Investigating the Effect of Distribution Function and Potential Evapotranspiration Assessment Method in Determining Reconnaissance Drought Index

Document Type : Research Paper



Iran is located in arid and semi-arid regions in the world and therefore, drought monitoring has an important role in there. Drought assessment is conventionally based on drought indices such as Reconnaissance Drought Index (RDI). On the basis of definition, Reconnaissance Drought Index is estimated by fitting Log-normal distribution on the ratio of precipitation to potential evapotranspiration (calculated by Thornthwaite method). In this research, the effect of the change of distribution function and potential evapotranspiration calculation method was investigated in estimating Reconnaissance Drought Index in Iran. For this purpose, meteorological data of 30 synoptic stations were used in the period of 1960-2014. The potential evapotranspiration was calculated using the FAO Penman-Monteith as standard method. Beside standard method, 20 different methods were used to calculate evapotranspiration value. The superior evapotranspiration calculating method was obtained using Root Mean Square Error statistic. Then, the Reconnaissance Drought Index values were calculated using different evapotranspiration values and by fitting several probability distribution functions. On the basis of obtained results, the change of probability distribution function and evapotranspiration calculation method can affect the determining Reconnaissance Drought Index. Also, the comparison results of the calculated Reconnaissance Drought Index based on the fitting the superior probability distribution function on the ratio of precipitation to potential evapotranspiration which was calculated using superior and standard methods showed that the FAO Penman-Monteith method should be used in 90% of the studied stations to calculate Reconnaissance Drought Index in cases of data available.


1-       شکوهی، ع. 1391. مقایسه شاخص­های RDI و SPI برای تحلیل خشکسالی در مقیاس ایستگاهی با تکیه بر خشکسالی کشاورزی (مطالعه موردی: قزوین و تاکستان). فصلنامه مهندسی آبیاری و آب، 3(9): 122-111.
2-       علیزاده، ا.، خانجانی، م. ج.، تراز، ح. و م. ح. رهنورد. 1385. بررسی اثرات اصلاح داده­های دما بر دقت محاسبات تبخیر و تعرق و مقایسه­ی آن با نتایج به­دست آمده از لایسیمتر وزنی. مجله جغرافیا و توسعه ناحیه­ای، 6: 99-91.
3-       قبائی­سوق، م. و ا. مساعدی. 1392. اصلاح شاخص خشکسالی RDI بر اساس مناسب­ترین روش برآورد تبخیر و تعرق پتانسیل و تابع توزیع احتمال. مجله مرتع و آبخیزداری، 66(4): 582-565.
4-       محمدیان، آ.، علیزاده، ا. و س. جوانمرد. 1384. محاسبه میزان فرابرآورد تبخیر-تعرق مرجع با استفاده از داده­های ایستگاه­های هواشناسی غیرمرجع در ایران. مجله تحقیقات مهندسی کشاورزی، 6(23): 84-67.
5-       Asadi, A. and S.F. Vahdat. 2013.  The efficiency of meteorological drought indices for drought monitoring and evaluating in Kohgilouye and Boyerahmad province, Iran. International Journal of Modern Engineering Research (IJMER), 3(4):2407-2411.
6-       Asadi Zarch, M. A., Malekinezhad, H., Mobin, M. H., Dastorani, M. T. and M. R. Kousari. 2011. Drought monitoring by Reconnaissance Drought Index (RDI) in Iran. Journal of Water Resources Management, 25 (13):3485-3504.
7-       Al-Ghobari, H. M. 2000. Estimation of reference evapotranspiration for southern region of Saudi Arabia. Journal of Irrigation Science, 19:81–86.
8-       Bakhtiari, B., Ghahreman, N., Liaghat, A.M. and G. Hoogenboom. 2011. Evaluation of reference evapotranspiration models for a semiarid environment using lysimeter measurements. Journal of Agricultural Science and Technology, 13:223-237.
9-       Borg, D. S. 2009. An application of drought indices in Malta, Case Study. Journal of European Water, 25/26:25-38.
10-   Djaman, K., Balde, A. B., Sow, A., Muller, B., Irmak, S., N’Diaye, M. K., Manneh, B., Moukoumbi, Y. D., Futakuchi, K. and K. Saito. 2015. Evaluation of sixteen reference evapotranspiration methods under sahelian conditions in the Senegal River Valley. Journal of Hydrology: Regional Studies, 3:139-159.
11-   Heydari, M. M., Nasiri Noushabadi, R., Vahedi, M., Abbasi, A. and M. Heydari. 2013. Comparison of evapotranspiration models for estimating reference evapotranspiration in arid environment. Middle-East Journal of Scientific Research, 15(9):1331-1337.
12-   Khalili, D., Farnoud, T., Jamshidi, H., Kamgar-Haghighi, A. A. and S. Zand-Parsa. 2011. Comparability analyses of the SPI and RDI meteorological drought indices in different climatic zones. Journal of Water Resources Management, 25(6):1737-1757.
13-   Oudin, L., Moulin, L., Bendjoudi, H. and P. Ribstein. 2010. Estimating potential evapotranspiration without continuous daily data: possible errors and impact on water balance simulations. Journal of Hydrological Sciences, 55(2):209-222.
14-   Priestley, C. H. B. and R. J. Taylor. 1972. On the assessment of surface heat flux and evaporation using large scale parameters. Monthly Weather Reviews, 80:81-92.
15-   Racz, C., Nagy, J. and A. C. Dobos. 2013. Comparison of several methods for calculation of reference evapotranspiration. Journal of Acta Silvatica et Lignaria Hungarica, 9:9–24.
16-   Ravazzani, G., Corbari, C., Morella, S., Gianoli, P. and M. Mancini. 2012. Modified Hargreaves-Samani equation for the assessment of reference evapotranspiration in Alpine river basins. Journal of Irrigation and Drainage Engineering, 138:592-599. 
17-   Shamsnia, S. A. 2014.  Comparison of Reconnaissance Drought Index (RDI) and Standardized Precipitation Index (SPI) for drought monitoring in arid and semiarid Regions. Indian Journal of Fundamental and Applied Life Sciences, 4(3):39-44.
18-   Steele, D. D., Sajid, A. H. and L. D. Prunty. 1996. New corn evapotranspiration crop curves for southeastern North Dakota. Journal of Transactions of the ASAE, 39(3):931-936.
19-   Tsakiris, G. and H. Vangelis. 2005. Establishing a drought index incorporating evapotranspiration. Journal of European Water, 9/10:3-11.
20-   Tsakiris, G., Pangalou, D. and H. Vangelis. 2007. Regional drought assessment based on the reconnaissance drought index (RDI). Journal of Water Resources Management, 21(5):821-833.
21-   Tukimat, N. N. A., Harun, S. and S. Shahid. 2012. Comparison of different methods in estimating potential evapotranspiration at Muda irrigation scheme of Malaysia. Journal of Agriculture and Rural Development in the Tropics and Subtropics, 113(1):77–85.
22-   Vangelis, H., Tigkas, D., and G. Tsakiris. 2013. The effect of PET method on Reconnaissance Drought Index (RDI) calculation. Journal of Arid Environments, 88:130-140.
23-   Xu, C. Y. and V. P. Singh. 2001. Evaluation and generalization of temperature-based methods for calculating evaporation. Journal of Hydrological Processes, 15:305–319.
24-   Xu, C. Y. and V. P. Singh. 1998. Dependence of evaporation on meteorological variables at different time-scales and intercomparison of estimation methods. Journal of Hydrological Processes, 12:429-442.
25-   Zehtabian, G., Karimi, K., Nakhaee Nezhad Fard, S., Mirdashtvan, M. and H. Khosravi. 2013. Comparability analyses of the SPI and RDI meteorological drought indices in South Khorasan province in Iran. International Journal of Advanced Biological and Biomedical Research, 1(9):981-992.
Volume 40, 1-1
Special Issue
June 2017
Pages 167-183
  • Receive Date: 24 February 2016
  • Revise Date: 07 June 2017
  • Accept Date: 14 May 2016
  • Publish Date: 01 January 1970