Monitoring and zoning of droughts in Iran

Academic Thesis for Master's Degree

Field: Geography Major: Climatology in Environmental Planning

Abstract:

In this research, monitoring and zoning of drought as well as examining its various dimensions in the country of Iran using statistics and information related to precipitation and temperature for 30 years (1981-2010) of the National Meteorological Organization have been done. In order to analyze the data, SPI [1] and RDI [2] index methods were used, and to calculate the RDI index, potential evaporation and transpiration was calculated using the Trentwhite method [3]. In the following, these indicators were used to determine the different factors of drought (severity, duration, extent, frequency and sequence) and were compared with each other. The results showed that the SPI index can be used to estimate various factors of drought in all of Iran and can be used as a model to monitor droughts, but the RDI index did not perform the same due to the great climatic diversity in Iran and does not have this ability. Also, the values ??obtained for these two indicators were analyzed by clusters using the Ward method and the total difference of each data from a cluster was done with the average vector of that cluster (Euclidean distance). As a result of this action, the stations were divided into 6 groups based on the SPI index and 5 separate groups based on the similarity in weather conditions based on the RDI index. The frequency of droughts was calculated by counting the months in which the SPI index had negative values, and the relationship between duration and frequency was calculated for all stations. The results showed that the duration-frequency relationship in the stations is of logarithmic type, 4th, 5th and 6th degree equations and does not follow a linear trend. Through mediation methods, drought zoning was done based on its severity in selected dry periods and the area of ??the zones was calculated. From the information obtained in this way, it was determined that in all the eight intervals of the drought classification system, the best fitting function of the real data is the lognormal function of two metametrics. It was also determined that the intensity-extent relationship in all the mentioned ranges except for extreme droughts more than 2, which is of the 3rd degree equation, in the rest of the intervals, it is of the 2nd degree equation.

Key words: drought monitoring, spatial analysis, standardized precipitation index (SPI), drought identification index (RDI), Iran

Chapter 1

Overview of the research

- Chapter 1 (Overview) Research)

1-1  Introduction

Mankind has always faced factors that have affected his life and forced him to leave his country, migrate or spend heavy expenses to continue his life by causing a lot of damage or even the complete destruction of his place of life. Since these factors cause damage to economic, social and physical infrastructures such as life and financial losses, damage to infrastructure facilities, damage to the agricultural sector and generally damage to economic resources, they are called natural disasters. Natural disasters include earthquakes, floods, landslides, hurricanes, volcanoes, droughts, etc. Compensation for the damage caused due to the occurrence of any of these disasters may take a long time or even be irreparable. Therefore, the knowledge and study of these factors, especially from the point of view of risk management, can greatly reduce the severity of possible damage.

Among the natural disasters, drought is different from the others. Drought has destructive effects in various fields, both directly and indirectly. The most important direct effect of drought is on the water resources of each region. With the decrease of rainfall or its absence for a long period of the year (drought), pastures, forests, fields and gardens whose source of water supply is atmospheric precipitation, as well as soil and other natural resources, because their surface and underground water sources are also atmospheric precipitation, are directly damaged. Therefore, the activities and facilities related to them, whether urban, rural, industrial, etc., will be affected and damaged (Kordavani, 1380, Tehran University Press). Many climatologists recognize drought as a slow and creeping phenomenon, unlike other natural disasters, and since it can have different intensity and duration, and it is very wide in terms of scope, so that millions of people are affected by it, it is very important.

Since many factors and variables directly or indirectly affect how this phenomenon occurs, a complete and comprehensive definition that all researchers agree on is difficult. Perhaps, in general, drought can be considered as a continuous period with a lack of rainfall, which leads to damage to agricultural products and a decrease in yield (Omidwar, 2019, Yazd University Press). Experts in hydrology and meteorology classify types of drought as meteorological drought, hydrological drought, agricultural drought and socio-economic drought, and in the definition of meteorological drought, they consider it as a state with a lack of precipitation compared to average conditions. In fact, meteorological drought starts with a decrease in precipitation compared to the normal state, and with the continuation of these conditions, other dimensions of drought (hydrological drought, agricultural drought, and socio-economic drought) appear. Of course, it should be noted that the definitions of drought must be considered on a case-by-case basis for each specific region because the atmospheric conditions that cause a lack of precipitation vary greatly from one region to another.

In order to study and identify the phenomenon of drought, several indicators have been presented by scientists and experts in hydrology and meteorology, and the use of each of these indicators in specific conditions and in different places has its strengths and weaknesses.

One of the most important parameters used in the calculations of the indicators Drought is used is precipitation. Based on this, whenever the rainfall is below normal during a consecutive period of time, a drought occurs. Climatologists use mathematical models and indicators used in climatology to investigate other characteristics of drought such as severity, duration and level involved, the relationships between them, as well as the zoning of droughts. Among these indicators, we can mention the SPI (Standardized Precipitation Index) and RDI (Drought Reconnaissance Indicator) indicators, which are described in the methods section.

The study, monitoring, review and analysis of drought around the world is of great importance due to the many damages caused by it. All regions of the world temporarily but irregularly suffer from the repetition of drought conditions, but this situation is more acute in regions that are affected by different air systems successively but irregularly in terms of climate (Thomson [1], 1999). The location of Iran on the dry belt of the earth has made this country a dry land with very low rainfall, so that the annual average of the country is about 250 mm, which is equivalent to one third of the average rainfall of the dry land of the earth (about 860 mm). On the other hand, the location and time of atmospheric precipitation does not match the needs of the agricultural sector, and most cities in Iran are located in areas far from permanent rivers whose runoff flow is directly supplied by atmospheric precipitation. Planning experts have considered the threshold of 1000 cubic meters per person per year as the limit of water scarcity for every country. This figure is 30 in Egypt, 40 in Qatar, 160 in Libya, and 140 cubic meters per person per year in Saudi Arabia, all of which are considered water-scarce countries, while in Iran, the amount of renewable water per capita is estimated to be about 1670 (for 1367) cubic meters per year. Considering the climatic changes and also the provision of the country's water needs in terms of agriculture, drinking and services in accordance with the increase in population, Iran is also expected to be one of the countries with the problem of water shortage. Since it is not possible to completely prevent the water shortage, but by analyzing the records of the drought phenomenon and relying on the available statistics and information, it is possible to estimate and determine the return period of the drought for different regions, and by preparing plans to deal with the drought, the problems caused by the drought can be reduced to a large extent. Also, the costs incurred to compensate for drought damages (crisis management) are far more than the cost of this type of studies in determining appropriate coping strategies before the occurrence of drought (risk management) (Rahmanian, Mahabqods Quarterly, 1379). In this research, it has been tried to investigate the different dimensions of drought throughout Iran and to identify the relationship between them in order to provide the best possible solutions to adapt to the phenomenon of drought. 1-2 Statement of the problem Drought generally means a decrease in the amount of rainfall in a period compared to the long-term average rainfall and is one of the most important issues discussed in the field of climatology.