Statistical projections of the mean changes in intra-seasonal rainfall characteristics over Zambia from the reference period 1971-2000 to the future 2021-2050.

Nephat Mwanza , Suman Jain

As the Earth continues to warm, extreme seasonal precipitation events such as dry spells, floods, and droughts are expected to become more frequent and severe worldwide, including in Zambia. Zambia's agricultural sector, heavily dependent on seasonal rainfall, is highly sensitive to such fluctuations, with longer dry spells and floods threatening farmer livelihoods and national food security. This study investigates potential changes in intra-seasonal rainfall characteristics over Zambia from 1971-2000 to 2021-2050 using an ensemble of 22 experiments from the Coordinated Regional Climate Downscaling Experiment (CORDEX). Model performance in reproducing monthly climatology, spatial climatology, and inter-annual variability of rainfall was evaluated against the Global Precipitation Climatology Centre (GPCC; 1982-2000) observational dataset. The RCM simulations reasonably captured the monthly and spatial climatology of Zambian rainfall, with individual models exhibiting wet or dry biases, while the ensemble mean showed better agreement with observations than any individual model. Projections for 2021-2050 relative to the 1971-2000 baseline indicated a statistically significant median increase of 0.6 and 1.85 days in consecutive dry days (CDD) over JFM and OND, respectively, alongside a median reduction of 1.1 and 0.95 days in consecutive wet days (CWD) over the same seasons. The greatest projected increases in CDD occurred in Southern, Lusaka, Eastern, and Western provinces, whereas the projected reduction in CWD was more evenly distributed nationwide. These findings have important implications for Zambia's rain-fed agriculture: longer dry spells and flash floods during critical periods such as JFM may reduce crop yields and undermine food security. The projections presented here offer agricultural scientists and policymakers the spatially resolved evidence needed to design adaptation strategies tailored to Zambia's changing rainfall patterns.