Kaba Diallo, Andrew Charles Whitaker, Al- Shakil, Aaron Conte, Antonio Machava Junior
Hydrological Research Letters 20(2), pp 135-142
Abstract
There is a need to evaluate and understand how ongoing climate change is impacting hydrological regimes and seasonal flows in Japan’s heavy snowfall region along the Sea of Japan. This study analyzed various flow duration curves from the Takiya River (19.45 km2), Ara River (240 km2), and Uono River (1,408 km2) to evaluate the distinct influence of basin characteristics, climate change, and dam regulation on flow regimes. Seasonal flow duration curves showed consistent dominance of spring flows associated with snowmelt, most pronounced in basins with higher elevations and greater snow accumulation. The moderately regulated Uono River exhibits reduced flood peaks, flattened median flows, and more persistent summer–autumn low flows, reflecting dam operations. A comparison of the periods 1961–1990 and 1991–2023 for the Uono River shows significant increases in winter runoff (Q50 +15%) and a significant shift in the spring flow regime (Q10 –16%, Q90 +23%), consistent with warming trends. In addition, the development of stochastic flow duration curves made it possible to assess the impact of climate change on flow regimes in a probabilistic manner. These findings underline the dual impacts of climate change and flow regulation, with implications for flood control and water supply.
Figure 2. Seasonal flow duration curves for the recent period 2000-2022 comparing the dam-regulated Uono River (1,408 km2), with the unregulated Ara River (240 km2), and the unregulated Takiya River (19.45 km2) for each season; (a) winter DJF, (b) spring MAM, (c) summer JJA, and (d) autumn SON
Figure 3. Seasonal flow duration curves for the Uono River showing changes between Period 1 (1961-1990) and Period 2 (1991-2023) for (a) winter (DJF) and spring (MAM), and (b) summer (JJA) and autumn (SON). The change in mean seasonal runoff is notable for DJF (12% increase) and MAM (7.5% decrease), but not notable for JJA or SON. Using a sample of water years (2003-2009), we also show seasonal flow duration curves for measured and reconstructed runoff for (c) winter (DJF) and spring (MAM), and (d) summer (JJA) and autumn (SON). Natural runoff was reconstructed by computing inflow minus outflow for each of the four dams which were operational, and adding the result to the measured runoff
