Impact of climate change on the severity, duration, and frequency of drought in a semi-arid agricultural basin

Abstract

Background: Climate change is one of the greatest threats facing the world today and future generations. A change in climate can alter the frequency and duration of drought especially in arid and semi-arid regions. This study aims at investigating the impact of climate change on the severity, duration, and frequency of drought in a semi-arid agricultural basin in Khuzestan, Iran. Results: The largest increases in duration of drought occur for the normal (SPI < -0.5) and extreme (SPI < -2) conditions while the largest increases in frequency of drought occur under the warmer and drier climate scenario in the western portion of the basin. The frequency of moderate (SPI < -1) and severe (SPI < -1.5) droughts decreases under all scenarios whereas most scenarios show an increase in the frequency of extreme (SPI < -2) drought. Conclusions: This study applied the Standardized Precipitation Index (SPI) along with a combination of GCM-scenarios to create the severity-duration-frequency (SDF) curves of drought for the period 2020-2044. An average period of six months (ending in May) was used for the SPI, corresponding to the agricultural growing season of the region, to assess drought conditions under five plausible climate scenarios. The selected GCM-scenarios were GISS-ER A1B (warmer and drier), CSIROMk3.5 B1 (cooler and drier), INGV-SXG A1B (median conditions), ECHO-G A2 (warmer and wetter) and ECHAM5 B1 (cooler and wetter) and they were downscaled with an Artificial Neural Network (ANN) approach. Results reveal that most scenarios exhibit an increase in the duration of extreme drought while the duration of moderate drought decreases under all scenarios. The largest increases in the frequency of extreme droughts occur in the western portion of the basin in response to the warmer and drier climate scenario. An increase in the number of extreme (SPI < -2) drought conditions with a longer duration can influence the growing season.