ANALYSIS OF DROUGHTS OF NORTHWEST OF IRAN USING THE RECONNAISSANCE DROUGHT INDEX

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HOSSEINI S.B.; DINPASJHOH Y.; NIKBAKHT J.

Title

ANALYSIS OF DROUGHTS OF NORTHWEST OF IRAN USING THE RECONNAISSANCE DROUGHT INDEX

Author(s)

HOSSEINI S.B. | DINPASJHOH Y. | NIKBAKHT J. | Issue Writer Certificate

Keywords

DROUGHTQ2

NORTHWEST OF IRANQ2

PENMAN-MONTHEISQ2

RDIQ2

Abstract

Introduction: DROUGHT is a creeping natural phenomenon, which can occur in any region. Such phenomenonnot only affects the region subjected to DROUGHT, but its adverse effects can also be extended to other adjacentregions. This phenomenon mainly starts with water deficiency (say less than long- term mean of variable understudy such as rainfall, streamflow, groundwater level or soil moisture) and progress in time. This period can beended by increasing the rainfall and reaching the mean level. Even after the ending of a DROUGHT period, itsadverse effects can be continued for several months. Although, it is not possible (at least at this time) to preventthe occurrence of DROUGHT in a given region, it is not impossible to alleviate the DROUGHT consequences byscientific water management. Such a management should be employed before DROUGHT initiation as well asduring it and continue on even after the end of the DROUGHT period. The frequency of the main DROUGHT characteristics is a major concern of this study. The NORTHWEST OF IRAN recently encountered severe and prolongedDROUGHTs, such that a major portion of the Urmia Lake surface disappeared during the last DROUGHT in recentyears. In order to study DROUGHT characteristics, we used the Reconnaissance DROUGHT Index (RDI). This index isbased on annual rainfall and potential reference crop evapotranspiration (abbreviated by PET here). This studyemployed the Monte Carlo simulation technique for synthetic data generation for analysis.Materials and Methods: The information from the 17 synoptic weather stations located in the North-west ofIran was used for DROUGHT analysis. Data was gathered from the Islamic Republic of Iran’s MeteorologicalOrganization (IRIMO). In the first stage of research, the ratio of long term mean annual precipitation toevapotranspiration was calculated for each of the stations. For this purpose, the PENMAN-MONTHEIS (FAO 56) method was selected for PET estimation. In the second stage, the 64 candidate statistical distributions were fittedfor the mentioned RDI’s of each station. The best statistical distribution was selected among the 64 candidatedistributions. The best fitted distribution was identified by the chi-square criterion. The parameters of thedistribution were estimated by the Maximum Likelihood Estimation (MLE) scheme. Then 500 synthetic timeseries (each of them have the same number of observed data) were generated employing the parent populationparameters. The three main DROUGHT characteristics (namely duration, severity and magnitude) were obtained foreach of the mentioned artificial time series. The maximum values for each of the mentioned DROUGHTcharacteristic were selected for each year. Then, a new time series having the 500 elements were obtained bycollecting the chosen values for each station. Once again the best distribution was selected for each series. DROUGHT characteristics for different return periods (2, 10, 25, 50, 100 and 200 years) were estimated for eachstation.Results and Discussion: Preliminary results indicated that a negative trend existed in annual rainfall timeseries for almost all of the stations. On the other hand, the pattern of monthly PET histograms were more or lesssimilar for all of the selected stations. The peak of the PET was mainly observed in the hottest month of year, whereas the lowest value of the monthly PET belonged to the coldest month of year. The results showed that theamount of annual rainfall time series decreases sharply, after the year 1991. However, PET values significantlyincrease for all of the selected stations. After calculation of RDI values, the histogram of annual RDI’s wasplotted against the year. This is repeated for all of the selected stations. Figure.6 shows the mentioned diagramfor Tabriz station as an example. In the mentioned Figure, negative values of RDI (shown by red bars) indicatedthe DROUGHT years. A critical prolonged DROUGHT with a sixteen years duration period (neglecting the 2001 inwhich RDI value was a small positive value) was experienced in Tabriz. The maximum DROUGHT severity inTabriz was estimated to be about -7 in RDI units. Urmia station experienced the longest DROUGHT period, startingfrom 1995 and ending in 2005. It can be concluded that although few sparse wet years were observed in some of the selected stations in the studied period, they cannot compensate the water deficiency accumulated duringseveral consecutive years. The results showed that the lowest value of the ratio of DROUGHT severity in a 100 yearreturn period to the corresponding value for 2 year return period was about 2.13 (belonged to the Tabriz station), whereas the highest value was 3.17 (belonged to the Tekab station). On the other hand, the lowest value for theratio of DROUGHT duration in 100 year return period to its corresponding value for 2 year return period was 1.95 (experienced in the Makoo station). The highest mentioned ratio was 9.18 (observed in the Sardasht station). Thelowest and highest value of the ratio of DROUGHT magnitude in 100 year return period to its corresponding valuefor 2 year return period were 1.17 and 2.74, respectively. The mentioned DROUGHT magnitude ratios wereobserved in the Urmia and the Khalkhal stations, respectively. The isoplethes of the three main DROUGHT characteristics (severity, magnitude, duration) for a 10 year return period was illustrated for the study area (Northwest of Iran).Conclusion: In the present study RDI values were used to analyze DROUGHT characteristics of Northwest ofIran. The PENMAN-MONTHEIS method was used to estimate PET (needed for RDI) values of the stations. The mainthree DROUGHT characteristics were calculated for each of the 500 synthetic time series. The results showed thatnearly all of the areas under study experienced severe and prolonged DROUGHTs. It can be concluded that a sharpdecrease in annual precipitation as well as the increase in PET (due to greenhouse effects of consuming fossilfuels as the main source of energy in the region) from 1995 to 2005 was observed in the study area. Scientificmanagement of available water in the study area is extremely vital to alleviate the adverse consequences ofDROUGHT. Several economic and social problems were anticipated in these arid and semi-arid regions of Iran.

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APA: Copy

HOSSEINI, S.B., DINPASJHOH, Y., & NIKBAKHT, J.. (2015). ANALYSIS OF DROUGHTS OF NORTHWEST OF IRAN USING THE RECONNAISSANCE DROUGHT INDEX. JOURNAL OF WATER AND SOIL (AGRICULTURAL SCIENCES AND TECHNOLOGY), 29(2), 295-310. SID. https://sid.ir/paper/141069/en

Vancouver: Copy

HOSSEINI S.B., DINPASJHOH Y., NIKBAKHT J.. ANALYSIS OF DROUGHTS OF NORTHWEST OF IRAN USING THE RECONNAISSANCE DROUGHT INDEX. JOURNAL OF WATER AND SOIL (AGRICULTURAL SCIENCES AND TECHNOLOGY)[Internet]. 2015;29(2):295-310. Available from: https://sid.ir/paper/141069/en

IEEE: Copy

S.B. HOSSEINI, Y. DINPASJHOH, and J. NIKBAKHT, “ANALYSIS OF DROUGHTS OF NORTHWEST OF IRAN USING THE RECONNAISSANCE DROUGHT INDEX,” JOURNAL OF WATER AND SOIL (AGRICULTURAL SCIENCES AND TECHNOLOGY), vol. 29, no. 2, pp. 295–310, 2015, [Online]. Available: https://sid.ir/paper/141069/en

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ISSN: 2588-4824

Journal Paper

ANALYSIS OF DROUGHTS OF NORTHWEST OF IRAN USING THE RECONNAISSANCE DROUGHT INDEX