Spatio-Temporal Variability of Rainfall over Bangladesh During the Time Period 1969-2003

Shamsuddin Shahid,Osman Salleh Khairulmaini 한국기상학회 2009 Asia-Pacific Journal of Atmospheric Sciences Vol.45 No.3

Spatial and temporal variability of rainfall in Bangladesh has been studied in this paper from thirty-five years (1969-2003) of rainfall data recorded at 24 rain gauges distributed over the country. Long-term annual average rainfall, coefficient of variation of annual rainfall, precipitation concentration and aridity indices at each station have been computed and then interpolated using kriging method within a geographic information system to show the temporal and spatial variability of rainfall. Mann-Kendall test has been used to analyze the trend in rainfall data in different recording stations and the Sen’s slope method has been used to determine the magnitude of change. A moderate variation in inter-annual rainfall and high variation in intra-annual rainfall in Bangladesh have been observed. Non-significant positive trend of annual, monsoon and pre-monsoon rainfall, and a negative trend in winter rainfall are found in Bangladesh. Spatial distribution of rainfall trends shows that rainfall is increasing in the coastal zone and northern Bangladesh, and decreasing in the central part of the country. A declining trend of precipitation concentration is also observed in most of the stations. These results may be a first indication of the precipitation response to global warming ? a hypothesis which needs to be further investigated by means of climate model projections.

Characteristics of Annual and Seasonal Trends of Rainfall and Temperature in Iraq

Saleem A. Salman,Shamsuddin Shahid,Tarmizi Ismail,Kamal Ahmed,Eun-Sung Chung,Xiao-Jun Wang 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.3

Changes in the temperature and precipitation have significantly affected water resources and agricultural productions in many countries across the world. The objective of the present study is to analyze the changing patterns of annual and seasonal precipitation and temperature in Iraq for the period 1961–2010. Monthly gridded precipitation and temperature data of Global precipitation climate center (GPCC) and climate research unit (CRU) respectively having a spatial resolution of 0.5° were used in this study to show the spatial pattern in trends. The rate of change in rainfall and temperature was estimated using Sen’s slope method while the significance of change was confirmed using Mann-Kendal test (MK) and the modified Mann-Kendall test (mMK). The results revealed large differences in the number of grid points showing significant changes in rainfall and temperature using MK and mMK methods. The mMK method revealed that the annual rainfall is decreasing at a rate of −1.0 to −5.0 mm/year in the northwest part of Iraq. The seasonal precipitations were found to decrease in spring (−0.4 to −2.56 mm/ year) and winter (−0.4 to −2.0 mm/year), increase in summer (0.06 to 0.21 mm/year) at a few grid points and no change in autumn. On the other hand, a sharp rise in annual average of daily mean (0.42 to 0.64 °C/decade), maximum (0.39 to 0.65 °C/ decade) and minimum (0.36 to 0.69 °C/decade) temperature was observed.

Distributional Changes in Rainfall and River Flow in Sarawak, Malaysia

Zulfaqar Sa’adi,Shamsuddin Shahid,Tarmizi Ismail,정은성,Xiao-Jun Wang 한국기상학회 2017 Asia-Pacific Journal of Atmospheric Sciences Vol.53 No.4

Climate change may not change the rainfall mean, but the variability and extremes. Therefore, it is required to explore the possible distributional changes of rainfall characteristics over time. The objective of present study is to assess the distributional changes in annual and northeast monsoon rainfall (November-January) and river flow in Sarawak where small changes in rainfall or river flow variability/distribution may have severe implications on ecology and agriculture. A quantile regression-based approach was used to assess the changes of scale and location of empirical probability density function over the period 1980-2014 at 31 observational stations. The results indicate that diverse variation patterns exist at all stations for annual rainfall but mainly increasing quantile trend at the lowers, and higher quantiles for the month of January and December. The significant increase in annual rainfall is found mostly in the north and central-coastal region and monsoon month rainfalls in the interior and north of Sarawak. Trends in river flow data show that changes in rainfall distribution have affected higher quantiles of river flow in monsoon months at some of the basins and therefore more flooding. The study reveals that quantile trend can provide more information of rainfall change which may be useful for climate change mitigation and adaptation planning.

Replicability of Annual and Seasonal Precipitation by CMIP5 and CMIP6 GCMs over East Asia

Mohammed Sanusi Shiru,Shamsuddin Shahid,채승택,정은성 대한토목학회 2022 KSCE Journal of Civil Engineering Vol.26 No.4

Global climate models (GCMs) structure is a source of uncertainty in climate change projections. Therefore, evaluation of the performances of GCMs is crucial for development of adaptation and mitigation measures and risk reduction against climate change impacts. This study quantified the performances of 10 GCMs of the Coupled Model Intercomparison Project 5 (CMIP5) and their CMIP6 equivalents in replicating precipitation over East Asia during 1975 – 2005. The CMIP5 and CMIP6 GCMs and their multi-model ensembles (MMEs) were annually and seasonally compared with the Global Precipitation Climatology Centre (GPCC) precipitation. Compromise Programming was used to rank GCMs by aggregating their scores obtained using statistical performance indices. Taylor diagram was used to assess their relative performances and GCMs' ability to replicate seasonal precipitation distribution was evaluated. Results revealed most CMIP6 GCMs' have better replicability of GPCC precipitation than CMIP5 GCMs. The MME mean of the CMIP6 showed better replicability of annual and seasonal GPCC precipitation than that of CMIP5. The CMIP6 MME also showed efficiency in simulating the seasonal precipitation distribution over East Asia. This study indicates improvements of some CMIP5 GCMs in their CMIP6 equivalents over East Asia. Findings from this study can be significant to policy makers and engineers in reducing the uncertainties in prediction of events such as floods and droughts.

Joint Modelling of Drought Severity and Duration using Copula Theory: A Case Study of Ghana

Gyamfi Kwame Adutwum,정은성,Mohammed Sanusi Shiru,Shamsuddin Shahid 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.4

Analysing and understanding the occurrence and development of droughts is of great significance in mitigating drought impacts. This study assessed the possible changes in the joint distribution of drought duration and severity in two major cities of Ghana, Accra and Yendi. The duration and severity of droughts, estimated using the Standardized Precipitation Index (SPI), were determined based on run theory. The best-fitted Copula models were used to combine the drought duration and severity to analyse the drought return period. The gamma, lognormal and Weibull distributions were considered to select the marginal distributions for the duration and severity, while the normal, t, Gumbel, Joe, Clayton and Frank copulas to select the best-fit Copula model. Bias corrected climate simulations of six Global Climate Models (GCMs) of the CMIP6 were used to project drought characteristics for the near and far futures. The results showed the Clayton and Frank copulas as the most suitable for fitting the joint distribution of drought duration and severity at Accra and Yendi, respectively. Lognormal and Weibull distributions were the most suitable for the marginal distributions of severity and duration, respectively. The joint return periods of droughts showed almost no change in the future compared to the historical period in Accra with a historical mean of 11.36 and a near and far future mean of 12.26 and 10.30 respectively but significantly reduced return periods in the future in Yendi with a near and far future means of 1.47 and 2.13 respectively compared to a historical mean of 17.40. The drought risks estimated for different future periods can provide useful information in planning, management, and assessing the adequacy of the water structures in the region.

Development of an Optimal Reservoir Pumping Operation for Adaptation to Climate Change

Tarmizi Ismail,Sobri Harun,Zaitul Marlizawati Zainudin,Shamsuddin Shahid,Abu Bakar Fadzil,Usman Ullah Sheikh 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.1

Optimization of operation rule curve of Layang reservoir located in southern part of peninsular Malaysia under climate change uncertainties has been presented in this study. Downscaled climate data were incorporated in a lumped rainfall-runoff model to project daily reservoir inflow, which was then used to determine the reservoir operation rule curves to minimize the operation cost. The results reveal that climatic change will cause a rise of temperature in the range of 1.5-2.9oC, but decrease in rainfall in most of the months in the end of this century which will casue a change in the seasonal pattern of inflow to reservoir. Comparison of historical and model generated operation costs indicates that annual savings of 23% and 33% is possible with optimized reservoir operation rule curves. Assessment of the performance of the optimized operation curve under climate change scenarios shows that it will be able to cope with the changing pattern of reservoir inflow with proper adjustment. It is expected that the method presented in this paper to derive pumping operation curves to optimize the total volume of water to be pumped from various sources to reservoir can be useful for reservoir operators in the context of climate change.

Groundwater Dynamics and Balance in the Western Part of Greater Kushtia District of Bangladesh

M. Nozibul Haque,Mumnunul Keramat,Shamsuddin Shahid,Morteza Mohsenipour,Xiao-Jun Wang 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.5

Groundwater dynamics and balance have been studied for the assessment of groundwater abstraction status in the western part of grater Kushtia district, Bangladesh using data from 28 groundwater level monitoring wells, 180 lithologs, and one rainfall station for the period 2001-2007. The groundwater levels in the study area were found to vary at a depth between 0.0 m and 9.34 m. During peak season of groundwater abstraction (pre-monsoon), the maximum and minimum groundwater level with respect to mean sea level (MSL) were found to vary from 9.36 to 11.3 m and 2.3 to 4.9 m, respectively, whereas in post-monsoon these values were found to vary from 13.2 to 15.6 m and 7.6 to 9.6 m, respectively. The groundwater flow in the area was driven by topography, directed from the northwest to the southeast. This study revealed a declining trend in groundwater table both in pre- and post-monsoon seasons in the area. It has also been noticed that the rate of declination is increasing with time. The volumetric analysis of groundwater also showed a net negative balance, which indicates overexploitation of groundwater. The study concluded that the unsustainable utilization of groundwater resources in the study area has caused depletion in groundwater table.

Assessment of Spatiotemporal Variability of Meteorological Droughts in Northern Iraq Using Satellite Rainfall Data

Hafed Qasem Ahmad,Samira A. Kamaruddin,Sobri B. Harun,Nadhir Al-Ansari,Shamsuddin Shahid,Ruqaya M. Jasim 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.11

The absence of a dense rainfall monitoring network and longer period data are the major hindrances of hydroclimatic study in arid and semi-arid regions. An attempt has been made for the evaluation of spatiotemporal changes in droughts at the northern semi-arid region of Iraq for the period 1981 − 2018 using high-resolution (0.05°) precipitation data of Climate Hazards Group Infrared Precipitation with Stations (CHIRPS). The performance of CHIRPS in replicating rainfall and Standard Precipitation Index (SPI) for different timescales at eleven locations for the available period of observation data (2000 − 2014) was evaluated. The SPI was also used to estimate drought frequency and evaluate drought trends at all the CHIRPS grid points. A modified version of the non-parametric Mann-Kendall (MK) test was employed for a robust evaluation of the spatial distribution of temporal trends in droughts. The results showed a good ability of CHIRPS in reconstructing observed SPI with a correlation coefficient ranged from 0.64 to 0.87, BIAS between 1.05 and 1.81, Nash-Sutcliff efficiency from 0.39 to 0.55, and Willmott Index between 0.67 and 0.79. The CHIRPS also able to reconstruct the time series and probability distribution of observed SPI reasonably. Spatial distribution of droughts revealed a higher frequency of droughts of all categories and timescales in the east and north of Northern Iraq, mainly due to high rainfall variance. The MK test revealed a reduction in 6- and 12-month droughts in the northwest and an intensification at a few northeastern grids. It indicates droughts became more recurrent in the already drought-prone region and lessened in a less drought-prone region.