Country‐wide flood exposure analysis using Sentinel‐1 synthetic aperture radar data: Case study of 2019 Iran flood

Abstract

Extreme precipitation and flooding often lead to human and economic losses. However, the high-resolution nationwide flooding exposure data are scarce.Availability of all-weather space-borne SAR satellite data can potentially improve the ability to generate high-resolution flood map extent and exposure globally. In Iran, flooding is a major concern, given the socioeconomic vulnerabilities and increased likelihood of climate extremes. Iran experienced extreme flooding during January to March 2019, attributed to significant precipitation during October 2018 to March 2019, which is well above the longterm averages for 1999-2019. Using Pettitt and Mann Kendall tests, nationwide precipitation records were identified by significant decreasing and increasing trends in north and south, respectively. Utilizing 673 Sentinel-1 SAR intensity images, we applied a fast-marching algorithm for image segmentation in combination with a Bayesian framework to obtain high-resolution probabilistic flood maps. We found, 22, 9, and 15 states in January, February, and March, respectively, experienced flooding that covered >15% of their area with high flooded area percent in the northwestern and southeastern region. We estimated that >15, >11.32, and >11.33 million people were exposed to floods in January, February, and March, respectively. Our datasets inform flooding models and management efforts under increasing climate extremes and changing land use and cover.

Climatology of cyclones in western and northwestern Iran using reanalysis and remote sensing data

“…These characteristics cause the region to have most land usable for cropping and agriculture based on the suitability index, of which one of the parameters is precipitation (Mesgaran et al ., 2016). However, followed by Caspian Sea coastal regions, extreme precipitation events both in magnitude and frequency are highest in western Zagros (Alijani et al ., 2008; Sherpa and Shirzaei, 2022) which has a negative impact on these agricultural lands. In winter and spring, the region is frequently affected by merged Mediterranean and Sudanese systems, which produce heavy rainfall exceeding 100 mm·hr −1 (Ghasemifar et al ., 2017; Kiani et al ., 2020).…”

“…Some recent studies (e.g., Modarres et al ., 2016; Alavinia and Zarei, 2020) showed that although the overall trend of precipitation has decreased, flood magnitude has increased in western and northwestern Iran. This trend is highly correlated with changes in Mediterranean and Sudanese cyclone intensity (Khoshakhlagh et al ., 2008; Sabziparvar et al ., 2010; Heydari and Khoshakhlag, 2015; Bayat et al ., 2017; Kiani et al ., 2020; Rezaei et al ., 2021; Sherpa and Shirzaei, 2022).…”

“…As the most impactful Iranian natural disasters in the past 100 years, floods have cost Iran about 6.1 billion USD (Seddighi and Seddighi, 2020). One example is the recent deadly flood event in January–April 2019 (SRC on Iran Floods, 2020; Sherpa and Shirzaei, 2022). Out of the 31 Iranian states, 22, 9 and 15 states were exposed to flash floods during January, February and March 2019 respectively, which influenced 11.5 million people across the country (Sherpa and Shirzaei, 2022).…”

“…One example is the recent deadly flood event in January–April 2019 (SRC on Iran Floods, 2020; Sherpa and Shirzaei, 2022). Out of the 31 Iranian states, 22, 9 and 15 states were exposed to flash floods during January, February and March 2019 respectively, which influenced 11.5 million people across the country (Sherpa and Shirzaei, 2022). The systems producing the rainfall especially during March (77%) were combined Mediterranean and Sudanese cyclones and were responsible for 77 deaths and ~1 billion USD in losses in the agriculture and hydrological sectors (Alijani et al ., 2020; Khazaei and Nikfal, 2021).…”

Interrelations of vegetation growth and water scarcity in Iran revealed by satellite time series

“…Figure 1e depicts the meteorological dynamics in relation to the availability periods of the global data products used in this study. It shows that for Iran, the analyzed period of vegetation dynamics (covered by MODIS data) coincides with a pronounced severe dry period between 1999 and 2001 forming the onset of a 20-year warm and dry period (compared to 1980-2000) ending with a very wet year in 2019, which was characterized by extensive flooding [61][62][63][64] . Thus, the available MODIS based vegetation growth observations almost exclusively comprise a continuous warm and dry period that started in the year 1999.…”