Spatial modelling of minimum temperatures over Ghana between the periods 2021-2040 and 2041-2060

 Abstract 4

1. Introduction 5

2. Methodology 7

3. Results and discussion 10

4.Conclusion 13

References 13

 

SPATIAL MODELLING OF MINIMUM TEMPERATURES OVER GHANA BETWEEN THE PERIODS 2021-2040 AND 2041-2060

Abstract

Global climate change is a prominent topic of concern globally and rising temperatures have been the most crucial marker of its occurrence. This study examines future minimum temperature variations (t-min) in Ghana under the high-emission Shared Socioeconomic Pathway scenario SSP5-8.5 using CMIP6-based projections for the next decades: 2021-2040 and 2041-2060. By calculating spatial differences and temperature anomalies during these periods, the projection identifies regions most exposed to warming trends. The projected maps demonstrate an intensifying trend in minimum temperatures, with the highest warming observed in northern and transitional ecological areas. These increases are expected to exacerbate threats in agricultural productivity, water resources, and human health. The findings underscore the importance of tailored adaptation policies and climate-resilient growth. Two-time frames in the future were selected to be compared, 2021-2040, the near-future climate baseline, appropriate to short- to-mid-term planning for adaptation. 2041-2060, the mid-century climate outlook, spanning incremental warming under continued high emission pathways. These data are accessible via this link: https://www.worldclim.org/data/cmip6/cmip6_clim10m.html. A temperature anomaly map was also simulated by subtracting the near-future (2021-2040) and mid-century (2041-2060) projections.

Keywords: Minimum temperature, SSP5-8.5, CMIP6 projections, Ghana, climate change, regional vulnerability, temperature anomaly.

Citation: Sanusi, A., (2025). Spatial modelling of minimum temperatures over Ghana between the periods 2021-2040 and 2041-2060. DOI:10.13140/RG.2.2.10597.67047.

1. Introduction

Anthropogenic climate change remains one of the defining environmental challenges of the 21st century, with temperature increases serving as a key indicator of global warming [1]. The rise in minimum temperatures plays a significant role in altering ecosystem dynamics, agricultural productivity, hydrological cycles, and human health outcomes [2]. Across sub-Saharan Africa, warming trends are accelerating faster than the global average, exacerbating existing socio-economic vulnerabilities [3].

Temperature projections are essential for identifying climate risks across ecological zones and informing adaptation strategies aligned with national development goals and international commitments, including Ghana’s Nationally Determined Contributions (NDCs) and the United Nations Sustainable Development Goals (SDGs). Previous studies on Ghana’s climate indicate a consistent rise in mean annual temperature between 0.21°C and 0.54°C per decade, with northern regions warming at a significantly faster pace [4]. However, there remains a need for detailed spatial analysis focusing on projected minimum temperatures, particularly during transitional climatic periods such as May, which influences agricultural planting cycles and hydrological patterns. Using CMIP6 projections from the Global Climate Model ACCESS-CM2, this study evaluates future minimum temperature distributions for two timeframes (2021-2040 and 2041-2060) under the SSP5-8.5 scenario. The analysis examines temporal shifts, quantifies temperature anomalies, and highlights spatial disparities in vulnerability.

Accordingly, this study aims to address the following objectives:

 (i) To analyse projected minimum temperatures across Ghana for the periods 2021-2040 and 2041-2060 under SSP5-8.5

 (ii) To quantify spatial anomalies in temperature between the two periods

 (iii) To identify ecological regions most vulnerable to rising minimum temperatures

1.1 Study area

Figure 1. Projected maps showing minimum temperatures and anomaly map between periods 2021-2040 and 2041-2060.

2. Methodology

2.1 Study area

This study focuses on the minimum temperatures over Ghana, in the Sub-Saharan Region with 4°45′N and 11°11′N Latitude and 3°15′W and 1°15′E Longitude. Ghana sits in the tropics, and its climate is typical for the region. Ghana is vulnerable to swings in temperature and the looming impacts of climate change, which makes it a key place to dig into future temperature trends.

2.2 Data source

I accessed and downloaded future minimum temperature data from the WorldClim version 2.1 CMIP6 dataset. I used the ACCESS-CM2 global climate model under the high emissions scenario SSP5-8.5. The dataset offers monthly minimum temperatures (t-min). I chose two time periods for this study: 2021-2040 (near-future) and 2041-2060 (mid-century). The data processing and mapping was done in QGIS version 3.44.1. To set the boundaries, I downloaded Ghana’s administrative boundary from the Global Administrative Areas (GADM) database and used the boundary as a mask for clipping the data.

2.3 Temperature data preparation

I loaded the downloaded dataset for both 2021-2040 and 2041-2060 files (GeoTiIFF) into QGIS (Layer → Add Layer → Add Raster Layer) with the correct Coordinate Reference System WGS84 (EPSG: 4326). I extracted all the months of May layers for the two periods 2021-2040 and 2041-2060 by using Raster Calculator and then clipped them to the Ghana boundary. To see how minimum May temperatures change between the near-future and mid-century, the anomaly was computed as:

 (Δt-min)

Δt_May = (t_May, 2041-2060) – (t_May, 2021-2040). Where, Δt_May is the change in minimum May temperature (in °C). t_May, 2041-2060 is the projected mean minimum for May in the mid-century 2041-2060, and t_May, 2021–2040 is the same for the near-term. If Δt_May results are positive, that indicates warming and negative results indicates cooling.

2.4 Map visualisation

I used QGIS’s “Singleband pseudocolour” renderer to visualise the rasters. To show temperature distributions, sequential gradient ramp was used like Reds for the temperature change (Δt-min). Discrete was used for interpolation and I kept the classification ranges the same across maps, so they are easy to compare. Finished maps were exported at high resolution and labelled with scale bars, north arrows, and legends for easy interpretation.

2.5 Uncertainty and model limitations

Even though WorldClim applies bias correction to the CMIP6 models, there is still uncertainty model structures, scenario assumptions, and the way data gets downscaled. For this study, GCM (ACCESS-CM2) was only used. Future studies should look at multi-model ensemble means or compare different SSPs.

3. Results and discussion

(i). Map: 2021-2040 t-min (Baseline Future Period for May) see figure 1 above.

This map shows near-future projected baseline minimum temperatures for May.

Warmer zones are also observed in north and central Ghana, with comparatively milder conditions persisting in southern and coastal belts.

Significance:

It gives a reference period to make comparisons in the future.

It allows detection of early signs of warming, especially in the transition and savannah zones.

(ii). Map: 2041-2060 t-min (Projected mid-century conditions in May) see figure 1 above.

This map illustrates persistent warming trends under ongoing emissions.

The northern sector becomes much warmer with the minimum temperatures rising further.

Coastal and forest areas also show detectable warming.

Significance:

It shows long-term warming magnitude.

It signals a shift from moderate to more heat stress times.

It Informs long-term adaptation plans, especially for future urban development and agricultural lands.

(iii). Map: Anomaly (2041-2060 vs 2021-2040) see figure 1 above.

Most critical map, it shows the difference between the two periods.

Regions with darker red hues are those with the greatest temperature rises.

The highest temperature anomaly is seen in northern Ghana, followed by transitional central regions.

Significance:

It quantifies the degree of warming.

It reveals emerging hotspots of climate vulnerability.

It is useful for intervention area prioritisation.

PROJECTED MINIMUM TEMPERATURES FOR 2021-2040 (Near-Future Period)

The modelled minimum temperature trend for the near-future (2021-2040) depicts a consistent increase over Ghana, with apparent spatial differentiation along a north-south transect. There are comparatively lower minimum temperatures over the southern coastal and forest zones, while the transitional and savannah zones experience relatively higher minima.

Of observation is that the Coastal Savannah and Forest zones maintain moderately warm night-time temperatures, consistent with maritime and humid climatic influences.

The Transitional zone shows a large jump compared with the Forest zone, marking the onset of high warming. Guinea and Sudan Savannah regions in the north experience the highest minimum temperatures projected, consistent with their semi-arid climatic conditions. These projections suggest that minimum temperature increases are already showing up as early signals of incremental warming in the northern parts of Ghana.

PROJECTED MINIMUM TEMPERATURES FOR 2041-2060 (Mid-Century Period)

By the mid-century period (2041-2060), minimum temperature projections show further intensification of warming across all ecological zones. The pattern of warming becomes more spatially consistent, with the northern sections registering significant increase in night-time temperatures. The Transitional and Bono East areas also show increased warmth, reflecting the expansion of semi-arid climatic conditions.

The southern regions, which cover the Forest and Coastal Savannah zones, also show greater minimum temperature values than the near-future period. The warming rate, nevertheless, is slightly lower than that of the northern and transitional ecological zones. The observed change has the implication that northern Ghana will face a greater risk of heat-related stress and reduced night-time cooling, with ramifications for both ecological sustainability and human well-being.

TEMPERATURE ANOMALY BETWEEN 2041-2060 AND 2021-2040

The anomaly projection, computed as the difference between the near future (2021-2040) and the mid-century (2041-2060), reveals distinct hotspots of warming. The northern regions of the country, namely the Northern, Upper East, Upper West, Northeast, and Savannah Regions, present the highest anomaly values, indicating an extreme rise in minimum temperatures.

The Transitional zone, which includes areas such as Bono East and the northern sections of the Ashanti Region, has modest anomalies, suggesting increasing exposure to heat stress. The southern ecological zones, despite relatively smaller anomalies, continue to exhibit ongoing warming trends, which may result in cumulative thermal stress over the long term.

4.Conclusion

 In all projections, a prominent north–south warming gradient is obvious. Systematically higher projected minimum temperatures and greater anomaly values are present for northern Ghana relative to central and southern Ghana. The susceptibility of savannah-dominant regions to incremental climatic warming is therefore high, with greater likelihoods of enhanced land degradation, drought occurrence, and socio-economic exposures. The projections demonstrate an incremental rise in minimum temperatures across all ecological zones in Ghana, with the greatest increments being projected in the northern region.

References

[1] R.P. Allan, P.A. Arias, S. Berger, J.G. Canadell, C. Cassou, D.L. Chen, A.

Cherchi, S.L Connors, E. Coppola, F.A. Cruz, et al.

Summary for policymakers. Climate Change 2021: The Physical Science Basis: Working

Group I Contribution to the Sixth Assessment Report of IPCC

Cambridge University Press (2021).

[2] P.K. Thornton et al. A framework for priority-setting in climate smart agriculture research. Agricultural Systems, vol. 167, pp. 161-175, Elsevier BV, 2018.

[3] Niang, I., et al. (2014). Africa. In: Barros, V.R., et al., Eds., Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK, 1199-1265 https://doi.org/10.2134/agronj2010.0303.

[4] Amekudzi, L.K., Yamba, E.I., Preko, K., Asare, E.O., Aryee, J., Baidu, M. et al. (2015) Variabilities in rainfall onset, cessation and length of rainy season for the various agro-ecological zones of Ghana. Climate 3, 416–434. https://doi.org/10.3390/cli3020416