Page 142 - AJWEP-22-5

Messel, et al.

The MK trend test (Table 2) revealed that the experienced moderate mean rainfall (≈234.2 mm), with
monthly rainfall trends in January, March, and October a positive MK trend (Kendall’s tau: 0.022), p-value
were 0.033, 0.014, and 0.006, respectively, indicating a of 0.718 and a Sen’s slope of 0.031. The difference in
non-significant upward rainfall trend. The MK trend test results is likely due to the geographical location of the
for August yielded −0.185 (p=0.002), with Sen’s slope study sites. Gebremichael et al. indicated that the
[54]
of −0.225, indicating a significantly downward rainfall spatial variability of rainfall in the Lake Tana Basin is
trend. Conversely, the rainfall trend in November was highly influenced by terrain orientation in the region and
significantly upward (MK test: 0.125, p=0.04; Sen’s other geographical factors, including altitude, slope, and
slope: 0.045). The remaining months experienced non- the associated diurnal wind direction. However, large-
significant downward rainfall trends with negative Sen’s scale spatial patterns demonstrate that annual rainfall
slope values. Shekuru et al. reported statistically decreases from the south (ca. 1600 mm) to the north (ca.
[49]
significant decreasing rainfall trends for only 2 months 1200 mm). Therefore, the southern part of the basin has
(February and June). Likewise, Mekonen and Berlie higher precipitation than both the western and northern
[10]
revealed a statistically non significant decreasing rainfall parts. South Wollo is located in the rain shadow area
[55]
trend in February, May, and September. However, these of Ethiopia, in contrast to the Lake Tana Basin, which
reports are contrary to the case in the Lake Tana sub- is situated on the windward side of the country’s central
basin, likely due to differences in the physical attributes highlands.
of the studied sites or the magnitude of the data used by The annual CV (Table 2) exhibited a less variable
these studies. trend (CV: 6.49%), and the MK test results (Kendall’s
The CVs presented in Table 2 validated the tau: −0.081; p=0.181) revealed a non-significant
variability of seasonal rainfall in the Lake Tana sub- downward trend, with a Sen’s slope of −0.291, consistent
basin, ranging from 7.8% in summer (low variability) with a previous report. However, Tesfaw et al. and
[8]
[17]
to 49.9% in winter (high variability). Addisu et al. Weldegerima et al. noted that the annual rainfall in
[20]
[17]
and Mekonen and Berlie consistently reported the Lake Tana Basin is trending upward, though not
[10]
much higher CVs for spring and comparatively less statistically significant.
variable rainfall during the summer season in the Lake The decadal rainfall (Table 2) displayed less
Tana sub-basin and South Wollo, respectively. Other variability and a non-significant downward trend
comparative studies conducted in the Amhara region (Kendall’s tau: −0.359; p=0.100; Sen’s slope: −0.373).
of Ethiopia have also reported similar results. The The overall rainfall analysis highlights significant
[50]
seasonal MK trend test revealed that summer presented seasonal and monthly variations, with particular concern
the highest seasonal mean rainfall (≈778.4 mm), but for summer (August), where significant downward
exhibited a downward trend, as indicated by Kendall’s trends could impact water availability. Although the
tau of −0.154, a significant p-value of 0.011, and a annual and decadal trends suggest a general decline,
Sen’s slope of −0.335. This implies that rainfall during most of these trends are statistically non-significant
the summer season in the Lake Tana sub-basin is high downward trends, except in certain months such as
but significantly decreases over time. Climate change November. As November is one of the crop-harvesting
significantly affects livelihoods, food production, and months in the northwestern highlands of Ethiopia,
the overall economy, particularly agriculture-based continuous monitoring and analysis are warranted.
economies (e.g., crop production, livestock production, However, our results, consistent with the findings by
horticultural crops, aquaculture [fish production], and Suryabhagavan, Esayas et al., and Shekuru et
[56]
[57]
apiculture) in developing nations. In addition, ongoing al., indicate a statistically non-significant downward
[49]
climate change is expected to exacerbate desertification rainfall trend.
and disrupt crop-growing seasons. The observed variability in rainfall could have
The significantly downward trend in summer significant consequences for smallholder farmers,
rainfall has also been reported across different parts affecting their agricultural practices and crop
of Ethiopia. Gemeda et al. and Asfaw et al. production. Having adequate and timely rainfall during
[51]
[53]
[52]
observed decreasing Kiremt rainfall in different parts of the cropping seasons (Belg and Kiremt) is critical for
Ethiopia, including the central highlands. Contrary to farming practices. However, the short growing season
this, Mekonen and Berlie highlighted non significant caused by the variability and inconsistency of rainfall
[10]
decreasing trend in summer rainfall for the Wollo Zone during cropping seasons, as well as the inadequacy of
of north-eastern Ethiopia; they also revealed that autumn soil moisture to support crop production for most of

Volume 22 Issue 5 (2025) 136 doi: 10.36922/AJWEP025190142