Climate change is real and its consequences will be with us for the greater part of this century. If appropriate measures are taken now to stem the increase in the emission of Green House Gases (GHG) into the atmosphere that is responsible for the global warming then there will be a reversal of the consequences. The Intergovernmental Panel on Climate change (IPCC) has established through its science based research that the effect of global warming will linger for longer period if the present trend of GHG emission is not curtailed. The Intergovernmental body has also shown that the anthropogenic activities has contributed significantly to the variations and changes observed in the world climate system since the post industrial revolution era apart from the contributions of natural climate modifiers such as continental drift, volcanoes, ocean currents, earth’s tilt, comets and meteorites. All living things are affected by the climate systems and in particularly by the climate extremes which threatens safety of lives and property and sustainability of socio-economic activities. Since weather and climate know no natural, geographical, political or disciplinary boundaries, cooperation amongst relevant institutions become very necessary to put in place a robust and effective mitigation and adaptation measures to the variability and change of the climate systems in order to achieve the much desired stabilization. It is therefore not surprising that climate change remains one of the greatest challenges of our time towards attainment of sustainable economic development and calls for reinforced interdisciplinary cooperation to stem its devastating consequences.
It is important to mention here that climate systems are not all about the extreme events and the associated devastating effects. There are also benefits associated with climate systems especially when considered as a resource that if factored into decision-making and development and policy formulation, produces beneficial results to mankind. It is in recognition of this that the World Meteorological Organization (WMO) established the Global Framework for Climate Services (GFCS).The main goal of GFCS is to “enable better management of the risks of climate variability and change and adaptation to climate change, through the development and incorporation of science-based climate information and prediction into planning, policy and practice on the global, regional and national scale’’ (World Climate Conference-3). Investment therefore in climate services translates to economic prosperity for both citizens and institutions through appropriate adaptation strategies to climate variability and change. It is noteworthy to mention that adaptation to risks and opportunities from climate vulnerability and change especially to the most vulnerable communities saves life and property and creates wealth for the citizenry.
The 2012 Nigeria Climate Review has shown very interesting features in the variability of the atmospheric elements compared to their long term averages. Notable amongst the observed features are positive rainfall anomaly recorded in most parts of the country. Indeed the Northeast zone recorded positive anomaly for the first time in the last 5 years and the highest anomaly in the last 10 years. The above normal rainfall resulted in unprecedented flooding which caused loss of lives and properties. The magnitude of the losses recorded could be attributed to non adherence of relevant Agencies to the early warning provided by NIMET with very good lead time. The Little Dry (Harmattan) Season was very pronounced in the Southwest. Its severity and the duration was the highest recorded in the last 5 years. Most states in the North also recorded above normal day time temperatures at early part of the year which increased the discomfort level.
Nigeria Climate Review Bulletin is one of the many science based publications of NIMET geared towards informing all stakeholders and the general public of the variations in climatic elements for better decision making and policy formulations. It is produced yearly and provides wealth of information on the climate of the year under review. It also highlights in particular the temporal and spatial variations of temperature, rainfall, dust outbreaks, harmattan season and hailstone occurrence in the course of the year. The publication also contains catalogue of extreme weather events and the socio-economic benefits of climate variations and changes. Government will continue to support and encourage such scientific based publication that will help achieve the transformation Agenda and the Millennium Development Goals (MDGs). I highly recommend the Nigeria Climate Review Bulletin for all scientists and practitioners especially those who seek adaptation to risks and opportunities from climate variability and change especially to the most vulnerable sectors of the economy and communities to climate related hazards.
1.0 INTRODUCTION The climate of Nigeria has shown considerable temporal and spatial shifts in its variability and change. Extreme climate and weather events (drought, flood, heatwaves, ocean surges, etc) have become more regular. The impacts of extreme weather and climate may be gradual but they are destructive to lives and property, negatively impact on the economy. Floods have become a perennial challenge with increasing intensity each year, leaving colossal losses and trauma. The low-lying coast of the country experiences perennial inundation due to ocean surges and strong tidal waves.
The 2012 Nigerian Climate Review bulletin has added new climate indicators such as ‘rainfall months’ anomaly, extreme meteorological parameters, etc., in addition to standard statistically examined climatic elements (maximum and minimum temperatures, rainfall amounts and patterns of onset and cessation of rainfall). This innovation is to provide scientists and experts in the socio-economic sectors more useful information on variability and trends with a view to addressing the many multi-hazard challenges facing the country.
The synoptic features indicated dominance of the subtropical high pressure systems at the beginning of the year, leading to the raising of dust particles at the surface in the Sahara Desert and subsequent transportation and reduction of horizontal visibility across the country. The southwesterly winds gained momentum at the coast and progressively moved inland at the end of first quarter of the year. The monsoon trough remained very active across the country till the end of the third quarter, and this brought about enhanced rainfall and thunderstorms, flash flooding and the associated impacts.
The seasonal and meridional oscillations of the Inter-Tropical Discontinuity (ITD) attained a peak position of about latitude 18.8oN in August. In addition, the dynamics of the atmosphere showed unusual surging and pulsation of the ITD, such that severe storms were experienced over the coast as early as February in 2012, particularly over Lagos. Further scientific studies are presently being undertaken to understand the causative factors.
Rainfall amounts were normal to above normal with high intensity rainfall duration in some occasions leading to flooding during the months of July, August and September. It is important to note that for the first time since 2008, the northeast had rainfall more than normal values in more than ten consecutive years. Widespread flooding peaked between September and mid-October across the country and was particularly severe in the northcentral and coastal states. Nigeria experienced the worst flooding in 2012 for more than a century.
The hot season in 2012 was warmer than normal in the north but normal in the south except over the extreme southeast which was colder than normal. The comfort index anomaly showed greater than normal discomfort during the hot season in the north but other regions were comfortable over the same period. The August break of 2012 over southwest Nigeria lasted for about two weeks at Ibadan and five weeks at Ikeja. The phenomena lasted till the first week in September.
Extreme weather and climate events in 2012 led to significant socioeconomic impacts. Strong winds in the magnitude of 60-70knots were experienced in the south and the north for the months of February and June respectively. Daily maximum temperatures of 40.0oC and higher were experienced in the northern part of the country and in some places for sixty days, although the days were not consecutive. High impact daily rainfalls of 100.0mm and higher values were recorded in the year between May and August.
Preliminary analyses in the agricultural sector suggest that out of the major food crops (Yam, Cassava, Maize, Sorghum and Rice) being produced in the country, yam would be the mostly affected, followed by rice and cassava. There were outbreaks of cholera in some states due to food and water contamination from floods. Mostly affected states by the flooding were Kogi, Adamawa, Delta and Bayelsa States. Storms destroyed infrastructures leading to disruption of socioeconomic activities.
This Bulletin has provided scientific information and data for further research, source of materials for experts in the socioeconomic sectors to further appraise the year 2012 in multidisciplinary analyses of the climate events. In all, the bulletin is highly recommended for those who are affected by the Nigerian climate in one way or the other. It is indeed a valuable document as reference material for libraries.
2.0 EVIDENCE OF CLIMATE CHANGE The climate of Nigeria has shown considerable signals of a changing climate through the careful study of meteorological data. Analysis of long term trends of meteorological parameters such as rainfall, in terms of onset and cessation of the rainy season, hail frequency and average maximum temperature during the hot season (February - April) lend support to this deduction.
2.1 ONSET AND CESSATION OF WET SEASON
The onset of the rainy (wet) season between 1941 and 1970 was mostly from “early to normal” (Fig. 1a). Isolated places around Sokoto, Maiduguri, Owerri, Port Harcourt and Calabar had late onset of the rainy season. However, increasingly late onset of the rainy season characterised later years such that by 1971-2000 a vast portion of the country now experience late onset of the rains (Fig. 1b).
The period of the rainy season in the country has been reduced from 1941 when the onset and cessation were generally normal to 1971 when signals of late onset and early cessation of the rainy season set in. Since then, the length of the rainy season has remained shrinking while annual total rainfall is about the same, thereby giving rise to high impact rainfall, resulting in flash floods.
2.2 HAIL FREQUENCY The occurrence of hail during the rainy season in the country has steadily diminished and virtually disappeared by the turn of the century.
Jos, which was one of the places in Nigeria where hail occurrence was a common characteristic of the rainy during the mid 20th century, no longer experience this phenomenon on an annual basis from the end of the century. The time series of decadal hail occurrence at Jos (Fig. 3) shows a very high frequency of occurrence between 1942 and 1951, but rapidly reduced with time and completely disappeared by 1992.
The same trend of hail occurrence has been observed over the country as a whole, which goes to further strengthen the evidence of general warming across the country.
Fig. 3: Jos Hail Frequency 1942 - 2010
2.3 MEAN TEMPERATURE
Temperatures across the country show an increasing trend from mid 20th century to date. The mean temperature anomaly (Fig. 4a) shows clearly the prevalence of warming in the country. Temperatures have increased from 0.2 – 0.5C in the high ground areas of Jos, Yelwa and Ilorin in the north and Shaki, Iseyin and Ondo in the southwest to 0.9 - 1.9C over the rest parts of the country.
Fig. 4a: Mean Temperature Anomaly: 1942 - 2000 The area averaged maximum temperature during the hot season also show increasing trends in both the south and in the north (Figs 4b & 4c). In addition, the trend analyses reveal a higher rate of temperature increase per decade in the south (2.5C) than in the north (1.4C).
3.0 SYNOPTIC FEATURES 3.1 SURFACE PRESSURE AND WINDS The Climate of Nigeria is basically tropical in the south and savannah in the north. The seasonal north-south movement of the dry north easterly winds from the Sahara Desert and the moist south westerly winds from the Atlantic Ocean defines this climate.
At the surface, pressure values over North Africa, fluctuated between 1021 – 1026 hPa during the first quarter. The north easterly winds periodically raised dust particles into the atmosphere over the Sahara Desert, following the occasional strengthening of the surface high pressure in the region. The raised dust particles were progressively transported southwards across the country and horizontally visibility was occasional reduced to less than 1000m particularly in the north. At the lower levels (up to 1,500m), moderate north easterly winds dominated the flow pattern. The speed of the low level winds fluctuated between 12 – 28 knots (6 – 14m/s).
The low-level wind convergences which appeared occasionally along the coast during the first quarter of the year became well established and active in the second quarter, giving rise to early rainfall in the south. This development was aided by the weakening of the Saharan High pressure and strengthening of the St Helena High pressure which resulted in the northward movement of moist southwesterly winds. The monsoon trough remained very active across the country till the end of the third quarter, brought about enhanced rainfall and thunderstorms, flooding and record socio-economic implications. At the height of 1,500m, the moist southwesterly winds penetrated inlands to reach an average position of latitude 13.8oN.
During the fourth quarter, the Saharan High pressure over North Africa intensified again, leading to the cessation of the rainy season and beginning of the dry season in the country. This led to the dominance of dry northly winds over the wind regime, raising of dust particles at the Sahara Desert and the subsequent southward transport of the dust plumes into the northern parts of the country.
3.2 INTER-TROPICAL DISCONTINUITY (ITD)
Variations in the location of the Inter-Tropical Discontinuity (ITD) influence the rainfall over Nigeria. Dry weather conditions prevail to the north of its position while convection and rainfall take place to the south. The ITD was located at a mean position of latitude 7.2 °N in January 2012 (Fig. 5). It pushed northward rapidly from 20th January to 28th February to reach latitude 11.1°N which was far higher than normal and out of phase with the normal. The ITD slowed down thereafter and remained lower than normal till 10th May but maintained a nearly normal position till 30th September. The peak position of the ITD in 2012 was latitude 18.8°N reached in the second dekad of August. From October, there was a rapid southward movement of its position reaching latitude 7.6 °N in December.
Fig. 5: Dekad positions of ITD in 2012
During the months of February and March, the positions of the ITD were above normal (Fig. 6). This accounted for the early onset of rainfall in the south in February. However, it was below normal throughout the rest of the year.
Fig: 6. 2012 ITD position Anomaly. 3.3 SEA SURFACE TEMPERATURE ANOMALIES (SSTAs)
AND GLOBAL CIRCULATIONS
The La Niña condition which prevailed during the later months of 2011 continued in early 2012 with below average sea surface temperatures (SSTs). However, the SST in the Niño-3.4 region which was near –1.0°C began to warm and by the end of February, the La Niña weakened to near –0.5°C below average SSTs (Fig. 7). This trend continued in March, April and May, with large scale atmospheric circulation anomalies and the Southern Oscillation Index (SOI) indicative of a transition from La Niña to ENSO-neutral condition.
ENSO-neutral condition started in June in both the oceanic and atmospheric anomalies with increased tendency for El Nino but by positive equatorial Pacific sea surface temperature (SST) anomalies have exceeded +0.5°C by August, although still within the limits of ENSO-neutral condition. The remaining months of the year clearly indicated ENSO-neutral conditions despite above average SSTs.
Fig. 7: Oceanic Nino Index (ONI) over Nino 3.4 region
The second half of 2012 clearly showed warm-neutral ENSO condition. Upper and lower-level zonal winds were near average, and convection was slightly suppressed over most of the tropical atmosphere.
The outlook for 2013 is that the warm-neutral ENSO condition is likely to last till Northern Hemisphere summer. However, it will be in the ENSO-neutral range even though the average dynamical model forecast is warmer than the statistical model mean.
Maximum temperatures during the hot season (February and March) in the south and (March and April) in the north, showed that temperature ranged between 30.1 – 40.0°C (Fig. 8). The maximum temperature gradually increased inland from the coastal areas, with the exception of Jos and its environs. The southeast coastal areas had mean maximum temperatures of 30.0 – 33.0°C, while the coast of the southwest and the inland cities of the south recorded maximum temperatures between 33.0 – 36.0°C. Maximum temperatures over the central areas and the north central parts ranged between 36.0° -38.0°C during the period except for Jos and its environs which had mean maximum temperature ranging between 30° -36°C. Jos recorded the lowest maximum temperature of 30.1°C. Elsewhere in the north, maximum temperatures were between 38.0° - 40.0°C.
Fig. 8: 2012 Hot Season Maximum Temperature
4.2 HOT SEASON MAXIMUM TEMPERATURE ANOMALY
The hot season in 2012 was warmer than normal in the northern parts of the country with maximum temperature departures ranging from 0.5 - 2.5°C (Fig.9). Normal temperature conditions were experienced at the southern and central parts of the country in the year, except for Makurdi and Bida where maximum temperatures were 0.5-1.5°C higher than normal maximum temperatures. On the other hand, Calabar, Uyo and Eket, in the extreme southeast coast, recorded maximum temperatures lower than normal by 0.5 - 2.5°C.
Fig. 9: 2012 Hot Season Maximum Temperature Anomaly
4.3 COLD SEASON MINIMUM TEMPERATURES
Monthly minimum temperature across the country during the cold season (January) showed that low minimum temperatures, between 10.0 - 14.0°C, were recorded in the northeast, Kano, Katsina and the areas around Jos in the central region (Fig. 10). The remaining parts of the north experienced season minimum temperatures between 14.0 -18.0°C while cold season minimum temperatures ranged between 18.0 – 22.0°C over the northcentral and the south except at the coastal cities which experienced the highest temperatures range of 22.0 – 24.0°C. The highest cold season minimum temperature in the south (24.1°C) was recorded at Eket.
Lower minimum temperatures were recorded in the extreme northeast and Jos in the cold season of 2011 than over the same area in 2012.
Fig. 10: 2012 Cold Season Minimum Temperature
4.4 COLD SEASON MINIMUM TEMPERATURE ANOMALY
Cold season minimum temperatures in 2012 were generally normal across the country when compared with 1971 – 2000 average values (Fig. 11).
Colder than normal temperatures (0.5 - 3.0°C) were recorded during the season in places such as Sokoto, Katsina, Kano, Jos and Ilorin in the north, as well as over Iseyin, Oshogbo, Akure, Benin and Enugu in the south. However, Owerri in the southeast recorded the lowest cold season minimum temperature anomaly of -3.2°C.
Warmer than normal temperatures (0.5° -2°C) were experienced over Ibi, Bida and Makurdi in the central states, and over Eket in the southeast coast. Minimum temperatures were normal in other parts of the country during the cold season.
Comparatively, 2012 cold season was similar to 2011 but colder than 2010.