Net Primary Productivity Trends in Uganda (2001–2024): Regional Divergence, Climate Associations and Land-cover Diagnostics
Josiah Nakaana
Jiangsu Provincial University Key Laboratory of Agricultural and Ecological Meteorology, Nanjing University of Information Science and Technology, Nanjing, China.
Gerverse Kamukama Ebaju
*
Jiangsu Provincial University Key Laboratory of Agricultural and Ecological Meteorology, Nanjing University of Information Science and Technology, Nanjing, China.
Wankpo Souvegnin Fourg Audrey
School of Business, Nanjing University of Information Science and Technology, Nanjing, China.
*Author to whom correspondence should be addressed.
Abstract
Net primary productivity (NPP) integrates the carbon uptake of terrestrial vegetation with the biomass available to agriculture and pastoralism, yet its recent trajectory across Uganda has not been resolved at the scale at which land is managed. We analysed the complete MODIS MOD17 record (2001–2024) for Uganda and its nine agro-ecological zones, together with satellite precipitation, reanalysis meteorology, land cover and burned area, in a zone-resolved assessment of national productivity dynamics. Trends were estimated with the Theil–Sen slope and an autocorrelation-corrected Mann–Kendall test, and were accepted as supported only where confirmed by a circular block bootstrap, with false discovery rate control throughout. National NPP increased by 15.2% (6.22 g C m⁻² yr⁻¹ per year, p < 0.001), with 65.0% of the classified area showing a significant increase, compared with 2.1% showing a decrease. This aggregate concealed marked divergence: the Mid-Northern and West Nile zones gained 31.1% and 30.9%, the Eastern Highlands was the only zone with a negative slope, and supported seasonal increases were confined to the October–December short rains. No climate variable was associated with national productivity; significant coupling was confined to the semi-arid North Eastern Dry Land, where soil moisture explained 69.0% of interannual variance. Matched land-cover transition attribution showed that cropland expansion was associated with productivity gains in the Mid-Northern zone but losses elsewhere, while the two most cropland-saturated zones contained too few eligible transition pixels for comparison. A parameter diagnostic indicated that the leading-zone gains were not primarily an artefact of the algorithm's land cover parameterisation. Uganda's productivity gains are thus concentrated where cultivation is still expanding, while intensively cultivated zones stagnate or decline, a pattern invisible to national aggregate reporting of the kind used for SDG indicator 15.3.1.
Keywords: Net primary productivity, MODIS MOD17, agro-ecological zones, land-cover change, climate associations, Theil–Sen trend, Mann–Kendall test, rainy-season productivity, land degradation neutrality