Use of surface water and groundwater under climate change: Khorramabad basin, Iran

The impacts of climate change on the conjunctive use of surface water and groundwater resources of the Khorramabad basin were evaluated. Monthly temperature and rainfall modelled using HadCM3 and CGCM2 under greenhouse gas emissions scenarios (GHGESs) A2 and B2 were downscaled to baseline (1971-2000) and future periods (2040-2069 and 2070-2099). Simulations were performed for four climate change scenarios (CCSs) (A2-2040-2069, A2-2070-2099, B2-2040-2069 and B2-2070-2099). The projections indicated an increase in temperature and a decrease in rainfall. Future surface water resources were simulated using IHACRES. The results indicated that average annual runoff under GHGESs A2 and B2 would decrease by, respectively, 2.03% and 4.17% in 2040-2069 and by 6.64% and 8.94% in 2070-2099. Groundwater simulation was carried out using ModFlow. The results showed that under, the four CCSs, groundwater level would decline by 2.3, 3.0, 2.5 and 3.4%, respectively, relative to the baseline. Aquifer recharge under the four scenarios would decline by 1.43, 5.71, 2.86 and 7.14%, respectively. The results from IHACRES and ModFlow were employed to develop a conjunctive operation model with the Weap model. Several CCSs with various levels of future water demand were assessed using Weap. A 20% increase in water demand relative to the baseline, for instance, was projected to produce annual deficits in future agricultural water supply of 3.3, 5.08, 3.05 and 5.18 (x 10(6) m(3)), respectively, under the four CCSs.