Review on Effect of Climate Change and Urbanization on Agriculture

Climate is the primary important factor for agricultural production. The work topics concentrate possible physical effects of climatic change on agriculture, such as changes in crop and livestock yields as well as the economic consequences of these potential yield changes. In addition to this understanding of long-term changes in precipitation and temperature patterns is important in the detection and characterization of climate change. The role that climatic change has played in the pattern of urbanization in sub-Saharan African countries compared to the rest of the developing world and climatic changes represented by rainfall, has acted to change urbanization in sub-Saharan Africa. The cultivated land loss due to urbanization not only threatens food security in, but has also led to ecological system degradation to which close attention should be paid. In other hand climate change and urbanization have caused temporal changes in precipitation and temperature. Finally this paper reviews the effects of climate change and urbanization on agriculture. The main interests, concerning the role of human adaptations in responding to climate change, the impacts of climate change and urbanization, possible regional impacts to agricultural systems and potential changes in patterns of food production.


INTRODUCTION
The term climate describes the overall long-term characteristics of the weather experienced at a place. The ecosystems, agriculture, livelihoods and settlements of a region are very dependent on its climate. Climate change refers to a change in the state of the climate that can be identified by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcing or persistent anthropogenic changes in the composition of the atmosphere or in land-use (IPCC, 2007b).
The Intergovernmental Panel on Climate Change (IPCC) predicts increases in the mean global temperature of up to 5.8 0 C by 2050 as well as more frequent ENSO (El Nin˜o/La Nin˜a) events with climatic conditions expected to become generally more variable as a consequence of these global environmental changes (GEC) and increasing temperatures the life history traits of indigenous and invasive species may be impacted (IPCC, 2007).
practice to burn large quantities of crop residue, which results killing of insects and other pests as well as disease causing organisms and neutralizes soil acidity. To less extent, CO2 is released from the fossil fuels used in agricultural production and from livestock production. Nowadays, high-intensity animal production has become the biggest consumer of fossil energy in modern agriculture (IPCC, 1996).

Methane (CH4)
Methane CH4 is the most significant greenhouse gas released within the agriculture sector. Most of the methane releases come from paddy fields (91%) and less significantly from animal husbandry (7%) and burning of agricultural wastes (2%) (Figure 1). The quantification of rice paddy emissions has proven difficult as the emissions vary with the amount of land in cultivation, fertilizer use, water management, density of rice plants and other agricultural practices. Among too many Asian countries, China is a very large source of CH4 emissions. Livestock and associated manure management causes 16% of the total annual production of CH4. These emissions are a direct result of the ability of buffalo and cattle to utilize large amounts of fibrous grasses that cannot be used as human food or as feed for pigs and poultry. Buffalo and cattle contribute about 80% of the global CH4 emissions from domestic livestock annually (Aydinalp and Cresser, 2008).

.3. Nitrous oxide (N2O)
Most of the agriculture based N2O emissions come from nitrogen fertilizer usage, legume cropping and animal waste. Many farmers use nitrogen fertilizers on their fields to enhance crop growth. The crop takes up most of the nitrogen, but some of them leach into surrounding surface and ground waters and some of it enters the atmosphere. The nitrogen flux depends on the microbial activity in the soil. For example, wet rice absorbs only one-third of the nitrogen in the fertilizers, while upland crops about half. The rest of nitrogen is denitrified and diffused into the atmosphere, which is contributing to global warming. However, the amount of N2O emitted is much lower in volume than the amount of CH4 (Aydinalp and Cresser, 2008).

Climate change could adversely influence agricultural production
Geographical shifts and yield changes in agriculture, reduction in the quantity of water available for irrigation and loss of land through sea level rise and associated salinization. The yields of different crops and geographic limits may be altered by changes in soil moisture, temperature, precipitation, cloud cover, as well as increases in CO2 concentrations. The lowest rainfall and high temperature could reduce soil moisture in many areas, particularly in some tropical and mid-continental regions, reducing the available water for irrigation and impairing crop growth in non-irrigated areas of the many regions. The changes in soil properties such as erosion are a likely consequence of climate change for some soils in some climatic zones (WRI, 1998). The risk of losses due to weeds, insects and diseases is likely to increase. The range of many insects will change or expand and new combinations of diseases and pests may emerge as natural ecosystems respond to shifts in temperature and precipitation profiles. The effect of climate on pests may add to the effect of other factors such as the over use of pesticides and the loss of biodiversity, which already contribute to plant pest and disease outbreaks. Agriculture in low-lying coastal areas or adjacent to river deltas may be affected by a rise in sea level. Flooding will probably become a significant problem in some already flood-prone regions of Asia such as China, further south in Eastern Asia and similar environments in the world. Decreases in productivity are most likely in these regions,  Vol.11, No.5, 2019 which are already flood-insecure. Climatic events, changes in rainfall and temperature could be damaging and costly to agriculture (WRI, 1998).

Plant Yield and Climate Change
Plant physiology has been greatly influenced by climate variability by several means. Environmental extremes and climate variability enhanced the chances of numerous stresses on plants (Thornton et al., 2014). Climate change affects crop production by means of direct, indirect, and socio-economic effects as described in Figure 2. Furthermore, climate change (drought, flood, high temperature, storm etc.) events are increased dramatically as reported by Food and Agriculture Organization (FAO) and as shown in Figure 3. Boyer reported that the climate changes have reduced the crop yield up to 70% since 1982. According to the study of FAO 2007 (http://www.fao.org/home/en/) all cultivated areas in the world are affected by climatic changes and only 3.5% of areas are safe from environmental limitations (Van, 2007). Whereas the outcomes of a biotic stresses on crop yield are hard to calculate accurately, it is believed that a biotic stresses have a substantial influence on crop production depending upon the extent of damage to the total area under cultivation. In future, the productivity of the major crops is estimated to drop in many countries of the world due to global warming, water shortage, and other environmental impacts (Bonan and Doney, 2018).
Wheat production is heavily affected by the temperature extremes due to climate change in many countries, and may reduce the crop yield by 6% for each •C rise in temperature (Asseng et al., 2015). Drought and high temperatures are key stress factors with high impact on cereal yields (Barnabás et al., 2008) and Rubisco, the central enzyme of photosynthesis, is disrupted if the temperature increases from 35•C and stops the photosynthetic process (Griffin et al.,2004). Due to climate change, water deficit and temperature extremes influence the reproductive phase of plant growth.
It was described that the flower initiation and inflorescence is badly affected by the water stress in cereals (Winkel et al.,1997). Similarly, if the temperature increases of about 30•C during floret development it can cause sterility in cereals (Saini and Aspinall et al.,1982). During the meiotic phase, wheat and rice suffered from the 35-75% reduction in grain set due to water deficit (Sheoran and Saini, 1997). In rice, drought stress greatly disturbs the process of fertilization and anthesis. Zhao et al. (2017) carried an experiment to analyze the climate  Vol.11, No.5, 2019 31 change impact on major crop yields and showed considerable yield reductions of 6%, 3.2%, 3.1%, and 7.4% in wheat, rice, soybean, and maize respectively. To tackle the climate change new discoveries in genomics are enabling climate-smart agriculture by developing climate resilient crops (Scheben et al., 2016).

Crop Adaptation to Overall Extreme Climate Stresses
With the increase of the Earth's temperature, the climate undergoes severe alterations and becomes a biotically stressful environmental changes are very damaging and pose various threats to naturally prevailing crop species ( Espeland and Kettenring, 2018). Under field circumstances, drought and heat are the most predominant stresses and have a significant influence on plants ( Pereira, 2016). These climatic problems severely distress plant development and yield, produce enormous responses, comprising molecular, biochemical, physiological and morphological modifications (Zandalinas et al., 2018). Overall, global warming and climate change both have some negative and positive effects on agricultural crops as well as on humans as explained in Figure 4.

Effect of Climate Change on Livestock
Climate change could affect livestock and dairy production. The pattern of animal husbandry may be affected by alterations in climate, cropping patterns, as well as ranges of disease vectors. The higher temperatures would likely result in a decline in dairy production, reduced animal weight gain and reproduction and lower feedconversion efficiency in warm regions. More mixed impacts are predicted for cooler regions. If the intensity and length of cold periods in temperate areas are reduced by warming, feed requirements may be reduced, survival of young animals enhanced and energy costs for heating of animal quarters reduced (Aydinalp and Cresser, 2008). Incidence of diseases of livestock and other animals are likely to be affected by climate change, since most diseases are transmitted by vectors such as ticks and flies, the development stages of which are often heavily dependent on temperature. Cattle, goat, horse and sheep are also vulnerable to an extensive range of nematode worm infections, most of which have their development stages influenced by climatic conditions. In general; intensely managed livestock systems have more potential for adaptation than mixed livestock cropping systems. Adaptation may be more problematic in pastoral systems where production is very sensitive to climate change, technology changes introduce new risks and the rate of technology adoption is slow. Livestock production may also be affected by potential changes in grain prices brought on by changing yields in some areas or by changes in rangeland and pasture productivity. For developing countries, livestock are better able to survive severe weather events such as drought than are crops and therefore a better option in terms of income protection and food security (Aydinalp and Cresser, 2008). Livestock producers can adapt to climate change by the provision of shading, sprinklers, improved air flow, lessened crowding, altered diets, and more care in handling animals. Herds or the locus of livestock production may also be moved to more hospitable locations. In the longer term, new crop varieties and livestock breeds may be developed that perform better under the anticipated future climate regime (IPCC, 1996).

Agriculture and Climate Change Mitigation
Regardless of the projected or actual impacts of climate change, agriculture is also likely to be directly or indirectly involved in climate change mitigation efforts. Greenhouse gas emissions (GHGE) constitute a global production externality which is likely to adversely affect climate. Actions under that convention yielded the Kyoto Protocol which represents the first significant international agreement towards GHGE reduction. Agriculture (using a definition including forestry) is mentioned as both an emitter and a sink in the protocol. Agriculture as an emission sources from enteric fermentation, manure management, rice cultivation, soil management, field burning and deforestation (Table 4). The protocol also lists agriculturally related sinks of afforestation and reforestation (Table 5). Additional sources and sinks are under consideration including agricultural soil carbon (McCarl et al., 2001).  Schneider (1999, 2000a) there are at least four ways agriculture may participate in or be influenced by greenhouse gas mitigation efforts. Agriculture may need to reduce emissions because it releases substantial amounts of methane, nitrous oxide, and carbon dioxide, agriculture may enhance its absorption of GHGE by creating or expanding sinks, agriculture may provide products which substitute for GHGE intensive products displacing emissions and agriculture may find itself operating in a world where commodity and input prices have been altered by GHGE related policies.

General Findings on Climate Change Impact
Several key findings have emerged across the large number of studies measuring the physiological effects of climate change on crops and to a lesser extent livestock. The effects of changes in temperature, precipitation and carbon dioxide concentrations on crop productivity have been studied extensively using crop simulation models. The combined effects of climate change have been found to have implications for dry land and irrigated crop yields as well as irrigation water use (Rosenzweig and Iglesias, 1994). IPCC (1996) noted that different crops exhibit different sensitivity. It is thus important that the full range of cropping possibilities is considered when assessing climate change. Treatment of only selected crops can bias the results. For example, early US studies only examined corn, soybeans and wheat, in contrast to later studies which included many more heat tolerant crops. The CO2 fertilization effect is an important factor. Inclusion of the effect in yield studies significantly raises the estimates of climate affected yields of many crops. It is however somewhat controversial (Reilly et al., 2000b;2001) yield effects vary latitudinally across the world. Yields generally improve in the higher latitudes. On the other hand there are estimates that there will be net reductions in crop yields in warmer, low latitude areas and semi-arid areas (Adams et al., 1998;Lewandrowski, 1999) yield changes can be reduced or enhanced by adaptations made by producers. Farmers may adapt by changing planting dates, substituting cultivars or crops, changing irrigation practices, changing land allocations to crop production, pasture and other uses (Adams et al., 1999;Kaiser et al., 1993) livestock effects can be significant.
The Environmental Protection and Research Institute sponsored (Adams et al., 1999) and recent US national assessment (Reilly et al., 2000a,b) used livestock productivity alterations ranging from -1.5 to -5% changes in rate of gain and milk production coupled with proportional adjustments in feed and grazing requirements and reductions in input usage costs at a rate of 40% of the reduction in productivity. Irrigation water availability is an issue. Data from the US National assessment water study (Jacobs et al., 2000) were used in the parallel agricultural assessment (Reilly et al., 2000a,b) under the assumption that the same percentage change occurring in total water supply also occurred in the agricultural water supply.

Effects of Land Use Change on ESV
The effect of land use change on ESV was assessed when cultivated land was converted to urban areas. Land use change led to the overall decrease of ESV except for soil conservation (Table 2). Urban expansion almost resulted in the complete loss of water conservation. As a result of the increase in water conservation due to climate change, land use change totally led to the decrease of 124.03% in water conservation. The ecosystem service of nutrient cycling, gas regulation and organic production also decreased by 31.91%, 7.18%, 7.18%, respectively. However, urban expansion improved soil conservation with an increase in ESV of 2.40%.  Vol.11, No.5, 2019 33

Source: Chinese Academy of Sciences
Land use change significantly reduced the total ecosystem service value in the central NC decreased by 43%-100%, while it increased the ESV in the western NCP ranging from 15% to 128% ( Figure 5). Except for several regions in the northwest, all water conservation decreased by over 100% in the NCP. Soil conservation was improved in 65.28% of the counties in the NCP due to urban expansion.

Impact of Urbanization on Agriculture
Urbanization affects all spheres of human life both in the rural and urban setting. Urbanization increased residential population and expansion of non-farm business and industry increases the pressure on farmers and makes it more costly and difficult to farm in the traditional way. The issue is complicated by the fact that population and business industry growth often takes place in prime agricultural areas (Asamoah, 2010). Urbanization has led to land use conversion from agricultural land to urban land use, such as for infrastructure, industrial, residential or commercial uses. Such land use conversion often reduces the most fertile land and therefore the impact on agricultural production and food security is often larger than the absolute amount of land involved (Francis et al., 2013). Regmi (2014) noted that all of the future world's population growth will occur in urban areas; partially reflective of rural-urban migration trends driven by relative livelihood opportunities. He stated that approximately 35% of current urban population growth globally is attributed to rural-urban migration and in sub-Saharan Africa; urban population is expected to triple in the next 40 years. Growing urbanization across the globe, therefore, has important "push" and "pull" implications for agricultural research for development. Pramanik et al. (2010) noted that urbanization and population growth has serious effect on agriculture. Iheke and Nto (2010) noted that urbanization is an important driving force in migration and commuting because urban areas offer many economic opportunities to rural people through better jobs, new skills and cultural changes. Motamed et al. (2014) reported that locations with more favorable natural agriculture endowments tend to get urbanized earlier in history. Improvement in agricultural productivity is hence believed to be an important contributor to the urbanization process.

Expansion of urban to rural agricultural land
Land conversion is a process by which land is converted from agricultural to urban uses. Tan et al. (2009) stated that land conversion is a phenomenon that is almost inevitable during economic development and population growth periods. However, uncontrolled land conversion has greater impact on environment in general and agricultural yield in particular. Lichtenberg and Ding (2008) asserted that subsequently, some countries such as China, Japan and USA have tried to conserve agricultural land from being transformed to other uses. Higher population density, rapid economic development and the urbanization process are assumed to be the main factors of resulting agricultural land conversion in China. Agus and Irawan (2006) showed that, in 1995, ALC (agricultural land conversion) accounted for more than two-third of the loss in cultivated land in several areas. During 1996During -2000, the rate of agricultural land conversion in the Netherlands was only 17ha per day while in Germany in 2006 the rate was 114ha per day. Such rates are much lower than in China and Indonesia which respectively experienced 802 ha in 2004 and 514ha per day in 2000-2002. The above report makes it clear that the rate of agricultural land conversion is different in both developed and developing countries. According to Lichtenberg and Ding, 2008 there are two major drivers that contribute to agricultural land conversion; internal and external; land degradation and development and industrialization. The internal drivers land degradation is related to the location and land potential including land productivity, ownership pattern including land size and household size and income. The later includes urbanization, socio-economic conditions and government policies. The combined effects of various changes are still highly uncertain (IPCC, 2007) global land-use patterns will change in the future. Projecting their future development; it is important to study both their impacts on the earth system as well as the limitations of land use, since freshwater and fertile land is only available in limited amounts ( Figure 6). Figure 6: Estimated projected urban and rural population in the world .
Source: United Nations, 2002 The increase of urban population to more than 7 million would lead to a loss in agricultural land around 0.233 km 2 per capita. People's migration to urban areas needs more land (Figure 7). The increase need for job, housing, recreation, commercial area, parking sites, road infrastructure, educational and other facilities that create social welfare, increases demand for land. According to Liu et al. (2008) there is a relation between economic growth and ALC.  Source: Chinese Academy of Sciences 2.9.2 Cultivated land loss due to urbanization in the NCP During the period 1986-2003, urban expansion in China occupied more than 33,400 km 2 of cultivated land, accounting for 21% of total cultivated land loss (Chen, 2007) many negative effects of urbanization have been well documented, such as resource removal (Rebele, 1994) the decrease in native biodiversity (Su et al., 2011) the urban heat island effect (Arola and Korkka-Niemi, 2014) and air and water pollution (Figure 9). Many www.iiste.org ISSN 2224-5790 (Paper) ISSN 2225-0514 (Online) DOI: 10.7176/CER Vol.11, No.5, 2019 35 researchers have taken note of this, and assessed the changes in ecosystem service in response to urbanization. For example Long et al. (2014) assessed that the ecosystem service value (ESV) of the Tianjin Binhai New Areas decreased by 25.9% between 1985 and 2010 due to the conversion from ecological land to construction land.

Figure 9: (a) Urban expansion rate and (b) cultivated land loss ratio in urban
Source: Chinese Academy of Sciences In addition, about 19.89% of the expanded urban areas were converted from other construction land (i.e., rural settlement, industrial and mining land), 0.75%, 1.19%, and 1.36% from forestry areas, grasslands and water areas, respectively. The ratio of cultivated land loss in urban expansion is higher in the southeastern NCP, ranging from 90% to 100% (Figure 9).

Relationship between Climate Change and Urbanization
The Intergovernmental Panel on Climate Change (IPCC) highlighted a need for more specific information about climate change on regional and local scales, because understanding temporal trends of climate variability is fundamental for comprehensive environmental assessments at regional and/or national scales (Baigorria et al., 2010). A shift in mean climate conditions, such as a change in temperature distributions, could lead to a corresponding change in climate extremes. Im et al.(2011) by analyzing historical data trends, observed annual mean temperatures, shows a warming trend in South Korea of 0.23•c per decade during the period between 1954 and 1999 and the data also indicate positive trends in both maximum and minimum temperatures for all seasons ( Figure 10) (Jung et al., 2002).

. Climatic change and rural-urban migration
In particular, long-run climate change scenarios tend to suggest that extreme climate variations and more specifically, water shortage are likely to cause abrupt changes in human settlements and urbanization patterns in sub-Saharan Africa more than anywhere else in the world (Watson et al., 1998). The specific effects of climate change on rural-urban migration in sub-Saharan Africa have, however, as of date been poorly documented. A particularly important starting-point is that sub-Saharan African agriculture is especially dependent on rainfall compared to most other developing countries, which triggers the potential impact of rainfall variations on economic activity (Barrios et al., 2003).

The rainfall dependence of sub-Saharan African agriculture
Generally speaking, agriculture in the African tropical area is seriously hampered by high temperature, fragile soils and low yield potential. The vulnerability to rainfall in the arid and semiarid areas of the continent also translates into a poor capacity of most African soils to retain moisture. Furthermore, evapo-transpiration is in