Introduction 

The global climate changes observed in recent decades have caused social and environmental impacts across the planet. Floods, droughts, greater irregularity in rainfall, increased temperature and heat waves, sea level rise, are examples of phenomena linked to climate change that highlight the vulnerabilities of territories and aggravate risks in different natural and environmental systems. The increase in the concentration of greenhouse gases of anthropogenic origin is the main cause of the warming of the atmosphere, oceans, and the earth’s surface, intensifying these extreme climatic events.

According to the IPCC, natural disasters are increasingly frequent and severe, and governments, especially those in less developed countries, have limited capabilities to deal with the associated risks, to ensure the protection of their citizens. The global average surface temperature in 2011–2020 was 1.1°C higher than in the pre-industrial period [(1850–1900); (IPCC, 2023)], and the impacts of climate change will have disproportionate consequences globally and will be particularly severe in developing countries, where poor communities are highly dependent on the direct use of local natural resources.

On the African continent, the economy of most countries is strongly dependent on rain-fed agriculture, particularly in West Africa and including Guinea-Bissau, representing one of the major concerns regarding the planning of agricultural activities and food security. The relevance of these problems motivated the carrying out of the present investigation, dedicated to the study of climate trends in a small country in West Africa (Guinea-Bissau).

Mangrove rice farming is of great importance for food security in the country, since rice is the basis of the Guinean population’s diet, with an annual per capita consumption of approximately 125 kg and its cultivation depends solely on rainfall. Reduced rainfall can contribute to an increase in salt concentration in cultivated areas, which is particularly detrimental to rice crops, which cannot withstand excess salt. Extreme rainfall floods the plots and hinders agricultural activities and the development of rice due to the lack of water management capacity. Despite many studies that have analyzed the past climatic trends in West Africa, no one has focused on this specific territory to investigate the potential effects of recent climate variability on rice production.

West Africa has been affected by strong interannual variability in precipitation, manifested by severe droughts and floods over recent years. According to the IPCC report, negative trends in the evolution of precipitation were observed in West Africa between 1960 and 1980, accompanied by an increase in its variability. The economy of most countries in this region depends on rain-fed agriculture and climate variability strongly affects these countries due to the irregularity of the rainfall regime, which can be manifested by its late onset and/or early end.

Results and discussion 

Precipitation trends

The study of the evolution of precipitation in Guinea-Bissau over the longer period 1960–2020 reveals that, despite the slight reduction observed in Figure 3 in each of the three meteorological stations, no significant trend was detected. In a more detailed analysis, in addition to this general trend of decreasing precipitation throughout the climatological series, it is possible to identify three particular periods: the first period corresponds to 1960–1967, characterized as being the wettest period of the entire series; the second period is defined by the years 1968–1990, characterized by a greater predominance of dry years, such as the years 1968 (Figure 3, a–c), 1972 (Figure 3 b, c), 1977 and 1984 (Figure 3 a, b) and 1981 and 1982 (Figure 3, c); finally, the third and final period.

Discussion

In the present investigation, the monthly average maximum temperatures showed significant increasing trends in the period 1960–2020, especially in the months that coincide with the different phases of the development of the mangal rice plant (June to November), while the monthly average minimum temperatures also followed the same increasing trend (except for June and July, in Bolama). As maximum temperatures continue to rise during critical stages of rice development, this crop will inevitably suffer, leading to adverse effects on production. This may jeopardize the food sovereignty of the peasant communities reliant on rice farming for their sustenance.

With the rise in monthly temperatures, the average annual maximum and minimum temperatures have also increased over the same period. The detected trend of increasing maximum and minimum temperature in Guinea-Bissau over the period 1960–2020 is in line with regional trends identified in other studies focused on West Africa, such as USAID. Other studies conducted in different regions of the world also indicate an increase in annual average maximum and minimum temperatures.

Regarding the evolution of total annual precipitation (1981–2020), an increase of 42,0–82.6 mm/decade was detected in the study, being significant in Bafatá, contrary to what was found in the longer climatological series − 1960–2020, where a slight decreasing behavior was observed. In fact, the period of the 70s was predominantly dry in West Africa.

The reduction in total rainfall and its irregularity in the country can impact the mangrove rice crop, which needs enough water for the leaching of salt in the plots for a good development of the crops. Mangrove ecosystems, due to their location between the sea and the mainland, will be impacted by rising temperature trends because this phenomenon is related to sea level rise that will flood the mangroves and if they exceed the physiological tolerance of the trees, and impact will be even greater.

Regarding the effects of recent climate change on agriculture and the cultivation of mangrove rice in the coastal regions of Guinea-Bissau, several adaptation strategies and measures can be explored. According to Hussain et al., and Padhy et al., these adaptation measures that be carried out by the peasants include four main issues: adjustments of cultivation dates; use of climate forecasts for planning agricultural activities; choice of cycle varieties suitable for each rain season; and development of protective dike structures resistant to rising sea level. On the other hand, it is very important that the entities responsible for national agricultural policy can support investment in rice cultivars with higher yields and tolerance to salt and water stress.