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A Trend Analysis of Temperature and Rainfall to Predict Climate Change for Northwestern Region of Bangladesh

Md. Didarul Islam Bhuyan*
Department of Physics, Mawlana Bhashani Science and Technology University, Santosh, Tangail, Bangladesh

Md. Mohymenul Islam
Department of Physics, Mawlana Bhashani Science and Technology University, Santosh, Tangail, Bangladesh

Md. Ebrahim Khalil Bhuiyan
Department of Textile Engineering, Bangladesh University of Business and Technology, Dhaka, Bangladesh

Abstract/ Executive Summary:

Bangladesh is one in all the foremost climate vulnerable countries of the world. In recent years, climate change studies over the country get plenty of attention by the researchers and policymakers. A substantial quantity of global climate change studies over the country use climate models to estimate future projections and uncertainties. Maximum temperature, precipitation and their potential future changes are evaluated in an ensemble of the 5th Phase Coupled Model Inter-comparison Project (CMIP5) within the Intergovernmental Panel on Climate Change (IPCC) diagnostic exercise for the Fifth Assessment Report (AR5) and the available historical data collected by the Bangladesh Meteorological Department (BMD) during the period 1981-2008 in the north-western region of Bangladesh and also the comparison between these two values. It has been found that average maximum temperature shows a positive trend of increase at a rate of 0.29⁰C and 5.3⁰C per century respectively, for BMD data and MPI-ESM-LR (CMIP5) model data. But the rainfall is decreasing at a rate of 8.8 mm and 40.1 mm per century respectively for BMD data and MPI-ESM-LR (CMIP5) model data. It is seen that July was the maximum monsoon rainfall month and January was the lowest rainfall month. The peak frequency is slightly smaller than 12 months, which indicates that the major events are occurring before ending a year compared to the previous year. According to MPI-ESM-LR (CMIP5) model data, future normal temperature on north-western region will be increased at a rate of 1.62⁰C during the period 2040-2100.

Keywords: Trend Analysis, Mann-Kendall Test, Sen’s Slope Estimator, Z-Test, CMIP5 Model and Periodicity

Location: Bogra, Rangpur, Dinajpur, Ishurdi, Rajshahi and Sydpur

Start Date: 00-00-1981

End Date: 00-00-2008

Program Area: Socio-economic and Policy

Commodity: Trend analysis, Climate change, Temperature, Rainfall

Objectives:

This paper will go for the North-Western part of Bangladesh to investigate climate characteristics and comparison between Bangladesh Meteorological Department (BMD) data and 5th Phase Coupled Model Inter-comparison Project (CMIP5) model data for maximum temperature and rainfall during the period 1981 to 2008 and also the detection of trend of future mean temperature during the period 2040 to 2100 by using MPI-ESM-LR (CMIP5) model data. The remaining part of this paper is structured as the following: Section 2 gives data and methodology, Section 3 presents the results and discussion, while Section 4 gives the conclusion of the study.

Methodology:

2.1. Study Area The north-western part of Bangladesh denotes the Rajshahi Division and Rangpur Division. Generally, it is the area lying west of Jamuna River and north of Padma River, and includes the Barind Tract. There are six meteorological stations are situated in this region which are Bogra, Rangpur, Dinajpur, Ishurdi, Rajshahi and Sydpur.

2.2. Data Sources and Processing Daily maximum temperature and normal daily rainfall data were collected from Bangladesh Meteorological Department (BMD) for the period 1981-2008. But the data during the period 1981-1990 for the station of Sydpur was not available so that only for this station the value is calculated from 1991-2008. The missing data of temperature have been filled by inverse distance weighting method (IDW). Missing data of rainfall has been filled by data of the neighbor station. On the other hand, to get and prepare MPI-ESM-LR (CMIP5) model data for calculation is complex and takes several processes. First of all, download the Netcdf file of the data and then crack the NC file by using ArcMap software. Daily maximum temperature and normal daily rainfall data were collected for north-western region of Bangladesh for the period 1981-2008. But the rainfall data was available for the period 1981-2005. The MPI-ESM-LR (CMIP5) model data gives the same value for Rangpur, Dinajpur and Sydpur due to very near longitude and latitude and also same for the station Rajshahi and Ishurdi.

Trend analysis is the prediction of future outcome by using historical result. Increasing or decreasing trend of all the independent weather parameters (e.g. annual and seasonal temperature, rainfalls, sunshine etc.) were statistically examined in two phases. First one is the using of non-parametric Mann-Kendall test and second one is the nonparametric Sens slope estimator. The increasing or decreasing trend was tested based on normalized test statistics (Z) value. When Z is positive, trend is said to be increasing and when Z is negative, it is said to be decreasing. The trend’s slope gives the annual rate and direction of change.

Source of Information: American Journal of Climate Change, 2018, 7, 115-134

Article Link (Online Journal): https://doi.org/10.4236/ajcc.2018.72009

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

An examination on air temperature and precipitation behavior is important for short-term planning and the prediction of future climate conditions. Trends in precipitation and temperature at annual, seasonal and monthly time scales for the periods of 1981-2008 have been analyzed using BMD data and MPI-ESM-LR (CMIP5) model data. Also, the results herein form a good basis of future studies on temperature variability. Considering all seasons (winter, pre-monsoon, monsoon and post-monsoon), maximum temperature has increased significantly in all seasons except winter which is insignificant over the whole study area for BMD data but for MPI-ESM-LR (CMIP5) model data maximum temperature is on increase in the region. On average, temperature over the entire region increased by 0.29⁰C and 5.3⁰C per century respectively for BMD data and MPI-ESM-LR (CMIP5) model data. It has clearly found that maximum temperature has been increased dramatically during the period of 1981-2008. In future, the normal temperature will be beyond 31⁰C. The highest future normal temperature has occurred in Bogra at 8⁰C per century. For north-western region, the highest 63.58% and 63.80% of total rainfall have occurred in monsoon respectively in accordance with BMD data and MPI-ESM-LR (CMIP5) model data. In Dinajpur, the highest percent of rainfall occurred in monsoon for both BMD data and MPI-ESM-LR (CMIP5) model data. Winter rainfall has decreased 1.28 mm per year for BMD data and for MPI-ESM-LR (CMIP5) model data only post-monsoon rainfall has increased 2.41 mm which is significant. Only 1.92% rainfall has occurred in winter in conformity with BMD data and only 1.60% rainfall has occurred in winter in conformity with MPI-ESM-LR (CMIP5) model data. The lowest rainfall occurred in Sydpur with 8.30 mm in winter for BMD data and only 2.17 mm rainfall occurred in Rajshahi and Ishurdi for MPI-ESM-LR (CMIP5) model data. Overall, the rainfall is decreasing in the north-western region. MPI-ESM-LR (CMIP5) temperature projections are larger than BMD climate projections but MPI-ESM-LR (CMIP5) precipitation projections are smaller than BMD climate projections. Though there is a difference between the values of BMD and MPI-ESM-LR (CMIP5), the decisions are almost the same for a small region like the north-western region of Bangladesh. That’s why considering new MPI-ESM-LR (CMIP5) projections will be more helpful for decision-makers as they have a comparatively better representation of the earth’s physical processes.

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