The dominant plant species in many African wetlands is Cyperus papyrus. Its adaption to saturated and low oxygen conditions and its dense structure and height provide breeding and feeding grounds for unique flora and fauna. As a keystone species adapted to local hydrology, the flow regime of papyrus offers the full range of hydrologic conditions and events essential to ecosystem health. However, no study has attempted to link papyrus wetlands’ flow regimes to their biologically-relevant hydrologic attributes. The Indicators of Hydrologic Alteration (IHA) enable the evaluation of changes to flow regimes by examining hydrologic records and linking them to biologically-relevant hydrologic characteristics through the Environmental Flow Components (EFCs) approach. This study assesses hydrologic alterations of a papyrus wetland’s flow regime due to rice irrigation. We develop a conceptual ecological model linking papyrus to hydrologic attributes to determine the consequences of changed EFCs (extreme low flows, base flow, high flow pulses, and small and large floods) on papyrus as a habitat. We find that agricultural water management considerably alters the magnitude, duration, timing and rate of change of EFCs for the irrigated area to catchment area ratio greater than 1:153, affecting both sexual and asexual reproduction in papyri plants. Overall, a better understanding of the threats of water diversion for agriculture is made by linking papyrus’ flow regimes to biologically-relevant hydrologic attributes. Knowledge of the roles of the various EFCs could provide opportunities for conserving and protecting papyrus wetlands, especially for systems at risk of altered flows.

Papyrus wetlands, native to central and eastern Africa and attaining heights up to 5 to 6 m, occur as rooted or floating marshes in riverine and lacustrine landscapes. This study assessed and quantified the impacts of these papyrus wetlands on historical baseflow and quickflow, and future flood and low flows in the Mpologoma catchment in Uganda. By estimating the Wetland Specific Impact (metric of increase or decrease in flow to wetland area) for a 30-year historical period and indices of flow duration, magnitude, and frequency for the future period, it was possible to demonstrate the role that papyrus-dominated floodplain wetlands play in regulating river flow at the catchment scale. Assessment over the historic period shows that wetlands strongly attenuate quickflow while moderately enhancing baseflow. They play a moderating role in most months, except for the first dry season (June and July), due to the reversal of flows between wetlands and rivers that often occurs during this period. Annual estimates show that wetlands are four times better at regulating quickflow than baseflow. Examination of changes at 2 and 4°C global warming levels (GWLs) indicate that wetlands will play critical roles in mitigating flood risks, with a lesser role in supporting low flows. Wetlands are predicted to lower future mean flood magnitude by 5.2 and 7.8% at GWL2 and GWL4, respectively, as well as halving the average number of flood events in a year, irrespective of the warming level. However, the mean flood duration is expected to increase by 77.8% (56 days) and 80.3% (49 days), respectively. This study highlights the need for the conservation and protection of papyrus-dominated wetlands.