Tamale is the capital city of the Northern Region which used to be the largest region by land size. Due to its proximity to the Sahel and the Sahara, the region has a dry and hazy atmosphere with high temperature for a larger part of the year. Landscapes are mostly grasslands with groups of drought-resistant trees such as baobabs, neem and acacias trees. The dry season lasts from January to March [22] . The rainy season lasts from July to October, and it usually rains 750 to 1050 mm (30 to 40 inches) a year. During the day, it can be 40˚C (104˚F) and at night, it can be 14˚C (59˚F) [22] .

The air quality in the region is of significant interest, particularly in relation to cooking and biomass burning, which impact regional air quality. According to the 2021 Population and Housing Census, the northern region has a population of 2,310,934 consisting of 1,143,439 males and 1,167,495 females ( Figure 1 ).

Long-term rainfall, temperature and relative humidity data (observed daily for 23 years) were investigated to detect trends between 1990 and 2023 in Tamale. The daily temperature, rainfall, and relative humidity data were obtained from the Ghana Meteorological Agency for the periods 1990 to 2023. Tables 1-4 summarized the monthly central tendency and dispersion measures for T_max, T_min, rainfall and relative humidity (average). The annual rainfall was maximum with the value of 1608.12 mm in 1991 and yearly minimum rainfall amounting to 878.96 mm was obtained in 2015. The analysis of the current investigation is the monthly and annual minimum temperature (T_min) and the maximum temperature (T_max) during 1990-2023. Annually maximum temperature observed was 41.58˚C in 2016, whereas the minimum temperature was found in 1991. Relative humidity (RH_aveg) analysis showed that monthly average minimum and maximum values were found to be 71 and 135 in 2020 and 1991, respectively.

The annual and monthly temperature data (maximum and minimum) showed a considerable variation in the annual maximum temperature during the investigation period. After the MK test had identified the trends, the Theli Sen slope was estimated to quantify the magnitude of the slope. The MK Test value and Theli Sen slope for maximum temperature are shown in Table 5 . Monthly temperature trends exhibited the following patterns:

- Minimum temperature: A consistent statistically increasing trend was observed across all 12 months, from January (month 1.0) to December (month 12.0) ( Figure 3 , A-L; representing the months January to December respectively).

- Maximum temperature: Trends varied by month, with statistically significant increases observed in January, February, May, July, November, and December. No discernible trends were detected in March, April, June, and October. A statistically significant decreasing trend was noted in September.

The analysis of annual and monthly temperature data revealed notable variations in maximum temperature over the study period. The Mann-Kendall (MK) test was employed to identify trends, and the Theil-Sen slope estimator was used to quantify their magnitudes. Results showed that minimum temperatures exhibited a statistically consistent upward trend across all twelve months, while maximum temperatures demonstrated a more heterogeneous pattern. Specifically, significant increases in maximum temperature were observed in January, February, May, July, November, and December. Conversely, no clear trends were found in March, April, June, and October, and a significant decreasing trend was observed in September.

These findings are consistent with several studies conducted in Ghana and across Africa, though they also reveal nuanced differences. The consistent rise in minimum temperatures aligns with the work of Owusu and Waylen (2009) [25] , who documented a general warming trend in minimum temperatures across northern Ghana over a similar temporal scale. Similarly, Nkrumah et al. (2014) [26] reported that minimum temperatures in southern Ghana have shown a persistent increase, attributing this pattern to urbanization and land surface changes. These observations suggest that nighttime warming is a widespread phenomenon, likely driven by increased heat retention in modified land surfaces and the broader effects of climate change.

Comparatively, studies from other African contexts echo similar trends. For instance, Gebrechorkos et al. (2019) [27] , in a study covering Eastern Africa, noted consistent upward trends in minimum temperatures across various climate zones, emphasizing the regional nature of nocturnal warming. Likewise, Boko et al. (2007) [28] in the IPCC Fourth Assessment Report identified rising minimum temperatures as a key feature of climate change impacts in sub-Saharan Africa, with implications for health, agriculture, and energy consumption.

In contrast, maximum temperature trends presented more complexity. The observed intra-annual variability, with both increasing and decreasing trends, reflects findings by Asante and Amuakwa-Mensah (2015) [29] , who also identified spatial and temporal inconsistencies in maximum temperature changes across Ghana. Their study noted that while certain agro-ecological zones recorded increasing maximum temperatures, others showed either stable or declining trends, particularly during the minor rainy seasons. Similarly, Klutse et al. (2018) [30] identified varied monthly patterns of maximum temperature trends in West Africa, highlighting the influence of local climatic systems, vegetation cover, and atmospheric circulation patterns.

The significant decreasing trend in maximum temperature during September may be linked to the peak of the rainy season in many parts of Ghana, where increased cloud cover and precipitation reduce solar radiation. This has also been noted by Owusu and Waylen (2009) [25] , who observed a seasonal modulation of temperature patterns due to rainfall distribution. On the other hand, the increasing maximum temperatures in the dry season months such as January and February coincide with the Harmattan period, during which clear skies and low humidity promote higher daytime temperatures, a phenomenon corroborated by studies from Nyatuame, Kasei, and Martey (2014) [31] .

These temperature trends have important human dimensions. Rising minimum temperatures, for example, can alter the growing periods for staple crops, influence disease vector activity, and affect human thermal comfort, especially at night. The variability in maximum temperatures, particularly the extremes, poses challenges for outdoor labor productivity, food preservation, and energy demand for cooling. The observed trends also reflect local perceptions of climate variability reported in several qualitative studies among Ghanaian farming communities, where shifts in temperature patterns are associated with declining agricultural productivity and changing livelihood strategies.

The implications of rising minimum temperatures are multidimensional. Firstly, shifts in the timing of flowering and fruiting due to warmer nights can disrupt the phenological synchrony of crops. Secondly, increased nocturnal respiration rates can reduce net photosynthesis, contributing to lower yields. Thirdly, higher night temperatures elevate water demand due to increased evapotranspiration, thereby compounding challenges in water-scarce areas. These results are consistent with the conclusions of Owusu and Waylen (2009) [25] , who emphasized that temperature increases in Ghana’s northern belt significantly affect soil moisture regimes and crop performance.

In contrast, the variable trends in maximum temperature offer a more nuanced outlook. The rainy season months of May through August showed mixed patterns. While May and July recorded rising trends, June and August exhibited no significant change, and September experienced a decline. These results mirror the seasonal patterns reported by Adiku et al. (2015) [32] , who noted an intensification of heat during the onset of the rains but relative thermal stability mid-season. Likewise, Kasei et al. (2010) [33] reported increased maximum temperatures in northern Ghana between May and July, attributing them to early cessation of rainfall and delayed planting, which have knock-on effects on crop performance.

Increased maximum temperatures during the early rainy season, particularly in May, can accelerate evaporation, reduce soil moisture, and affect seedling emergence and establishment. This is especially problematic for early-maturing crops like groundnuts and maize. July’s rising temperature can support photosynthesis but may induce thermal stress if thresholds are exceeded. These findings resonate with those of Laube et al. (2012) [34] , who linked similar patterns of increasing Tmax in northern Ghana with heat stress impacts on maize. On the other hand, the lack of discernible trends in June and August suggests windows of relative climatic stability, beneficial for crop development. This finding supports the work of Yiran and Stringer (2016) [18] , who argued that intra-seasonal temperature stability is critical for ensuring crop resilience in northern Ghana.

The decreasing maximum temperature in September is particularly noteworthy and somewhat atypical. While few studies report declining Tmax during this period, similar patterns were observed by Apata et al. (2016) [35] in parts of Nigeria, where late-season cooling was attributed to increased cloud cover and delayed rainfall events. However, in Ghana, the implications may vary depending on crop type and harvest schedules.

Increasing minimum temperatures across all months in a tropical region like Ghana can have significant implications for crop production:

1) Changes in growing seasons: Warmer nights can lead to earlier flowering and fruiting, potentially disrupting the synchronization of growth stages and impacting yields;

2) Heat stress: Higher minimum temperatures can cause heat stress in crops, especially those sensitive to temperature fluctuations, leading to reduced growth, yields, and quality;

3) Water requirements: Increased temperatures can enhance evapotranspiration, leading to higher water demands for crops, potentially straining water resources;

4) Shifts in suitable crop zones: Rising temperatures can cause areas to become more or less suitable for specific crops, potentially requiring adjustments in crop selection and farming practices;

5) Pest and disease dynamics: Changes in temperature regimes can alter the distribution, prevalence, and behavior of pests and diseases, potentially impacting crop health;

6) Yield reductions: Overall, increasing minimum temperatures can lead to reduced crop yields, decreased quality, and lower productivity.

The implications for the trends in Tmax for the rainy season period of May to August are:

1) May: increasing temperatures can lead to faster evaporation of water from the soil, potentially reducing soil moisture and affecting seed germination and early growth stages of crops;

2) June: no trend in temperature suggests stable conditions, which is beneficial for crop growth and development;

3) July: increasing temperatures can enhance crop growth, but excessive heat can lead to heat stress, particularly for crops sensitive to temperature fluctuations;

4) August: no trend in temperature indicates stable conditions, allowing crops to mature and ripen normally ( Figure 3 ).

Overall, these temperature trends may impact: crop water requirements and soil moisture levels; growth and development stages of crops; heat stress and crop yields and timing of planting and harvesting. It should be pointed out that these implications are specific to the rainy season in the Tamale Metropolis and may vary depending on local conditions and crop types.

Based on our analysis, the implications for Tamale and its environs are:

1) No trend in rainfall (Jan, Feb, Apr, May, Jun, Jul, Sep, Oct, Nov)—Stable rainfall patterns, allowing for predictable agricultural planning and water resource management.

2) Increasing rainfall in March—Potential for: improved crop yields and vegetation growth; replenished water sources and improved water security; increased flood risk, potentially affecting settlements and infrastructure.

3) Decreasing rainfall in August and December—Potential for: water scarcity and drought impacts on crops and livestock; reduced water availability for domestic and industrial use and increased risk of bush fires and land degradation ( Figure 4 ).

Overall, these trends may impact: agricultural productivity and food security, water resource management and availability, flood and drought risk management and ecosystem health and biodiversity. In Tamale and its environs, these implications may be particularly significant for:

- Agriculture: Impacts on crop yields, livestock productivity, and food security.

- Water resources: Impacts on water availability, quality, and management.

- Ecosystems: Impacts on vegetation, wildlife, and biodiversity.

- Human settlements: Impacts on flood risk, water access, and livelihoods.

Stakeholders, including farmers, water managers, and policymakers, may need to adapt strategies to address these implications, such as: implementing climate-smart agriculture practices, enhancing water harvesting and storage infrastructure, improving flood and drought early warning systems and promoting ecosystem conservation and restoration efforts.

The analysis of rainfall trends in Tamale and its environs reveals a complex yet critical pattern with implications for agriculture, water resources, ecosystems, and human settlements. The data suggest no significant trends in rainfall for most months, indicating relative stability that supports predictable agricultural activities and effective water resource management. This aligns with the findings of Kasei et al. (2010) [36] , who noted stable intra-annual rainfall in the Northern Region, conducive to traditional cropping cycles. However, this contrasts with Nyadzi et al. (2015) [37] , whose regional study indicated erratic rainfall patterns in some areas of northern Ghana, suggesting that microclimatic variations remain important in local planning.

An observed increase in rainfall in March could benefit agricultural productivity through improved soil moisture and early planting opportunities. Similar findings were reported by Owusu and Waylen (2009) [25] , who observed early onset of rains in parts of northern Ghana, enhancing maize and sorghum yields. On the other hand, Yiran and Stringer (2016) [18] argued that while increased rainfall can improve vegetation cover, it can also raise the risk of localised flooding, particularly in peri-urban areas with poor drainage. This dual effect highlights the need to balance opportunities for agricultural expansion with risks to infrastructure and settlement, especially for vulnerable populations living in flood-prone zones.

Conversely, the decreasing rainfall in August and December raises concerns about water scarcity and the health of ecosystems. A reduction in August rainfall, a typically wet month, may disrupt crop maturation and livestock water access. In agreement, Antwi-Agyei et al. (2012) [16] highlighted how rainfall deficits during critical months severely affect farming communities, leading to food insecurity and reduced income. Similarly, Dietz et al. (2004) [38] noted that such changes can trigger seasonal migration and alter household labour allocation in northern Ghana. The decline in December rainfall also has implications for dry-season farming and domestic water supply, echoing observations by Gbetibouo and Hassan (2005) [39] in semi-arid regions of South Africa, where late-year rainfall decline led to increased vulnerability of smallholder farmers to water stress.

The broader implications of these rainfall changes span across agricultural productivity, water availability, and ecological balance. With erratic rainfall in some months and reductions in others, crop planning becomes more uncertain. This supports the arguments made by Laube et al. (2012) [34] , who emphasised that climate variability significantly undermines rainfed agriculture in West Africa. The consequence for human livelihoods is substantial, especially for subsistence farmers whose yields are directly tied to rainfall performance. Water resources may also be affected, not only in terms of quantity but also quality, as observed by Adjei et al. (2020) [40] , who reported increased sedimentation in water bodies during heavy rains and reduced recharge during dry spells.

Moreover, ecosystem degradation resulting from irregular rainfall and extended dry periods may lead to biodiversity loss, a concern raised by Ntiamoa-Baidu (2008) [41] , who linked habitat fragmentation in Ghana to climate-induced vegetation changes. Human settlements are not spared, as shifts in rainfall increase the risks of both flooding and droughts. According to Tschakert et al. (2010) [42] , such climatic extremes disproportionately affect the poor, who often reside in poorly planned or informal settlements with limited access to adaptive infrastructure.

To respond to these emerging challenges, the involvement of stakeholders—farmers, water managers, local authorities, and policymakers—is essential. Approaches such as climate-resilient agriculture, rainwater harvesting, and early warning systems for extreme weather events should be prioritised. These interventions are consistent with the recommendations by Ampadu et al. (2021) [43] , who highlighted the value of community-based adaptation strategies in northern Ghana. Additionally, efforts to restore degraded lands and conserve native vegetation may help improve ecosystem resilience, as suggested by Mertz et al. (2009) [44] in their broader study on Sahelian adaptation.

Decreasing relative humidity (RH) every month, except March ( Figure 5 ), in a tropical area like northern Ghana has several implications for the environment and crop production:

(1) Environmental Implications:

a) Increased evaporation: Lower RH leads to faster evaporation from water bodies, soil, and plants, potentially altering the water cycle.

b) Drier air: Decreased RH can lead to drier air, potentially increasing the risk of bush fires and land degradation.

c) Disrupted ecosystems: Changes in RH can impact ecosystems, potentially affecting biodiversity and wildlife habitats.

(2) Crop Production Implications:

a) Water stress: Decreased RH can lead to increased water loss through transpiration, potentially causing water stress in crops.

b) Reduced yields: Water stress can result in reduced crop yields, decreased quality, and lower productivity.

c) Shifts in growing seasons: Changes in RH can disrupt growing seasons, potentially requiring adjustments in planting dates and crop selection.

d) Increased pest and disease pressure: Drier conditions can lead to increased pest and disease pressure, potentially impacting crop health.

In Tamale and its environs, these implications may be particularly significant for:

1) Agriculture: Impacts on crop yields, quality, and productivity.

2) Water resources: Impacts on water availability, quality, and management.

3) Ecosystems: Impacts on biodiversity, wildlife habitats, and ecosystem services.

Stakeholders may need to adapt strategies to address these implications, such as:

1) Irrigation management: Implementing efficient irrigation systems to mitigate water stress.

2) Crop selection: Choosing drought-tolerant crop varieties or adjusting planting dates.

3) Soil conservation: Implementing conservation agriculture practices to reduce soil moisture loss.

4) Ecosystem restoration: Restoring degraded lands and promoting ecosystem service.

The observed monthly decrease in relative humidity (RH), with the exception of March, in northern Ghana particularly in Tamale and its environs has far-reaching implications for environmental stability and crop production. As relative humidity plays a key role in maintaining ecological balance and supporting agricultural activities, its steady decline presents a pressing concern. These changes are particularly significant in tropical zones where smallholder agriculture and natural ecosystems are highly sensitive to climate variability.

Environmentally, reduced RH enhances evaporation rates from water bodies and soil surfaces. According to Nkrumah et al. (2020) [45] , prolonged low humidity increases evaporation in northern Ghana, thereby reducing the retention of moisture in soil and open water sources critical for both agriculture and domestic use. Similarly, Anyadike (2009) [46] notes that in arid regions of West Africa, declining RH leads to increased atmospheric dryness, which in turn escalates the risk of bushfires and contributes to the degradation of vegetation cover. These findings are consistent with observations by Owusu and Waylen (2013) [25] , who highlight that lower RH disrupts natural moisture cycles and can diminish ecosystem resilience in the savannah ecological zone. Compared to areas in southern Ghana where higher RH levels contribute to more stable microclimates [47] , the north is evidently more vulnerable to climatic extremes, making environmental management more urgent.

From an agricultural perspective, decreasing RH results in increased crop water loss through transpiration, which places considerable water stress on crops. According to Antwi-Agyei et al. (2012) [16] , low RH conditions exacerbate water stress and significantly affect maize and sorghum productivity in the Upper East Region. Similarly, Sarr (2012) [48] identifies that in the Sahelian belt, reduced RH coupled with higher temperatures leads to shorter growing periods, thereby reducing yield potential. These results are echoed in the work of Laube et al. (2012) [34] , who found that in northern Ghana, water stress during the growing season frequently leads to crop failure, particularly among resource-poor farmers. Compared with areas like southern Nigeria where RH remains relatively stable and supports longer growing seasons [49] , the north faces a more constrained agricultural calendar, making traditional farming practices less reliable.

Furthermore, decreasing RH affects pest and disease dynamics. Drought-like conditions often favour the spread of certain pests such as the fall armyworm, as observed by Tambo et al. (2021) [50] in Ghanaian maize fields. In contrast, wetter environments tend to favour fungal and bacterial infections. Waha et al. (2013) [51] corroborate this finding in their regional climate-agriculture analysis across Sub-Saharan Africa, noting that reduced RH can shift the pest population spectrum and increase vulnerability to outbreaks, especially when coupled with poor adaptive capacity among smallholder farmers.

The implications of these changes are human as well as ecological. In Tamale and nearby communities where agriculture serves as the primary livelihood, reduced RH directly translates into food insecurity, income loss, and heightened poverty. Access to water becomes more constrained, and communities reliant on rain-fed farming struggle to sustain productivity. As Acheampong et al. (2014) [52] argue, climate-related stresses such as humidity fluctuations disproportionately affect rural populations with limited access to irrigation and adaptive technologies.

In response, adaptation strategies must be locally relevant and scientifically informed. Efficient irrigation systems, such as drip irrigation promoted by Badu-Apraku et al. (2010) [53] , can help manage water stress, while the adoption of drought-tolerant crop varieties as suggested by Partey et al. (2018) [54] offers a longer-term solution. Soil conservation measures, including mulching and zero tillage, can also improve moisture retention and buffer the effects of RH decline. On the ecological front, restoring degraded lands and protecting tree cover activities emphasized by Codjoe and Owusu (2011) [55] can help moderate microclimates and sustain biodiversity.

N = “no trend”, + = “Increase trend”, − = “negative trend”.