Abstract. Although many studies have explored the effect of teleconnection patterns on floods, few investigations have focused on the assessment of expected flood damage under such large-scale atmospheric signals. This study aims to determine the effect of the most emblematic teleconnection, El Niño, on the expected damage due to floods with short return periods in the Kan River basin, Iran. To determine the flood damage costs, the median of annual precipitation changes (ΔP) during El Niño conditions was used, although ΔP cannot necessarily be transferred to extreme values. Then the flooded area was determined under the increased rainfall due to El Niño for 5-, 10-, and 50-year return periods. The results showed that El Niño has increased the annual precipitation by 12.2 %. Flood damage assessment using damage–depth curves showed that the relative increase in expected damage during El Niño conditions is much higher for short return period floods than that for long return period floods. In general, a 12.2 % increase in the annual precipitation would increase the damage by 1671 % and 176 %, respectively, for the return periods of 5 and 10 years. However, in the case of a 50-year flood, this increased percentile decreased to 52 %. These results indicate the importance of small flood events in flood management planning during El Niño.

Abstract. Although many studies have explored the effect of teleconnection indicators on flood, few investigations have focused on the assessment of the expected damages resulted by flood under the El-Niño or La-Niña condition. Therefore, this study’s aim was to determine the effect of El-Niño on the expected flood damage in the Kan River basin, Iran. To determine the flood damage costs, first, the precipitation enhancement during El-Niño condition was estimated then using a probabilistic approach the inundation area was determined under 5, 10 and 50 year return periods. The results showed that El-Niño increases the precipitation amount up to 8.2 % and 31 % with 60 % and 90 % confidence level, respectively. Flood damage assessment using damage-elevation curves showed that the expected increase percentile in flood damage for smaller return periods, which is more frequent, is much more than that for larger return periods. In general, for the return periods of 5- and 10-year, 31 % increase in the precipitation would result in 2416 % and 239 % damage increase, respectively. However, for the 50-year rainfall this increase amount will be about 74 %. These results indicate the importance of small flood events in flood management planning during El-Niño.