In order to cope with the decreases in the streamflow of branch streams owing to climate change, it is necessary to review the capacity of agricultural reservoirs to supply instreamflow and the amount of potential increases in downstream streamflow by supplying instream flow from agricultural reservoirs located upstream.
To evaluate the water supply capability of agricultural reservoir considering climate change, reservoir simulation models can be utilized, and bias correction in the climate change scenarios is necessary. In the simulation analysis on agricultural reservoir operations for estimating the possibility of instreamflow supply, irrigation water demand preferentially was calculated because it is required as input data for the simulation model. Furthermore, the agricultural reservoir simulation models should be utilized for determining appropriate reservoir operation rules and for evaluating changes in downstream streamflow under various instreamflow supply conditions for reservoir operation. However, the entire process for simulating instreamflow supply of agricultural reservoirs under the impact of climate change has not been established in a single system yet.
Accordingly, in this study, a system for simulating instremaflow of agricultural reservoirs considering climate change was developed. The developed system was named as the CARISS (Climate change based Agricultural Reservoirs Instreamflow Simulation System)
The CARISS comprises a climate change preprocessing module, a runoff simulation module, a module for agricultural reservoir operation including various conditions for instreamflow supply, a module for determining the operation rules for agricultural reservoirs to supply irrigation water in addition to the instreamflow, a streamflow simulation module, and a module for evaluating the water supply capability and the streamflow by agricultural reservoir operation. In addition, the system features climate change scenarios database(RCP 4.5 and 8.5) and batch processing to swiftly analyze the changes in downstream streamflow by simulating reservoir operation based on various operational conditions for instreamflow supply under the background of climate change.
The system was applied to 9 agricultural reservoirs, with a water storage volume of more than 1 million ton, in Bukil Watershed. At the rainfall and weather stations in the watershed, bias of the raw data was corrected using the climate change preprocessing module under RCP 4.5/8.5 scenarios. The runoff simulation module and the agricultural reservoir operation module were calibrated and validated using observed streamflow and reservoir storage data. After the calibration and verification of the system parameters, the simulated values were found to be in good agreement with the observed data. Changes in the downstream streamflow and water supply capacity of the 9 agricultural reservoirs were evaluated under the condition that the reservoirs do not supply instreamflow based on external factors such as climate change and raising the reservoir embankment. Furthermore, the operation rules for the respective reservoirs were determined by quantitatively estimating the instreamflow, and the changes in the downstream streamflow and water supply capacity of the agricultural reservoirs were evaluated under various instreamflow supply conditions for reservoir operation based on climate change. Additionally, the variation in the patterns of streamflow under various instreamflow supply conditions were analyzed using this system, and the quantitative increases in streamflow were calculated by comparing the simulated streamflow under the different instreamflow supply conditions for reservoir operation, and streamflow under the operation condition where in the reservoirs do not supply instreamflow.
This system consists of a sub-module that can extract the climate data for the study area from the raw data of climate change scenarios database, and the bias of the raw data can be corrected using a statistical method without the need for separate data handling. This feature also enables a swift evaluation of streamflow under climate change because simulations for operation based on various insteamflow supply conditions of agricultural reservoirs can be performed simultaneously.
Therefore, this system can be utilized as a tool for establishing agricultural reservoir operation rules in terms of instreamflow supply. and as a tool for quantitatively analyzing the changes in downstream streamflow based on different instreamflow supply conditions for agricultural reservoir operation considering climate change.