Trend Analysis of the Mean Annual Temperature in Rwanda during the Last Fifty Two Years

Bonfils Safari

Department of Physics, National University of Rwanda, Butare, Rwanda.

DOI: 10.4236/jep.2012.36065                

Abstract

Climate change and global warming are widely recognized as the most significant environmental dilemma the world is experiencing today. Recent studies have shown that the Earth’s surface air temperature has increased by 0.6°C - 0.8°C during the 20^th century, along with changes in the hydrological cycle. This has alerted the international community and brought great interest to climate scientists leading to several studies on climate trend detection at various scales. This paper examines the long-term modification of the near surface air temperature in Rwanda. Time series of near surface air temperature data for the period ranging from 1958 to 2010 for five weather observatories were collected from the Rwanda National Meteorological Service. Variations and trends of annual mean temperature time series were examined. The cumulative sum charts (CUSUM) and bootstrapping and the sequential version of the Mann Kendall Rank Statistic were used for the detection of abrupt changes. Regression analysis was performed for the trends and the Mann-Kendall Rank Statistic Test was used for the examination of their significance. Statistically significant abrupt changes and trends have been detected. The major change point in the annual mean temperature occurred around 1977-1979. The analysis of the annual mean temperature showed for all observatories a not very significant cooling trend during the period ranging from 1958 to 1977-1979 while a significant warming trend was furthermore observed for the period after the 1977-1979 where Kigali, the Capital of Rwanda, presented the highest values of the slope (0.0455/year) with high value of coefficient of determination (R² = 0.6798), the Kendall’s tau statistic (M-K = 0.62), the Kendall Score (S = 328) with a two-sided p-value far less than the confidence level α of 5%). This is most likely explained by the growing population and increasing urbanization and industrialization the country has experienced, especially the Capital City Kigali, during the last decades.

Keywords

Climate Change; Global Warming; Trend Detection; Mann-Kendall Rank Statistic Test; CUSUM and Bootstrapping; Temperature; Rwanda

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	IPCC, “Climate Change 2007: Synthesis Report,” In: R. K. Pachauri and A. Reisinger, Eds., Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), Cambridge University Press, Cambridge, 2007.
[2]	IPCC, “Climate Change 2007: The Physical Science Basis,” In: S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller, Eds., Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), Cambridge University Press, Cambridge, 2007.
[3]	IPCC, “Climate Change 2007: Impacts, Adaptation and Vulnerability,” In: M. L. Parry, O. F. Canziani, J. P. Palutikof, P. J. van der Linden and C. E. Hanson, Eds., Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), Cambridge University Press, Cambridge, 2007.
[4]	IPCC, “Climate Change 2007: Mitigation of Climate Change,” In: B. Metz, O. R. Davidson, P. R. Bosch, R. Dave and L. A. Meyer, Eds., Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), Cambridge University Press, Cambridge, 2007.
[5]	R. Joeri, H. William, H. L. Jason, D. P. van Vuuren, R. Keywan, B. Matthews, H. Tatsuya, J. Kejun and M. Malte, “Emission Pathways Consistent with a 2?C Global Temperature Limit,” Nature Climate Change, Vol. 1, No. 1, 2011, pp. 413-418. doi:10.1038/nclimate1258
[6]	R. W. Spencer, “The Discovery of Global Warming,” American Institute of Physics, Harvard University Press, 2008. http://www.aip.org/history/climate/co2.htm
[7]	Joint Science Academies’ Statement: Global Response to Climate Change, 2005. http://nationalacademies.org/onpi/06072005.pdf
[8]	D. E. Parker and L. V. Alexander, “Global and Regional Climate in 2001,” Weather, Vol. 57, No. 9, 2002, pp. 328-340. doi:10.1256/00431650260283505
[9]	P. Brohan, J. J. Kennedy, I. Harris, S. F. B. Tett and P. D. Jones, “Uncertainty Estimates in Regional and Global Observed Temperature Changes: A New Dataset from 1850,” Journal of Geophysical Research, Vol. 111, 2006. D12106. doi:10.1029/2005JD006548
[10]	P. D. Jones and A. Moberg, “Hemispheric and LargeScale Surface Air Temperature Variations: An Extensive Revision and Update to 2001,” Journal of Climate, Vol. 16, 2003, pp. 206-223. doi:10.1175/1520-0442(2003)016<0206:HALSSA>2.0.CO;2
[11]	W. Soon, S. Baliunas, E. S. Posmentier and P. Okeke, “Variations of Solar Coronal Hole Area and Terrestrial Lower Tropospheric Air Temperature from 1979 to Mid-1998: Astronomical Forcing of Change in Earth’s Climate,” New Astron, Vol. 4, No. 8, 2000, pp. 563-579. doi:10.1016/S1384-1076(00)00002-6
[12]	T. Landscheidt, “Solar Wind near Earth: Indicator of Variations in Global Temperature,” Proceedings of the 1st Solar and Space Weather Euroconference on the So-lar Cycle and Terrestrial Climate, Tenerife, 2000, pp. 497-500.
[13]	K. Y. Vinnikov and N. C. Grody, “Global Warming Trend of Mean Troposphere Temperature Observed by Satellites,” Science, Vol. 302, No. 5643, 2003, pp. 269-272. doi:10.1126/science.1087910
[14]	P. D. Jones, D. E. Parker, T. J. Osborn and K. R. Briffa, “Global and Hemispheric Temperature Anomalies-Land and Marine Instrumental Records,” Trends: A Compendium of Data on Global Change, 2011. http://cdiac.ornl.gov/trends/temp/jonescru/jones.html
[15]	S. Christoph Sch?r, L. V. Pier, L. Daniel, F. Christoph, H. Christian, A. L. Mark and A. Christof, “The Role of Increasing Temperature Variability in European Summer Heatwaves,” Nature, Vol. 427, 2004, pp. 332-336. doi:10.1038/nature02300
[16]	N. W. Arnell, “The Effect of Climate Change on Hydrological Regimes in Europe: A Continental Per-Spective,” Global Environmental Change, Vol. 9, No. 1, 1999, pp. 5-23. doi:10.1016/S0959-3780(98)00015-6
[17]	A. M. Aesawy and H. M. Hasanean, “Annual and Seasonal Climatic Analysis of Surface Air Temperature Variations at Six Southern Mediterranean Observatories,” Theoretical and Applied Climatology, Vol. 61, 1998, pp. 55-68. doi:10.1007/s007040050051
[18]	K. Mikdat, “Trends in Surface Air Temperature Data over Turkey,” International Journal of Climatology, Vol. 17, 1997, pp. 511-520. doi:doi:10.1002/(SICI)1097-0088(199704)17:5<511::AID-JOC130>3.0.CO;2-0
[19]	R. W. Hinggis, A. Leetmaa and V. E. Kousky, “Relationships between Climate Variability and Winter Temperature Extreme in the United States,” Journal of Climate, Vol. 15, 2002, pp. 1555-1572. doi:10.1175/1520-0442(2002)015<1555:RBCVAW>2.0.CO;2
[20]	D. R. Easterling, H. F. Diaz, A. V. Douglas, W. D. Hogg, K. E. Kunkel, J. C. Rogers and J. F. Wilkinson, “LongTerm Observations for Monitoring Extremes in the Americas,” Climatic Change, Vol. 42, 1999, pp. 285-308. doi:10.1023/A:1005484820026
[21]	D. P. Lettenmaier, E. F. Wood and J. R. Wallis, “HydroClimatological Trends in the Continental United States 1948-1988,” Journal of Climate, Vol. 7, 1994, pp. 586-607. doi:10.1175/1520-0442(1994)007<0586:HCTITC>2.0.CO;2
[22]	M. S. Mahmoud Smadi and Z. Ahmed, “A Sudden Change in Rainfall Characteristics in Amman, Jordan during the Mid 1950s,” American Journal of Environmental Sciences, Vol. 2, No. 3, 2006, pp. 84-91. doi:10.3844/ajessp.2006.84.91
[23]	S. Al-Fahed, O. Al-Hawaj and W. Chakroun, “The Recent Air Temperature Rise in Kuwait,” Renewable Energy, Vol. 12, No. 1, 1997, pp. 83-90. doi:10.1016/S0960-1481(97)00015-3
[24]	N. A. Elagib and A. S. Abdu, “Climate Variability and Aridity in Bahrain,” Journal of Arid Environmental, Vol. 36, No. 3, 1997, pp. 405-419. doi:10.1006/jare.1996.0237
[25]	K. Mikdat and S. Levent, “Trends of Growing DegreeDays in Turkey,” Water, Air and Soil Pollution, Vol. 126, No. 1-2, 2000, pp. 83-96. doi:10.1023/A:1005299619084
[26]	N. I. Obot, M. A. C. Chendo, S. O. Udo and I. O. Ewona, “Evaluation of Rainfall Trends in Nigeria for 30 Years (1978-2007),” International Journal of the Physical Sciences, Vol. 5, No. 14, 2010, pp. 2217-2222.
[27]	E. Aguilar, et al., “Changes in Temperature and Precipitation Extremes in Western Central Africa, Guinea Conakry, and Zimbabwe, 1955-2006,” Journal of Geophysical Research, Vol. 11, 2009, D02115. doi:10.1029/2008JD011010
[28]	Paeth, Heiko, B. Kai Born, G. Robin, P. Ralf, J. Daniela, “Regional Climate Change in Tropical and Northern Africa Due to Greenhouse Forcing and Land Use Changes,” Journal of Climate, Vol. 22, 2009, pp. 114-132. doi:10.1175/2008JCLI2390.1
[29]	M. New, et al., “Evidence of Trends in Daily Climate Extremes over Southern and West Africa,” Journal of Geophysical Research, Vol. 11, 2006, pp. 1-11. doi:10.1029/2005JD006289
[30]	A. C. Kruger, “Observed Trends in Daily Precipitations Indices in South Africa: 1919-2004,” International Journal of Climatology, Vol. 26, 2006, pp. 2275-2285. doi:10.1002/joc.1368
[31]	S. E. Nicholson, “Climatic and Environmental Change in Africa during the Last Two Centuries,” Climate Research, Vol. 17, 2001, pp. 123-144. doi:10.3354/cr017123
[32]	M. R. Hulme, T. Doherty Ngara and D. Lister, “African Climate Change: 1900-2100,” Climate Research, Vol. 17, 2001, pp. 145-168. doi:10.3354/cr017145
[33]	S. E. Nicholson, “The Nature of Rainfall Variability over Africa on Time Scales of Decades to Millennia,” Global and Planetary Change, Vol. 26, 2000, pp. 137-158. doi:10.1016/S0921-8181(00)00040-0
[34]	S. M. King’uyu, L. A. Ogallo and E. K. Anyamba, “Recent Trends on Minimum and Maximum Surface Temperatures over Eastern Africa,” Journal of Climate, Vol. 13, No. 13, 2000, pp. 2876-2886. doi:10.1175/1520-0442(2000)013<2876:RTOMAM>2.0.CO;2
[35]	J. M. Collins, “Temperature Variability over Africa,” Journal of Climate, Vol. 24, No. 14, 2011, pp. 3649-3666. doi:10.1175/2011JCLI3753.1
[36]	S. E. Nicholson and J. Kim, “The Relationship of the El Ni?o Southern Oscillation to African Rainfall,” International Journal of Climatology, Vol. 17, 1997, pp. 117-135. doi:10.1002/(SICI)1097-0088(199702)17:2<117::AID-JOC84>3.0.CO;2-O
[37]	R. A. Pielke, “Land Use and Climate Change,” Science, Vol. 310, No. 5754, 2005, pp. 1625-1626. doi:10.1126/science.1120529
[38]	E. Kalnay and M. Cai, “Impact of Urbanization and Land-Use Change on Climate,” Nature, Vol. 423, 2003, pp. 528-531. doi:10.1038/nature01675
[39]	P. I. Figuerola and A. N. Mazzeo, “Urban-Rural Temperature Differences in Buenos Aires,” International Journal of Climatology, Vol. 18, No. 15, 1998, pp. 17091723. doi:10.1002/(SICI)1097-0088(199812)18:15<1709::AID-JOC338>3.0.CO;2-I
[40]	R. Bohn, “Urban Bias in Temperature Time Series—A Case Study for the City of Vienna, Austria,” Climatic Change, Vol. 38, No. 1, 1998, pp. 113-128. doi:10.1023/A:1005338514333
[41]	M. Tayanc and H. Toros, “Urbanization Effects on Regional Climate Change in the Case of Four Large Cities of Turkey,” Climatic Change, Vol. 35, No. 4, 1997, pp. 501-524. doi:10.1023/A:1005357915441
[42]	Y. R. Adebayo, “A Note on the Effect of Urbanization on Temperature in Ibadan,” Journal of Climatology, Vol. 7, No. 2, 1987, pp. 185-192. doi:10.1002/joc.3370070209
[43]	R. C. Robert Jr. and W. B. Sandra, “The Impact of Rapid Urbanization on Pan Evaporation in Phoenix, Arizona,” Journal of Climatology, Vol. 7, No. 6, 1987, pp. 593-597. doi:10.1002/joc.3370070607
[44]	E. Aguilar, I. Auer, M. Brunet, T. Peterson and J. Wieringa, “Guidelines on Climate Metadata and Homogenization,” WMO TD. No. 1186 (WCDMP2), World Meteorological Organization, Geneva, 2003.
[45]	W. P. He, G. L. Feng, Q. Wu, T. He, S. Q. Wan and J. F. Chou, “A New Method for Abrupt Dynamic Change Detection of Correlated Time Series,” International Journal of Climatology, 2011. doi:10.1002/joc.2367
[46]	M. J. Menne and C. N. Williams Jr., “Homogenization of Temperature Series via Pairwise Comparisons,” Journal of Climate, Vol. 22, No. 7, 2009, pp. 1700-1717. doi:10.1175/2008JCLI2263.1
[47]	M. Brunet, et al., “Temporal and Spatial Temperature Variability and Change over Spain during 1850-2005,” Journal of Geophysical Research, Vol. 112, 2007, D12117. doi:10.1029/2006JD008249
[48]	P. M. Della-Marta and H. Wanner, “A Method of Homogenizing the Extremes and Mean of Daily Temperature Measurements,” Journal of Climate, Vol. 19, 2006, pp. 4179-4197. doi:10.1175/JCLI3855.1
[49]	C. Serra, A. Burgueno and X. Lana, “Analysis of Maximum and Minimum Daily Temperatures Recorded at Fabra Observatory (Barcelona, Ne Spain) in the Period 1917-1998,” International Journal of Climatology, Vol. 21, 2001, pp. 617-636. doi:10.1002/joc.633
[50]	T. C. Peterson, D. R. Easterling, T. R. Karl, et al., “Homogeneity Adjustments of in Situ Atmospheric Climate Data: A Review,” International Journal of Climatology, Vol. 18, No. 13, 1998, pp. 1493-1517. doi:10.1002/(SICI)1097-0088(19981115)18:13<1493::AID-JOC329>3.0.CO;2-T
[51]	T. R. Karl and C. N. Williams Jr., “An Approach to Adjusting Climatological Time Series for Discontinuous Inhomogeneities,” Journal of Climate & Applied Meteorology, Vol. 26, No. 12, 1987, pp. 1744-1763. doi:10.1175/1520-0450(1987)026<1744:AATACT>2.0.CO;2
[52]	H. Alexanderson, “A Homogeneity Test Applied to Precipitation Data,” Journal of Climatology, Vol. 6, 1986, pp. 661-675. doi:10.1002/joc.3370060607
[53]	T. A. Buishan, “Some Methods for Testing the Homogeneity of Rainfall Records,” Journal of Hydrology, Vol. 58, 1982, pp. 11-27. doi:10.1016/0022-1694(82)90066-X
[54]	W. Taylor, “Change-Point Analysis: A Powerful New Tool for Detecting Changes,” Taylor Enterprises, Libertyville, 2000. http://www.variation.com/cpa/tech/changepoint
[55]	W. Taylor, “Change-Point Analyzer 2.3 Software Package,” Taylor Enterprises, Libertyville, 2000. http://www.variation.com/cpa/tech/changepoint
[56]	A. C. Davison and D. V. Hinkley, “Bootstrap Methods and Their Application,” Cambridge University Press, Cambridge, 1997.
[57]	Y. Sheng and P. Paul, “A Comparison of the Power of the t Test, Mann-Kendall and Bootstrap Tests for Trend Detection”, Hydrological Sciences Journal, Vol. 49, No. 1, 2004, pp. 21-37. doi:10.1623/hysj.49.1.21.53996
[58]	R. Sneyers, “On the Statistical Analysis of Series of Observations,” WMO Technical Note 143, WMO No. 415, TP-103, World Meteorological Organization, Geneva, 1990.
[59]	A. John, “Fisher and Regression,” Statistical Science, Vol. 20, No. 4, 2005, pp. 401-417. doi:10.1214/088342305000000331
[60]	M. G. Kendall and J. D. Gibbons, “Rank Correlation Methods,” 4th Edition, Griffin, London, 1990.