Agricultural production is affected by seasonal and sub-seasonal temperature and precipitation patterns, as well as solar radiation (the amount of incoming radiation from the sun) and evapotranspiration (the rate at which water evaporates from the soil and leaves of plants). In addition to the direct effects of climate change, the productivity of agricultural systems is also affected by the indirect effects of socially and ecologically-mediated responses to climate change, including changing soil properties, pest and disease outbreaks, and planting decisions. More broadly, the effects of climate change on agricultural systems occur within a context of other large-scale trends, such as a shift towards increased use of irrigation. Although a review of the impacts of these non-climate-related trends is beyond the scope of this manual, it is important to consider that their effects may be substantial, and may amplify or mitigate the effects of climate change in complex and non-linear ways. 

Changes in precipitation, temperature, and evapotranspiration can affect the quantity and quality of crop yields. In the tropics, many crops show decreased productivity with increasing temperatures (Figure 2.1). Temperature data, in contrast to precipitation data, show less spatial variability. Agricultural planners concerned with general temperature trends may find relatively coarse projections useful. Those concerned with identifying specific thresholds, especially in areas with varied orography, may need to consider tradeoffs between higher resolution models and increased uncertainty.

Agricultural impact assessments should consider not only the total quantity of precipitation, but also the variability of precipitation. Precipitation indices such as the length of dry spells, the intensity of rainfall on rainy days, and seasonal patterns can help to inform adaptation practices within the agricultural sector. However, daily precipitation is poorly modeled by both GCMs and RCMs. Models tend to project more days with light rain, while observations show fewer rainy days but more intense precipitation. This discrepancy makes accurate projections of precipitation variability indices difficult, and accounting for this uncertainty in crop models is crucial.  

Changes in cloud cover can also affect the amount of solar insolation an area receives. Whether or how clouds will change in the future remains one of the greatest outstanding sources of uncertainty in climate projections. While projections of future solar radiation in the region remain unsettled, agriculturalists should consider the consequences of this uncertainty.  

Evapotranspiration rates are determined by temperature, surface winds, plant characteristics, and air moisture content. Higher evapotranspiration rates decrease available soil moisture and crops’ water use efficiency, affecting agricultural productivity. Even in cases where models project increases in precipitation, soil moisture may remain unchanged or even decline if the increased evaporation expected with rising temperatures outweighs the effects of increased precipitation. Planting decisions, including what crops to plant, should consider the effect of evapotranspiration rates on water availability.  Changes in temperature and soil moisture content can also affect the rate of plant decomposition, which may alter soil nutrient composition. Increases in intense rainfall episodes can also cause increased runoff and soil erosion, which can affect crop productivity as well as the quality of neighboring water resources. 

The frequency and intensity of insect and disease outbreaks can also be affected by changes in temperature and precipitation. In some locations, pest outbreaks are tempered by the exceedance of certain low-temperature extremes; many pest populations cannot survive below specific temperature thresholds, and so an increase in mean temperatures could increase the probability that insect outbreaks occur. Agriculturalists concerned with pest and disease incidence may find tools focusing on climate extremes particularly useful. 

Livestock productivity is affected by the availability of grazing land, and the presence of parasites and pathogens. In general, higher temperature and humidity leads to increased rates of parasitism and pathogenesis. Indirect climate impacts, such as the disruption of traditional trade pathways, may also increase the risk of the introduction of new diseases to an area. Alterations to local vegetation from changes in precipitation, temperature, solar radiation, and evapotranspiration affect the availability of suitable grazing land, which in turn affects livestock productivity. 

In its simplest term, biodiversity refers to the variety of living things in an area. Biodiversity loss is of concern to conservationists, farmers, and natural resource managers. Ecosystems are complex systems, making assessments of the impact of climate change on biodiversity complicated. The same change in a climate variable in one area may yield different results in another. Adaptation practitioners interested in biodiversity require knowledge of the local ecosystem sensitivities to different climate variables.

Primary productivity refers to the amount of photosynthetically driven biological activity in an area. It may be generated by land or aquatic plants (i.e., algae), and ultimately forms the foundation of all ecosystem activity. Changes in incoming solar radiation (e.g., from changes in cloud cover) can impact the amount of primary productivity. Where temperatures are moderate, increases in temperature can increase plant productivity. Where temperatures are already high, further increases may have deleterious effects on productivity. Similarly, increases in rainfall may in many cases lead to an increase in primary productivity, yet flooding or intense rainfall can damage plants and reduce productivity. 

Many species prefer specific climates, and alterations in temperature and precipitation in a region can affect species abundance and distribution. This is especially true for land species. Higher temperatures may cause temperature-sensitive organisms to migrate to cooler locations, such as higher elevations. Changes in precipitation may affect some species more than others; physiological adaptations allow some plants to use water more efficiently, making these species more resistant to decreased precipitation. Changes in the variability of temperature or precipitation can also affect biodiversity, even when the mean for each variable remains steady. Many organisms have temperature or precipitation thresholds that they cannot exceed, and when these thresholds are exceeded species may migrate to more suitable climate zones (if they are able) or risk local extinction.

Finally, the departure of one species can effect the prevalence of others. Organisms that depend on the others (i.e. predators on prey) will likely respond similarly to the same climate variables. In contrast, organisms that compete with one another (i.e., plant species that compete for space) may increase if their competitors prove more sensitive to climate change. Understanding ecosystem responses to climate change requires knowledge of climate sensitivities and local ecosystem dynamics in addition to predictions regarding climate variables. 

Coral reefs exist along the coasts of Ghana, Côte d’Ivoire, and Guinea. They serve as tourist attractions and essential habitats for many economically important marine species. Reef-building coral species enjoy symbiotic relationships with single-cell plankton species called zooxanthellae that are sensitive to temperature changes. The presence of zooxanthellae is what gives coral its vibrant color. Increases in Sea Surface Temperatures (SSTs) can lead to the departure of these zooxanthellae, referred to as “coral bleaching.” Without this relationship most hard coral species struggle to survive. Absent reef-building hard coral, reef structures become degraded and other marine organisms may lose an important habitat.

The concerns of coastal adaptation practitioners likely overlap with other 

sectors, particularly infrastructure, biodiversity, and water resource management. Coastal zones are particularly sensitive to sea level rise and storm surge, which increases the probability of flooding and salt water incursion. Because of their detailed topography, coasts are poorly represented by coarse-resolution models. Downscaled regional models with precise topographical mapping are often necessary to assess coastal impacts.

Coastal erosion is often driven by wave activity. Changes in sea level, wind, and atmospheric pressure can drive changes in coastal wave patterns, affecting coastal erosion. Changes to the frequency and intensity of precipitation, together with human alterations to the landscape, can alter runoff patterns and impact erosive processes. Wind can also transport sediment, and changes in wind patterns can be an important factor in the erosion of sandy beaches or coastal dunes. Erosion can reshape coastal topography, which in turn affects coastal inundation patterns. 

Coastal flooding is heavily impacted by sea level rise, surge, and inland rainfall. An increase in the intensity of rain events—something that will become more common in a warming climate—can also lead to heightened flood risk, even absent an overall increase in precipitation. Assessments of coastal flood risk should consider changes in sea level, precipitation patterns (cumulative precipitation and precipitation intensity) as well as topographical changes such as coastal subsidence. 

The storm surge return period refers to the average length of time between storm surges of a particular height. With sea level rise, areas that may once have experienced storm surge every 100 years may now experience salt water inundation more frequently. An increase in the frequency of salt water inundation can affect coastal ecosystems and infrastructure. Projections of storm surge return periods require information on sea level rise, local topography and bathymetry, and expected changes in storm patterns and frequency. 

While beyond the scope of this manual, increasing carbon-dioxide concentrations leads to ocean acidification, which can have important impacts on ocean biodiversity and fisheries.

Climate change can directly affect the demand for energy. As temperatures rise, air-conditioning use, especially in summer, is expected to increase. While this will contribute to heightened energy demand, economic development is projected to be the primary driver of rising energy use in low-income, warm-climate countries. Projections of air-conditioning usage over the next century estimate that 25% of the expected increase will be attributable to climate change, while 75% will be attributable to higher incomes.

On the supply side, higher temperatures reduce the efficiency of electricity production and distribution. An increased probability of extreme events also poses a high risk to facilities for hydro, thermal, and renewable energy production, as flooding and debris from high winds can damage production facilities and power grids. Droughts or floods can also hinder fuel supply chains, especially those that rely on barges or rail, hence disrupting distribution. It should be noted that energy supplied from hydropower is particularly sensitive to changes in the hydrological cycle. Whether the mean annual precipitation in the West Africa region will increase or decrease remains uncertain, and professionals in the energy sector should account for this uncertainty when developing energy plans. Changes in precipitation intensity and seasonality can also affect the efficiency of hydropower production; seasonal shifts in inflow and increases in extreme precipitation can result in higher peak flows, which in turn can result in lost output, as the use of bypass channels will result in lost productivity while extreme water volumes increase the likelihood that damage to dams and turbines will occur. As temperatures increase, evaporation will also increase, reducing surface water availability absent comparable increases in precipitation. The effects of droughts on hydropower facilities will be enhanced under warmer climates, as increased evaporation will further reduce the storage buffer and, as a result, lessen the productivity of hydropower stations. Countries with energy sectors highly reliant on hydropower will need to prepare for future uncertainty. Increases in hydropower storage capacity can help offset the potential loss due to changes in peak flows, while investment in other renewable energy sources can help to mitigate against potential reductions in water availability.

As interest in other forms of renewable energy grows, value assessments should consider projected regional changes to relevant climate variables. Biofuel is produced from agricultural products, and like all agricultural products biofuel crops are highly vulnerable to increases in the frequency and intensity of drought. Sea level rise and extreme rainfall can also damage biofuel crops, as can reductions in the availability of water. Increases in mean temperatures are expected to stress biofuel production moderately. Solar and wind energy remain relatively resilient to drought, changes in the variability of water flow, and rising temperatures. Changes in surface winds can affect the productivity of wind turbines, as a reduction in mean wind velocity can reduce productivity while extremely high winds can damage wind energy infrastructure. Sea level rise and storm surge can cause flooding and thus pose a moderate threat to all forms of renewables, as salt water incursion can damage cropland and solar and wind energy infrastructure. An increase in extreme rainfall and flooding poses a high threat to all forms of energy production, including all forms of renewable energy, which can damage production infrastructure, and power grids, and disturb distribution paths. However, decentralized systems, such as solar micro-grids, can increase energy sector resilience to natural hazards, and may be particularly appealing in remote regions where connections to larger grids are more costly.

Higher temperatures can have direct impacts on human health, increasing the incidence of heat stroke and heat-related respiratory illnesses. Heat stress occurs when the body is not able to cool itself fast enough to maintain a healthy temperature. Left untreated, heat stress can result in heat stroke and eventually death. Children, the elderly, and people with certain cardiovascular or respiratory conditions are particularly vulnerable to heat-related death.

Higher temperatures and increased humidity substantially impact the human body’s ability to maintain a healthy temperature. Evaporative cooling from sweat is one of the human body’s primary methods of thermoregulation. High environmental temperatures and/or physical exertion lead to increases in body temperature. When humidity increases, the rate at which sweat can evaporate decreases, and cooling occurs less efficiently. Together, these effects can lead to increased potential for heat stress and heat stroke. In assessing the probability of heat related illnesses, healthcare practitioners and public health officials should consider a heat index, like wet bulb global temperature, that accounts for both temperature and humidity (figure 2.3).

With mean temperatures in West Africa expected to increase, public health officials should also consider projections related to the length and intensity of heat waves, as well as other factors that could influence heat, such as increases in impervious surfaces associated with urbanization, and the exacerbation of the urban heat island effect. This climate information should be considered alongside population characteristics, such as the age and health status of the general population.

The incidence of infectious diseases can also be affected by changes in climate. Vector-borne diseases such as malaria and dengue depend on climatic conditions (temperature, water availability) suitable for vector populations. As temperatures increase, malaria zones are expected to shift or expand. In particular, many communities at higher elevations, which historically have had little exposure to malaria, are expected to see the encroachment of malaria endemism. Public health officials should consider that these human populations likely have less resistance to the disease than their low-lying counterparts, who are more likely to have some native immunity from generations of exposure.

GCMs provide coarse resolution projections that may not capture the level of topographical detail necessary to represent precise temperatures in mountainous regions. However, using projected temperature anomalies, practitioners can consider shifts in temperature thresholds and anticipate the migration of malaria zones.

Waterborne diseases like cholera may also be impacted by changing precipitation patterns, especially increases in high-impact rain events. Increases in the incidence of natural hazards, particularly flooding, can lead to contamination of surface water sources. Public health officials should collaborate with practitioners focused on water resources and natural hazards to determine the likelihood of contamination. Recent progress in disease early warning systems may also allow the deployment of preventative and early intervention measures.

Civil engineers and urban and regional planners are concerned with how changes in climate will affect the construction and maintenance of hard infrastructure. Infrastructure planning can occur at varied spatial scales; projects can range from regional rail systems to a single building. Accordingly, climate projections from regional to local scales may be relevant to infrastructure adaptation. Tradeoffs between spatial precision and the increase in uncertainty in downscaled models should be considered by sectoral practitioners.

Sea level rise and changes in the intensity of rainfall can increase the probability of flooding over bridges and roads. Builders should consider sea level rise, storm surge, and changes in flow regimes when determining the height and pitch of bridges that cross coastal waterways. Further inland, an expected increase in precipitation intensity should be considered. With heavier rainstorms, flash flooding is expected to occur more often. Unpaved roads are particularly vulnerable to increasingly intense precipitation, which can result in washout. Changes in flood patterns are also affected by other sectors. For example, coastal erosion and water management policies can affect flow regimes and hence the vulnerability of infrastructure projects to flooding. In addition to climate information, infrastructure managers will likely require input from other relevant sectors.

Construction of new buildings and retrofitting of existing structures should also consider the impacts of increased temperatures. Increases in temperature and humidity will require more airflow within buildings, which may necessitate improvements to fans or air-conditioning systems. Climate change can also affect the weathering of infrastructure. At higher temperatures transportation infrastructure softens and expands, which can cause permanent structural damage. Salt water incursion can also enhance weathering of both transportation infrastructure and buildings, leading to higher maintenance costs.

Water resource managers are concerned with water availability, accessibility, and potability. Changes to surface and groundwater levels are determined by the balance between water inflow and outflow, and impact assessments should be wary of uncertainties in precipitation projections and future human use patterns. Responses to climate change by other sectors can also indirectly affect the availability of potable water in a region. For example, changes in agricultural practices can lead to increased runoff, affecting water quality; impacts to the energy sector, such as increased frequency of electricity outages and disruption of fuel supply chains, can affect groundwater accessibility. Water resource managers are familiar with other impacts on the water supply, such as changes in human populations or the impacts of new industries on water use, and should consider how climate impacts on different sectors may affect water availability.

Water flows to an area are determined by precipitation and surface runoff, and below-ground movement of water from one location to another. Water flow paths are determined by surface topography and the structure and features below ground. In mountainous areas a substantial portion of rainfall is provided by orographic precipitation. In these areas, coarse-resolution GCMs may be inadequate to project future rainfall and therefore surface water availability. On the other hand, spatial precision may be less necessary when considering water supply over a large watershed, and so the type of data used may depend on the size of the geographic area of interest.

The best data for precipitation are derived from station measurements. However these provide little insight into future precipitation trends. Precipitation tends to show considerable spatial variability, so interpolated or reanalysis data should be used with caution, particularly over areas with sparse meteorological stations or variable topography. GCM simulations of precipitation also poorly replicate daily precipitation. Models tend to project more days with light rain, while observations typically show fewer rainy days with more intense precipitation. High rainfall intensity can increase surface runoff (and reduce soil moisture recharge), so local hydrologists should consider that GCM and RCM projections of rainfall likely underestimate the daily variability of precipitation and may overestimate soil moisture recharge.

Loss from a watershed is determined by evaporation rates, human usage, and outflow rates. Evaporation rates increase with higher temperatures and faster surface winds. However, they decrease with increased humidity. Temperatures in target countries are expected to increase over the next century. While humidity may also increase in some areas, an overall trend towards increased evaporation is expected. Accessibility and potability can also be affected by water storage patterns. Groundwater (water stored in aquifers below ground) can be more difficult to access than surface water (water stored in lakes or rivers). However, groundwater, which is filtered by layers of rock and soil, is also less susceptible to contamination.

Because adaptation assessments often originate from the need to understand and address changes in natural hazards and climate impact, we focus here on climate information requirements to better characterize the frequency and intensity of natural hazards. For example, an analysis of changes in the length of dry spells over a historical period for a particular region would enable understanding of the severity and extent of drought conditions. Of course, not all climate-related disasters are caused by climate change; for example, flooding may be due to changes in land cover, and the impact on society that makes it a “disaster” depends on the exposure of things that humans value (e.g. buildings, infrastructures, farms). However, understanding the role of climate change in exacerbating these impacts is vital for adaptation. Through the identification of climate analyses that help explain historical, current and future changes in natural hazards/climate impacts, stakeholders can focus their efforts on understanding a specified subset of climate information.

SEVERE DROUGHT

The greatest contributing climatic factor in the duration and spatial extent of severe drought is precipitation. Temperature,  human-induced land use change, agricultural practices, and soil quality and moisture can also contribute. Analysis of extremely low rainfall amounts over a historical time-period can demonstrate the anticipated duration of a drought event, while monitoring and forecasting of seasonal rainfall can provide an early drought warning, and projected changes in precipitation can show worsening or alleviating drought conditions over the course of the 21st century. Table 1.2 provides a summary of climate analyses that are needed to understand severe drought at various timescales.

Typical Variables		Time Frame
	Historical Climate	Monitoring & EWS	Projections
Number of consecutive days with high maximum temperature Maximum temperature	Historical changes in maximum temperature Maximum temperature thresholds Duration of high temperature sequences (above a certain critical threshold)	High temperature sequence monitoring Weather/extended weather forecast Seasonal probabilistic temperature forecast	Downscaled projections of changes in maximum temperature: magnitude; duration Probabilities of exceeding high temperature sequences

CHANGES IN RAINFALL PATTERNS AND GENERAL DROUGHT CONDITIONS

Changes in rainfall patterns (i.e. the spatial distribution of rainfall, its seasonal onset, and general drought conditions) can be understood through analysis of average precipitation. Since it is vital for the agricultural sector to know about changes in the onset of the rainy season and how much rainfall is expected, investigation of total annual and seasonal precipitation is necessary. Unlike severe drought, which involves analysis of extreme precipitation, understanding changes in rainfall patterns and general drought conditions requires analysis of changes in average precipitation. Deviations from average precipitation are referred to as anomalies and can be calculated for each year and/or season. Table 1.3 provides a summary of climate analyses that are needed to understand potential changes in rainfall patterns and general drought conditions at various timescales.

Typical Variables		Time Frame
	Historical Climate	Monitoring & EWS	Projections
Climate Analysis	Historical changes in average seasonal or annual precipitation Historical changes in average daily precipitation (i.e. dry spell duration)	Cumulative rainfall Seasonal probabilistic rainfall forecast	Downscaled projections of changes in average seasonal or annual precipitation Changes in the amplitude of variability

FLASH FLOODS

In contrast to severe drought, understanding flash floods requires analysis of extreme precipitation events. Rapid flooding of low-lying areas is often associated with heavy rain and severe storms. Soil moisture is also an important non-climatic influencer. Historical analysis of extreme high precipitation events can help to understand the probability of a rare flood event and the chances of one happening in the future. Flood early warning systems are essential for disaster preparedness and evacuation. Regional projections of extreme high precipitation events are needed since climate change might negatively affect the frequency and intensity of such events. Furthermore, hydrological, infrastructural, and adaptation planning processes require this type of information. Table 1.4 provides a summary of climate analyses that are needed to understand flash flood events at various timescales.

Typical Variables		Time Frame
	Historical Climate	Monitoring & EWS	Projections
Hourly or daily rainfall or rainfall intensities	Historical variability and trends in extreme high precipitation Thresholds based on past events	Weather forecast 10-day climate Bulletin-Dekadal probabilistic rainfall forecast	Downscaled projections of extreme precipitation, using thresholds based on historical analysis

SEASONAL FLOODING

Most West African countries experience seasonal flooding during the rainy season, which can vary in intensity depending on the West African Monsoon and other large-scale convective processes. Seasonal rainfall is a natural phenomenon that occurs due the north-south movement of the Intertropical Convergence Zone (ITCZ). Predictors with the greatest correlation to seasonal flooding include total seasonal rainfall and seasonal rainfall intensity, defined as total precipitation divided by the number of rainy days (de Perez et al., 2017). Understanding such predictors has become increasingly important due to observed changes in the rainy season and increased flooding intensity in certain areas as a possible impact of climate change. Additionally, sea level rise is another important climate change impact that should be investigated locally since it may exacerbate seasonal flooding.

Typical Variables		Time Frame
	Historical Climate	Monitoring & EWS	Projections
Average daily precipitation Consecutive number of rainy days	Historical changes in average precipitation and length of wet sequences	Seasonal probabilistic rainfall forecast	Downscaled projections of changes in average precipitation and length of wet sequences

EXTREME HEAT EVENTS

An extreme heat event refers to an extended period of time (several days or more) with unusually hot weather conditions that can potentially harm human health. Increases in average global temperature are projected to make heat events last longer and occur more frequently. Both average and extreme temperature can be analyzed to better understand extreme heat events at various time scales. As shown in figure 2.3, an increase in average future temperature results in more “hot weather”.
In addition to average temperature analysis, projections using GCMs and RCMs for number of days above a certain temperature threshold can also be made to specifically analyze changes extreme heat events. Temperature monitoring is needed for short-term forecasting and early warning in preparation for such extreme events. Although there is emphasis on rainfall early warning systems for agricultural purposes, temperature early warning systems are just as important for human health and survival. Table 6 provides a summary of climate analyses that are needed to understand extreme heat events at various timescales.

Typical variables		Time Frame
	Historical climate	Monitoring & EWS	Projections
Cumulative rainfall amounts Dry spells (number of days with rainfall below a certain amount) Evapotranspiration	Historical variability and trends of cumulative rainfall Historical length and distribution of dry spell lengths	Standardized Precipitation Index (SPI) Length of current dry spell Water satisfaction index (WRSI) Seasonal rainfall forecast	Seasonal rainfall and temperature Daily rainfall distribution Daily maximal and minimal temperature Changes in distribution of length of dry spells Probability distribution of WRSI

DISEASE OUTBREAKS

Appropriate climate and weather conditions are necessary for the survival, reproduction, distribution, and transmission of disease pathogens, vectors, and hosts. Therefore, changes in climate or weather conditions impact the ability of infectious diseases to survive and proliferate. Particularly, excessive heat can increase mortality rates for some pathogens; rising temperatures can influence their reproduction and extrinsic incubation period; and extended periods of hot weather can raise the average temperature of water bodies and food environments, which may provide an agreeable environment for microorganism reproduction and algal blooms. With increased precipitation there is often an associated increase in fecal pathogens during the rainy season; droughts/low rainfall lead to slow river flows, causing a concentration of effluent water-borne pathogens. Humidity, sunshine, and wind also impact the survival, reproduction, distribution, and environment of disease pathogens and hosts (Wu et al., 2016). Due to the variety of climatic factors and interactions that influence disease outbreaks, it is difficult to model disease outbreaks. However, there are disease monitoring resources available, including the Malaria Early Warning System (MEWS), developed by the International Research Institute for Climate and Society (IRI) and National Malaria Control Program (NMCP).