olusolayemi/niger-stlawrence-hydro-extremes

# Divergent Hydrological Extremes Under Climate Change: Niger vs. St. Lawrence/Ontario Comparative analysis of climate-driven change in river discharge extremes, multifractal scaling, and river-network topology across two hydroclimatically contrasting basins: the Niger River (West Africa) and the St. Lawrence River / Lake Ontario tributary system (eastern North America). ## Overview This project tests whether large-scale basin storage, natural lake regulation and hydraulic control in the St. Lawrence/Great Lakes system, versus the largely unregulated (outside the Inner Niger Delta) Niger system, mediates how a projected climate change signal propagates into observable discharge extremes and scaling behavior. Three complementary methods are applied to 90 GRDC gauging stations (45 per basin group): 1. **Extreme value analysis** — GEV (L-moments) fits to annual maximum daily discharge, historical (1985–2014) vs. future (2041–2070, SSP3-7.0), with bootstrap-based significance testing of 20-, 50-, and 100-year return level change. 2. **Multifractal Detrended Fluctuation Analysis (MF-DFA)** — spectrum width, dominant singularity exponent, and asymmetry of log-transformed, deseasonalized daily discharge. 3. **River network topology** — directed graph constructed from GRDC downstream-routing metadata, used to test whether the spatial pattern of change is organized by network position (distance to outlet, upstream drainage size, betweenness centrality). ## Key findings (summary) - The Niger basin shows a statistically significant, spatially coherent divergence: **flood magnitude decreases at headwater/Guinean tributaries** (Bani, Bagoé, Baoulé) and **increases through the Sahel-zone mainstem and left-bank tributaries** (Gorouol, Dargol, Sirba, Tapoa), consistent with a Sahelian-paradox-type pattern. - This divergence is strongly organized by network position: significant decreases occur at network distance ≥8 steps from the outlet; significant increases at ≤6 steps. - …