Investigating changes of land use and hydroclimatic extreme indices in Minab River Basin

Introduction and Objective
In the last three decades, land use in Minab river basin has undergone significant changes and these changes along with climate change in the basin can affect the trend of hydroclimatic variables. Due to the changes that have occurred in the climate and land use of the Minab River watershed in the past decades until now, the investigation of trends and changes in the threshold indicators of precipitation, temperature and flow rate becomes particularly important. Therefore, the aim of the current research is to investigate the trend of land use changes and hydroclimatic variables in the Minab basin.

Materials and Methods
In the current research, the data of hydrometric, rain gauge and evapotranspiration stations of Minab watershed were analyzed to extract threshold indices based on ETCCDI standard including precipitation, temperature and river flow. Non-parametric Mann-Kendall test was used for trend analysis. Also, land use changes were extracted using TM series Landsat satellite images in 1368, 1383, and 1399 from TM, ETM+, and OLI sensors, respectively, and the accuracy of the extracted images was confirmed with Kappa statistics.

Results and Discussion
The results showed that all the temperature limit indices, including tropical nights, hot days, hot nights and the range of day and night temperature, have an increasing trend. In extreme precipitation indices, heavy precipitation of 10, 20, and 30 mm in some stations has an increasing trend, but the annual average precipitation has an increasing trend. The number of wet days is decreasing and the number of dry days is increasing. This means that the number of rainy days is decreasing and the number of dry days is increasing. The investigation of the changes in the rainfall regime of the region showed that the intensity of the rainfall is increasing in the duration of 15 and 45 minutes. Due to the increase in the number of dry days and the decrease in wet days and the increase in the intensity of short-term rainfall, the change of the rainfall regime in the region is inevitable. The survey of land use changes over the past three decades showed that 22% of the pasture land area has decreased, and residential and agricultural land have increased by 280 and 220%, respectively.

Conclusion and Suggestion
Finally, in examining the trend of hydro-climatic variables and land use, it can be acknowledged that climate change has occurred in the region during the past three decades, and land use changes can be one of the factors that cause or exacerbate it, this is a warning for those who are in charge of studying climate change impacts, water resources and agricultural issues and restoration and preservation of natural resources in the region of study.