J. Environ. Sci. & Natural Resources, 7(2): 141-149, 2014 ISSN 1999-7361 Analysis of Variability in Rainfall Patterns in Greater Rajshahi Division using GIS M. Shamsuzzoha1, A. Parvez2 and A.F.M.K.Chowdhury3* 1Department of Emergency Management, 2Department of Environmental Science, 3Department of Resource Management, Patuakhali Science and Technology University, Bangladesh; * Corresponding author: [email protected]
Abstract The study entitled ‘Analysis of Changes in Rainfall Patterns in Rajshahi Division using GIS’ is an experimental climatological research. The main objectives of the study is to examine the long-term changes in rainfall patterns of Rajshahi Division. Secondary data of rainfall distribution have been collected from Bangladesh Meteorological Department (BMD), Dhaka. The study has analysed monthly, seasonal and annual rainfall distribution pattern from 1962 to 2007 of five selected weather stations namely Bogra, Dinajpur, Ishurdi, Rajshahi and Rangpur. For convenience of analysis, the data has been divided into two halves of time period as 1962-1984 and 1985-2007. Based on GIS, the study gifts the spatial analysis of rainfall patten using Thiessen Polygon Method, Isohytal and Hytograph Method and Percentage Method. It has been found that there is evidence of annual rainfall change with an increasing pattern in Bogra, Dinajpur, Rajshahi and Rangpur. In these four stations, the changing pattern in Rangpur is the highest. Downward shift of annual rainfall shows a decreasing pattern in Ishurdi. The descending order of monthly and seasonal rainfall pattern for Ishurdi, Rajshahi and Rangpur has been found as July > June > September >August > October > April > March > February > November > December. Although Bogra and Dinajpur have contained this trend in the same order from July to March, anomalies pattern has been found for last four months. The seasonal variation of rainfall has been established as Monsoon > Pre – Monsoon > Post Monsoon > Winter for all those five stations. Evaluating the rainfall contour lines, it has been found that the rainfall annually varies from 1542.1 mm to 2235.8 mm in Rajshahi Division. The average number of rainy days in this region mostly varies from 86 to 112 days per year.
Key words: GIS, Rainfall, Rajshahi
Introduction
The climate of Rajshahi Division is generally and monthly trends of rainfall (maximum, marked with a typically tropical monsoon climate minimum and average) at Rajshahi Division. characterized by high temperature, heavy rainfall, often excessive humidity, and fairly marked Materials and Methods seasonal variations (Islam and Neelim, 2010). In Secondary data of daily rainfall (in mm) for the terms of rainfall, a variation within 10 percent in a time period of 1962-2007 has been collected from year is marked as normal which exhibit a mild five selected weather stations (e.g. Bogra, Dinajpur, economic impact while a variation greater than 10 Ishurdi, Rajshahi and Rangpur) of Rajshahsi percent may exhibit an adverse impact to the (Figure: 01) which have been being maintained by economy and normal life style of the people Bangladesh Meteorological Department (BMD, (Sivasami, 2000). Likewise other part of the 2007). For convenience of analysis and to obtain a Bangladesh, the economy of Rajshahi Division is comparative pattern of rainfall variation, the also largely dependent on rain-fed agriculture. So, available rainfall data (1962-2007) have been the changes of rainfall pattern may largely impact divided into two halves of time period as 1962- the agricultural economy of the region. Therefore, it 1984 and 1985-2007. Other information, images is essential to find out whether there are changes in and base maps have been collected from various rainfall patterns or not, so that information can be sources i.e. books, journals, websites and official used for adjusting the planning and management of records. Quantitative techniques like Mean, irrigation project, supplying drinking water, Median, Mode, Percentage, Frequency, Standard planning of fishery extension department and other Deviation (SD), Sample Variance, Kurtosis, water resources related issues and movements. Skewness, Range, Sum, Moving Average (5-years) Based on the above mentioned rationale and and Co-efficient of variance (COV) have been used statement, the study has been conducted with the in data analysis to obtain a contented tabular & following specific objectives: 1. Evaluation of long- graphical presentation. Thiessen polygon method term changes in rainfall (maximum, minimum and and Isohyetal Map Method have been adopted for average) at Rajshahi Division; 2. Assessment of spatial analysis. The results have been presented in annual, seasonal (monsoon, pre-monsoon, post- the maps by using ArcGIS. monsoon, winter, dry season and critical period)
141 J. Environ. Sci. & Natural Resources, 7(2): 141-149, 2014 ISSN 1999-7361
88° 89° 90° RAJSHAHI DIVISION
$ INDIA PANCHAGAR H
N 26° $ NILPHAM ARI 26° THAKU RGAON $ $ LALMONIRHAT $ $ b KURIGRAM RAN GP UR $ b DINAJPU R INDEX INDIA $ GAIBANDH A b Weather Station $ JAIPURH AT $ District Headquarter 25° 25° DHAKA $ DIVISION %[ Divisional Headquarter $ b NAOGAON BOGR A NAW ABGANJ International Boundary $
Divisional Boundary $ %[ bRAJ SHAHI $ NATOR SIRAJGANJ District Boundary INDIA bISHU R DI 24° $ PABNA 24°
0 15 30 60 KM KHULNA DIVISION 88° 89° 90°
Fig.1. Five selected weather stations of greater Rajshahi Division, Bangladesh
Results and Discussion
Rainfall is the most dominant climatic element. Ishurdi, Rajshahi and Rangpur the ranking order The dry winter monsoon seldom carries any rain of highest rainfall months can be described as bearing clouds in Rajshahi Division. Most of the July > June > September >August > October > rainfall occurs in the summer monsoon season. It April > March > February > November > has been found that there is no typical trend in December (Figure 2, 3 and 4). Although Bogra the rainfall variation in five selective weather and Dinajpur have contained this trend in the stations in study areas. There are also mixed same order from July to March, anomalies results of upwards and downwards shift in both pattern has been found for last four months. For seasonal and annual rainfall. Seasonal results are Bogra and Dinajpur the order of highest rainfall based on monthly analysis. month has been established as November > February > December > January and January > In context of monthly variation, for all of the February > November > December respectively five weather stations, July is the highest month for the last four months (Figure 5 and 6). of rainfall while December is the lowest one. For
Mean Monthly Rainfall of Ishurdi
400 350 300 250 1962 - 1984 200 1985 - 2007 150 1962 - 2007
Rainfall Rainfall (mm) 100 50 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Fig.2. Mean Monthly Rainfall of Ishurdi
Mean Monthly Rainfall in Rajshahi
400 350 300 250 1962 - 1984 200 1985 - 2007 150 1962 - 2007
Rainfall Rainfall (mm) 100 50 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months
Fig.3. Mean Monthly Rainfall of Rajshahi
142 J. Environ. Sci. & Natural Resources, 7(2): 141-149, 2014 ISSN 1999-7361
Mean Monthly Rainfall of Rangpur
600 500
400 1962 - 1984 300 1985 - 2007
200 1962 - 2007 Rainfall Rainfall (mm) 100 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months
Fig.4. Mean Monthly Rainfall of Rangpur
Mean Monthly Rainfall of Bogra
500
400 1962 - 1984 300 1985 - 2007 200 1962 - 2007
Rainfall Rainfall (mm) 100
0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months
Fig.5. Mean Monthly Rainfall of Bogra
Mean Monthly Rainfall in Dinajpur
600 500
400 1962 - 1984 300 1985 - 2007 200 1962 - 2007 Rainfall (mm) Rainfall 100 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months
Fig.6. Mean Monthly Rainfall of Dinajpur
Considering seasonal variation for all those five of the year is being participated in the monsoon. stations, it has been found that monsoon is the Pre monsoon is the second highest season in highest season of rainfall while dry cool winter rainfall occurrence (Figure 7, 8, 9, 10 and 11). is the lowest one. Al most 70% of total rainfall
Mean Seasonal and Annual Rainfall of Rangpur
Annual
Post - Monsoon 1962 - 2007 Monsoon 1985 - 2007
Seasons 1962 -1984 Pre - Monsoon
Winter
0 500 1000 1500 2000 2500 Rainfall (mm)
Fig.7. Mean Seasonal and Annual Rainfall (mm) of Rangpur
143 J. Environ. Sci. & Natural Resources, 7(2): 141-149, 2014 ISSN 1999-7361
Mean Seasonal and Annual Rainfall of Dinajpur
Annual
Post - Monsoon 1962 - 2007 Monsoon 1985 - 2007
Seasons 1962 -1984 Pre - Monsoon
Winter
0 500 1000 1500 2000 2500 Rainfall (mm)
Fig.8. Mean Seasonal and Annual Rainfall (mm) of Dinajpur
Mean Seasonal and Annual Rainfall of Bogra
Annual
Post - Monsoon 1962 - 2007 Monsoon 1985 - 2007
Seasons 1962 -1984 Pre - Monsoon
Winter
0 500 1000 1500 2000 Rainfall (mm)
Fig.9. Mean Seasonal and Annual Rainfall (mm) of Bogra
Mean Seasonal and Annual Rainfall of Ishurdi
Annual
Post - Monsoon 1962 - 2007 Monsoon 1985 - 2007
Seasons 1962 -1984 Pre - Monsoon
Winter
0 200 400 600 800 1000 1200 1400 1600 1800 Rainfall (mm)
Fig.10. Mean Seasonal and Annual Rainfall (mm) of Ishurdi
Mean Seasonal and Annual Rainfall of Rajshahi
Annual
Post - Monsoon 1962 - 2007 Monsoon 1985 - 2007
Seasons 1962 -1984 Pre - Monsoon
Winter
0 200 400 600 800 1000 1200 1400 1600 1800 Rainfall (mm)
Fig.11. Mean Seasonal and Annual Rainfall (mm) of Rajshahi
Comparing the mean monthly, seasonal and annual rainfall variation between the two halves Evaluating the rainfall contour lines, it has been of time period 1962-1984 and 1985-2007, it has found that the rainfall annually varies from been found an increasing pattern in Rangpur, 1542.1 mm to 2235.8 mm in Rajshahi (Figure: Dinajpur and Bogra while a decreasing pattern in 12). From July to September, when the monsoon Ishurdi and Rajshahi. The results have been established firmly, its south-eastern river basins interpreted by isohyetal maps by GIS (Figure: of Jamuna, Tista and lower portion of Atrai and 12).
144 J. Environ. Sci. & Natural Resources, 7(2): 141-149, 2014 ISSN 1999-7361
Chalan Beel have been being flooded due to heavy rainfall.
RAJSHAHI DIVISION RAJSHAHI DIVISION
Mean Annual Rainfall , 1985 - 2007 Mean Annual Rainfalll, 1962 - 1984
in millimetre (in millimeter)
2400 2400 Dinajpur Dinajpur # # 0 10 00 2 # 21 # Rangpur Rangpur N N
2 2 1 1 00 0 800 0 18 0 1 0
1500 1500
# #
Bogra Bogra Rajshahi Rajshahi 1800 1800 # #
LEGEND LEGEND 800 800 600 # Ishurdi 600 # Ishurdi 400 # 400 # 200 200 JFMAMJJASOND JFMAMJJASOND 0 45 Km 0 45 Km Isohyet (mm) Isohyet (mm)
Fig.12. Isohyetal and hytograph map of Rajshahi Division for time series of 1962-1984 and 1985-2007
For both the time period of 1962-1984 and 1985- total area of 34513 sq. km for the time period of 2007, the order of highest ranking rainy region 1962-1984 and 1985-2007 respectively. Ishurdi has been established as Rangpur > Dinajpur > comprises about 5763.6 and 5208.2 sq. km of Bogra > Rajshahi > Ishurdi (Figure 13). Rangpur rain zone for 1962-1984 and 1985-2007 is the rainiest area in this region comprising respectively being the lowest rainfall region in 7556.2 and 7930.7 sq. km of rain zone within a the Rajshahi Division.
RAJSHAHI DIVISION RAJSHAHI DIVISION RAINFALL REGION MAP, 1962 - 1984 RAINFALL REGION MAP, 1985 - 2007
N N
W E W E
S S
Dinajpur Dinajpur # # # # Rangpur Rangpur Using Thiessen Using Thiessen Polygon Method Polygon Method based on Mean based on Mean Annual Rainfall Annual Rainfall
# # Bogra Bogra Rajshahi Rajshahi
# # Ishurdi Ishurdi Area Indices in Sq. Km # Area Indices in Sq. Km #
Rangpur 7556.204 Rangpur 7930.736 Dinajpur 7343.049 Dinajpur 7806.759 # W eather Station W eather Station Bogra 7109.321 Bogra 6634.882 #
Rajshahi 6740.776 Catchment boundary Rajshahi 6932.366 Catchment boundary
Ishurdi 5763.646 0 25 50 Km Ishurdi 5208.253 0 25 50 Km Total Area - 34512.996 Total Area - 34512.996
Fig. 13. Rainfall region map of Rajshahi Division for the time period of 1962-1984 and 1985-2007
Two maps of rainfall percentage have also been Dinajpur for the time period of 1962-1984 while prepared on the basis of Thiessen Polygon 71% in Ishurdi to 76% in Dinajpur for the time Method. These maps have showed that monsoon period of 1985-2007. In Bogra, the monsoon is the highest season of rainfall while winter is rainfall percentage has been decreased from 74% least one in Rajshahi region. In monsoon it to 72% while its compared between the two varies from 71% of rainfall in Ishurdi to 78% in halves of time period. A decreasing pattern has
145 J. Environ. Sci. & Natural Resources, 7(2): 141-149, 2014 ISSN 1999-7361 also been established for monsoon rainfall Ishurdi and Rangpur has showed an increasing percentage in Rangpur while it varies in a trend of post-monsoon rainfall percentage while similar manner to Bogra. But the monsoon Rajshahi comprised a decreasing trend. rainfall percentage has remained same in Therefore, it has been revealed that there is an Rajshahi for both the halves of time period inverse trend of pre and post monsoon rainfall (Figure: 14). percentage in Rajshahi Division. However, the However, in case of pre-monsoon rainfall, it has winter rainfall percentage has remained almost found an increasing trend for Rajshahi while the same for the entire division comprising no rest comprised a decreasing trend between the variation between the two halves of time period two halves of time period. Dinajpur, Bogra, (Figure 14).
RAJSHAHI DIVISION RAJSHAHI DIVISION Rainfall Percentage Map, 1985 - 2007 Rainfall Percentage Map, 1962 - 1984
N N Mean Mean Annual - 2104 mm Annual - 1799 mm
15% 14% 18% 1% 76% 1% 78% 19% 72% 1% 6% 9% 9% 74% 1% # 6% # # Using Thiessen Rangpur # Dinajpur Using Thiessen Rangpur Polygon Method Mean Dinajpur Polygon Method Mean For Calculate Annual - 2371 mm For Calculate Annual - 2068 mm Catchment Boundary Catchment Boundary Mean Mean Annual - 1840 mm Annual - 1681 mm 17% 16% 2% Rajshahi Rajshahi 74% 2% 7% 72% 10% 15% 13% # 75% # 2% 2% Mean 75% Bogra 10% 8% Annual - 1524 mm Bogra Mean Mean Mean # # Annual - 1640 mm Annual - 1497 mm Annual - 1532 mm 18% 19% 2% 2% 71% 71% 9% 8% # # Ishurdi Ishurdi INDEX INDEX
W inter W inter # W eather Station # W eather Station Pre-Monsoon Pre-Monsoon Catchment boundary Catchment boundary Monsoon Monsoon
Post-Monsoon 0 25 50 Km Post-Monsoon 0 25 50 Km
Fig. 14. Rainfall percentage map of Rajshahi Division for the time period of 1962-1984 and 1985-2007
The average number of rainy days in this region the study area. In all seasons, rainy days have mostly varies from 86 to 112 days per year. increased and it also maximally continued in Total number of rainy days analyses has monthly and annual pattern (Figure 15 and 16). revealed an increasing pattern of rainy days in
Total Rainy Days of Bogra (1962 - 2007) Total Rainy Days of Dinajpur (1962 - 2007)
4% 9% 7% 3% 20% 18%
Winter Winter Pre - Monsoon Pre - Monsoon Monsoon Monsoon Post -monsoon Post monsoon
67% 72%
Fig.15. Percentages of Total Rainy Days in a year in Bogra and Dinajpur
146 J. Environ. Sci. & Natural Resources, 7(2): 141-149, 2014 ISSN 1999-7361
Total Rainy Days of Ishurdi (1962 -2007) Total Rainy Days of Rajshahi (1962 - 2007)
9% 4% 8% 4% 19% 17%
Winter Winter Pre - Monsoon Pre - Monsoon Monsoon Monsoon Post - Monsoon Post - monsoon
68% 71%
Total Rainy Days of Rangpur (1962 - 2007)
8% 4%
22% Winter Pre - Monsoon Monsoon Post monsoon
66%
Fig. 16. Percentages of Total Rainy Days in a year in Ishurdi, Rajshahi and Rangpur
Finally, the annual time series trend of rainfall an increasing pattern of annual rainfall in Bogra, pattern has been illustrated that 1988, 2007, Dinajpur, Rajshahi and Rangpur in the recent 1977, 1981, and 1989 comprised the highest years while a decreasing pattern in Ishurdi rainfall year for Bogra, Dinajpur, Ishurdi, (Figure 17, 18, 19, 20 and 21). Rajshahi and Rangpur respectively. It has found
Annual Time Series Trend of Rainfall Pattern in Bogra (based on 5-year moving averages)
2200 2000 1800 1600
Rainfall Rainfall (mm) 1400 1200
1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 Years
Fig. 17. Annual Time Series Trend of Rainfall Pattern in Bogra
Annual Time Series Trend of Rainfall Pattern in Dinajpur (based on 5-year moving averages)
2600 2400 2200 2000 1800 1600
Rainfall Rainfall (mm) 1400 1200
1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 Years
Fig. 18. Annual Time Series Trend of Rainfall Pattern in Dinajpur
147 J. Environ. Sci. & Natural Resources, 7(2): 141-149, 2014 ISSN 1999-7361
Annual Time Series Trend of Rainfall Pattern in Ishurdi (based on 5-year moving averages)
2400 2200 2000 1800 1600
Rainfall Rainfall (mm) 1400
1200
1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 Years
Fig. 19. Annual Time Series Trend of Rainfall Pattern in Ishurdi
Annual Time Series Trend of Rainfall Pattern in Rajshahi (based on 5-year moving averages)
1900 1800 1700 1600 1500 1400 Rainfall Rainfall (mm) 1300
1200
1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 Years
Fig. 20. Annual Time Series Trend of Rainfall Pattern in Rajshahi
Annual Time Series Trend of Rainfall Pattern in Rangpur (based on 5-year moving averages)
3200
2700
2200
1700 Rainfall Rainfall (mm) 1200
1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 Years
Fig. 21. Annual Time Series Trend of Rainfall Pattern in Rangpur
The study has revealed the following hypotheses Rainfall distribution has showed an irregular for the rainfall pattern in Rajshahi division changing pattern and the reasons for rainfall There is evidence of annual rainfall change with an decreasing trend still have to be investigated. increasing pattern in Bogra, Dinajpur, Rajshahi and Based on rainfall distribution of the time period of Rangpur. In these four stations, the changing 1962-2007, the descending order of monthly and pattern in Rangpur is the highest. Downward shift seasonal rainfall pattern in Rajshahi Division can be of annual rainfall shows a decreasing pattern in summarized as below: Ishurdi. The time period 1985-2007 shows mostly Monthly rainfall pattern an increasing trend, which is being reversed during a) Ishurdi, Rajshahi and Rangpur 1962 – 1984. In Rajshahi Division the mean annual July > June > September > August > October > and seasonal rainfall have increased in its northern April > March > February > November > January > portion and decreased in southern parts. Also the December frequencies of rainy days pattern in every season for all of those five stations have increased. Results b) Bogra from the mean annual and seasonal rainfall and the July > June > September > August > October > moving average data are slightly different. Hence, April > March > November > February > periodic or cyclic of annual rainfall may exist and December > January can partially be changed.
148 J. Environ. Sci. & Natural Resources, 7(2): 141-149, 2014 ISSN 1999-7361 c) Dinajpur Conclusions July > June > September > August > October > April > March > January > February > November > The study has revealed that the changes in rainfall December. patterns in Rajshahi Division have been taken place over the years. It is found an increasing pattern in Seasonal rainfall pattern (for all stations) mean monthly, seasonal and annual rainfall in most Monsoon > Pre – Monsoon > Post Monsoon > of the region of Rajshahi Division. However, Winter rainfall is a very important climatic factor for availability of water supply for rain fed cultivation, Weather stations irrigation, storage in reservoirs for dry seasonal Rangpur > Dinajpur > Bogra > Ishurdi > Rajshahi using purpose, water resource management and planning, navigation, fresh water fish cultivation, From both the halves of time period, Rangpur has aquifer’s recharging, and maintenance other water obtained highest area of catchments area and proves related issues and projects. This study is a very that it is the biggest rainfall region of Rajshahi short but elementary work which will be helpful in Division. The study has been distinctly observed an future studies. The future studies should consider increasing trend of catchments boundaries for these changes in order to receive more accurate Rangpur, Dinajpur and Rajshahi and a decreasing solutions of existing and new water related projects. trend in Bogra and Ishurdi. Evaluating the rainfall contour lines, it has been found that the rainfall References annually varies from 1542.1 mm to 2235.8 mm in Rajshahi Division. The average number of rainy Islam, T. and Neelim, A. 2010. Climate Change in days in this region mostly varies from 86 to 112 Bangladesh, University Press Limited, Dhaka, days per year. 72-140. Sivasami, K. S. 2000. Droughts and Rainfall Pattern in India, 1877–1999. Published online in Wiley Inter science, (www.interscience.wiley.com).
BMD, (Bangladesh Meteorological Department) 2007. Dhaka, Bangladesh.
149