Assessing meteorological, agricultural, and hydrological drought characteristics, trends, propagation, and their implications for sustainable livestock grazing management in a semiarid catchment

Abstract

ABSTRACT A graphical abstract for assessing meteorological, agricultural, and hydrological drought characteristics, trends, propagation in a semi-arid catchment showing input data, methods and results. Semiarid catchments in Tanzania are vital for livestock grazing but highly vulnerable to recurrent drought. This study characterizes meteorological, agricultural, and hydrological droughts (1984–2022) across 3-, 6-, and 12-month timescales, using the standardized precipitation index (SPI), standardized streamflow index (SSI), and standardized soil moisture index (SSMI), respectively. Normalized Difference Vegetation Index (NDVI) anomalies were used as a proxy for pasture condition. Results indicate a unimodal rainfall regime (November–April) and persistent dry-season water deficits (June–October) driven by high evapotranspiration. Short-term droughts (SPI-3 and SSMI-3) occur frequently (0.9–1.8 events year−1), whereas SSI-3 are less frequent but longer-lasting (duration: 5–16 months). Long-term trends are weak overall, although a significant decline in streamflow is observed at the catchment outlet. Propagation is strongly timescale-dependent: short-term rainfall deficits rapidly translate into soil moisture anomalies in lowlands (SPI-3 to SSMI-3, lag 0–1 month, r ≈ 0.5–0.6), while SSI reflects cumulative multiseason deficits. NDVI responds most strongly to SPI-3 and SSMI-6 (lag 0–2 months; r up to 0.48), indicating rapid pasture sensitivity. These findings highlight a narrow early-warning window for forage decline and support adaptive strategies including timely destocking, rotational grazing, and improved dry-season water management to enhance resilience under increasing drought variability.