Sharghi et al. (2025) Practical investigation of climate extremes and IDF curves under climate change with applications of SSP scenarios (case study: Silakhor Plain, Iran)

Identification

• Journal: Environmental Monitoring and Assessment
• Year: 2025
• Date: 2025-10-10
• Authors: Ali Sharghi, Mehdi Komasi
• DOI: 10.1007/s10661-025-14568-4

Research Groups

• Department of Civil Engineering, Faculty of Engineering, Ayatollah Boroujerdi University, Boroujerd, Iran

Short Summary

This study projects future climate extremes and Intensity-Duration-Frequency (IDF) curves for the Silakhor Plain, Iran, using downscaled CMIP6 GCM data under SSP2-4.5 and SSP5-8.5 scenarios, revealing increased intensity of heatwaves and sub-daily extreme precipitation, alongside a decline in frost waves and overall wet spell frequency.

Objective

• To project future variations of climate extremes (heatwaves, frost waves, wet spells) and Intensity-Duration-Frequency (IDF) curves in the Silakhor Plain, Iran, under SSP2-4.5 and SSP5-8.5 climate change scenarios, with a focus on practical impacts on health and agriculture.

Study Configuration

• Spatial Scale: Silakhor Plain, Iran (area of 1019.81 km², located between 33°45′–34°7′ N and 48°29′ – 48°57′ E).
• Temporal Scale:
  • Historical/Baseline: 1950–2020 (GCMs), 2002–2020 (observational).
  • Near-future: 2021–2060.
  • Far-future: 2061–2100.

Methodology and Data

• Models used:
  • General Circulation Models (GCMs) from CMIP6: CAS-ESM2-0, ACCESS-ESM1-5, HadGM3-GC3.1-LL, MRI-ESM2-0 (ACCESS-ESM1-5 was selected for projections).
  • Downscaling model: LARS-WG (stochastic weather generator).
  • IDF curve derivation: Adapted Bell’s equation (Ghahraman & Abkhezr, 2004).
• Data sources:
  • Observational data: 19 years (2002–2020) of daily maximum temperature (Tmax), minimum temperature (Tmin), and precipitation from Silakhor synoptic station.
  • Model data: Historical (1950–2020), near-future (2021–2060), and far-future (2061–2100) daily GCM data for SSP2-4.5 and SSP5-8.5 scenarios from the CMIP6 website.

Main Results

• Temperature Projections:
  • Near-future (SSP2-4.5): Mean Tmin increase of 1.2 °C, Tmax increase of 1.1 °C.
  • Far-future (SSP5-8.5): Maximum Tmax increase of 3.9 °C, Tmin increase of 3.5 °C.
  • Average temperature increases are consistent with the magnitude of radiative forcing and emissions in SSP scenarios.
• Heatwaves (HW-37 for health, HW-34 for agriculture):
  • Projected increases in average temperature, frequency, and duration of HW-34 and HW-37 under both SSP2-4.5 and SSP5-8.5 scenarios.
  • Observed HW-37 frequency was 5 times per year; projected to increase to 7.8 (SSP2-4.5) and 8.5 (SSP5-8.5) times per year in the near-future.
  • Maximum HW-37 duration is projected to increase from 24 days (near-future SSP5-8.5) to 79 days (far-future SSP5-8.5).
  • HW-37 events may occur as early as May and June under the SSP5-8.5 scenario.
  • Projected HW-34 durations in June (critical for wheat) under SSP5-8.5 (2061–2100) exceed the 16-day threshold twice, showing a statistically significant increasing trend.
• Frost Waves (-8 °C):
  • Projected decrease in both frequency and duration of -8 °C frost waves, with an increase in their average temperatures.
  • Historically, a 1-day -8 °C frost wave occurred at least once a year; future projections show longer but less regular occurrences, potentially reducing Sunn pest mortality.
• Precipitation (Total and Wet Spells):
  • Near-future (SSP5-8.5): Highest decrease in annual precipitation (31.2 mm) in fall months, while summer precipitation shows a slight increase.
  • Far-future (SSP5-8.5): A 53.8 mm decrease in fall precipitation is projected. Total annual precipitation is projected to increase under all scenarios, but not consistently with CO2 emissions.
  • The intensity of 1–2-day rainfall events is projected to increase significantly (P < 0.05) under climate change scenarios, particularly SSP5-8.5 (1.6 mm/day increase in near-future SSP5-8.5).
  • The probability of short-duration wet spells (1–2 days) is expected to rise (3.2% increase in near-future SSP5-8.5), while the occurrence of long-duration rainfall events is likely to decrease.
  • The overall frequency of wet spells is predicted to decline in both near and far-future under all scenarios.
  • Greatest increases in rainfall intensity are likely to occur in March and October.
• Intensity-Duration-Frequency (IDF) Curves:
  • IDF curves are projected to shift towards increasing the intensity of sub-daily extreme precipitation.
  • The intensity of extreme precipitation increases in relation to the level of forcing and CO2 emissions for each scenario, with SSP5-8.5 showing the largest deviation from observational data for both 20-year and 100-year return periods.
  • Near-future SSP5-8.5 projects a reduction in total precipitation but increased intensity for 1-day and 1-hour precipitation events.

Contributions

• Provides a practical evaluation of climate extreme indices (HW-37 for human health, HW-34 for agricultural impacts, and -8 °C frost waves for pest control) under climate change scenarios.
• Conducts a detailed examination of wet spell characteristics (frequency, duration, and intensity) under Shared Socioeconomic Pathways (SSP) scenarios.
• Addresses the challenge of extracting sub-daily IDF curves from daily downscaled data by driving Bell’s equation with modified regional coefficients specific to the study area.
• Applies downscaling techniques to CMIP6 outputs for a small-scale, mountainous region (Silakhor Plain), contributing to regional climate impact assessments where GCM resolution is typically insufficient.
• Reinforces the theory that the intensity of various climate extreme indices is sensitive to the amount of greenhouse gas emissions in different scenarios.

Funding

• The Iran Meteorological Organization (IRIMO) provided necessary data and information.
• The World Climate Research Program (WCRP) made the CMIP6 dataset available.
• The Earth System Grid Federation (ESGF) archived and provided access to the CMIP6 dataset.

Citation

@article{Sharghi2025Practical,
  author = {Sharghi, Ali and Komasi, Mehdi},
  title = {Practical investigation of climate extremes and IDF curves under climate change with applications of SSP scenarios (case study: Silakhor Plain, Iran)},
  journal = {Environmental Monitoring and Assessment},
  year = {2025},
  doi = {10.1007/s10661-025-14568-4},
  url = {https://doi.org/10.1007/s10661-025-14568-4}
}