A Multi-model Perspective of Droughts in Future Climate and Implications for Irrigation in Malawi

Abstract Historical droughts and projected increase in drought risk have created an impetus for irrigation development across much of Sub-Saharan Africa, including Malawi. While irrigation can boost incomes and enhance food security, interactions between drought risk and irrigation planning are insufficiently explored, heightening the risks for expensive irrigation infrastructure and competition for water resources. We use a suite of bias-corrected outputs of 18 Global Climate Models coupled with a Soil Water Assessment Tool (SWAT) model to examine the dynamics of water availability and irrigation water demand (IWD) in five river basins over Malawi, southern Africa. We find that a strong coupling between precipitation and streamflow creates conditions suitable for quick propagation of drought signals typified by short lags between meteorological and hydrological droughts. Consequently, episodic spikes in IWD often coincide with periods of diminished streamflow thus reducing water supply for irrigation when IWD is most pronounced. Mean IWD is projected to increase across the five river basins (ranging from 20% to 50% for the low-mitigation scenario). The frequency of IWD spikes is also projected to increase. Meteorological-hydrological drought lags are projected to become shorter, increasing the prospect of IWD spikes coinciding with hydrological droughts more often. Having grounded the study on extremes, our results highlight other dimensions of climate risks for irrigation aside changing average climatic conditions. Such information is critical in supporting decisions around sustainable and resilient irrigation landscapes, but prevailing uncertainties demand robust decision-making approaches and model improvements.