EVALUATION OF MONTHLY DROUGHT PROSPECT AND RESERVOIR OPERATION RULE FOR DROUGHT RESPONSE USING RESERVOIR DROUGHT INDEX (RDI)

Recently, as climate change intensifies, the frequency and intensity of drought
occurrence are increasing. Unlike floods, drought is challenging to know the
beginning and end, so it is challenging to respond pre-emptively. In Korea, the
vulnerability of agricultural reservoirs to disaster response is increasing due to climate
change and the aging of facilities. So it is necessary to estimate an appropriate
drought index to predict drought disasters and operate reservoirs that respond preemptively to drought. Drought can be largely classified into meteorological,
agricultural, hydrological, and socioeconomic drought. Various drought indexes have
been researched and developed depending on the subject field. Each drought index
uses different variables according to its focus subject. In Korea, more than 17,000
reservoirs have a total effective storage capacity of 31 tons approximately and
contribute more than 75% of the total agricultural water. From June to August,
precipitation is stored in the reservoirs as much as possible when rainfall is
concentrated. Then water is supplied from April to September, the rice paddy growth
period, to ensure stable crop cultivation. Hence if the reservoir storage is sufficient, it
is possible to supply stable agricultural water to cultivate even in meteorological
droughts. On the other hand, if the reservoir storage is insufficient, it is difficult to
respond to a drought disaster. So the management of reservoir storage is a
significant factor in the efficient management of agricultural water and stable crop
production.
In this study, the reservoir drought index (RDI), one of the hydrological drought
indexes, was estimated and utilized to predict drought. Then the pre-emptive drought
response operation rule was applied. First, monthly runoff and agricultural water
demand were estimated. Then the multiple regression analysis was conducted to
1 Graduate student, Department of Rural Systems Engineering, College of Agriculture and Life Sciences,
Seoul National University, Seoul 08826, Republic of Korea, Email: mnkm53@snu.ac.kr
2
Professor, Department of Rural Systems Engineering, College of Agriculture and Life Sciences, Seoul
National University, Seoul 08826, Republic of Korea, Email: iamchoi@snu.ac.kr
3 Graduate student, Department of Rural Systems Engineering, College of Agriculture and Life Sciences,
Seoul National University, Seoul 08826, Republic of Korea
4 Graduate student, Department of Rural Systems Engineering, College of Agriculture and Life Sciences,
Seoul National University, Seoul 08826, Republic of Korea
5 Graduate student, Department of Rural Systems Engineering, College of Agriculture and Life Sciences,
Seoul National University, Seoul 08826, Republic of Korea
24th International Congress on Irrigation and Drainage
03-10 October 2022, Adelaide, South Australia
Special Session
SS.R.2.26
2
predict reservoir storage at the beginning of the following month. The reservoir
storage at the beginning of the month, monthly runoff, and monthly agricultural water
demand were used as independent variables. The RDI was calculated from estimated
reservoir storage and annual reservoir storage. The estimated RDI was compared to
the observed RDI to verify the applicability. The result of the multiple regression
analysis showed above 0.65 coefficient of determination, and the RDI showed better
performance because it was classified according to criteria range. In order to
establish reservoir operation rules for drought response, this study conducted a
survey of reservoir managers in Korea. As a result of the survey, the main factors
influencing the suspension of reservoir water supply were rainfall, rainfall forecast,
and reservoir storage rate. For the reservoir operation for drought response, the
existing criteria of reservoir managers for stopping the supply of reservoir water were
used. The agricultural water demand was always supplied considering the gross
water requirement estimated by the Penman-Monteith equation when there were no
suspension factors in the irrigation period. The result of the reservoir operation rules
for drought response was evaluated by comparison to the result of reservoir operation
according to theoretical water requirements.