Assessing Change Impacts on Flood and Drought hazard in Thua Thien Hue province using Standardized Precipitation Index (SPI)

Abstract

The objective of this study is to comprehensively analyze short- and long-term drought and flood occurrences, providing valuable insights into the potential impact of climate change in the future. Our analysis, utilizing the SPI-6 and SPI-12 indices, focuses on historical data spanning from 1979 to 2019, revealing noteworthy patterns. Notable periods of severe drought include September 1982 to August 1983, September 2004 to August 2005, and October 2014 to August 2015. Conversely, instances of elevated humidity and extreme inundation were recorded from October 1980 to August 1981, October 1995 to June 1997, November 1999 to October 2000, November 2007 to October 2008, October 2011 to August 2012, and January 2017 to August 2018. These findings are consistent with historical records of drought and flood events in Thua Thien Hue Province over the past four decades. Incorporating the SPI-6 and SPI-12 indices alongside rainfall forecasts based on updated climate change and sea-level rise scenarios for 2020 in Vietnam, our study extends its projections to the period from 2020 to 2035. These projections indicate a significant departure from typical annual conditions, with both the severity and frequency of drought and flood events expected to increase. Specifically, Thua Thien Hue weather stations estimate a flood frequency of 14% (SPI-12) and 16% (SPI-6), equivalent to approximately one dry month every seven months. High humidity events are projected to occur at an 18% frequency, roughly once every 5-6 months. Analysis of future scenarios under RCP4.5 and RCP8.5 reveals varying levels of risk associated with drought and flood occurrences. Generally, the risk of flooding is slightly lower than that of drought, with only marginal differences observed in scenario RCP8.5. When considering seasonal rainfall patterns—where half of the year experiences a dry season and the other half is rainy—the incidence of drought surpasses that of high humidity in scenario RCP4.5. In contrast, in scenario RCP8.5, the likelihood of flooding outweighs that of drought. It’s noteworthy that historically, mountainous areas within Thua Thien Hue Province have experienced fewer droughts in comparison to coastal regions. Furthermore, the severity of drought and flood events is more pronounced in scenario RCP8.5, particularly concerning flood events. This underscores that despite higher total rainfall in RCP8.5, leading to more severe inundation events, the distribution exhibits unevenness marked by extreme conditions, including more severe drought events.