Drought Hazards
Modelling Drought Hazard, Vulnerability and Risk: A Case Study of Bangladesh
Shamsuddin Shahid Department of Geology University of Malaya 50603 Kuala Lumpur, Malaysia E‐mail: [email protected]
Bangladesh one of the most vulnerable countries of the world to natural disaster due to its: •Geographical position •high population density •high incidence of poverty •poor institutional capacity •inadequate financial resources ,and •insufficient infrastructure •wide variation of rainfall 12/07/2010
S.Shahid, UM
2
Climate of Bangladesh: Rainfall Bangladesh has a sub‐tropical humid climate characterized by wide seasonal variations in rainfall, moderately warm temperatures, and high humidity. •
Rainfall in Bangladesh varies from 1400 mm in the west to more than 4400 mm in the east.
•
The gradient of rainfall is almost 7 mm/km from west to east of the country.
•
More than 75% of rainfall in Bangladesh occurs during the monsoon (June to September)
•
Less than 3% rainfall occurs in dry winter (December to February) 3
Climate of Bangladesh: Temperature
12/07/2010
S.Shahid, UM
•
The average temperature of the country ranges from 19.20C in winter to 29.10C in summer.
•
In winter minimum temperature sometimes goes as low as 50C.
•
In Summer maximum temperature sometimes goes as high as 450C
•
Daily maximum temperature of Bangladesh exceeds 300C in more than 250 days 4 of a year.
12/07/2010
S.Shahid, UM
12/07/2010
S.Shahid, UM
6
12/07/2010
S.Shahid, UM
7
12/07/2010
S.Shahid, UM
8
12/07/2010
S.Shahid, UM
9
Objectives Droughts cannot be prevented. However, strategic preparedness can help to cope with droughts , which includes : ¾ A knowledge‐base about drought risk, and ¾ Contingency plans and response tactics
The objectives of the present study are to use the existing tools and method to model: ¾ ¾ ¾
12/07/2010
Characteristics of Drought Hazards People and property vulnerable to droughts Geographical distribution of drought risk to society
S.Shahid, UM
10
Some Points About Droughts ¾
There is no globally accepted definition of droughts.
¾
Droughts may occur in any climatic zones.
¾
Drought characteristics vary significantly from one region to another.
¾
Drought differs from other natural hazards in several ways. ‐ it is a slow onset, creeping phenomenon making its onset and end difficult to determine.
¾
Due to absence of universally accepted definition, drought often adds to the confusion about whether or not a drought exists.
¾
Drought affects more people than any other natural hazard.
¾
It is a recurring natural phenomenon and therefore, cannot be prevented.
12/07/2010
S.Shahid, UM
11
Methodology: Drought Hazard Characterization Numerous indices are there to model the severity of drought conditions: ¾Percentage of Normal Index, ¾Precipitation Deciles Index, ¾Bhalme–Mooley Drought Index, ¾Standardized Precipitation Index, ¾Effective Drought Index, etc. For better understanding of droughts, it is necessary to characterize: ¾Drought Duration, ¾Frequency of occurrence, and ¾Drought severity. Standardized Precipitation Index (SPI) (McKee et al. 1993) can be used for characterize droughts by their duration, frequency and severity and therefore, widely used for modeling of droughts. 12/07/2010
S.Shahid, UM
12
Methodology: Drought Vulnerability Vulnerability of population to droughts has been identified from various socio‐economic and physical/structural indicators: •Socio‐economic indicators: (a) population density (PD) (b) female to male ratio (FMR) (c) people living below poverty level (PL) (d) people depend on agriculture (AO) •Physical/structural indicators: (a) irrigated land (IL) (b) soil type (SWHC) (c) food production per unit area (FP)
12/07/2010
S.Shahid, UM
13
Methodology: Drought Risk Risk is computed as the product of hazard and vulnerability: Risk = Hazard × Vulnerability
Spatial Modeling Drought investigation over a large area requires assimilation of information from many sites, each with a unique geographic location. Geographical Information System (GIS) maintains the spatial location of sampling points, and provides tools to relate the sampling data through a relational database. GIS is used for the spatial modelling of droughts in western Bangladesh at various time‐scales.
12/07/2010
S.Shahid, UM
14
Data and Sources
12/07/2010
¾
Monthly rainfall data for the period of 1958–2007 from 18 rain‐gauge stations of Bangladesh Meteorological Department (BMD).
¾
Data of population density, percentage of people depending on agriculture, poverty, female to male ratio, irrigated land, and food production per land unit from Bangladesh Bureau of Statistics.
¾
Soil moisture holding capacity data from Soil Resources Development Institute of Bangladesh.
S.Shahid, UM
15
Results: Drought Hazards Frequency of occurrence of moderate and severe droughts at six‐ month time steps.
12/07/2010
S.Shahid, UM
16
Drought Hazards Frequency of occurrence of moderate and severe droughts at twelve‐month time steps.
12/07/2010
S.Shahid, UM
17
Aridity Maps of Bangladesh
12/07/2010
S.Shahid, UM
18
Drought Vulnerability • socio‐economic indicators: (a) population density (b) female to male ratio (c) people living below poverty level (d) people depend on agriculture
• Physical/structural indicators: (a) irrigated land (b) soil type (c) food production per unit area
12/07/2010
S.Shahid, UM
19
Spatial Pattern of Drought Risk Risk is computed as the product of hazard and vulnerability:
Risk = Hazard × Vulnerability The areas of highest hazard and risk correspond very well, in general, with the areas that are usually thought as drought prone and have records of high levels of agricultural damage due to droughts. Therefore, it can be assumed that the techniques used in the present study are appropriate for drought modeling of Bangladesh. 12/07/2010
S.Shahid, UM
20
Global Climate Change and Bangladesh ¾ Bangladesh has been ranked as most vulnerable country in the world to climatic change. ¾ Climate modelers forecast that as the world warm, the monsoon rains will concentrate into a shorter period. ¾ This will cause a cruel combination of more extreme floods and longer periods of droughts. ¾ Due to the land use changes within the country and in neighbouring country, concern among scientists has grown on frequent occurrence of droughts in Bangladesh. ¾ Upstream glaciers which are the sources of our rivers are melting fast. As a result, the supply of water may reduced. It may increase the drought risk in Bangladesh.
12/07/2010
S.Shahid, UM
21
Trends in Temperature and Related Extreme Events Mann‐Kendall trend test over fifty years (1958‐2007) of temperature data shows significant increase of daily mean temperature at a rate of 0.097°C/decade. Significant increases of hot days (1.3 days/decade) and heat wave frequency are also observed (1.1 events/decade).
12/07/2010
S.Shahid, UM
22
Projection of temperature in 21st Century
General Circulation Models (GCM) run with the IPCC B2 SRES scenario predict an average increase of temperature of 0.8°C in 2025, 1.4°C in 2050, 1.9°C in 2075, and 2.4°C in 2100.
12/07/2010
S.Shahid, UM
23
Increasing Rainfall and Related Extreme Events It has been observed that rainfall in Bangladesh has increased significantly at a rate of 5.25mm/year in last fifty years (1958‐2007). Significant increase of heavy rainfall days has also increased significantly at a rate of 1.2 days/decade.
12/07/2010
S.Shahid, UM
24
Trends in Rainfall and River Discharge The climatic models project an increase of rainfall during the summer monsoon by about 6% and decrease in the winter by about 3%. • Examining the stream flow from 1948‐2004, Dai et al. (2009) found that Ganges, the lifeline of Bangladesh is losing water because of climate change. Kundzewicz et al. (2009) also observed lowering of river discharge during low‐discharge season. •
12/07/2010
S.Shahid, UM
25
Causes of Droughts in Bangladesh
¾
There is no relation between rainfall amount and drought severity and frequency
¾
There is exist a significant relation between year‐to‐year variation of rainfall and frequency of occurrence of droughts
12/07/2010
S.Shahid, UM
26
ENSO and Year‐to‐Year Variation of Rainfall in Bangladesh
12/07/2010
S.Shahid, UM
27
Trend in ENSO
¾ ¾ ¾
Last several decades the number of El Niño events increased, and the number of La Niña events decreased. It is not clear whether this is a random fluctuation or the result of global climate changes towards global warming. The current results do not confidently tell us about the changes in Droughts.
12/07/2010
S.Shahid, UM
28
Conclusion ¾
The drought risk zone is concentrated in the northeast part of Bangladesh as the area coincides with higher frequency of droughts occurrence and most vulnerable population to droughts.
¾
Rainfall in Bangladesh has increase significantly is last fifty years, but it has no impacts on drought frequency and severity as there is no relation between rainfall amount and droughts in Bangladesh.
¾
Droughts in Bangladesh mainly depends on inter‐annual variability of rainfall which is directly related to ENSO index.
¾
As it is still not clear about the effect of climate change on ENSO, it is not possible to come to a decision about climate change impacts on droughts of Bangladesh.
12/07/2010
S.Shahid, UM
29
Thank you very much Special Thanks to: Asia-Pacific Association of Forest Research Institute (APAFRI)
Shamsuddin Shahid Department of Geology University of Malaya 50603 Kuala Lumpur, Malaysia E‐mail: [email protected]
Bangladesh one of the most vulnerable countries of the world to natural disaster due to its: •Geographical position •high population density •high incidence of poverty •poor institutional capacity •inadequate financial resources ,and •insufficient infrastructure •wide variation of rainfall 12/07/2010
S.Shahid, UM
2
Climate of Bangladesh: Rainfall Bangladesh has a sub‐tropical humid climate characterized by wide seasonal variations in rainfall, moderately warm temperatures, and high humidity. •
Rainfall in Bangladesh varies from 1400 mm in the west to more than 4400 mm in the east.
•
The gradient of rainfall is almost 7 mm/km from west to east of the country.
•
More than 75% of rainfall in Bangladesh occurs during the monsoon (June to September)
•
Less than 3% rainfall occurs in dry winter (December to February) 3
Climate of Bangladesh: Temperature
12/07/2010
S.Shahid, UM
•
The average temperature of the country ranges from 19.20C in winter to 29.10C in summer.
•
In winter minimum temperature sometimes goes as low as 50C.
•
In Summer maximum temperature sometimes goes as high as 450C
•
Daily maximum temperature of Bangladesh exceeds 300C in more than 250 days 4 of a year.
12/07/2010
S.Shahid, UM
12/07/2010
S.Shahid, UM
6
12/07/2010
S.Shahid, UM
7
12/07/2010
S.Shahid, UM
8
12/07/2010
S.Shahid, UM
9
Objectives Droughts cannot be prevented. However, strategic preparedness can help to cope with droughts , which includes : ¾ A knowledge‐base about drought risk, and ¾ Contingency plans and response tactics
The objectives of the present study are to use the existing tools and method to model: ¾ ¾ ¾
12/07/2010
Characteristics of Drought Hazards People and property vulnerable to droughts Geographical distribution of drought risk to society
S.Shahid, UM
10
Some Points About Droughts ¾
There is no globally accepted definition of droughts.
¾
Droughts may occur in any climatic zones.
¾
Drought characteristics vary significantly from one region to another.
¾
Drought differs from other natural hazards in several ways. ‐ it is a slow onset, creeping phenomenon making its onset and end difficult to determine.
¾
Due to absence of universally accepted definition, drought often adds to the confusion about whether or not a drought exists.
¾
Drought affects more people than any other natural hazard.
¾
It is a recurring natural phenomenon and therefore, cannot be prevented.
12/07/2010
S.Shahid, UM
11
Methodology: Drought Hazard Characterization Numerous indices are there to model the severity of drought conditions: ¾Percentage of Normal Index, ¾Precipitation Deciles Index, ¾Bhalme–Mooley Drought Index, ¾Standardized Precipitation Index, ¾Effective Drought Index, etc. For better understanding of droughts, it is necessary to characterize: ¾Drought Duration, ¾Frequency of occurrence, and ¾Drought severity. Standardized Precipitation Index (SPI) (McKee et al. 1993) can be used for characterize droughts by their duration, frequency and severity and therefore, widely used for modeling of droughts. 12/07/2010
S.Shahid, UM
12
Methodology: Drought Vulnerability Vulnerability of population to droughts has been identified from various socio‐economic and physical/structural indicators: •Socio‐economic indicators: (a) population density (PD) (b) female to male ratio (FMR) (c) people living below poverty level (PL) (d) people depend on agriculture (AO) •Physical/structural indicators: (a) irrigated land (IL) (b) soil type (SWHC) (c) food production per unit area (FP)
12/07/2010
S.Shahid, UM
13
Methodology: Drought Risk Risk is computed as the product of hazard and vulnerability: Risk = Hazard × Vulnerability
Spatial Modeling Drought investigation over a large area requires assimilation of information from many sites, each with a unique geographic location. Geographical Information System (GIS) maintains the spatial location of sampling points, and provides tools to relate the sampling data through a relational database. GIS is used for the spatial modelling of droughts in western Bangladesh at various time‐scales.
12/07/2010
S.Shahid, UM
14
Data and Sources
12/07/2010
¾
Monthly rainfall data for the period of 1958–2007 from 18 rain‐gauge stations of Bangladesh Meteorological Department (BMD).
¾
Data of population density, percentage of people depending on agriculture, poverty, female to male ratio, irrigated land, and food production per land unit from Bangladesh Bureau of Statistics.
¾
Soil moisture holding capacity data from Soil Resources Development Institute of Bangladesh.
S.Shahid, UM
15
Results: Drought Hazards Frequency of occurrence of moderate and severe droughts at six‐ month time steps.
12/07/2010
S.Shahid, UM
16
Drought Hazards Frequency of occurrence of moderate and severe droughts at twelve‐month time steps.
12/07/2010
S.Shahid, UM
17
Aridity Maps of Bangladesh
12/07/2010
S.Shahid, UM
18
Drought Vulnerability • socio‐economic indicators: (a) population density (b) female to male ratio (c) people living below poverty level (d) people depend on agriculture
• Physical/structural indicators: (a) irrigated land (b) soil type (c) food production per unit area
12/07/2010
S.Shahid, UM
19
Spatial Pattern of Drought Risk Risk is computed as the product of hazard and vulnerability:
Risk = Hazard × Vulnerability The areas of highest hazard and risk correspond very well, in general, with the areas that are usually thought as drought prone and have records of high levels of agricultural damage due to droughts. Therefore, it can be assumed that the techniques used in the present study are appropriate for drought modeling of Bangladesh. 12/07/2010
S.Shahid, UM
20
Global Climate Change and Bangladesh ¾ Bangladesh has been ranked as most vulnerable country in the world to climatic change. ¾ Climate modelers forecast that as the world warm, the monsoon rains will concentrate into a shorter period. ¾ This will cause a cruel combination of more extreme floods and longer periods of droughts. ¾ Due to the land use changes within the country and in neighbouring country, concern among scientists has grown on frequent occurrence of droughts in Bangladesh. ¾ Upstream glaciers which are the sources of our rivers are melting fast. As a result, the supply of water may reduced. It may increase the drought risk in Bangladesh.
12/07/2010
S.Shahid, UM
21
Trends in Temperature and Related Extreme Events Mann‐Kendall trend test over fifty years (1958‐2007) of temperature data shows significant increase of daily mean temperature at a rate of 0.097°C/decade. Significant increases of hot days (1.3 days/decade) and heat wave frequency are also observed (1.1 events/decade).
12/07/2010
S.Shahid, UM
22
Projection of temperature in 21st Century
General Circulation Models (GCM) run with the IPCC B2 SRES scenario predict an average increase of temperature of 0.8°C in 2025, 1.4°C in 2050, 1.9°C in 2075, and 2.4°C in 2100.
12/07/2010
S.Shahid, UM
23
Increasing Rainfall and Related Extreme Events It has been observed that rainfall in Bangladesh has increased significantly at a rate of 5.25mm/year in last fifty years (1958‐2007). Significant increase of heavy rainfall days has also increased significantly at a rate of 1.2 days/decade.
12/07/2010
S.Shahid, UM
24
Trends in Rainfall and River Discharge The climatic models project an increase of rainfall during the summer monsoon by about 6% and decrease in the winter by about 3%. • Examining the stream flow from 1948‐2004, Dai et al. (2009) found that Ganges, the lifeline of Bangladesh is losing water because of climate change. Kundzewicz et al. (2009) also observed lowering of river discharge during low‐discharge season. •
12/07/2010
S.Shahid, UM
25
Causes of Droughts in Bangladesh
¾
There is no relation between rainfall amount and drought severity and frequency
¾
There is exist a significant relation between year‐to‐year variation of rainfall and frequency of occurrence of droughts
12/07/2010
S.Shahid, UM
26
ENSO and Year‐to‐Year Variation of Rainfall in Bangladesh
12/07/2010
S.Shahid, UM
27
Trend in ENSO
¾ ¾ ¾
Last several decades the number of El Niño events increased, and the number of La Niña events decreased. It is not clear whether this is a random fluctuation or the result of global climate changes towards global warming. The current results do not confidently tell us about the changes in Droughts.
12/07/2010
S.Shahid, UM
28
Conclusion ¾
The drought risk zone is concentrated in the northeast part of Bangladesh as the area coincides with higher frequency of droughts occurrence and most vulnerable population to droughts.
¾
Rainfall in Bangladesh has increase significantly is last fifty years, but it has no impacts on drought frequency and severity as there is no relation between rainfall amount and droughts in Bangladesh.
¾
Droughts in Bangladesh mainly depends on inter‐annual variability of rainfall which is directly related to ENSO index.
¾
As it is still not clear about the effect of climate change on ENSO, it is not possible to come to a decision about climate change impacts on droughts of Bangladesh.
12/07/2010
S.Shahid, UM
29
Thank you very much Special Thanks to: Asia-Pacific Association of Forest Research Institute (APAFRI)
