Hydrological impacts of climate change on rice cultivated riparian wetlands in the Upper Meghna River Basin (Bangladesh and India) Mohammed M. Rahman a,b,*, Julian R. Thompson b, and Roger J. Flower b a Department of Irrigation and Water Management, Bangladesh Agricultural University, Mymensingh, Bangladesh b Wetland Research Unit, Department of Geography, University College London, London WC1E 6BT, UK * Corresponding author: email
[email protected] Tel: +88 01717 825850; Fax: +88 091 61510 Abstract Riparian depressional wetlands (haors) in the Upper Meghna River Basin of Bangladesh are invaluable agricultural resources. They are completely flooded between June and November and planted with Boro rice when floodwater recedes in December. However, early harvest period (April/May) floods frequently damage ripening rice. A calibrated/validated Soil and Water Assessment Tool for riparian wetland (SWATrw) model is perturbed with bias free (using an improved quantile mapping approach) climate projections from 17 general circulation models (GCMs) for the period 2031–2050. Projected mean annual rainfall increases (200–500 mm per 7–10%). However, during the harvest period lower rainfall (21–75%) and higher evapotranspiration (1–8%) reduces river discharge (5–18%) and wetland inundation (inundation fraction declines of 0.005–0.14). Flooding risk for Boro rice consequently declines (rationalized flood risk reductions of 0.02–0.12). However, the loss of cultivable land (15.3%) to increases in permanent haor inundation represents a major threat to regional food security. Keywords haor wetlands; Boro rice; floods; Bangladesh; climate change; SWAT 1 Introduction The potential consequences of climate change on hydrological processes and associated sectors such as water resources, agriculture, aquatic ecology and human livelihoods have been extensively documented (e.g.