Assessing the Resilience of Agricultural Reservoirs in Ungauged Catchments under Climate Change Using a Ratio Correction Factors-Based Calibration and Run Theory

Abstract

This study applied ratio correction factor (RCF) optimization to calibrate the daily storage of agricultural reservoirs located in ungauged catchments that lack stream flow data. Using Run theory, we then assessed the impacts of climate change on the resilience of agricultural reservoir operations during reservoir drought conditions. First, we optimized the RCFs of inflow and outflow in three agricultural reservoirs in Korea using limited measurement data from 2008 to 2017; the results showed high performance regarding the simulation of daily reservoir storage. Second, we simulated daily storage volume in reservoirs from 2018 to 2099, using future climate change data, and analyzed the duration and intensity of reservoir drought conditions, which indicated that the storage capacity is under the critical value. Without calibration, the correlation between the simulated and measured reservoir water volumes was very low, but the correlation increased after calibration of the simulated water volumes. A linear relationship between the simulated and measured volumes was observed with a correlation coefficient value of 0.9, indicating that the simulated reservoir values after calibration closely match the measured values. In addition, the maximum intensity of reservoir drought in the Kicheon reservoir was determined to be 486,000 m3 before calibration but 506,000 m3 after calibration. The duration results showed that long-term reservoir drought conditions will be observed more often in the future owing to climate change, and this could be a negative factor affecting the resilience of reservoir operations.

Water Supply Reliability of Agricultural Reservoirs under Varying Climate and Rice Farming Practices

“…In Korea, nursery transplanting to ponded fields is the most common rice cultivation practice, and IWR is the depth of water required to compensate for water losses as ET c and soil infiltration, excluding the rainwater contribution as effective rainfall (ER) [9,11].…”

“…Paddy water balance model requires water consumption data during nursery raising and transplanting in addition to the reference evapotranspiration (ET o ), crop coefficient and soil infiltration rates [4,9].…”

“…where I = Infiltration (mm), ER = effective rainfall (mm), NPW = nursery preparation water (crop management water) (mm), D np = days of nursery preparation (day), A n = nursery area (ha), A = rice crop area (ha), ET c = crop evapotranspiration, TW = transplanting water (crop management water) (mm), D t = days of transplanting period (day), A t = transplanting area (ha), np = nursery preparation period (day), n = nursery period (day), t = transplanting period (day), and g = growing period (day) During most of the rice season, the soil remains saturated in ponded fields and incident rainfall directly contributes to the ponding depth [9], therefore ER is the rainfall that contributes to ponding depth excluding the surface runoff. We used the freeboard model of ER estimation to simulate the ponding depth in the rice field [8,11].…”

“…During the last five years, average temperature and rainfall in Korea have increased by 0.6 • C and decreased by 150 mm, respectively, compared to the last three decades [7]. Agricultural reservoirs are the primary irrigation source to sustain rice production against rampant droughts, which is also the focal point of agricultural management and development policies of the Korean government [9][10][11].…”

“…The climate vulnerability of Korea has been extensively examined by identifying the design water requirements for a 10-year return period drought under the historic [27] and future climate change trends [4,9,11,28], development and application of an irrigation vulnerability assessment model for agricultural reservoirs [1,24,29], meteorological and agricultural drought risk assessment [13,24,30], and improving the monitoring and management of reservoir operation to stabilize the irrigation water supply [31,32]. In addition to the hydrological repercussions, climate change is also transforming rice farming practices, crop growth periods, and yields [33], and irrigation water supply from agricultural reservoirs is highly dependent on the operational and physical characteristics of the irrigation district dictated by agricultural practices [25].…”