Papers by Kanak Kanti Kar
Journal of Hydrology, 2020
Collected rainfall records by gauges lead to key forcings in most hydrological studies. Depending... more Collected rainfall records by gauges lead to key forcings in most hydrological studies. Depending on sensor type and recording systems, such data are characterized by different time-resolutions (or temporal aggregations), ta. We present an historical analysis of the time-evolution of ta based on a large database of rain gauge networks operative in many study areas. Globally, ta data were collected for 25,423 rain gauge stations across 32 geographic areas, with larger contributions from Australia, USA, Italy and Spain. For very old networks early recordings were manual with coarse time-resolution, typically daily or sometimes monthly. With a few exceptions, mechanical recordings on paper rolls began in the first half of the 20th century, typically with ta of 1 h or 30 min. Digital registrations started only during the last three decades of the 20th century. This short period limits investigations that require long time-series of sub-daily rainfall data, e.g, analyses of the effects of climate change on short-duration (sub-hourly) heavy rainfall. In addition, in the areas with rainfall data characterized for many years by coarse time-resolutions, annual maximum rainfall depths of short duration can be potentially underestimated and their use would produce errors in the results of successive applications. Currently, only 50% of the stations provide useful data at any time-resolution, that practically means ta = 1 min. However, a significant reduction of these issues can be obtained through the information content of the present database. Finally, we suggest an integration of the database by including additional rain gauge networks to enhance its usefulness particularly in a comparative analysis of the effects of climate change on extreme rainfalls of short duration available in different locations.
International Journal of Climatology, 2019
Rainfall in Bangladesh exhibits persistent wet and dry anomalies associated with occurrence of fl... more Rainfall in Bangladesh exhibits persistent wet and dry anomalies associated with occurrence of floods and droughts. Assessing inter‐annual variability of rainfall is vital to account these hydrological extremes in the design and operations of water systems. However, the inter‐annual variability obtained from short record rainfall data might be misleading as it does not contain whole climate variability which signifies the utmost importance of stochastic rainfall models. Since the inter‐annual variability and stochastic models have not been explored adequately for rainfall in Bangladesh, this study evaluated (a) the spatio‐temporal variability of rainfall focusing on inter‐annual variability, and (b) applicability of a stochastic daily rainfall model, referred as the Decadal and Hierarchical Markov Chain (DHMC) model. Daily rainfall data of 1973–2012 for 18 stations across Bangladesh were used to investigate the probability distributions and autocorrelations of rainfall, and the model performances. Results show a higher magnitude of inter‐annual variabilities of rainfall depth (standard deviation 80–250 mm) and wet spells (standard deviation 4–6 days) in wetter months (June to September) across rainfall stations in the east region of the country. In contrast, higher rates of inter‐annual variabilities (i.e., coefficients of variations) were observed in drier months across the west region. Spatially, the dry spells were observed consistent across the country. Monthly rainfall showed decreasing trend over the region from west to the middle part of the country, whereas monthly number of wet days showed increasing trend over the eastern part. The DHMC was found to preserve the observed variabilities of rainfall at daily to multiyear resolutions at all stations, except a tendency to underestimate the autocorrelation of monthly rainfall depth. Despite this limitation, DHMC can be considered as a suitable stochastic rainfall simulator for a tropical monsoon climate like Bangladesh.
Background: Extreme rainfall events are enormously frequent and abrupt in tropical areas like the... more Background: Extreme rainfall events are enormously frequent and abrupt in tropical areas like the Jeju Island of South Korea, impacting the hydrological functions as well as the social and economic situation. Rainfall magnitude and frequency distribution related information are essential for water system design, water resources management and hydro-meteorological emergencies. This study therefore has investigated the use of L-moments approach for hourly regional rainfall frequency estimation so as to ensure better accuracy and efficiency of the estimation process from the usually limited data sets. Results: The Hancheon catchment was considered as the primary study domain and several best fitted statistical tools were used to analyze consecutive hour rainfall data from five hydro-meteorological stations (Jeju, Ara, Eorimok, Witsaeorum and Jindallaebat) adjacent to the area. The cluster analysis and discordancy measure categorized the Hancheon catchment in three regions (1, 2 and 3). Based on the L-moments heterogeneity and goodness-of-fit measure, Gumbel and generalized extreme value (GEV) distribution were identified as robust distributions for the study area. The RMSE ratios for the catchment were found as 0.014 to 0.237 for Gumbel and 0.115 to 0.301 for GEV distribution. The linear regression analysis of the different rainfall quantiles inferred r-square values from 0.842 to 0.974. Conclusions: The L-moments and other statistical information derived from the study can be useful for important hydrological design considerations in connection with flood risk management, mitigation and safety; whereas the methodological framework of the study may be suitable for other small scaled catchment areas with high slope.
Bangladesh is mainly formed by alluvial deposits, facing riverbank erosion very frequently due to... more Bangladesh is mainly formed by alluvial deposits, facing riverbank erosion very frequently due to unvarying alteration of river channels. This study is aimed at computing the actual bank shifting along the Manu River within Bangladesh for a period of thirteen years (1997-2010). The entire course of Manu River from upstream of India Border, Moulvibazar to the confluence with the Kushiyara River at Manumukh, Sherpur for a stretch of around 69 km has been studied using an integrated approach of Remote Sensing and Geographical Information System (GIS). The channel configuration of the Manu River has been mapped for the years 1997 and 2010 using Landsat satellite images. The analysis divulged that the Manu River is a highly meandering river with several very critical sections where the river has been suffering enormously with the erosion problem and shifting characteristics. The enumerated river shifting was found very high as the maximum left bank shifting and maximum right bank shifting had occurred at Rajnagar, Moulvibazar of 656 m and 628 m respectively, in the mentioned period. The results deliver latest and steadfast evidence on the dynamic fluvio-geomorphology of the Manu River for designing and execution of erosion control schemes.
The south west coastal zone of Bangladesh has been affected by rampant water logging due to vulne... more The south west coastal zone of Bangladesh has been affected by rampant water logging due to vulnerable climate, silted rivers and stumpy terrain; and introduction of IWRM and TRM at some places of the zone has substantially safeguarded the circumstance. This study aims to assess the benefits achieved due to implementation of IWRM in parts of Khulna and Jessore districts, and investigate some technical aspects evolving TRM. Analyses have been carried out using satellite images, RS and GIS technology, Digital Elevation Model (DEM) and field investigations. A mathematical formulation has been made to assess rate of tidal sedimentation due to TRM and selection strategies of tidal basins. The study comes up with evidences of considerable advancements in regional livelihood i.e. flood resistance, cultivated lands, cultivable area, cropping intensities and food security due to IWRM. Moreover, the technical facts established on TRM would help planners to have vivid perception regarding the process.
Rainfall-runoff linkage is one of the most important relationships in hydrologic analysis.Runoff ... more Rainfall-runoff linkage is one of the most important relationships in hydrologic analysis.Runoff needs to be estimated for assessment of water availability for multifaceted water uses and functions, to underscore the modalities for efficient water utilization. Rainfall, on the other hand, is a primary input for basin level runoff computation. The estimation of rainfall-runoff plays a pivotal role in water resource system management and feasibility level planning for resources distribution. Based on these importance a study was carried out in Jeju Island where distinctive hydrological characteristics are shown due to the continuous, heavy rainfall and high permeable geologicalfeatures. The purpose of this study was to estimate peak runoff and time of peak based on storm rainfalls unit hydrograph method. For analyzing simulated runoff, five storm rainfall events were selected randomly from recent years' rainfall and HEC-HMS program was used for rainfall and runoff data processing. Then, the simulation result showed that peak runoff varies from 164 CMS (cubic meter per second) to 548 CMS where the peak time varies 3 hr to 27 hr. In addition, a comprehensive relationship between Clark unit hydrograph parameters (Tc, R) was also derived in this study. Finally, parameters optimization was statistically verified by analysis of variance (ANOVA) method. The significant level was more than 95%; in terms of calibration and validation and results were also appreciated reasonably. Thus, we can say unit hydrograph model response are utmost important for flood hazard management.
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Papers by Kanak Kanti Kar