Annual trend analysis of climate parameters of temperature and precipitation in decuple agroecology regions of Iran

Climate change is exacerbated by natural factors such as aridity and drought or human activities. Identifying and revealing the changes in each factor and what cause them is considered the first step in the study of the process of climatic elements. The trend analysis might be due to natural changes, such as drought or human activities e.g. increasing greenhouse gas emissions. However the trend in the climatic factors of each area might be normal, its continuity in the coming years may have more significant effects on the economic and social components. Climate change in a region can be detected by investigating the changes in the average rainfall and temperature. This research was carried out in order to identify the time variation of climate parameters (temperature and precipitation) in decuple agroecology regions of Iran.

For this study, data on temperature and precipitation variables were extracted annually from all provinces of the country during the period 1985-2015 from the Meteorological Organization of Iran. Since the distribution of a number of climatic parameters such as temperature and precipitation climatic series is not normal, the non-parametric Mann-Kendall method was used for analyzing their distribution.  To determine the level of significance in variables and to determine the trend of annual changes, Mann-Kendall test was used with XLSTAT extension software.

The results showed that temperature variable in Central, Northwest, Caspian Coastal Plain, Khuzestan, Central Zagros, Arid Southern, Khorasan, Southern Coastal Plain Arid Central zones had an upward trend and no trend in Southern Zagros zone. Precipitation variable was decreasing in Khuzestan and Khorasan. Precipitation variables in Central, Northwest, Caspian Coastal Plain, Central Zagros, Arid South, Arid Southern, Arid Central and Central Zagros zones were not trendy. The increase in temperature will lead to a significant increase in the annual evapotranspiration rate (which is already higher than annual precipitation in most parts of Iran). The Intergovernmental Panel on Climate Change regards this issue as a serious challenge to arid and low rainfall regions, including Iran, and as a consequence, predicts that the production of strategic products in Iran will decrease compared to the current level of production. The vastness of Iran, along with its geographic location, and the location of heights, prevent the region from fully absorbing the atmospheric humidity. The existence of such conditions causes an inhomogeneity in the amount and pattern of precipitation that has crystallized in the temporal and spatial behavior of the climatic factors. This could be a warning to a country like Iran that is heavily in need of water, and will face water scarcity in the future.

The results of the research showed that the mean annual temperature significantly increased in all stations. However, there is no particular trend for the rainfall situation Due to the arid and semi-arid climate of Iran; Iran is one of the countries facing water shortage. Obviously, this shortage will greatly affect agricultural production.