In recent years, a noticeable variability has been observed in hydro-climate due mainly to unsustainable human activities that has contributed to the unpredictability in climate change pattern (Sharafati et al., 2019; Jarju et al., 2021; Dehghannik et al., 2021). This variability in climatic pattern significantly increased the impact of hydro-climatic hazards such as drought, hurricanes, floods and heat waves hence decision-makers across the globe are concern. Gurain-Sherman, (2012) opined that drought is complex; the duration of drought, the time it occurs as per the growth stage of crops, the characteristics of the particular soil affected, the temperature at the time, farmers’ choices of crops are all factors that influence the drought intensity/severity and how it may eventually impact food production. Orimoloye et al., (2020) stated that the harshness of drought may comprise reduction in the quantity and quality of potable water, compromise food security, cause an outbreak of hunger-related diseases and in severe cases food scarcity.
Unlike earthquake or flood, drought can occur anywhere. Drought moves slowly, its beginning and termination have been noted to be difficult to predict, and drought repercussions can endure for years after the event has ended (Wilhite & Glantz, 1985; Komuscu, 1999; Dai, 2011; Carrão et al., 2016; Achberger, 2020). Due to their slow onset, vast spatial extent and prolonged duration, droughts belong to the world's most catastrophic natural calamities, the consequences of which have been observed across Africa (Ahmadalipour & Moradkhani, 2018; Winkler et al., 2017). Disasters that are climate-related such as flood, storm, sea-level rise, drought and other extreme weather events accounts for 91% of all disasters worldwide between 1998 and 2017 (CRED & UNISDR, 2018). Of this, 4.8% accounts for drought within the ten years period affecting about 1.5 billion people. Although prevalence in terms of occurrence is lower, drought affects large populations than any other disaster. “In years when serious droughts occur in major food-producing regions, crop losses can affect the global food supply and food prices. This occurred in 2008, when Australia, a major global wheat producer, lost substantial production because of severe drought” (Gurian-Sherman, 2012).
Drought and Climate Change
Himanshu et al., (2015) opined that drought is considered to be the most intricate but least understood of all natural hazards, considering the large number of people its impacts affect. Causes of drought is attributed to two main factors (Smith & Petley, 2013; Eldho, 2014), these are physical and human factors. Typically, physical causes of drought are initiated by atmospheric circulation and weather systems that resulted in lower precipitation and/or higher evaporation than the “normal” of a region and can be directly triggered by human activities (Sierra-Soler et al., 2016; Bi et al., 2021). Teleconnections, which means the “linkages between climate anomalies occurring at long distances apart”, sea-surface temperature anomalies (SSTAs), and descending air due to El Nino conditions (ENSO) are all implicated in the causes of drought phenomenon (Smith & Petley, 2013). Human factors attributed to causes of drought range from bad agricultural practices, deforestation, excessive irrigation, soil erosion, climate change due to emission of GHGs, urbanization and so on. Major droughts are centred in semi-arid regions of the world such as the Great Plains of USA, West African Sahel, East and South Africa, India and Australia (Wilhite, 2012; Smith & Petley, 2013). In developing countries, (Smith & Petley, 2013) drought is best described as a “complex emergency” due to the myriad issues that makes vulnerability to drought impact severe. Climate drivers such as precipitation changes and temperature trends are commonly used at a spatiotemporal scale to observe the effects of climate change (Menzel et al., 2020; Islam et al., 2021). Climate has a significant impact on vegetation dynamics and growth. It has an impact on soil moisture, nutrients, microbial activity, and atmospheric conditions, affecting plant physiology and growth as a result (Islam et al., 2021).
Adaptation Strategies
Although drought hazards begin slowly and have severe results, the impacts of drought catastrophes can be mitigated with careful planning and mitigation measures. According to the UNEP's Adaptation Gap Report (2020), the benefits of investing in adaptation outweigh the costs. A $1.8 trillion investment in early warning systems, climate resilient infrastructure, improved dryland agriculture, global mangrove protection, and resilient water resources, according to the Global Commission on Adaptation, could result in $7.1 trillion in avoided costs and non-monetary social and environmental benefits. To achieve disaster mitigation plan components, the following strategies can be used: forecast, monitoring, impact assessment, and reaction (Orimoloye et al., 2020). The monitoring of meteorological droughts is the most important part of drought avoidance. However, it is exceedingly difficult to detect, forecast, and track meteorological droughts and their spatial fluctuation (Dai et al., 2020). According to Javadinejad et al. (2020), a hazardous environment does not imply or correlate with harm and vulnerability. A lack of resilience and mitigation techniques, as well as a lack of knowledge and perception, all contribute to the population's suffering. According to Quraishi (2018), drought adaptation measures include both on-farm and off-farm activities. These programmes are intended to strengthen farmers' resistance to the effects of drought on agricultural products and farmers' livelihoods. On-farm resilience adaption options include, but are not limited to, postponing planting date, modifying cropping system, applying mulch, gap filling where prior crop germination failed, resowing, and crop irrigation/dripping system application. Income diversification, business/trade, migration, non-agricultural labour, and asset sale are examples of off-farm fundamental adaptation techniques. Ngwaru (2021) observed several adaptation practises such as rainwater harvesting in tanks and ponds to be used during dry spells or drought; trainings on soil and water conservation strategies; and the cultivation of drought-tolerant cereals such as pearl millet, sorghum, and finger millet that can be stored for longer periods without spoiling. Another key adaptation method was public awareness campaigns, which educate residents for future natural disasters by developing community-based disaster risk reduction initiatives. According to him, this allows for the identification of local priority levels, which leads to the development of initiatives that help to the mitigation of drought impacts.
Farmers in The Gambia have implemented many drought adaptation tactics, including the use of improved crop varieties such as NERICA (New Rice for Africa) and early maize; crop rotation; water saving techniques; water diversion; and the use of natural and artificial fertilizers. Furthermore, mixed farming is utilized. Poultry farming and animal husbandry have been fostered in various rural communities, particularly in the North Bank Region and Central River Region, where the drought phenomenon is common. This is done to lessen the likelihood of a bad crop in the event of low rainfall or a drought (Har, 2019; GoTG/UNCCD, 2020). These methods and improved crop types are utilised to attenuate and develop population resilience (Bagagnan et al., 2019; Segnon et al., 2021).
Three rainfall periods were experienced in the Sahel region between 1950 and 2020. The first period (1950-1969) was characterised by positive rainfall, having abundant rainfall. The second period was between 1970 and 1993 when a negative (anomaly) was experienced. This period witnessed the long and persistent Sahelian drought which causes havoc on humans and livestock. The last period was between 1994 to-date. This period experienced neither persistent heavy rainfall nor continuous drought but variability of heavy rainfall years and dry periods (GoTG/UNCCD, 2020).
According to GoTG/UNDP, (2015) and Carré et al., (2019) “Historical climate records in The Gambia indicate a shift in the rainfall pattern. From 1950 to 2000, annual rainfall amounts have decreased by about 30%. This decrease has been evident in the reduction in the length of the rainy season and also the quantity of rainfall amounts recorded in the month of August, particularly during the period 1968 to 1985, and in 2002. The erratic rainfall pattern has caused some impacts on the farming system such as reduction in the length of growing season and the additional and frequent mid-season dry-spell also causes drought conditions for farming purposes even during normal rainfall conditions. The Gambia is very sensitive to loss and damage from climate change, notably from climate extreme events such as droughts, as predicted long-term trends in drought and rainfall variability are projected (GoTG/UNCCD, 2020).
A number of indicators have been developed to detect and monitor meteorological droughts such as Standardized Runoff Index (SRI), Standardized Precipitation Index (SPI), standardized precipitation evapotranspiration index (SPEI), Palmer drought severity index (PDSI), effective drought index (EDI) and reconnaissance drought index (RDI) (Anshuka et al., 2019); Normalized Difference Vegetation Index (NDVI), Crop Moisture Index (CMI) Standardized Precipitation Index (SPI) and Surface Water Supply Index (SWSI) are most preferred indices for agricultural drought monitoring, forecasting and water resources management (Himanshu et al 2015); Vegetation Condition Index (VCI), Vegetation Health Index (VHI), Land Surface Temperature (LST), Temperature Condition Index (TCI) are satellite-based assessment indices to assess cumulative moisture, temperature, and vegetation health (Jiang et al. 2021). This paper used SPI, PAP and VCI. The former two indicators are mainly based on precipitation data which is easily accessible and computation is easy. VCI was used to complement the precipitation data in order to highlight the impact of rainfall on vegetation quality. It is said to be more effective in portraying drought impact on vegetation compared to the commonly used NDVI.
The main objectives of this study are to determine the state of drought in The Gambia in terms of spatial extent and temporal variation and highlight local adaptation measures against drought hazard in The Gambia.