Impact of Climate Variability on Rice Yeild in Ayamelum Local Government Area of Anambra State
Climate variability interferes with crop yield directly by altering crop growth and development; and indirectly by altering land-use patterns. Increased rice yield is important to Nigeria’s food security. This study therefore examined the impact of climate variability (using climate elements such as rainfall, temperature, relative humidity and wind speed) on rice yield in Ayamelum LGA of Anambra State from 1985‒2014. Climate, and rice yield, data were obtained from the Nigerian Meteorological Agency (NIMET), and the National Bureau of Statistics (NBS), respectively. Deviations from the means, coefficients of variation, seasonality index and precipitation periodicity index were used to study variability in the climate data. One-Way ANOVA was used to test for differences between rice yields over time. The Mann-Kendall’s and Sen’s tests were used to examine the presence of significant trends in the climate variables. Pearson’s correlation coefficients were used to assess the relationship between climate variables and rice yield; while regression analysis was used to predict rice yield using climate data. The results show that among all the studied climatic factors, only rainfall had considerable variability during the study period. While rainfall had a significant negative trend (Z = ‒0.68; α > 0.1), relative humidity had a significant positive trend (Z = +0.38; α > 0.1). Temperature and wind speed had no significant trend. Though rice yield increased above the mean in the latter years, the differences were not significant (P > 0.05). Rice yield was significantly correlated with only rainfall (r = ‒0.647; P<0.05). The regression model accounted for 56.2 percent of the variance in rice yield, but nonetheless showed that none of the studied climate variables significantly predicted rice yield.
CHAPTER ONE: INTRODUCTION
1.1 Background of the Study
Since the late 1960s, the world’s climate has been characterised by intense variability (Walsh, McBride, Klotzbach et al., 2016). Climate change which ensues from such variability currently threatens the world. The Inter-Governmental Panel on Climate Change (IPCC) reports that the changes observed with respect to the climate are unprecedented in the last 400,000 years (IPCC, 2007a). In fact, the last 60 years have been the warmest in the last 1000 years, while fluctuations in precipitation have resulted in floods and droughts globally. Higher mean temperatures are thought to accompany higher variability and more frequent occurrence of extremes in climate variables (Katz and Brown, 1992). These factors ultimately result in poor crop yields (Larcher, 1980; Kuiper, 1993; Ekpoh, 1999). Furthermore, increasing temperatures would increase evaporation and the water demand of crops, thereby compounding the poor yield as water is essential for plant growth and development. Studies have shown that increased evaporative demand often exceeds increases in precipitation especially in tropical areas (Rosenzweig and Parry, 1994). The IPCC has indeed (in its fourth report) warned that climate warming in sub-Saharan Africa will indeed be greater than the global average (IPCC, 2007b). In most West African countries, for instance, increasing temperatures have occurred jointly with reduced precipitation (Le Barbé, Lebel, and Tapsoba 2002). Precipitation, especially rainfall, and atmospheric temperature (the most important weather variables affected by climate change) play crucial roles in agricultural production in sub-Sahara Africa (SSA). In fact, it is believed that the most profound and direct impacts of climate variability over the next few decades in Africa will be on agriculture (Kurukulasuriya and Mende, 2012).
Changing climatic conditions are intricately linked to agricultural productivity. It is estimated that by 2050, climate change will result in reductions of 3·2% in global food availability, per-person (Springmann, Mason–D’Croz, Robinson, et al., 2016). This will largely be due to poor yields of the major staple foods, chief among which is rice, botanically known as Oryza sativa (Asian rice) or Oryza glaberrima (African rice) (family: Gramineae). Rice and wheat are the two most important cereals for direct human consumption. Maize, wheat and rice however, together, account for 87 percent of all grain production worldwide and 43 percent of all food calories (Dyson, 1996). In fact, it is projected that over 116,000,000 tons of rice will be needed by the year 2035 to feed the growing population of the world (Seck, Diagne, Mohanty and Woperis, 2012). Rice consumption is nonetheless highest in tropical Africa and Asia where increases in temperature variability are more likely. In Africa alone, for example, rice is the major food for over 30,000,000 people (Seck et al., 2012). In Nigeria, the demand for rice has grown steadily at about 5.6 percent per annum since 1961 (Osiname, 2002). Its consumption is estimated to be currently rising at 11 percent per annum (Mbam and Edeh, 2011). Rice is nonetheless a staple food for both the rich and the poor.
An estimated 800,000,000 people globally (17 percent of the world’s population) are food-insecure. Thirty five percent of these reside in South Asia; 30 percent in East Asia; 22.5 percent in sub-Saharan Africa; and the other 12.5 percent live in Latin America, Middle East and North Africa (Pinstrop-Andersen, Pandy-Lorch and Rosegrant, 2001). This does not augur well for development especially when placed in context with data from future population growth dynamics, where the bulk of population growth is projected to occur in developing countries (Evans, 2009). The challenges of this confluence of pressures on agriculture require that the way crops are raised be improved. Studying the effect of variability in relevant climatic parameters on the yield of key food crops is an important step in that direction. Unfortunately, response to climate change in Nigeria has been reported to be slow (Ekpoh, 2014a).
It has been shown that rice productivity in Nigeria and Africa has increased significantly, with paddy rice production level up by 9.5 percent each year, owing to research (AGRA, 2014). Therefore more research effort is needed to improve and increase yield across all rice growing environments, especially in Nigeria. Such research will help in providing solutions/adaptations for climate variability or climate change and its impacts on agricultural productivity with particular reference to rice. It will also help improve rice yield and encourage maximum production especially for small scale farmers in remote areas who form the bulk of the farming population of Nigeria and sub-Saharan Africa in particular [where they represent 80 percent of all farmers (AGRA, 2014)]. Deliberate and aggressive research in agrarian areas such as Ayamelum Local Government Area (LGA) where 65.4 percent of the population are reported to be poor subsistence farmers (Nwalieji and Uzuegbunam, 2012) will help increase the rice yield of farmers despite the apparently precarious ecosystem available for rice farming. Improved yields come with food sufficiency, economic stability, employment generation and all the positive economic down-stream triple effects.
1.2 Statement of the Research Problem
In Nigeria, crop production is a very important part of agriculture and it contributes significantly to the economy. Agriculture employs about 60 percent of the Nigerian workforce and contributes an estimated 41 percent of GDP (Aye and Ater, 2012). Rice production in sub-Saharan Africa is weather-dependent and therefore relies largely on precipitation (the rain-fed system) as against irrigation in many parts of Asia. Unfortunately the average growth rate of irrigated areas in sub-Saharan Africa in the last 30 years was a paltry 2.3 percent and even this has slowed to a meagre 1.1 percent between 2000 and 2003 (You, Ringler, Nelson, et al., 2010).
Consequently, the rainy season and the availability of rains determine when crops are planted and the length of time available for growth. This in turn bears heavily and negatively on crop yield. Rainfall variability is very common and therefore important in the tropics because temperature and the other climatic variables rarely vary. Temperature does not exceed 5 percent coefficient of variation whereas that of rainfall is rarely less than 20 percent even in the same month (Adejuwon, 2005). Among the elements of whether and climate, rainfall and temperature are usually the most important parameters required in estimating variability and yield (Peng, Tang and Zou, 2009).
Rice as a pseudo-aquatic plant requires ample water from precipitation. Without prejudice to the above assertion, flooding may cause rice plants to be completely submerged in water and this could result in the death of the plants if they remain submerged for more than one week (Sarkar, Reddy, Sharma and Ismail, 2006). Rice grows optimally at a temperature range of 25 to 30ºC (Le Houerou, Popov and See, 1993; Seck et al, 2012). Increasing temperature during the heading and ripening period has been shown to result in poor grain quality of harvested rice. This may consistently cause ripped rice grains with visible defects which also contribute to poor yield. In fact, a 2‒4ºC increase in temperature above the optimal has been shown to reduce rice yields by 6‒16 percent (Seck et al., 2012). Exposure to high temperatures for only a few hours (especially at night) is sufficient to reduce pollen viability, cause spikelet sterility and ultimately poor yields (Kukla and Karl, 1993).
Based on the foregoing, it is important to study how variable the climate is, the impact of the climate variability on rice yield, and the possibility of predicting rice yield using climate data, in Ayamelum LGA of Anambra State. Such understanding would help in devising appropriate adaptation strategies and the development of protocols that can help prevent the destructive effects of future climate change events thereby helping farmers overcome the economic losses that may result from such variability in climate variables. Ultimately, since smallholder farmers constitute 80 percent of farmers, improving the yield of important crops such as rice would improve the economic position of many poor farming families.
1.3 Research Questions
This study will attempt to answer the following questions:
- Is there any evidence of climate variability in Ayamelum LGA?
- Is there a trend for the climate variables (rainfall, temperature, relative humidity and wind speed) in Ayamelum LGA?
- What is the annual average quantity of rice produced per square metre of land (yield) in Ayamelum LGA of Anambra State, and how does it vary over time?
- What is the effect of the climate variables above on annual changes in rice yield in Ayamelum LGA?
- Can the above climate variables predict rice yield in Ayamelum LGA?
1.4 Aim and Objectives of the Study
The aim of this work was to determine if there is evidence of climate variability in the study area and to investigate the effects of rainfall, temperature, humidity and wind speed on rice yield in the study area.
The specific objectives of the study were:
- To examine the degree of variability in the climate variables in Ayamelum LGA;
- To determine if there is a trend for the above climate variables in Ayamelum LGA;
- To determine if there is variations in annual average rice yield, in Ayamelum LGA of Anambra State;
- To examine whether variability climate variables affects rice yield in Ayamelum LGA;
- To determine the predictability of rice yield from climate variables in Ayamelum LGA.
1.5 Research Hypotheses
- H0: There is no significant climate variability in Ayamelum LGA;
- H0: There is no significant trend for the climate variables (rainfall, temperature, relative humidity, wind speed) in Ayamelum LGA;
- H0: The average quantity of rice produced per square metre of land (yield) does not vary significantly over time in Ayamelum LGA of Anambra State;
- H0: Variability in climate variables do not significantly affect rice yields in Ayamelum LGA;
- H0: Climate variables do not significantly predict rice yields in Ayamelum LGA.
1.6 Significance of the Study
The changes observed with respect to the climate parameters, especially with variability in temperature and rainfall have been shown to affect agricultural productivity in different climatic zones of the world (Kuiper 1993). The impact of these factors on rice yield in Ayamelum LGA of Anambra State has not been studied; as such evidence-based adaptation strategies cannot be developed. This knowledge-gap implies that poor farmers in the said area may remain vulnerable to the vagaries of climate variability and change.
Given that the rice farmers in Ayamelum LGA depend on the rice yields from typically rain-fed systems to sustain their families, and that increased productivity would in addition to ensuring food security for such families also increase the nation’s Gross Domestic Product (GDP), any effort geared towards improving rice yields is important and laudable. It is in this light that this study on the impact of climate variability on rice yield in Ayamelum LGA of Anambra State, finds its significance.
1.7 Scope of the Study
The study covers the thirty year period from 1985 to 2014. Rainfall, relative humidity, wind speed and temperature data collected at Amawbia, Awka, Anambra State, for the said period were obtained from Nigerian Metrological Agency (NIMET), Oshodi, Lagos. Awka is approximately 50 km from Ayamelum, so climate data collected there reflects the climate experience in Ayamelum. Data on land area cultivated and quantity of rice produced were obtained from the National Bureau of Statistics (NBS) for the period 1995 to 2006. The NBS currently has data on rice yield for only the said period. The study was carried out in four randomly selected towns in Ayamelum Local Government Area.
1.8 Definition of Key Concepts
Climate: Climate refers to the average weather condition of a place, usually for a very long period of time, over 30 years.
Climate Change: Climate change is any change in climate over time that is due, directly or indirectly, to human activity which changes the composition of the global atmosphere in addition to natural climate variability observed over comparable time periods.
Climate Variables: These are climatological parameters that are used to describe the nature or state of climate such as rainfall, temperature, humidity, wind speed, and so on.
Climate Variability: Climate variability refers to deviations, shifts, variations away from the average for climate variables. It may be caused by anthropogenic or natural processes within the climate systems.
Sensitivity to climate change: This refers to the degree to which a given community or ecosystem is affected by climatic stresses. For example, a rain-dependent rice-farming community is much more sensitive to changing rainfall patterns than one where pottery is the dominant means of livelihood.
Yield: This is a measure of productivity, calculated as the quantity produced per area of land cultivated, which is usually in tonnes per hectare or kilograms per square meter.
1.9 Study Area
The area chosen for this study is Ayamelum Local Government Area of Anambra State (Fig.3.1). Ayamelum LGA is one of the 21 LGAs in Anambra State. Its choice for this study is founded on reports that most of the rice produced in Anambra State is produced there (Nwalieji and Uzuegbunam, 2012). The LGA is made up of eight towns namely Anaku, Ifite-Ogwari, Igbakwu, Omasi, Omor, Umerum, Umueje and Umumbo.
Ayamelum LGA is located between longitudes 6º45ꞌ, 7º25′, and latitudes 6º21ꞌ, 6º65ꞌ. It is 213 m above sea level. The population of Ayamelum LGA as at 2006 was 158,152 people (81,605 males; 77,085 females) but was expected to have reached 181,920 people in 2011 (NPC, 2010).
1.9.2 Climate, topography, soil and land use pattern
The climate of Ayamelum LGA is tropical as it lies within the evergreen rainforest of South-Eastern Nigeria. The land is fertile and typically covered with luxuriant vegetation except in areas that have been cultivated intensively (Egboka, 1993). Oil palm trees are common and swampy areas have thick cover of raffia palms. The planting season in most places in the LGA starts around March/April, though farming could start as early as November along the banks and tributaries of the two major rivers in the LGA – Ezu and Anambra (called Omambala by the locals).
Similar to most parts of Anambra State, the temperature of the area varies from 27ºC to 34ºC but could drop to 18ºC (at the peak of the harmattan season). Again, similar to other parts of Nigeria, there are two seasons of the year – a rainy season characterised by rains that are driven by the South-West trade winds and a dry season, characterised by dust brought by the North-East trade winds. There is typically a slight break in the rainy season, termed the August break.
Soils support life, and without soils, many of the world’s living organisms will find it difficult to survive and thrive (Pimentel and Pimentel, 2003). Soil fertility plays a major role in rice farming in the area and is therefore a major constraint to rice yield. Soil allows plants such as rice to grow upright and turn towards the sun. It also provides needed nutrients to ensure enough yields. Water is also stored in, and supplied from, soils to plants. It is estimated that 99 percent of the food and fiber produced globally grow on soils; yet only 10-12 percent of the earth’s surface is covered by soils available for agriculture (Pimentel, 2006).
Soils also provide many more essential services for humans. They help filter water; they immobilize many toxic substances, they mineralize crop residues and store carbon, as well as exchange gases with the atmosphere (Smith, Cotrufo, Rumpel, et al., 2015). Soil is made up of air, water, mineral particles, organic matter, and organisms. About half of it is pore space that can be filled equally with water and air while most of the solid portion is made of mineral particles. Even though organic matter usually makes up about 2% of a top soil’s weight, it binds soil particles together, stores nutrients, and feeds soil organisms. Organic matter is created by tiny, living organisms that decompose dead plants and animals, creating nutrients that plants can use (Pimentel, 2006). Although these nutrients already come from the soil, some plants like rice may still need supplemental nutrients (those added to the soil with fertilizers) especially when higher yields are required for a growing population.
Soil fertility is an important factor in enhancing crop productivity but it is not commonly included in studies analysing the impacts of climate variability on crop yield (Kang, Khan, and Ma, 2009). Soil fertility parameters influence crop yield such as rice. Its status on fertility in an area may be influenced by soil organic carbon, available nitrogen, phosphorus and potassium concentration and production input. Soil fertility also significantly affects the parameters of the production function. Available soil potassium and soil nitrogen significantly increase rice productivity whereas available soil phosphorus has an opposite effect. The organic carbon content of a given soil also has a desirable
positive effect but the influence may not be significant.
The Anambra-Imo River Basin Development Authority had developed canals that took water from the Anambra River to towns such as Omasi, Umumbo and parts of Omor that do not have as much access to natural water bodies as the others. The canals opened up larger areas of land for agricultural activities. Majority of the inhabitants of the LGA are farmers while very few are artisans, traders, teachers and healthcare personnel. The major cash crops grown by the farmers are rice, maize, yams and cassava. Majority of the artisans and traders are engaged in agriculture-related activities/businesses. Despite these, about 65.4 percent of the population are poor (Anambra State Government, 2011).
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