Standing up to Climate Change

Chapter 6Returning Periods of Drought and ClimateChange in the Zayandeh Rud River BasinElaheh Motevali Bashi Naeini, Jahangir Abedi Koupai,and Ali Mohammad Akhoond-AliContents6.1 Introduction................................................................................ 1076.2 Methodology............................................................................... 1096.2.1 Standardized Precipitation Index (SPI)........................................... 1096.2.1.1 Historical Drought Analysis............................................ 1106.2.2 Copula-Based Multivariate Probability Distribution............................. 1126.2.2.1 Using Copula ............................................................ 1166.2.3 Return Periods Based on Copula................................................. 1196.2.4 Climate Scenarios ................................................................. 1206.2.5 Study Area......................................................................... 1216.2.6 Data ................................................................................ 1236.2.6.1 Observed Data ........................................................... 1236.2.6.2 Data Analysis ............................................................ 1246.3 Results and Discussion .................................................................... 1266.3.1 Historical Drought................................................................. 1276.3.2 Impacts of Climate Change on the Drought Under RCP4.5 Scenario ........... 1296.3.3 Impacts of Climate Change on the Drought Under RCP8.5 Scenario ........... 1316.4 Conclusion ................................................................................. 136References ....................................................................................... 1386.1 IntroductionDrought is the result of altered hydrological conditions, in particular, due to precip-itation deficit over a period of time, and is one of the most common disasters in allkinds of climate regimes (Chen et al.2013). Unlike other natural disasters, the effectsE. Motevali Bashi Naeini (*) · A. M. Akhoond-AliDepartment of Hydrology and Water Resources, Faculty of Water Science Engineering, ShahidChamran University of Ahvaz, Ahvaz, IranJ. Abedi KoupaiDepartment of Water Engineering, College of Agriculture, Isfahan University of Technology,Isfahan, Iran©Springer Nature Switzerland AG 2020S. Mohajeri et al. (eds.),Standing up to Climate Change,https://doi.org/10.1007/978-3-030-50684-1_6107

of drought appear gradually over time, typically on the order of several months toseveral years. Drought analysis usually involves estimating one of the droughtindices and then calculating drought characteristics based on the determined droughtindex such as severity, duration, and peak intensity (Yang2010). Among themethods for determining drought characteristics, the threshold value could providea frame of reference for drought assessment (Yevjevich1967). As climate change isexpected to vary worldwide due to natural and model ambiguities, predicting theimpact of climate change on future droughts is vital for water resources manage-ment. In the Northern Hemisphere—between 15and 45latitudes, including thecurrent study area—drought periods have been particularly severe (Mousavi2005).Several studies have investigated the impact of climate change on drought usingvarious drought indices. For example, in many regions of the world, the Standard-ized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) have beenused to analyze drought (Hoffman et al.2009; Kirono et al.2011; Lee et al.2013;Selvaraju and Baas2007; Serinaldi et al.2009). For the watersheds in Iran, previousstudies have used the Standardized Precipitation Index (SPI), ReconnaissanceDrought Index (RDI), Percent of Normal Precipitation Index (PNPI), AgriculturalRainfall Index (ARI), and Multivariate Standardized Drought Index (MSDI)(Dastorani et al.2011; Golian et al.2015; Madadgar and Moradkhani2011; Moradiet al.2011; Sayari et al.2013). The characterization of drought by severity andduration is widespread as these are interdependent parameters. In some cases, thereis a high correlation between the duration of drought and its severity (Madadgar andMoradkhani2011). Estimating drought return periods that are based solely on one ofthe drought characteristics, such as the duration or severity of drought, can bemisleading as these features are correlated. As a case,finding the return periods ofdrought only based on the drought duration doesn’t provide any information aboutother drought characteristics, namely, the severity of the drought or drought inten-sity. Hence, the severity of the drought may not be very severe on that duration, andthe managers don’t have to specifically plan for this drought, or it may be very severeso the water resources managers should plan for it earlier. Therefore, using a jointdistribution function to study drought return periods might be beneficial. Copula is amodel of multivariate distribution, which is becoming increasingly popular inhydrological studies (Chen et al.2013; Madadgar and Moradkhani2011; Serinaldiet al.2009).Even though there have been many studies regarding climate change and droughtin Iran, little is known about the impact of climate change on drought characteristicsin the Zayandeh Rud basin. This basin is one of the most complicated basins in Iraninvolving many problems with water recourses. In particular, there are limitedstudies that used bivariate and tri-variate joint functions to analyze spatial droughtcharacteristics in a changing climate.There are several agricultural areas in Isfahan province. Roodasht is one of themost important of these areas and is located in the eastern part of the Zayandeh Rudbasin. The state of water resources affects agricultural activities and their products. Itis very important to study the available water status, especially in the changingclimate, in order to make proper decisions for the agricultural activities in the eastern108E. Motevali Bashi Naeini et al.part of the basin based on the water condition perspective in this part, in the futureand under the climate change.The main objectives of this study are the use of copula functions to estimate thedrought frequencies, depicting the density contours of drought return period calcu-lations based on tri-variate copula functions by considering climate change. Spatialmaps of return periods of drought based on severity-duration-peak intensitytri-variate copula for the historical, the near future, and the far future periods in thebasin are also illustrated. The procedure of this study consists of three main parts:(1) identifying the drought duration, severity, and peak intensity based on SPI,adapting various distribution functions to the drought characteristics, andfindingone of the extreme historical drought occurrences and using appropriatefittedcopulas to estimate frequency of this historically significant drought event, (2) quan-tification of the effects of climate change using the general circulation models(GCMs) for future periods, and (3) evaluation of future drought characteristicsusing selected copulas and calculation of the frequency of future drought events.There are several parts in this article describing the copula’s approach andimplementation. Section6.2contains the methodology, including the descriptionof the SPI drought index, the copula which is a multivariate probability distribution,the methods for calculating the return period based on copula, the climate scenarios,and the brief introduction of the study area as well as the methods used for collectingand analyzing the data. Section6.3contains the results and discussion of thisresearch