Impact of climate change on the Hii River basin and salinity in Lake Shinji: A case study using the SWAT model and a regression curve

The impacts of climate change on water resources were analysed for the Hii River basin and downstream Lake Shinji. The variation between saline and fresh water within these systems means that they encompass diverse ecosystems. Changes in evapotranspiration (ET), snow water equivalent, discharge into the basin, and lake salinity were determined for different climate scenarios. The impact of climate change on a brackish water clam found in the lake was then examined using simulated monthly variations of lake salinity and information from prior studies of the clam. ET increased and snow water equivalent decreased for all scenarios incorporating temperature rise, particularly during the winter season. Furthermore, ET and snow water equivalent were not as sensitive to variations in precipitation and thus temperature rise was considered to be a major factor for these variables. Nevertheless, monthly discharge volume was more influenced by variation in precipitation than variations in temperature. Discharge increased during both the summer and winter season, since precipitation contributed to river discharge instead of being stored as snow pack during the winter season. The magnitudes of salinity dilutions and concentrations predicted under the climate change scenarios would not be lethal for adult clams. However, the egg-laying season of the clam would coincide with periods of strong salinity dilution in the lake. Since juveniles are less tolerant to changes in salinity, future generations of the clam may be affected and reproduction of the clam may be reduced by increasing precipitation in the future.