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Title: UNCERTAINTY OF CLIMATE CHANGE IMPACT ON THE FLOOD REGIME, CASE STUDY AIDOGHMOUSH BASIN, EAST AZARBAIJAN, IRAN

Author: A.R. Massah Bavani and P. Ashofteh

Year: 2009

Publisher: European Water Resources Association (EWRA)

Description:

This research work is aimed to describe a methodology for quantifying uncertainties involved in climate change impact on flood regime studies due to discrepancies in AOGCMs (Atmosphere-Ocean General Circulation Model) simulations of regional and local climate parameters; applied on Aidoghmoush basin in north-west of Iran.. This research work excludes uncertainties due to parameters and concepts of the rainfall-runoff model, climate sensitivity, emission scenarios, and downscaling techniques. Monthly temperature and precipitation
change scenarios of Aidoghmoush basin were constructed from 7 AOGCM models (CCSR/NIES, CGCM2, CSIRO MK2, ECHAM4/OPIYC3, GFDL R30, HadCM3 and NCAR DOE PCM) using baseline period (1971-2000) data and future period 2040-2069 (2050s) under the SRES emission scenario, namely A2. Then, these climate
change scenarios were downscaled spatially to the basin using original grid box information of each AOGCMs. Results showed that the temperature increase and the precipitation vary in 2050s relative to the baseline period. Monthly probability distribution functions (pdf) of temperature and precipitation change scenarios in 2050s were constructed by a weighting method (comparing 30-year monthly average of observed and AOGCMs temperature and precipitation data in the baseline period). A daily rainfall-runoff conceptual model (IHACRES) was calibrated for the basin. Carrying out Monte Carlo method, 2000 samples of temperature and precipitation were sampled from corresponding pdfs. Then 2000 temperature and precipitation time series for 2050s were constructed using
change factor method. These time series were introduced to IHACRES. By this, 2000 30-year time series of daily runoff were simulated in 2050s and 30 maximum annual flood of each time series were extracted. Appropriate theoretical probability distribution functions were fitted to each series as well as maximum annual flood of baseline. Finally changes in two flood indicators were discussed: Severity of flood events by comparing the magnitude of flood using fixed return periods and frequency of flood events by comparing the return period of a flood using fixed magnitude. Results show that for the return period less than 50-year, the probability of decrease in magnitude of future flood event relative to the baseline is more than the probability of increase. For the return period more than 50-year both situations have nearly same probability to occur. Analyzing the flood
frequencies show that in the future, floods less than 20 m3/s have less chance to occur relative to the baseline. On the other hand for flood magnitudes more than 60 m3/s this chance will increase. Finally it can be concluded that over-reliance on a single or very few AOGCMs climate scenarios could lead to inappropriate flood magnitude or frequency. Therefore for providing scientifically based advice to decision makers it is essential that climate change impact studies consider a range of weighted climate scenarios derived from different AOGCMs. The methodology and the final results of this research can play the base role for other disciplines such as dam operation, dam break risks, agricultural damage risks and adaptation policies that are greatly affected by changes in flood regime.