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Abstract:  
Introduction: In the last decades drought has become one of the natural disasters with most relevant impacts happened in Iran. Although rainfall is a major indicator of the availability of water, temperature is also an important factor that can influence the availability of water as it controls the rates of evapotranspiration. Parameters such as rainfall and temperature can be used as indicators of drought. Trend identification in observed historical data and their occurrence in space and time are important in water resources management. Studies of change are also important. The purpose of trend analysis is to determine if a series of observations of a random variable is generally increasing or decreasing with time.
 
Materials and methods: The Standardized Precipitation Evapotranspiration Index (SPEI) is a meteorological drought index that considers the variability of both precipitation and temperature to predict drought conditions in a region. The index has been used in the variety of drought analyzing recently. Drought events were characterized by Standardized Precipitation Evapotranspiration Index over both in 3 and 12-month timescales. The SPEI were calculated using long-term (1988–2018) observed precipitation and temperature data in eleven meteorological stations, distributed across Sistan and Baluchestan Province, Iran. The total geographical area of Sistan and Baluchestan Province is approximately 187,000 km2, located in 25° 03’ N to 31° 28’ N (latitudes), and 58° 47′ E to 63° 19′ E (longitudes). The province has an arid and semiarid climate with a mean annual rainfall of about 100 mm. The monthly precipitation and temperature data at the stations were obtained from the Sistan and Baluchestan Meteorological Organization. To explore the drought trends in each station both nonparametric trend tests (Mann-Kendall) and graphical Mann-Kendall model trend analysis (statistical significance at 95% confidence level) are applied. The purpose of trend analysis is to determine if a series of observations of a random variable is generally increasing or decreasing with time. Even though parametric trend tests are more powerful, non-parametric trend tests are widely used as they require the data be independent and could accommodate outliers in the data.
 
Results: The results indicate that, there is no negative trend of rainfall but we were able to detect significant trend of temperature. The computed SPEI values for short term time scale (SPEI 3) showed statistically significant downward trend for all stations. It could be associated with the consequences of climate change as it is postulated that droughts would become more common in the future. Result showed the maximum severity of drought was happened in Khash station and wet situation was related to Chabahar.
 
Discussion and Conclusion: This study aimed at identifying possible drought trends in Sistan and Baluchestan province using the Mann-Kendall test. The detection of changes is valuable information for future water resources management. From the observation of past drought events, it is expected that the severity of drought to be more often in the future. Even though this study did not seek to determine any possible causes of decreasing trends that were observed, the results presented herein will be useful as a benchmark towards further analysis of the effect of climate change.
     
Type of Study: Applicable | Subject: Desert
Received: 2020/09/1 | Accepted: 2021/06/29

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