Abstract
The water level of the Urmia Lake Basin (ULB), located in the northwest of Iran, started to decline dramatically about two decades ago. As a result, the area has become the focus of increasing scientific research. In order to improve understanding of the connections between declining lake level and changing local drought conditions, three common drought indices are employed to analyze the period 1981–2018: The Standard Precipitation Index (SPI), the Standard Precipitation-Evaporation Index (SPEI), and the Standardized Snow Melt and Rain Index (SMRI). Although rainfall is a significant indicator of water availability, temperature is also a key factor since it determines rates of evapotranspiration and snowmelt. These different processes are captured by the three drought indices mentioned above to describe drought in the catchment. Therefore, the main objective of this paper is to provide a comparative analysis of drought over the ULB by incorporating different drought indices. Since there is not enough long-term observational data of sufficiently high density for the ULB region, ECMWF Reanalysis data version 5(ERA5) has been used to estimate SPI, SPEI, and SMRI drought indicators. These are shown to work well, with AUC-ROC > 0.9, in capturing different classes of basin drought characteristics. The results show a downward trend for SPEI and SMRI (but not for SPI), suggesting that both evaporation and lack of snowmelt exacerbate droughts. Owing to the increasing temperatures in the basin and the decrease in snowfall, drought events have become particularly pronounced in the SPEI and SMRI time series since 1995. No significant SMRI drought was detected prior to 1995, thus indicating that sufficient snowfall was available at the beginning of the study period. The study results also reveal that the decrease in lake water level from 2010 to 2018 was not only caused by changes in the water balance components, but also by unsustainable water management.
Highlights
Droughts are significant natural hazards worldwide, with widespread impacts on humans and ecosystems
Urmia Lake Basin for the period 1995–2018) our analyses show that more severe droughts droughts of the Standard PrecipitationEvaporation Index (SPEI) type (i.e., those induced by changes in precipitation and of the SPEI type evapotranspiration) developed in most months, whereas for Standard Precipitation Index (SPI)-type droughts developed in most months, whereas for SPI-type droughts occurrence occurrence tends to be limited to late spring and summer
The results showed that the drought indices obtained by ECMWF Reanalysis v5 (ERA5) are highly consistent with observational data and that they provide an excellent alternative to such data
Summary
Droughts are significant natural hazards worldwide, with widespread impacts on humans and ecosystems. The Middle East and southwest Asia are waterstressed regions, societally vulnerable, and prone to severe droughts. Since the 1940s, there have been two severe drought periods in these regions, 1999–2001 and. Different drought indices have confirmed that 2001 was one of the most severe periods of drought in Iran [6,7]. Studies regarding the periodic behavior of drought in Iran show that, in addition to the dominant short-term periods over the northwest of Iran, long-term periods of 10 and 30 years have been observed. The average rainfall in southern Iran is much lower than in the north, short-term droughts in the north are more severe than in the south. Long-term droughts are more severe in Iran’s west, east, southeast, south, and center [8,9,10]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call