Bulletin of Geography. Physical Geography Series

The Statistical analysis of rainfall trend and its variability (1901–2020) in Kolkata, India

2022-03-30T13:01:10+02:00

The current study focuses on the altering historical rainfall data analysis and its variability in Kolkata (Kolkata Municipal Corporation), a metropolitan city in India. The research area experiences detrimental urban floods (pluvial floods) at near-annual regularity during the monsoon, and during the pre-monsoon seasons it commonly experiences water shortage problems. Analysing trends and temporal variability of rainfall over 120 years from 1901 to 2020 is the main objective of this study. The original Mann–Kendall (M–K) test has been applied to the rainfall dataset in conjunction with Sen’s Slope Estimator using Python 3.10, after the Durbin-Watson (DW) statistic initially suggested that there is no serial correlation effect. The M–K test, with a Kendall’s tau of 0.17058 (significant at a 5% level), shows an upward trend in annual rainfall between 1901 and 2020. The Sen’s slope, which measures the rate of change annually, has a value of 2.48152. Regression analysis and other dispersion measures are also used in this study to investigate the monthly rainfall trend and its variability. The phase-wise (30-year) analysis of annual rainfall variability reveals a considerable variation over 120 years. While fitting the linear regression line month by month over the entire
period, mostly negative trends were found in the pre-monsoon and positive trends in the monsoon and post-monsoon seasons. The findings of this analysis could be useful to urban planners for water supply and management in the study area. The primary concern of planners for effectively managing rainwater and the accompanying issues should be the growing variability of annual precipitation.

Rainfall dynamics in the Sudano-Sahelian zone of Nigeria under RCP 8.5

2022-11-23T09:31:36+01:00

The study analysed the historical (1961–90) and projected rainfall variability for the rainy season expected in the near future (2021–50) at selected locations within the Komadugu-Yobe and Sokoto-Rima River Basins in the Sudano-Sahelian zone of northern Nigeria. Three models were utilised, and analyses were based on Representative Concentration Pathway (RCP) 8.5. Projected changes in mean, level of variability and distribution of rainfall were analysed using the Relative Percentage Change Method and the Precipitation Concentration Index (PCI), while the performance of the models was evaluated using the Nash–Sutcliffe Efficiency (NSE) index. The results show that changes in mean rainfall will be predominantly negative, with a minimum and maximum level of change of ˗1.02 per cent at Nguru, and ˗70.4 per cent at Jos, based on the IPSL-CM5A and HadGEM2-ES models, respectively. The rainy season of the baseline period varied between low and moderate variability, while the near future ranges between low and high levels of variability. The validation indicates acceptable levels of performance, with most values ranging between 0.0 and 1.0. The PCI for the near future suggests that the rainy season will be mainly characterised by uniform and near-uniform rainfall distribution. Hence, the projected negative changes and high variability of rainfall at some locations call for the development of an Adaptive Benefit Mechanism that will minimise future natural resource conflicts.

Crenological Features of the Świętokrzyskie Voivodeship

2022-09-06T19:33:20+02:00

On the basis analysis of 53 hydrographic maps in the scale 1:50,000, an inventory of crenological objects in the Świętokrzyskie Voivodeship was made. A total of 462 of them were identyfied. Most of them are permanent springs, precisely 346, followed by: 60 permanent springs with intakes, then 34 periodic springs, 10 spring groups, 5 bog springs, 3 mineral springs, 3 observed springs and 1 other outflow. Moreover, the studies revealed the diversity and specificity of the region in terms of crenology. Total discharge of all springs is small as it was estimated at 459.04 dm³•s–1. The most efficient springs reach about 40 dm3•s–1 and only eight exceed 20 dm³•s–1. The total discharge of the 10 most efficient outflows amount to 258.6 dm³ s-1, which accounts for 56.3% of the output in the Świętokrzyskie Voivodeship. In terms of the number of crenological objects, there is a clear difference between the mountain and highland identyfied. In the area of the Świętokrzyski National Park, 25 outflows were registered. Their total output is 6.5 dm3•s–1. At the same time, on the northern slopes of the Świętokrzyski National Park, 21 crenological objects with a total discharge of 5.5 dm3•s–1 were identyfied.

Time of aggregate destruction as a parameter of soil water stability within an agricultural hummocky moraine landscape in northern Poland

2022-09-20T12:41:25+02:00

Slaking is a rapid wetting of soil aggregates that affects their stability in the face of the effects of water. The aggregate’s stability has an indirect influence on soil functioning through its minimising of soil erosion. Testing slaking is very simple, does not need additional complicated equipment and could be done for any point. Testing was performed for natural air-dry aggregates (7–10 mm) sampled from the arable layers of four different types of soils within a young hummocky moraine landscape: Eutric Regosol (Protocalcic), Haplic Luvisol (Protocalcic), Albic Luvisol, Mollic Gleysol. The soil tests were performed on a soil-erosive catena located in Chełmno Lake District (Northern Poland) from the tops of hummocks and from the shoulder to bottom part of depressions. The test results demonstrated a significant decrease in aggregate stability from Mollic Gleysol to Eutric Regosols (Protocalcic) – that is, from colluvial soils at depressions to completely eroded hummock-top soils. However, 75% of all aggregates in Eutric Regosols were unstable when time of aggregate destruction was less than 300 sec. Oppositely to Eutric Regosols laying on hummock tops, 70% of aggregates of Mollic Gleysols in depressions were water stable. The mean time for aggregate destruction for each soil from hummock-top to depression was 209 sec. for Eutric Regosol, 375 sec. for Haplic Luvisol, 616 sec. for Albic Luvisol and 772 sec. for Mollic Gleysol.
The main soil properties that affected the time of aggregate destruction are clay content (very strong negative correlation; r=–0.72); soil organic carbon content (strong positive correlation; r=0.69), and content of secondary carbonates (strong negative correlation; r=–0.69).

Temporal variations in the atmospheric pressure curve in the Bydgoszcz area

2022-10-14T11:42:49+02:00

Atmospheric pressure, the meteorological parameter describing pressure conditions in an area, was analysed based on daily values. The mean atmospheric pressure in the Bydgoszcz area in the examined multi-annual period from 1971 to 2010 was 1006.4 hPa. Comparison of the mean value of atmospheric pressure calculated for the periods from 1971 to 1990 and from 1991 to 2010 revealed bi-directional differences between them. The atmospheric pressure curve featured high yearto-year variability in the examined 40-year period. In Bydgoszcz, there was a statistically insignificant downward trend in mean annual atmospheric pressure (0.2 hPa/10 years) from 1971 to 2010.

Identification of prime factors of active river bank erosion in the lower course of Ganga Bhagirathi River: a study

2022-10-14T12:08:14+02:00

The present study aims to identify prime factors of active and continuous riverbank erosion. Field visits were conducted from 2015 to 2019. To fulfil the objective of the study, 21 study units prone to bank erosion were selected along the banks of Ganga-Bhagirathi at Jangipur sub-division. Remote sensing and geographic information system were used to measure the area under erosion and deposition from the 1985 to 2015 at five-year intervals. Bank height, bank angle, length of fracture from bank line, river velocity, and channel depth were measured for each study unit using different instruments like cup-type water current meter, clinometers, and measuring tape. Soil samples were collected for textural analysis. Factor analysis was performed to find out prime responsible factors
for active riverbank erosion. The result of the study shows that bank height, bank angle, channel width, and fracture length together comprise the first component, which explains 29.48 percent of variance. Riverbank erosion happens due to physical and manmade factors in the lower plain area of the Ganga-Bhagirathi River.