EVALUATION OF CLIMATE AND FLOW CHANGES IN THE PAST 40 YEARS IN THE OMARU RIVER CATCHMENT USING A DISTRIBUTED HYDROLOGICAL MODEL

Abstract

 To date few studies have tackled evaluation of flow alterations involved with changing climates at a watershed scale. Here we evaluated changes in climate in the past 40 years in the Omaru River catchment in south-west Japan, and resulted flow alterations as well as their spatial patterns using a distributed hydro-logical model and indicators of hydrologic alteration (IHA). We divided the study period into base and impact periods and the extents of the alterations were quantified by the ratio of IHA between them. Results show that the monthly median flow during winter season increased although the flow during spring season decreased. This attributes to the decline of snowfall in winter due to temperature rise in the impact period. We also found significant positive alteration in the annual maximum daily streamflow over middle to upstream. This may cause negative impacts on the ecosystem especially in the upper streams through promoting hydraulic erosion and passive drifts of benthic animals.