IMPLICATIONS OF CHANGING RAINFALL PATTERN ON BUILDING LOSS IN CALABAR

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IMPLICATIONS OF CHANGING RAINFALL PATTERN ON BUILDING LOSS IN CALABAR

1AFANGIDEH, A.I;

1EKPE, I.A & *

1 OFFIONG, R.A

1Dept. of Geography & Environmental Science University of Calabar, Nigeria

*E-mail of corresponding author: [email protected]

ABSTRACT

The study examined the implication of changing rainfall pattern on building loss in Calabar. Rainfall data for the study were collected from the Nigerian Meteorological Agency (NIMET), Margaret Ekpo

International Airport, Calabar. While data on cost of building loss to flood for the past 20 years was

gotten from the inhabitants of the flood prone areas in Calabar. Statistical techniques such as mean, standard deviation, standardized anomaly, coefficient of variation (CV) and Time Series Charts with

Trend line analysis (smoothen with 5-years running mean) were used to depict the temporal variation of

rainfall in Calabar. Furthermore, multiple regression statistics was used to test for the impact of rainfall on

building loss in the area. From the results, years 1995, 1996, 1997, 2001, 2004, 2007, 2010 and 2011 are years with above average rainfall with 1995 and 2011 showing the highest positive deviation from the

normal with coefficient of variation values 26% and 37% respectively. While 1993, 2005, 2006 and 2009

are years with rainfall below normal with 1993 and 2006 showing the highest negative deviation from the normal with coefficient of variation values of 14% and 17% respectively. From the standardized

coefficient, the results showed that annual rainfall intensity with beta coefficient of 0.437 has more

implication on cost of building loss to rainfall in Calabar than annual rainfall duration, with beta

coefficient of -0.063. Town planning and environmental laws therefore need to be enforced by the government so as to regulate building development and reduce the cost of managing flood disaster in the

area.

Keywords: Changing rainfall patterns, Time series analysis, Building loss, Calabar

INTRODUCTION

The Earth's climate is dynamic and varies on seasonal, decadal, centennial, and longer timescales. Each "up and down" fluctuation can lead to conditions which are warmer or colder, wetter or drier, more

stormy or quiescent. These changes in climate are generally known as climate change. Climate change

describes changes in the variability or average state of the atmosphere over time scales which may range

from decades to millions of years (Adejuwon, 2004). It may be caused by natural processes or anthropogenic factors, especially human activities that load the atmosphere with carbon and other

greenhouse gases (Ekpoh, 2007).

Apart from global increase in temperature (global warming), some of the current and projected manifestation of climate change include: a rise in sea level, shifting of global climate zones, melting of

polar ice, increased incidence and severity of extreme events, changes in the quality, duration and pattern

of rainfall leading to increased drought, desertification and flooding. It can also result in a significant loss of food security, natural disasters, vanishing coastlines, human displacement, natural resource depletion,

scarcity of safe drinking water, animal migration, pests management challenge, diseases and other health

problems, loss of cultural practices and traditional ways of life, economic losses and energy crises, among

others (IPPC, 2001a; Hulme, 2001, and IPPC, 2007). In Calabar, the changing pattern of rainfall is noticeable in the form of rainfall variability, which results in

unpredictable changes in the frequency and intensity of extreme weather events such as floods and

International Journal of Innovative Environmental Studies Research 1 (2):10-18,September 2013

© SEAHI PUBLICATIONS, 2013 www.seahipub.org

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erosion. While the number of geophysical disasters has remained fairly steady, the number of hydro-

meteorological disasters since 1996 has more than doubled. During the past decade over 90 percent of

those affected by natural disasters are linked to hydro-meteorological event such as flood (Paredes et al. 2006). The recent floods in the study area have highlighted how important it is to analyze the trends in the

rainfall regime of this area. This is because of its effects on the city’s population, environment and socio-

economic activities. Increasing flood risk is now being recognized as the most important sectorial threat from climate change in most parts of the world. This has prompted public debate on the apparent

increased frequency of extreme, and in particular, on perceived increases in rainfall intensities.

Several studies have adduced extreme rainfall to be the major cause of flood in Nigeria. Such studies includes Gobo (1988), McEwen (1989), Oriola (1994), Babatolu (1996); Fowler and Kilsby (2003),

Odekunle (2001), and Ologunorisa (2001, 2004). Other studies have identified the characteristics of

extreme rainfall that are associated with flood frequency to include duration, intensity, frequency,

seasonality, variability, trend and fluctuation (Olaniran, 1983; Ologunorisa, 2001; Ologunorisa and Diagi, 2005).

Adefolalu et. al. (2001) summed the impact of the 1999 flooding thus: ‘There were at least 56 deaths;

over N12 billion ha of farmlands washed away resulting in estimated farm produce loss of 100 million tons. Infrastructural facilities (houses, schools, roads, etc.) destroyed will cost over N50 billion to

rehabilitate or replace. Conversely, flood disasters as a result of heavy rainfall were recorded in 2001,

2002, 2003, 2005 and 2006 in Kafanchan. The floods of September, 2005 alone resulted in major disasters: the washing away of farmlands, disruption of socio-economic activities, displacement of

people, and damage of residences and infrastructure worth millions of naira (Abaje et. al, 2010).

This study therefore seeks to assess the implications of changing pattern of rainfall on building loss in

Calabar.

MATERIALS AND METHOD

Study Area Calabar is the capital of Cross River State. It is located at the Southern part of Cross River State as seen in

Fig.1, Calabar is located between longitudes 8017’00’’E and 8

020’00’’E latitudes 4

050’00’’N and

5010’00’’N. Calabar metropolis comprises of Calabar Municipality and Calabar South Local Government

Areas and covers an area of about 1,480 Sq km. As depicted in Fig.1 Calabar is sandwiched between the Great Kwa River to the East and the Calabar River to the West. The presence of urban area is on the

eastern bank of the Calabar River; its growth to the south is hindered by the mangrove swamps.

Calabar falls within tropical equatorial (Af) climate with high temperature, high relative humidity and abundant annual rainfall (Oguntoyimbo, 1978; Inyang, 1980). Two major air masses affect the climate of

Calabar as well as other contiguous locations in the West African region. The Tropical Maritime (mT)

and the tropical continental (cT) air masses affect the climate in two distinct seasons. mT air prevails and influences its moisture characteristic while the cT air influences the dry season condition due to is desert

source across the two air masses at the upper troposphere from east to west. This is called the Equatorial

Esterlies (EE). The two air masses meet at the pressure front called Inter Tropical discontinuity (ITD)

(Oguntoyimbo, 1978). There have been a massive development and urban expansion in the area over the last 10 years. This

development is not without repercussions on the natural environment as lands that were formally

vegetated, used for agriculture and as habitat for biodiversity are now being used for residential, commercial and industrial purposes to accommodate the growing population and businesses. The loss of

once vegetated land implies a corresponding alteration of the micro-climate of the area which in turn has

great impact on the long term climatic averages of the area.

Afangideh, , Ekpe & Offiong.. Int. J. Innovative Environ. Studies Res. 1 (2):10-18, 2013

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Types of Data and Source

The data required for this work was annual rainfall values over Calabar for the months January to

December from 1992 to 2011. Annual rainfall data for the period of 20 years (1992-2011) and annual rainfall duration data in days for the period 20 years (1992-2011) were obtained from the Nigerian

Meteorological Agency (NIMET), Margaret Ekpo International Airport, Calabar respectively. These data

were obtained mainly through secondary sources from the records section of the Nigerian Meteorological Agency, Margaret Ekpo International Airport, Calabar. Data on areas highly prone to flooding and

number of registered structures within the flood prone areas before 1992 were obtained from Ministry of

Environment and Town planning unit of Ministry of Lands and Survey, Calabar respectively. Data on rainfall intensity for the period of 20 years (1992-2011) were derived from the annual rainfall

data using a synthetic approach with the formula;

Rainfall intensity (mm) = annual rainfall amount (mm)

annual rainfall duration (days) Available data on cost of buildings (in naira) affected by flood disaster in the area for the past 20 years

(1992-2011) were obtained from the Cross River State Emergency Management Agency (SEMA),

Calabar, and synergized with the data collected from the primary source.

Techniques and Procedure

The purposive and random sampling techniques were used for data collection. Accordingly, since the

required rainfall data for this study can only be obtained from a known source (i.e. Nigerian Meteorological Agency (NIMET), Margaret Ekpo International Airport, Calabar). The purposive

sampling technique therefore becomes the best fit for the acquisition of such data. Furthermore, purposive

sampling technique was adopted in selecting sample residential units within the flood prone areas that

have suffered from flood incidence for the past 20 years. Here, family heads who have resided within the flood prone areas for a period of 21 years (before 1992) and above were purposively sampled. The flood

prone areas highlighted include Edim otop, Ekpo Abasi, Ndidem Usang Iso, Goldie by Target, Ebito, Big

Qua, Edibe Edibe, Atamunu, Akim Market Road, Otop Abasi and Ikot Eyo by Paliamentary Road. The random sampling technique on the other hand was applied in process of questionnaire administration to

the sampled respondents. This was done to enable the researcher source for information on the cost of

buildings affected by flood incidence in the area for the past 20 years. These were derived from a

structured questionnaire, semi-structured interview and available data from SEMA.

Data analysis

Statistical and graphical tools in Microsoft Office Excel were primarily employed in the analysis and

presentation of this study. These consist of the following: (a)Time series with trend lines analysis of the annual rainfall values to illustrate the trend pattern in

rainfall behavior.

(b) Standardized anomaly chart. ( c) Descriptive statistical analysis

(d) (i) Mean (x ) = (

)

Where; x = the variable

N = the number of years

(ii) Standard Deviation, S = √ ( ̅)

Where; x = the variable

x = the mean

N = the number of years

(e) Deviation scores X = x- x (f) Coefficient of variation (CV)


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(g) Similarly, data on the impact of the rainfall regime on building infrastructure in Calabar for the period

1992-2011 were presented and analyzed using tables and frequencies.

(h) On the other hand, the multiple regression analysis was used to examine the impact of rainfall on buildings in the area for the period 1992-2011.

RESULTS AND DISCUSSION

Changing Annual Rainfall Amount in Calabar:

The analysis of changing annual rainfall in Calabar for the period 1992 to 2011 (20-years) is presented in

Table 1, below. The table shows the annual rainfall amount, standard deviation, standardized anomalies

and coefficient of variation for rainfall in the area.

From the table, in terms of actual annual rainfall totals, the wettest years in the period of record were

1995 (3749.70mm), 1996 (3215.60mm), 1997 (3492.40mm), 1999 (3004.40mm), 2001 (3202.00mm),

2004 (3094.00mm), 2007 (3428.20), 2010 (3071.70mm) and 2011 (4002.80mm). On the other hand, the

driest years were 1993 (2511.30mm), 2006 (2492.10mm), and 2009 (2527.10mm).

Table 1: Annual rainfall amount, standard deviation, standardized anomalies and coefficient of

variation of rainfall in Calabar for the period 1992 – 2011.

S/N Year Annual Rainfall

Amount (mm)

(X)

Standard

Deviation

Standardized

Anomalies

Coefficient of

Variation (CV)

11 1992 2896.40 -5.29 -0.12 1% *

12 1993 2511.30 -43.8 -0.97 14% *

13 1994 2904.60 -4.47 -0.10 1% *

14 1995 3749.70 80.04 1.77 26% **

15 1996 3215.60 26.63 0.59 8% **

16 1997 3492.40 54.31 1.20 17% **

17 1998 2811.50 -13.78 -0.31 4% *

18 1999 3040.40 5.51 0.12 3% **

19 2000 2807.20 -14.21 -0.32 4% *

20 2001 3202.00 25.27 0.56 8% **

21 2002 2813.20 -13.61 -0.30 4% *

22 2003 2807.40 -14.19 -0.31 4.5% *

23 2004 3094.00 14.47 0.32 5% **

24 2005 2707.70 -24.16 -0.54 9% *

25 2006 2492.10 -45.72 -1.01 17% *

26 2007 3428.20 47.89 1.06 17% **

27 2008 2886.80 -6.25 -0.14 1% *

28 2009 2527.10 -42.22 -0.94 13% *

29 2010 3071.70 12.24 0.27 4% **

30 2011 4002.80 105.35 2.33 37% **

∑ 60426.1

x 3021.31 Coefficient of Variation: (Above Long term mean = **) (Below Long term mean = *)

Source: Author’s Analysis (2013)


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Furthermore, in Figure 1, annual total rainfall for Calabar was standardized and these standardized rainfall

deviations were averaged for the period (1992-2011). From the results, years 1995, 1996, 1997, 2001, 2004, 2007, 2010 and 2011 are years with above average rainfall with 1995 and 2011 showing the highest

positive deviation from the normal with coefficient of variation values 26% and 37% respectively. While

1993, 2005, 2006 and 2009 are years with rainfall below normal with 1993 and 2006 showing the highest negative deviation from the normal with coefficient of variation values of 14% and 17% respectively.

Fig. 1: Standardized rainfall anomalies of Calabar for the period 1992-2011

Trend of Annual Rainfall in Calabar:

Figure 2, shows the inter-annual rainfall change over Calabar for the years under consideration, the trend

suggests a general increase in rainfall values in recent times. Rainfall values for the years under consideration suggest values between 2492.10 and 4002.80mm. The inter-annual variability suggests an

upward trend in the pattern when a trend line was fitted. When a 5 year running mean was put through the

annual total rainfall series (figure 3), fluctuations involving increasing trend were most prominent in the

periods 1996 – 2001 and 2006 – 2011. A fluctuation involving decreasing rainfall trend was only prominent in the period 2001 – 2006. The trend analysis however shows that the 20 years period (1992-

2011) of rainfall in Calabar was characterized by an increasing rainfall and accompanied flooding in

recent time, an indication that the climate of Calabar is becoming wetter.

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

Standardized Anomalies

Standardized Anomalies


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Figure 2: Trend in annual rainfall for Calabar from 1992-2011

Figure 3: Trend in annual rainfall for Calabar smoothen with 5-years running mean

Implications of Changing Rainfall Pattern on Buildings loss in Calabar:

Table 2, below shows the cost of building lost to flooding annually in Calabar for the past 20

years. From the table, it is revealed that in 1993 with rainfall amount 2511.30 mm, rainfall

duration and intensity values of 174 and 14.43 respectively, total cost of building lost to flooding

stood at less than 1 million Nigerian naira. Whereas in 1994, with a rainfall amount 2904.60mm,

0

500

1000

1500

2000

2500

3000

3500

4000

4500

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

Mean value

Annual Rainfall

0

500

1000

1500

2000

2500

3000

3500

4000

4500

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

Annual Rainfall

5-year Running Mean


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rainfall duration and intensity values of 185 and 16.69 respectively, between 1 million to 10

million naira worth of buildings were being lost to flooding in the area. In the same vein, the

years 2007, 2008, 2009, 2010 and 2011 are years with cost of buildings between 20 million to 30

million naira being lost annually to flood in the area. The regression results revealed that given a

unit increase in rainfall duration while holding the effect of rainfall constant, cost of building loss

Table 2: Cost of Buildings Loss to Rainfall in Calabar for The Period 1992-2011 (20 Years).

S/N

Year

Annual Rainfall

Amount

(MM)

Rainfall

Duration

(Days)

Rainfall Intensity

(MM)

Cost of Building Lost

to Flood (Naira)

1

1992 2896.40 181

16.00 Less than

N1,000,000

2

1993 2511.30 174

14.43 Less than

N1,000,000

3

1994 2904.60 185

16.69 N1,000000 –

N10,000000

4 1995 3749.70 194

19.33 N10,100000 – N20,000000

5

1996 3215.60 195

16.49 N10,100000 –

N20,000000

6

1997 3492.40 188

18.58 N10,100000 –

N20,000000

7

1998 2811.50 186

15.12 N1,000000 –

N10,000000

8

1999 3004.40 199

15.10 Less than

N1,000,000

9

2000 2807.20 182

15.42 N1,000000 –

N10,000000

10

2001 3202.00 188

17.03 N1,000000 –

N10,000000

11

2002 2813.20 189

14.88 Less than

N1,000,000

12

2003 2807.40 178

15.77 Less than

N1,000,000

13

2004 3094.00 176

17.58 N20,000000 –

N30,000000

14

2005 2707.70 186

14.56 N1,000000 –

N10,000000

15

2006 2492.10 191

13.05 N1,000000 –

N10,000000

16

2007 3428.20 206

16.64 N30,000,000 and

above

17

2008 2886.80 168

17.18 N20,000000 –

N30,000000

18

2009 2527.10 176

14.36 N30,000,000 and

above

19

2010 3071.70 188

16.34 N20,000000 –

N30,000000

20

2011 4002.80 195

20.53 N30,000,000 and

above

Source: Author’s Field Report (2013)


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to rainfall will decrease by -76250.604 units. Also if the effect of rainfall duration is held

constant, there is a unit increase in rainfall intensity, cost of building loss to rainfall will increase

by 2690531.024 units. From the standardized coefficient, it can be concluded that annual rainfall

intensity with beta coefficient of 0.437, has more implication on cost of buildings loss to rainfall

in Calabar than annual rainfall duration, with beta coefficient of -0.063. This confirms earlier

findings by (Olaniran, 1983; Ologunorisa, 2001; Ologunorisa and Diagi, 2005).

CONCLUSION/RECOMMENDATIONS

The study results reflect a changing pattern of rainfall in Calabar. From the results, years 1995, 1996,

1997, 2001, 2004, 2007, 2010 and 2011 are years with above average rainfall with 1995 and 2011 showing the highest positive deviation from the normal. While 1993, 2005, 2006 and 2009 are years with

rainfall below normal with 1993 and 2006 showing the highest negative deviation from the normal. The

results also showed that the climate of the area is becoming wetter with an increasing trend. However, this has not been without impact on the socio-economic wellbeing of the inhabitants of Calabar, as building

worth millions of naira have loss to flood over the past 20 years. The government therefore needs to

ensure that the inhabitants of the area help to prevent flood by enforcing town planning and environmental laws when building houses.

REFERENCES Abaje, I.B., S, Ishaya and S.U. Usman (2010), An Analysis of Rainfall Trends in Kafanchan, Kaduna

State, Nigeria. Research Journal of Environmental and Earth Sciences 2(2): 89-96, 2010.

Adefolalu D.O. et. al. (2001), Climate Change and Natural Disasters During the 1999 Rainy Season.FUT

– NUC/U BR Res. Pub. 88 pp. Adejuwon, S.A ., (2004). Impacts of Climate Variability and Climate Change on Crop Yield in Nigeria.

Being the Lead Paper Presented at the Stake holders ’ Workshop on Assessment of

Impacts and Adaptation to Climate Change (A IAC C), Conference Centre Obafemi Awolowo University, Ile-Ife, Sept, 20-21. Retrieved from: http://www.lead-

awa.org/docs/Ife%20September%202004%20Paper-ADEJUWON .doc. (Accessed date:

May 16, 2009 ). Babatola, J. S. (1996). Recent Changes in Rainfall Patterns and its Implication for Flood Occurrence in

Ondo, Nigeria. Ondo Journal of Arts and Social Sciences, 1 (1), pp. 125 – 136.

Ekpoh, I. J. (2007). Climate and Society in Northern Nigeria: Rainfall variability and farming. The

InternationalJournal Series on Tropical issues, 8(3), 157-162. Fowler, H J; Kilsby, C.G. (2003) Implications of Changes in Seasonal and Annual Extreme Rainfall.

Geophysical Research Letters, 30 (13), pp. 17 – 20.

Gobo, A. E (1988). Relationship Between Rainfall Trends and Flooding in the Niger – Benue River Basin. The Journal of Meteorology,Vol. 13, No. 132, pp. 318 – 324.

Hulme, M. (2001). Climate perspectives on Sahelian desiccation; 1973-1998. Global Environmental

Change, 11,19-29. doi:10.1016/S0959-3780(00)00042-X, http://dx.doi.org/10.1016/S0959-3780(00)00042-X

Inyang, P. E. B. (1980). Pollution: a factor in the climate of Calabar and environs: geographic studies

published by department of geography, university of calabar for the 23rd

Nigerian

Geographic Association Conference, Calabar, 16th

-21st March, 1980.

IPCC. (2001). Climate Change: Impacts, Vulnerability and Adaptation. Working group II, WMO, Geneva

IPPC. (2007). Climate Change 2007: Fourth Assessment Report (AR4).

McEwen, L. J (1989). Extreme Rainfall and its Implication for Flood Frequency: A Case Study of Makurdi.


http://www.lead-awa.org/docs/

http://www.lead-awa.org/docs/

http://dx.doi.org/10.1016/S0959-3780(00)00042-X

18

Odekunle, T. O. (2001). The magnitude – Frequency Characteristic of Rainfall in Ondo, Southwestern

Nigeria. Ife Research Publications in Geography, Vol. 8, pp. 36 – 41.

Oguntoyimbo, J. S. (1978). Climatology of west Africa. New jersey Library of congress cataloguing in publication data.

Olaniran, O . J. (1983). Flood generating mechanisms at Ilorin, Nigeria GeoJournal. 7(3) 271 – 277

Ologunorisa, E .T (2004). Rainfall Flood Prediction in the Niger Delta, Nigeria (Abstract), International Conference in Hydrology: Science and Practice for the 21st Century, London, U.K.

Ologunorisa, E T; Diagi, P N (2005). Extreme Rainfall and its Implication for Flood Frequency in the

Western Niger Delta A Case Study of Warri. Nigerian Journal of Tropical Geography Vol. 1.

Ologunorisa, E.T (2001). An Assessment of Flood Risk in the Niger Delta, Nigeria. Unpublished Ph.D

Thesis Department of Geography and Environmental Management, University of Port

Harcourt, Port Harcourt, 303 pp. Oriola, E O (1994). Strategies for Combating Urban Flooding in a Developing Nation: A Case Study of

Ondo, Niger. The Environmentalist Vol. 14, pp. 57 – 62.

Paredes D, Trigo RM, Garcia-Herrera R. and Franco-Trigo I (2006) Understanding precipitation changes in Iberia in early spring: weather typing and storm-tracking approaches. Journal of

Hydrometeorology 7:101–113.


IMPLICATIONS OF CHANGING RAINFALL PATTERN ON BUILDING LOSS IN CALABAR

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