*4.3.1 Decadal*

The decades 1961–1970, 1971–1980, and 1981–1990 were those of decrease of temperature in Yelwa with that of 1981–1990 being significant. These decreases were in the early decades of the study period. However, in Kaduna, the decreases were in the decades of 1981–1990, 1991–2000, and 2001–2010 without any being significant. The decreases occurred mainly within the mid-decades of the study period. The decreases in Katsina temperature occurred in the decades 1971–1980, 1981–1990, and 1990–2000 with the last two being significant. Also, Potiskum was with a decrease in average decadal temperature in 1971–1980, 1981–1990, and 2011– 2020 without any being significant. These three decades constitute 50% of the study period. This indicates a shift in the climate of these sub-areas particularly of the


#### **Table 5.**

*Student's* t*-test (*td*) analysis for temperature (30-years overlapping).*

## *The Nature, Causes, Effects and Mitigation of Climate Change on the Environment*

element of temperature. Sokoto and Gusau had two decades (about 33.33% of decades) each with a decrease in temperature; 1971–1980 and 1981–1990 for Sokoto and 1981–1990, 2011–2020 in Gusau with only that of 1981–1990 in Sokoto being significant. The decadal value of 1981–1990 for Maiduguri was also significant and was the only decade (about 16.66% of decades) with a decrease in the sub-area during the study period.

All other decades in the stations/sub-areas indicated increases in temperature with the following being significant; 1991–2000 (Yelwa), 2011–2020 (Kaduna), 2001–2010 (Kano), and 2011–2020 (Nguru). These situations indicate fluctuations in the average decadal temperature of the study area and back up the assertion of climate variability being dominant as opposed to change in the climate of the study area.

### *4.3.2 Sub-periods (30 year overlapping)*

The values of the student's *t*-test (**Table 5**) show deviation and shift in trend from the sub-period, 1981–2010 to the sub-period, 1991–2020. They indicate a shift towards decreasing temperature (negative) in the series for most of the stations used during the study except for Potiskum and Maiduguri that indicated an increasing (positive) trend However, both increasing and decreasing trends were not significant.
