Nelly Hristova - Academia.edu (original) (raw)

Papers by Nelly Hristova

Air and Water Components of the Environment Conference, 2018

Annual streamflow of Bulgaria in the beginning of XXI century. Estimating the annual streamflow u... more Annual streamflow of Bulgaria in the beginning of XXI century. Estimating the annual streamflow under the climate change is a challenge for hydrology science and an important task for geography as well. There is no analysis about the basic statistical parameters of the annual runoff time-series after 2000 in scientific investigations in the country. This paper describes Bulgaria's annual streamflow during 2000-2016 for the main catchment areas in the country (Danube watershed, Black Sea catchment area and the Aegean Sea watershed). The work is based on publicly available data of annual streamflow. The screening of the hydrological data for homogeneity, randomness, probability distribution and the trend is based on statistical methods. The obtained results show regional differences in scale of fluctuation of hydrological variables around the norm for the referent periods, in the years with maximum and with the minimum volume of the water resources, in the probability distribution of empirical data. All timeseries are homogeneous, randomly and with the absence of the trend. The work draws a conclusion that annual streamflow of main catchment areas of Bulgaria in the beginning of XXI century is in the normal frame and with larger fluctuation than the referent periods and that the time-series statistical models need confirmation using the larger base of hydrological data. This work is the first estimation of the annual streamflow during XXI century in Bulgaria by major watersheds and it gives a new information about hydrological processes in the country.

Journal of the Geographical Institute Jovan Cviji?, SASA, 2010

This work focuses on hydrographic and hydrological specific of Nišava River. It uses all hydromet... more This work focuses on hydrographic and hydrological specific of Nišava River. It uses all hydrometric and cartographic information for the Bulgarian part of the catchment. Transboundary catchment of Nišava River includes four sub-basins, which are trans-borders too. There are a lot of karst areas in the river basin. The drainage density is 1.09 km/km 2. Water resources of Nišava River are 170 million m 3. They vary between 300.0 and 84.0 million m 3. The period of high water appears in March/April and finishes in June. The frequency of monthly maximum is biggest in April or May. The monthly minimum appears most often in September or October. Floods in the catchment of the river Nišava are most often in March, May and June. Some of the rivers lose its waters in the karst areas and dries up during the summer. The average number of days with ice is between 10 and 70. The chemical and ecological status of river water is good.

Forum geografic, 2014

The seasonality of stream flow variability indicates special feature of local cycle of precipitat... more The seasonality of stream flow variability indicates special feature of local cycle of precipitations, evaporation and the timing of snow melt. This study presents seasonal occurrence of maximal and minimal annual flows and spatial variability of seasonal index (Is) in the Middle and Lower Danube basin. The analysis is based on 47 time series of monthly runoff (12 for the Danube and 35 for its tributaries), which are collected from public database. The results show that the maximum annual stream flow appears during all months, but with highest frequency in April for 68% from watersheds. It varies between one and 60% (Danube-Baziaz). The monthly flow is concentrated in summer-autumn hydrological season, except for the Jalomita, Siret and Prut river basins, where it is in the winter. The highest frequency of minimum monthly runoff for the Danube and the Tisza is in October and November and for the Sava and Velika Morava-in August and September. The lowest and highest monthly discharge of the given month in the entire period were recorded in different years. Seasonal index (Is) is between 0.98 and 3.18. It is about 1.00 for the Danube and more than 2.00 for the Tisza, Ialomita, Siret and Prut watersheds. Is is stability-coefficient of variation is up to 0.30 with the exception of several river basins. Stream flow variability of the Middle and Lower Danube can provide valuable information for scientific studies and integrated management of water resources.

In 2019 the Studena reservoir, the only water supply source for the town of Pernik in Bulgaria, a... more In 2019 the Studena reservoir, the only water supply source for the town of Pernik in Bulgaria, accumulated less than half of its normal annual inflow. This factor, together with an inadequate and delayed response by the water resource managers caused a severe water supply crisis in the fall and winter of that year. As this situation was unprecedented, investigations were undertaken to determine the cause of the low inflow to the reservoir using the model CLM3 and available climatic and spatial data, and data that were collected in the watershed for the reservoir. The study was conducted by simulating the hydrological processes that take place in the watershed, and the monthly inflows to the reservoir for the period 2017–2019. It was found that hydrological parameters produced in the calibrated model were similar to those measured in the field and by another model. The achieved agreement was considered to be satisfactory given the complexity of their nature and assessment methods. T...

Forum Geografic, Dec 30, 2014

The seasonality of stream flow variability indicates special feature of local cycle of precipitat... more The seasonality of stream flow variability indicates special feature of local cycle of precipitations, evaporation and the timing of snow melt. This study presents seasonal occurrence of maximal and minimal annual flows and spatial variability of seasonal index (Is) in the Middle and Lower Danube basin. The analysis is based on 47 time series of monthly runoff (12 for the Danube and 35 for its tributaries), which are collected from public database. The results show that the maximum annual stream flow appears during all months, but with highest frequency in April for 68% from watersheds. It varies between one and 60% (Danube – Baziaz). The monthly flow is concentrated in summer–autumn hydrological season, except for the Jalomita, Siret and Prut river basins, where it is in the winter. The highest frequency of minimum monthly runoff for the Danube and the Tisza is in October and November and for the Sava and Velika Morava – in August and September. The lowest and highest monthly discharge of the given month in the entire period were recorded in different years. Seasonal index (Is) is between 0.98 and 3.18. It is about 1.00 for the Danube and more than 2.00 for the Tisza, Ialomita, Siret and Prut watersheds. Is is stability – coefficient of variation is up to 0.30 with the exception of several river basins. Stream flow variability of the Middle and Lower Danube can provide valuable information for scientific studies and integrated management of water resources.

Journal of Cleaner Production

Air and Water - Components of the Environment, 2018

Annual streamflow of Bulgaria in the beginning of XXI century. Estimating the annual streamflow u... more Annual streamflow of Bulgaria in the beginning of XXI century. Estimating the annual streamflow under the climate change is a challenge for hydrology science and an important task for geography as well. There is no analysis about the basic statistical parameters of the annual runoff time-series after 2000 in scientific investigations in the country. This paper describes Bulgaria's annual streamflow during 2000-2016 for the main catchment areas in the country (Danube watershed, Black Sea catchment area and the Aegean Sea watershed). The work is based on publicly available data of annual streamflow. The screening of the hydrological data for homogeneity, randomness, probability distribution and the trend is based on statistical methods. The obtained results show regional differences in scale of fluctuation of hydrological variables around the norm for the referent periods, in the years with maximum and with the minimum volume of the water resources, in the probability distribution of empirical data. All timeseries are homogeneous, randomly and with the absence of the trend. The work draws a conclusion that annual streamflow of main catchment areas of Bulgaria in the beginning of XXI century is in the normal frame and with larger fluctuation than the referent periods and that the time-series statistical models need confirmation using the larger base of hydrological data. This work is the first estimation of the annual streamflow during XXI century in Bulgaria by major watersheds and it gives a new information about hydrological processes in the country.

Air and Water Components of the Environment Conference, 2018

Annual streamflow of Bulgaria in the beginning of XXI century. Estimating the annual streamflow u... more Annual streamflow of Bulgaria in the beginning of XXI century. Estimating the annual streamflow under the climate change is a challenge for hydrology science and an important task for geography as well. There is no analysis about the basic statistical parameters of the annual runoff time-series after 2000 in scientific investigations in the country. This paper describes Bulgaria's annual streamflow during 2000-2016 for the main catchment areas in the country (Danube watershed, Black Sea catchment area and the Aegean Sea watershed). The work is based on publicly available data of annual streamflow. The screening of the hydrological data for homogeneity, randomness, probability distribution and the trend is based on statistical methods. The obtained results show regional differences in scale of fluctuation of hydrological variables around the norm for the referent periods, in the years with maximum and with the minimum volume of the water resources, in the probability distribution of empirical data. All timeseries are homogeneous, randomly and with the absence of the trend. The work draws a conclusion that annual streamflow of main catchment areas of Bulgaria in the beginning of XXI century is in the normal frame and with larger fluctuation than the referent periods and that the time-series statistical models need confirmation using the larger base of hydrological data. This work is the first estimation of the annual streamflow during XXI century in Bulgaria by major watersheds and it gives a new information about hydrological processes in the country.

Journal of the Geographical Institute Jovan Cviji?, SASA, 2010

This work focuses on hydrographic and hydrological specific of Nišava River. It uses all hydromet... more This work focuses on hydrographic and hydrological specific of Nišava River. It uses all hydrometric and cartographic information for the Bulgarian part of the catchment. Transboundary catchment of Nišava River includes four sub-basins, which are trans-borders too. There are a lot of karst areas in the river basin. The drainage density is 1.09 km/km 2. Water resources of Nišava River are 170 million m 3. They vary between 300.0 and 84.0 million m 3. The period of high water appears in March/April and finishes in June. The frequency of monthly maximum is biggest in April or May. The monthly minimum appears most often in September or October. Floods in the catchment of the river Nišava are most often in March, May and June. Some of the rivers lose its waters in the karst areas and dries up during the summer. The average number of days with ice is between 10 and 70. The chemical and ecological status of river water is good.

Forum geografic, 2014

The seasonality of stream flow variability indicates special feature of local cycle of precipitat... more The seasonality of stream flow variability indicates special feature of local cycle of precipitations, evaporation and the timing of snow melt. This study presents seasonal occurrence of maximal and minimal annual flows and spatial variability of seasonal index (Is) in the Middle and Lower Danube basin. The analysis is based on 47 time series of monthly runoff (12 for the Danube and 35 for its tributaries), which are collected from public database. The results show that the maximum annual stream flow appears during all months, but with highest frequency in April for 68% from watersheds. It varies between one and 60% (Danube-Baziaz). The monthly flow is concentrated in summer-autumn hydrological season, except for the Jalomita, Siret and Prut river basins, where it is in the winter. The highest frequency of minimum monthly runoff for the Danube and the Tisza is in October and November and for the Sava and Velika Morava-in August and September. The lowest and highest monthly discharge of the given month in the entire period were recorded in different years. Seasonal index (Is) is between 0.98 and 3.18. It is about 1.00 for the Danube and more than 2.00 for the Tisza, Ialomita, Siret and Prut watersheds. Is is stability-coefficient of variation is up to 0.30 with the exception of several river basins. Stream flow variability of the Middle and Lower Danube can provide valuable information for scientific studies and integrated management of water resources.

In 2019 the Studena reservoir, the only water supply source for the town of Pernik in Bulgaria, a... more In 2019 the Studena reservoir, the only water supply source for the town of Pernik in Bulgaria, accumulated less than half of its normal annual inflow. This factor, together with an inadequate and delayed response by the water resource managers caused a severe water supply crisis in the fall and winter of that year. As this situation was unprecedented, investigations were undertaken to determine the cause of the low inflow to the reservoir using the model CLM3 and available climatic and spatial data, and data that were collected in the watershed for the reservoir. The study was conducted by simulating the hydrological processes that take place in the watershed, and the monthly inflows to the reservoir for the period 2017–2019. It was found that hydrological parameters produced in the calibrated model were similar to those measured in the field and by another model. The achieved agreement was considered to be satisfactory given the complexity of their nature and assessment methods. T...

Forum Geografic, Dec 30, 2014

The seasonality of stream flow variability indicates special feature of local cycle of precipitat... more The seasonality of stream flow variability indicates special feature of local cycle of precipitations, evaporation and the timing of snow melt. This study presents seasonal occurrence of maximal and minimal annual flows and spatial variability of seasonal index (Is) in the Middle and Lower Danube basin. The analysis is based on 47 time series of monthly runoff (12 for the Danube and 35 for its tributaries), which are collected from public database. The results show that the maximum annual stream flow appears during all months, but with highest frequency in April for 68% from watersheds. It varies between one and 60% (Danube – Baziaz). The monthly flow is concentrated in summer–autumn hydrological season, except for the Jalomita, Siret and Prut river basins, where it is in the winter. The highest frequency of minimum monthly runoff for the Danube and the Tisza is in October and November and for the Sava and Velika Morava – in August and September. The lowest and highest monthly discharge of the given month in the entire period were recorded in different years. Seasonal index (Is) is between 0.98 and 3.18. It is about 1.00 for the Danube and more than 2.00 for the Tisza, Ialomita, Siret and Prut watersheds. Is is stability – coefficient of variation is up to 0.30 with the exception of several river basins. Stream flow variability of the Middle and Lower Danube can provide valuable information for scientific studies and integrated management of water resources.

Journal of Cleaner Production

Air and Water - Components of the Environment, 2018

Annual streamflow of Bulgaria in the beginning of XXI century. Estimating the annual streamflow u... more Annual streamflow of Bulgaria in the beginning of XXI century. Estimating the annual streamflow under the climate change is a challenge for hydrology science and an important task for geography as well. There is no analysis about the basic statistical parameters of the annual runoff time-series after 2000 in scientific investigations in the country. This paper describes Bulgaria's annual streamflow during 2000-2016 for the main catchment areas in the country (Danube watershed, Black Sea catchment area and the Aegean Sea watershed). The work is based on publicly available data of annual streamflow. The screening of the hydrological data for homogeneity, randomness, probability distribution and the trend is based on statistical methods. The obtained results show regional differences in scale of fluctuation of hydrological variables around the norm for the referent periods, in the years with maximum and with the minimum volume of the water resources, in the probability distribution of empirical data. All timeseries are homogeneous, randomly and with the absence of the trend. The work draws a conclusion that annual streamflow of main catchment areas of Bulgaria in the beginning of XXI century is in the normal frame and with larger fluctuation than the referent periods and that the time-series statistical models need confirmation using the larger base of hydrological data. This work is the first estimation of the annual streamflow during XXI century in Bulgaria by major watersheds and it gives a new information about hydrological processes in the country.