The Impact of Multiple Typhoons on Severe Floods in the Mid-Latitude Region (Hokkaido)

Abstract

Mid-latitude regions in the North Pacific are generally vulnerable to climatological disasters and are possibly more sensitive to future climate changes. Severe flood disasters struck Hokkaido in August 2016 because of the multiple, continuous typhoons that struck the island. We evaluated the effect of these typhoons on floods and changes in future floods using a distributed hydrological model in a watershed located in eastern Hokkaido. We conducted two numerical examinations: a simulation with a major typhoon only (which caused flood disasters) without other preceding typhoons, and a simulation with a simple assumed future climate (in which we employed higher precipitation). The result of the former simulation demonstrated that the impact of the preceding typhoons on the highest flood peak was significant during the early stage of the major typhoon but weaker after the middle stage of the major typhoon. The result of the latter simulation indicated that flood peaks potentially increased with an increase in precipitation. Based on the water level distributions in the surface layer, the impact of multiple typhoons and future weather conditions on potential flood peaks depends on the degree of soil saturation over our target watershed.

d4PDF: large-ensemble and high-resolution climate simulations for global warming risk assessment

“…Such analyses relevant to extremes are possible using the large ensembles without statistical hypothesis. Similar results were obtained in different river basins in Japan and other countries: the Nagara river basin by Harada et al (2018), the Hokkaido region by Kimura et al (2018) and (Masuya et al 2018), and Indochinese Peninsula by Hanittinan et al (2018).…”

Flood Simulations in Mid-Latitude Agricultural Land Using Regional Current and Future Extreme Weathers

“…According to our previous study [15], the soil had exhausted its water capacity in the southwest portion of the TR watershed before the fourth typhoon and, as a result, the severe flood disaster occurred during the fourth typhoon's approach toward Hokkaido. The agricultural damage areas at the Nakajima Bridge, Rrutanjyoryu, and Minamisatsunai Stations calculated in the current flood simulation were 3-10 km 2 along the tributaries where overflow events occurred, but not at Moiwa Station.…”

“…In other research related to the August 2016 disaster, Kimura et al [15] showed that with a hydrological model and observed rainfall data, the effect of the preceding three typhoons on flood disasters was crucial as the water capacity in soil in the west side of the TR watershed was exceeded before the fourth typhoon approached, which then made the flood disaster worse by producing massive rainfalls. However, this previous study was limited to understanding the future trend because there is no future rainfall data based on climate change scenarios as an extended investigation of the August 2016 disaster.…”

“…This study is important to reveal how much of the agricultural damage may be changed quantitatively in a specific area as an illustrative example. Note that we employed the flood model, appropriately calibrated in our previous study using on-site observations [15].…”

“…The model was calibrated in our previous study using appropriate parameters, along with the spatial and temporal resolutions [19]. Our previous work presents the flood model setup in detail [15]. Flood control dams were implemented in the flood model.…”