daily LSTnight and Tmin were found to be small, but they were greater between LSTday and Tmax. Furthermore, the temperature vegetation index (TVX) method was employed for achieving more accurate Tmax values from LSTday, after determining the normalized difference vegetation index of a full canopy (NDVImax). The TVX method was validated on ‘temporal’ basis, but when the method was tested spatially, the improvement on the Tmax estimates from LSTday was not encouraging, for being used operationally over Greece. Thus, LSTday or LSTnight MODIS data were used as inputs in three ET models [Hargreaves–Samani, Droogers–Allen, and Reference Evapotranspiration Model for Complex Terrains (REMCT)] and their estimations, as compared with ground-based Penman–Monteith estimates, indicated that the REMCT model achieved the most accurate ET predictions (r = 0.93, mean bias error = 0.44 mm day–1 and root mean square error = 0.74 mm day–1), which can allow the spatial analysis of ET at higher spatial resolutions in areas with lack of ground temperature data.
AbstractΤhis study evaluates the hourly actual evapotranspiration (AΕT), predicted either by the ... more AbstractΤhis study evaluates the hourly actual evapotranspiration (AΕT), predicted either by the two modified Penman-Monteith models (PM) which take into account the canopy resistance (rc) from the Katerji-Perrier (KP) or Todorovic (TD) models, or the simplified PM model with zero rc, as proposed by Priestley and Taylor (PT). The evaluation is based on comparisons with experimental measurements of AΕT applying the ‘Bowen ratio’ method. Hourly experimental data, of air temperature, humidity, wind speed and radiation balance measurements, taken at a 0.5 ha olive orchard in the rural area of Sparta (37° 04΄ N, 22°05΄ E), during the period from June 2010 up to July 2014, are used. The rc estimated by KP model is parameterized by a semi-empirical approach which requires a simple calibration procedure, while rc from TD model is parameterized using a theoretical approach. For estimating AET from minimum data (air temperature, humidity and radiation balance components) the PT model is also employed, since rc is not required and the aerodynamic term of PM is taken into account in the empirical parameter of the model. The results show that PT and KP models are the most appropriate [Refined Index of Agreement (RIA) equal to 0.89 or 0.88, respectively] followed by the TD model (RIA = 0.78). PT or KP models underestimate AET by 9.3% or 9.8%, respectively, while TD model overestimates AET by 15.0%, increased up to 25.8%, during warm period.
To determine the influence of global changes on surface hydrological fluxes the feedback mechanis... more To determine the influence of global changes on surface hydrological fluxes the feedback mechanisms between the land surface and atmosphere within the framework of Bouchet's complementary relationship between potential and actual evapotranspiration are investigated. Using meteorological observations and the advection-aridity model actual, potential and wet environment evapotranspiration are estimated for 28 or 16 stations in Greece for the period 1974 -2001 or 1957 -2001.Trends in actual and potential evapotranspiration are not increasing or decreasing uniformly over Greece. Directions of trends in actual and potential evapotranspiration (being in most cases opposite) are successfully used to offer observational evidence of the complementary relationship.
The water balance model underlying calculations of the Palmer Drought Severity index (PDSI) has b... more The water balance model underlying calculations of the Palmer Drought Severity index (PDSI) has been recently used on a worldwide long–term basis leading to the conclusion of continental drying during recent decades. In its traditional formulation potential evaporation (Ep) is estimated from Thornthwaite's empirical formula, based solely on air temperature (Tair). Consequently, as Tair steadily increases with global warming, the calculated value of Ep in the model also steadily increases. In contrast, calculations of reference evapotranspiration from Penman-Monteith method have been reported as declining in some regions of the world, in general agreement with declining pan evaporation records. Thus, assessing the hydrologic impacts of climate change, the conflicting estimates of declining evaporative demand must be taken into account. In this paper, the effects of three different parameterisations of potential evaporation on long-term trends in actual evaporative flux (AET) and ...
During the ongoing efforts for validating or invalidating the accelerating hydrological cycle, pa... more During the ongoing efforts for validating or invalidating the accelerating hydrological cycle, pan evaporation has come to the light, as an index of potential evaporation, often used together with precipitation measurements to obtain the surface moisture balance, and estimate its variability. Several studies have reported declines in pan evaporation rate throughout the Northern and Southern hemisphere for various periods since the 1950s. At individual sites, both increases and decreases in pan evaporation have also been reported. In this study, temporal analysis of daily pan evaporation measurements (Epan), Penman (ETp) and Penman-Monteith (ETp-m) evapotranspiration estimates, is presented for 16 stations in Greece, during the period 1979-1999. The high correlation between Epan and ETp-m on a yearly basis and the similarity in their annual time evolutions (in almost all stations of the study) indicate that pan evaporation can be used as an index of potential evapotranspiration in Gr...
In this study daily pan evaporation measurements made at 13 sites in Greece are analyzed for evid... more In this study daily pan evaporation measurements made at 13 sites in Greece are analyzed for evidence of long-term changes. Furthermore, the similarities between magnitude and trends in observed pan evaporation (Epan) and daily estimated Penman-Monteith reference evapotranspiration (ETp-m) are examined within the same period (1979–2004), for investigating the use of ETp-m estimates as a guide for future changes in evaporation. The results show that ETp-m and Epan are well correlated on a yearly, seasonal, warm and cold period and monthly basis. Trends in Epan and ETp-m are found positive for most of the stations on a yearly or warm and cold period or during the seasons (except of autumn). When examining Epan or ETp-m trends for every month separately, increases are mainly concluded for most of the months. Median trends in yearly and seasonal ETp-m and Epan are similar in sign. ETp-m and Epan median trends for each month are in agreement (mostly positive) for 75% of the months. When all stations are considered ‘as a whole’, annual, seasonal, warm and cold period Epan and ETp-m estimates show insignificant increases, while rainfall trends are significantly negative.
Climate change is anticipated to impact adversely diverse levels of organized life. Mediterranean... more Climate change is anticipated to impact adversely diverse levels of organized life. Mediterranean countries, counting Greece encounter the problem of increased desertification, with its islands being listed as areas of high risk. The Aegean islands are faced with major confrontations as areas of abandoned terraces with low vegetation cover. Nowadays, terrace fields are crucial as green infrastructures to mitigate climate change impacts, as they improve rainfall absorbency, reduce soil erosion, smooth extreme summer temperatures, moderate the risk of floods and forest fires while preserve the biodiversity and ecosystems services. LIFE–TERRASCAPE project aims to revitalize island terrace farming, through the implementation of Land Stewardship (LS) enterprise for the first time in Greece, in association to Information and Communication Technologies (ICT) applications. The study aims to measures of innovative agricultural establishment and production as an integrated adaptation strategy...
Drought is one of the major natural hazards, most often caused by a departure of the precipitatio... more Drought is one of the major natural hazards, most often caused by a departure of the precipitation from the normal amount. Quantitative drought definitions identifying the beginning, end, spatial extent and severity of a drought, formulated in terms of drought indices integrate various meteorological and hydrological parameters. One of the most widely used drought indices, the Standardized Precipitation Index (SPI), is based only on rainfall data and is accepted as a good measure of short-and long-term meteorological drought, for a monthly temporal resolution. In this study, SPI is calculated on 1-, 2-, or 3-months scale (SPI 1 , SPI 2, SPI 3, respectively) in 11 stations in Crete, for the period 1974-2001. These SPIs are compared with two other indices, the evapotranspiration deficit index (EDI) and the water balance drought index (WBI). Both indices based on daily evapotranspiration and rainfall data and a daily single layer water balance model, are selected as estimating droughts...
Water Resour Manage DOI 10.1007/s11269-012-0229-4, Dec 22, 2012
Abstract Evidence of global dimming/brightening is mainly based upon few measurements of
solar r... more Abstract Evidence of global dimming/brightening is mainly based upon few measurements of
solar radiation. A need for more research supported and extended with the use of other climatic
variables, such as sunshine duration, recorded for a longer time period and successfully used as a
proxy for solar radiation over the past 80 years, has already been urged. Thus, in this study,
residual sunshine duration series computed after removal of the cloudiness-related variability,
fromdaily sunshine duration and cloudiness data measured at theNationalObservatory of Athens
are used for highlighting global dimming or brightening periods in Athens, during the period
1951–2001. Furthermore, the consistency of trends in radiation records and their implications for
the hydrological cycle and especially the trends in reference evapotranspiration are examined,
during the period 1951–2001. The analysis focuses on the seasonal decadal variations, determines
and explains the causes of the seasonal trends from the inter-annual and decadal variability of the
sunshine duration during the last half past century, with a special emphasis in detecting possible
sub-periods in Athens. The signs of trends in the modeled annual and seasonal reference
evapotranspiration are estimated, according to the indicated global dimming/brightening periods.
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 116, D09107, doi:10.1029/2010JD015525, 2011, May 2011
In this study, the consistency of trends in radiation and temperature records and
their implicat... more In this study, the consistency of trends in radiation and temperature records and
their implications for the hydrological cycle and especially the trends in reference
evapotranspiration are examined during the period 1950–2001. The new reference
evapotranspiration model for complex terrains (REMCT), with monthly time step, is used
for estimating trends of reference evapotranspiration in Greece. REMCT is applied after
developing a methodology for calibrating its parameter values with Penman‐Monteith
estimates. The calibrated REMCT estimates are independently validated against available
pan evaporation measurements. The evolution of available sunshine duration anomalies
measured in Athens during the period 1951–2001 are used for highlighting global
dimming or brightening periods in Greece. The sign of trends in the modeled reference
evapotranspiration and precipitation are examined according to the dimming or
brightening periods 1950–1983 and 1958–1983 (for 16 and 22 stations, respectively) or
1983–2001 (for 16, 22, and 29 stations). The trends of REMCT estimates, precipitation,
number of rainy days, and mean, maximum, and minimum air temperature for all
sets of stations considered “as a whole” are evaluated during the same periods. The results
show that the annual calibrated reference evapotranspiration trend shows a decline
from 1950 until the early 1980s, followed by an upward trend until 2001, while the
annual precipitation and rainy days indicate a downward trend during the whole
period 1950–2001. The trends of mean, maximum, and minimum air temperature are
found almost negligible during the dimming period and rather increased during the
brightening period.
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Papers by Gianna Kitsara
solar radiation. A need for more research supported and extended with the use of other climatic
variables, such as sunshine duration, recorded for a longer time period and successfully used as a
proxy for solar radiation over the past 80 years, has already been urged. Thus, in this study,
residual sunshine duration series computed after removal of the cloudiness-related variability,
fromdaily sunshine duration and cloudiness data measured at theNationalObservatory of Athens
are used for highlighting global dimming or brightening periods in Athens, during the period
1951–2001. Furthermore, the consistency of trends in radiation records and their implications for
the hydrological cycle and especially the trends in reference evapotranspiration are examined,
during the period 1951–2001. The analysis focuses on the seasonal decadal variations, determines
and explains the causes of the seasonal trends from the inter-annual and decadal variability of the
sunshine duration during the last half past century, with a special emphasis in detecting possible
sub-periods in Athens. The signs of trends in the modeled annual and seasonal reference
evapotranspiration are estimated, according to the indicated global dimming/brightening periods.
their implications for the hydrological cycle and especially the trends in reference
evapotranspiration are examined during the period 1950–2001. The new reference
evapotranspiration model for complex terrains (REMCT), with monthly time step, is used
for estimating trends of reference evapotranspiration in Greece. REMCT is applied after
developing a methodology for calibrating its parameter values with Penman‐Monteith
estimates. The calibrated REMCT estimates are independently validated against available
pan evaporation measurements. The evolution of available sunshine duration anomalies
measured in Athens during the period 1951–2001 are used for highlighting global
dimming or brightening periods in Greece. The sign of trends in the modeled reference
evapotranspiration and precipitation are examined according to the dimming or
brightening periods 1950–1983 and 1958–1983 (for 16 and 22 stations, respectively) or
1983–2001 (for 16, 22, and 29 stations). The trends of REMCT estimates, precipitation,
number of rainy days, and mean, maximum, and minimum air temperature for all
sets of stations considered “as a whole” are evaluated during the same periods. The results
show that the annual calibrated reference evapotranspiration trend shows a decline
from 1950 until the early 1980s, followed by an upward trend until 2001, while the
annual precipitation and rainy days indicate a downward trend during the whole
period 1950–2001. The trends of mean, maximum, and minimum air temperature are
found almost negligible during the dimming period and rather increased during the
brightening period.