| Title: | Evaluating the Impact of Climate Change on Paddy Water Balance Using APEX-Paddy Model |
| Authors: | Mohammad Kamruzzaman , Syewoon Hwang , Soon-Kun Choi , Jaepil Cho , Inhong Song , Jung-hun Song , Hanseok Jeong , Taeil Jang and Seung-Hwan Yoo |
| Year: | 2020 |
| Journal: | Water |
| Volume: | 12 (3) |
| Pages: | 852 |
| DOI: | https://doi.org/10.3390/w12030852 |
| URL (non-DOI journals): | |
| Model: | APEX-Paddy |
| Broad Application Category: | hydrologic only |
| Primary Application Category: | hydrologic assessment |
| Secondary Application Category: | climate change |
| Watershed Description: | The experiment was conducted at the Seoul National University research field (35.9016◦N,
127.0331◦E), located near Ikasn city of the Jeonbuk province in South Korea, as shown in Figure 1. The
predominant soils at the Iksan experimental site are Jeonbug series. The series Jeonbug is a poorly
drained silty loam soil series built on the fluvio-marine plain. The upper layer of the soil’s physical
properties (~20 cm) contains 11.1% sand, 71.1% silt, and 17.8% clay. The daily metrological records of
this study were retrieved from the Jeonju metrological station. Total rainfall in the area during the
cropping season (May to October) ranged from 707.1 mm to 1860 mm in 1976–2005, and the average
annual rainfall of 30 years was around 1300 mm, whereas the average maximum and minimum
temperatures were around 27 ◦C and 17 ◦C, respectively. Seasonally, the monsoon, a rainy season in
Korea between July and August, is highly influenced by precipitation at the study sites. Approximately
52% of the annual rainfall occurs in this region during this time, and part of the increasing rice season
includes the monsoon period. |
| Calibration Summary: | The APEX-Paddy model was calibrated using the daily surface discharge data obtained from
the paddy fields with conventional management during the cropping period of 2013 and 2014. The
statistical measures of the R2
, NSE, and PBIAS downscale dynamical for the quantitative test of the
model performance. The results of model performance are displayed in Table 4. The hydrology
sub-module performed well with the statistics of 0.78, 0.65, and 5.41% for R2
, NSE, and PBIAS,
respectively, for the calibration period. The hydrological yield simulation model proved to be strong
enough for the long-term application according to Moriasi et al.’s [41] decision criteria. The detailed
calibrated results are found in the previous study [43]. |
| Validation Summary: | The calibrated APEX-Paddy model was validated using the daily surface discharge data obtained
during the cropping season of 2015 from the paddy fields under traditional management. The R2
, NSE,
and PBIAS statistical tests were used to quantitatively assess the model results. Figure 3 displays the
yield of the simulated surface discharge against the values observed for the validation periods. |
| General Comments: | The APEX-Paddy model is expected to be used as a tool for water management plans considering
climate change and for vulnerability assessment of rice productivity. This study has forecast changes
in the demands of agricultural water from climate change and has provided an index to quantitatively
reflect the water vulnerability of paddy rice. In addition, it has given policy baseline data and adaptive
solutions for agricultural water resources. Nonetheless, climate change projections include some
degree of uncertainty depending on the downscaling techniques or spatial resolution used [49,50].
Therefore, sensitivity analysis may produce different results.
This study refers directly to the Iksan area in South Korea, but indirectly to comparable regions
due to the advantages mentioned above in methodological terms. As a follow-up, APEX-Paddy will
continue to be used to demonstrate the feasibility of implementing best management practices (BMPs)
for sustainable water management in paddy fields at Korea’s national scale, and the results will be
incorporated into agricultural policy development. |
| Language: | English |
| Keywords: | water balance; paddy field; APEX-Paddy model; climate change; irrigation water demand |