Rainfall trend and variability in semi-arid northern Namibia: Implications for smallholder agricultural production

Rainfall defines livelihood patterns among agrarian communities of the climate-change vulnerable semi-arid Sub-Saharan Africa. However, it remains inadequately studied, resulting in ineffective water management policies and weak agricultural growth in the region. Monthly rainfall data collected between 1987 and 2018 at four stations along a 1200 km climatic gradient in northern Namibia were analysed for annual, seasonal and monthly trends and variability. Descriptive measures and the Mann-Kendall test were used for rainfall characterisation and trend detection, respectively. Results showed an annually increasing rainfall trend, but with a downward trend in the dry season decreasing by -0.14 mm year–1 and an upward trend in the rainy season increasing by 7.74 mm year–1 across the study area. The rainy-season mean monthly rainfall showed predominantly increasing trends, while the dry-season ones exhibited insignificant decreasing trends. The study detected a decreasing rainfall gradient from the northeast towards the northwest with a range of 156.8 mm and concomitant increasing spatial-temporal variability. The upward rainfall trend has implications for rainy season floods, whereas the downward trend suggests dry season drought intensification in the area. These results could be useful for rainwater management planning in the study area and other dryland regions.