Reza Modarres

Isfahan University of Technology | IUT · Faculty of Natural Resources

Vegetation is one of the important components of ecosystems that usually changes seasonally. An accurate parameterization of vegetation cover dynamics by developing time series models can strengthen our understanding of vegetation change. This research aims to investigate and model the temporal changes of net primary production (NPP) and normalized...

Vegetation is one of the important components of ecosystems that usually changes seasonally. An accurate parameterization of vegetation cover dynamics by developing time series models can strengthen our understanding of vegetation change. This research is aims to investigate and model the temporal changes of Net Primary Production (NPP) and Normali...

Heatwaves are defined as a period that temperatures exceed a threshold above normal in a given time and region. Most heatwave definitions, such as CTX90, have originated based on stationary assumptions. In this study, we suggest a modification for the CTX90 method and developed a new dynamic heatwave threshold (NS-Q90), based on Generalized Additiv...

This research addressed the forecast of 7-day and 30-day low flows using daily flow data at two hydrometric stations of Qaleh-Shahrokh and Eskandari in Isfahan province, Iran. The two methods of ordinary time series modeling and time series modeling with the help of wavelet (wavelet-time series) are used to forecast low flows. The research also emp...

For the first time, this study explored the dominant features of Marine HeatWaves (MHWs) in the Persian Gulf and Oman Sea (1982–2020). The spatial extent of MHWs has nearly doubled in the last 24 years. Since 1997, the average number of MHW days in the central parts of the Persian Gulf has increased about 19 times compared to the period 1982–1997....

The present study aims to investigate Iran’s agrometeorological drought history and its properties using Multivariate Standardized Drought Index (MSDI). For this purpose, precipitation and soil moisture recorded at 99 synoptic stations in Iran during 1985 to 2018 were selected. Based on MSDI time series, drought properties including duration and se...

1. Introduction Drought occurs due to lack of humidity and deficiency in precipitation amount. Therefore, it is important to recognize and investigate the effective factors on precipitation deficiency and consequently drought occurrence. Enso is a phenomenon of climatic teleconnection that can affect weather in different regions of the world. Enso...

Dust storms in arid and semi-arid regions have harmful impacts on the environment, the economy, and the health of local and global communities. In this study, the frequency of annual dust events in twenty-five stations and five climatic variables including rainfall, maximum annual wind speed, average annual wind speed, maximum annual temperature, a...

The present study aims to investigate Iran’s agrometeorological drought history and its properties using Multivariate Standardized Drought Index (MSDI). For this purpose precipitation and soil moisture recorded at 99 synoptic stations in Iran with more than 30 years observations were colected. Based on MSDI time series, drought properties including...

During last century, anthropogenic forcing and climate change have influenced the stationarity of the many extremes. Therefore, using of stationary pre-assumption-based Frequency Analysis (FA) techniques for estimating the risk of extremes may not be reliable anymore. In present study we introduced a nonstationary FA method to estimate risk of 24-h...

Dust storms are frequent phenomenon in arid and semi arid regions of Iran which cover near 60 percent of the entire country in the center of Iran. Due to geographic and climatic conditions of prolonged dry conditions as well as poor land use management, dust storms occur in almost all seasons across the region. Drought is a major fator affecting th...

_ ‫اتمسفری‬ ‫مسئول‬ ‫بسیاری‬ ‫از‬ ‫تغییرات‬ ‫اقلیمی‬ ‫خشکسالی‬ ‫مانند‬ ‫ها‬ ‫هستند‬. ‫ابتدا‬ ‫حاضر،‬ ‫تحقیق‬ ‫در‬ ‫بنابراین‬ ‫بارش‬ ‫شاخص‬ ‫استاندارد(‬ SPI ‫شاخص‬ ‫با‬ ‫آن‬ ‫ارتباط‬ ‫سپس‬ ‫و‬ ‫محاسبه‬) ‫اقیانوسی‬ ‫های‬ _ ‫اتمسفری‬ AMO ، NAO ، NINO4 ‫و‬ SOI ‫ایستگاه‬ ‫در‬ ‫مدل‬ ‫به‬ ‫اقدام‬ ‫نهایت‬ ‫در‬ ‫و‬ ‫بررسی‬ ‫تحلیلی‬ ‫آمار‬ ‫با‬ ‫کرج‬ ‫و‬ ‫شه...

Abstract Flood control and management is a fundamental issue for hydrology researchers and managers. Regarding the design and construction of different hydraulic structures such as reservoirs and dams, as effective techniques for flood control, accurate estimation of the magnitude and return periods of flood is required for appropriate estimation o...

Increasing the concentration of CO2 and other greenhouse gases in the atmosphere makes a large-scale change in atmospheric processes. Among the most dramatic effects of climate change, its impact on the type, amount, and intensity of rainfall is of particular importance. The goal of the present study was to provide a new method to investigate clima...

A new approach to select a model for fitting to a seasonal daily average rainfall semi-variogram was developed in this study by interpolating rainfall using geostatistical methods. Using two deterministic algorithms (Thiessen polygon, THI and inverse distance weighting, IDW) and two geostatistical algorithms (ordinary kriging, ORK and universal kri...

Drought is the most important threat to both environmental and socio-economic features of the arid and semi-arid regions of the world as it is closely associated with agricultural production losses, water supply shortage, and security. This study aims to regionalize extreme drought severity–duration (SD) index probability across Iran. The 12-month...

In this research, the Bayesian quantile regression model is applied to investigate the teleconnections between large oceanic–atmospheric indices and drought standardized precipitation index (SPI) in Iran. The 12-month SPI time series from 138 synoptic stations for 1952–2014 were selected as the drought index. Three oceanic–atmospheric indices, the...

Climate variability and change in arid regions are important factors in controlling emission, frequency and movement of dust storms. This study provides robust statistical methods including univariate Mann‐Kendall block bootstrapping method and three bivariate trend assessment methods, Covariance Inversion Test, Covariance Sum Test and The Covarian...

Better understanding of the Atlantic Multidecadal Oscillation (AMO) temporal evolution and the precise and reliable predictability of its phase-switching behaviour are of utmost importance in characterizing future climate change as well as its consequences. For the first time, this study investigated internal dynamics of the AMO in different warm/c...

This study investigated the relationship between ocean-atmospheric indices and drought in Iran. Using > 30-year precipitation data from 37 synoptic stations (ending 2015), standard precipitation index (SPI) was calculated for periods of 1-, 3-, 6-, 9-, 12-, 15-, 18-, 24-, and 48-month time scales. A set of monthly ocean-atmospheric oscillations (OA...

Desertification is a dynamic and complex system of land degradation. To understand it, physical and anthropogenic processes and their interrelations need to be identified. This study aimed to provide early warning information on desertification risk in the form of warning maps, using effective key indicators of land degradation in a 15-year period...

The transformation of rainfall into runoff is an important process in hydrological sciences. Different spatial and temporal scales are involved, from fast runoff response to heavy rainfall in small catchments to seasonal runoff response driven by precipitation-evapotranspiration-snow dynamics in large river basins. The rainfall-runoff transformatio...

In this study, region-of-influence (ROI) approach was used for modeling extreme values of 24-h maximum rainfall using seven groups of defined attributes including climatic, geographical, and statistical attributes and their hybrids. According to the degree of importance and the role of each defined attribute, different weighting scenarios were defi...

Regionalization is one of the useful tools for carrying out effective analyses in regions lacking data or with having only incomplete data. One of the regionalization methods widely used in the hydrological studies is the clustering approach. Moreover, another effective factor on clustering is the degree of importance and participation level for ea...

This study detects changes in hydrologic drought indices (HDIs), including magnitude (i.e., daily mean, low flows, and flow quantiles), variability (i.e., coefficient of variation), and duration, at 22 stations over Isfahan province and Zayandehrud basin, Iran by nonparametric Mann–Kendall tests. The results indicate a decreasing trend for average,...

Climate variability and change in arid regions are important factors controlling emission, frequency and movement of dust storms. This study provides robust statistical methods to detect trends in dust storm frequency across arid regions of Iran in relation to climate variability and trend in recent decades. The univariate trend assessment based on...

In recent years, the joint distribution properties of drought including severity and duration have been widely evaluated using copula. Few studies, however, have worked on drought modeling based on stream flow, especially in semi-arid regions such as the southern regions of Iran. This study followed two purposes. The first purpose was to find the a...

Climate change-induced extreme heat events are becoming a major issue in different parts of the world, especially in developing countries. The assessment of regional and temporal past and future change in heat waves is a crucial task for public health strategies and managements. The historical and future heat index (HI) time series are investigated...

Multivariate time series modeling approaches are known as useful tools for describing, simulating, and forecasting hydrologic variables as well as their changes over the time. These approaches also have temporal and cross-sectional spatial dependence in multiple measurements. Although the application of multivariate linear and nonlinear time series...

Dust storms are among natural and anthropogenic hazards for socioeconomic resources, especially in desert regions. In recent years, dust storms have become a serious problem, especially in desert regions of Iran. This study investigates temporal and spatial variation of dust storm frequency in desert regions of Iran. The number of dusty days (NDD)...

The lack of data in rainfall stations of Iran is one of the main problems in design and management of hydrologic systems. Moreover, the density of these stations network is not sufficient for estimation of rainfall at ungauged regions. Therefore, regionalization can be an essential tool to be applied for clustering the rainfall and spatial pattern...

Design storm is one of the most important tools to design hydraulic structures, hydrologic system and watershed management, mostly extracted by intensity- duration - frequency (IDF) curves for a given specific duration and return period. As for conventional methods to calculate IDF curves, the precipitation should be recorded for different duration...

Future changes in extreme rainfall arising from climate change may have a significant influence on flood and water erosion control and management strategies to a great extent. The maximum daily rainfall time series were projected for 2020–2049 using six general climate models and two scenarios through artificial neural networks for 22 stations acro...

This study suggests a different view of the change in water level fluctuation of Urmia Lake (UL), Northwestern Iran, and its descriptive statistics in term of the seasonal variation of monthly average time series during 1966–2012. A significant change is demonstrated in the descriptive statistical characteristics, such as the mean and the variance...

** Fulltext is available at: http://www.rezamodarres.iut.ac.ir/snow-water-equivalent-time-series-forecasting-ontario-canada-link-large-atmospheric-circulations ** The present study applies different time-series models for forecasting daily and monthly snow water equivalent (SWE) data in Ontario, Canada, during 1987–2011. For daily time series, whic...

***full text available at: http://www.rezamodarres.iut.ac.ir/spatial-patterns-and-temporal-trends-daily-precipitation-indices-iran*** Spatial patterns of daily precipitation indices and their temporal trends over Iran areinvestigated using the APHRODITE gridded daily precipitation dataset for the period 1961 – 2004. The performance and limitations...

*****Full text available at : http://www.rezamodarres.iut.ac.ir/publications-en **** This study describes a method for deriving the time varying second order moment, or heteroscedasticity, of local daily temperature and its association to large Coupled Canadian General Circulation Models predictors. This is carried out by applying a multivariate ge...

***full text available at: http://www.rezamodarres.iut.ac.ir/identification-homogeneous-regions-regionalization-watersheds-two-level-self-organizing-feature-maps*** One of the several methods in estimating flood quantiles in ungauged or data-scarce watersheds is regional frequency analysis. Amongst the approaches to regional frequency analysis, dif...

***fultext available at: http://www.rezamodarres.iut.ac.ir/modeling-relationship-between-climate-oscillations-and-drought-multivariate-garch-model*** Typical multivariate time series models may exhibit co-movement in mean but not in variance of hydrologic and climatic variables. This paper introduces Multivariate Generalized Autoregressive Conditio...

The El Niño–Southern Oscillation (ENSO) is by far the most energetic climate signal. Any change in ENSO characteristics will have serious consequences for the global climate system. This work suggests a different view at the change in ENSO volatility in addition to change in its descriptive statistics. The volatility or the conditional variance of...

***Fulltext available at: http://www.rezamodarres.iut.ac.ir/modeling-rainfall-runoff-relationship-using-multivariate-garch-mode **** The traditional hydrologic time series approaches are used for modeling, simulating and forecasting conditional mean of hydrologic variables but neglect their time varying variance or the second order moment. This pap...

***fulltext available at: http://www.rezamodarres.iut.ac.ir/modeling-climate-effects-hip-fracture-rate-multivariate-garch-model-montreal-region-canada*** Changes in extreme meteorological variables and the demographic shift towards an older population have made it important to investigate the association of climate variables and hip fracture by adv...

**fulltext available at: http://www.rezamodarres.iut.ac.ir/data-based-analysis-bivariate-copula-tail-dependence-drought-duration-and-severity*** In recent decades, copula functions have been applied in bivariate drought duration and severity frequency analysis. Among several potential copulas, Clayton has been mostly used in drought analysis. In th...

Time series modelling approaches are useful tools for simulating and forecasting hydrological variables and their change through time. Although linear time series models are common in hydrology, the nonlinear time series model, the Generalized Autoregressive Conditional Heteroscedasticity (GARCH) model, has rarely been used in hydrology and water r...

Drought is a multi-dimensional natural hazard with stochastic characteristics usually related to each other. Separate univariate statistical models cannot capture the important relationships among drought characteristics, that is, severity and duration. In this study, an empirical copula is employed to construct a bivariate model of droughts, where...

This study presents an exhaustive methodology of floodplain mapping at ungauged rivers. To present our methodology, we selected the Halilrud basin and Jiroft city in southeastern Iran as an example of hazardous regions. To estimate flood quantiles in different return periods at ungauged reaches, we used regional flood frequency analysis. By using t...

The existence of time-dependent variance or conditional variance, commonly called heteroscedasticity, in hydrologic time series has not been thoroughly investigated. This paper deals with modelling the heteroscedasticity in the residuals of the seasonal autoregressive integrated moving average (SARIMA) model using a generalized autoregressive condi...

Improving techniques of flood frequency estimation at ungauged catchments is one of the major challenges for hydrologists, especially in arid and semi-arid regions with insufficient information. Recently, popularity of flood seasonality-based descriptors has increased among hydrologists for delineating of hydrologically homogenous regions. This stu...

Iran is a large country with diverse geophysical and climatic conditions which are influenced by both large atmospheric circulation patterns and local effects. The density of rainfall station network of Iran is not enough for rainfall estimation at ungauged regions. Therefore, rainfall regionalization should be used to extend rainfall data to regio...

The spatial variation of the statistical characteristics of the extreme dry events, such as the annual maximum dry spell length (AMDSL), is a key practice for regional drought analysis and mitigation management. For arid and semi arid regions, where the data set is short and insufficient, the regionalization methods are applied to transfer at-site...

Hydrologic drought is a type of drought which directly affects the water supply of a region. Long streamflow dry spells or streamflow under a specific threshold are usually considered as hydrologic drought. The annual extreme hydrologic dry spell length (AEHDSL) data of the Halilrud basin in the southeastern semiarid region of Iran were considered...

Low flow spatial scaling relationships have been defined by log-log linearity between 7-, 15-, 30-, and 60-day low flow probability weighted moments (PWMs) and drainage area size in north of Iran. The PWMs are used to avoid the influence of outliers. Across the entire region, the regression relationship is not significant which is believed to be du...

Drought is a complex and multi-attribute natural hazard that has worldwide effects. Defined by a commonly used standardized precipitation index (SPI), each drought event is characterized by three correlated attributes: severity, duration and frequency. A probabilistic approach is developed to establish a drought severity-duration-frequency (SDF) re...

The estimation of maximum daily rainfall (PDmax) is usually required for the estimation of design flood (the maximum flood that any hydraulic structure can safely pass). However, PDmax estimation is usually required for watersheds where rainfall data are either not available or only available in short periods from various sites and so are unsuitabl...

In the present study the spatiotemporal trend analysis of the annual maximum dry spell length (AMDSL) and the annual number of dry spell periods (ANDSPs) of Isfahan Province in the center of Iran has been conducted based on daily rainfall records taken from 17 rain gauge stations. The autocorrelation functions (ACFs) of dry spell time series showed...

The relationship between catchment size and streamflow magnitude is a well known hydrological theory and is usually used for prediction at ungauged basins (PUB). However, the nonlinear behavior of this relationship generates a number of problems when used for flood peak prediction for design purposes due to increased uncertainty. In this study, art...

The present study performs the spatial and temporal trend analysis of the annual and 24-hr maximum rainfall of a set of 145 precipitation gauging stations of Iran. The study shows that the annual rainfall is decreasing at 67% of the stations while the 24-hr maximum rainfall is increasing at 50% of the stations. The negative trends of annual rainfal...

In this study we propose a comprehensive multi-criteria validation test for rainfall-runoff modeling by artificial neural networks. This study applies 17 global statistics and 3 additional non-parametric tests to evaluate the ANNs. The weakness of global statistics for validation of ANN is demonstrated by rainfall-runoff modeling of the Plasjan Bas...

A regional low flow frequency analysis in the north of Iran using L-moments was carried out. Low flow events have been represented by the 7-day annual minimum series and the L-moments approach was used to assign these data into homogenous regions. According to the homogeneity measure and climatic properties, two subdivisions were found - one in the...

Although many papers have been published on the role of wind speed on wind erosion, most of them did not consider the probability or return period of wind speed and its role in wind erosion. This study deals with this characteristic of wind speed in arid and semi-arid regions of Iran. Because at-site frequency analysis is not sufficient for extendi...

Estimating maximum wind speed is an essential task in many fields of environmental and engineering risk analysis. This study used prevalent westerly annual maximum wind speeds for the period of 1983-1998 for East Isfahan station in Isfahan Province, Iran. The frequency analysis of AM data wind speeds obtained by averaging the wind data over some ch...

In this study we propose a comprehensive multi-criteria validation test for rainfall-runoff modeling by artificial neural networks. This study applies 17 global statistics and 3 additional non-parametric tests to evaluate the ANNs. The weakness of global statistics for validation of ANN is demonstrated by rainfall-runoff modeling of the Plasjan Bas...

Time-series of annual rainfall, number of rainy-days per year and monthly rainfall of 20 stations were analyzed to assess climate variability in and and semi-arid regions of Iran. The results showed mixed trends of increasing and decreasing rainfall, which were statistically significant (p<0.05 and p<0.01) only for Sabzevar and Zahedan stations by...

In this study, regional climates of Iran were identified based on the properties of the monthly rainfall time series models of 28 main cities of Iran. The autocorrelation (ACF) and partial autocorrelation (PACF) of selected series revealed the seasonal behavior of the monthly rainfall. After the parameters of the models were estimated and the resid...

Drought is considered to be an extreme climatic event causing significant damage both in the natural environment and in human lives. Due to the important role of drought forecasting in water resources planning and management and the stochastic behavior of drought, a multiplicative seasonal autoregressive integrated moving average (SARIMA) model is...

Multiplicative seasonal autoregressive integrated moving average models are appropriate for the monthly stream flow of the Zayandehrud River in western Isfahan province, Iran, through the Box and Jenkins time series modeling approach. Among the selected models interpreted from ACF and PACF, seasonal multiplicative ARIMA (1,1,0) × (0,1,1) satisfied...

The determination of spatial distribution of drought attributes in Isfahan province is essential for the study and management of drought. In this study, using ten drought attributes based on severity, duration and frequency of standardized precipitation index in 45 stations in Isfahan province and cluster analysis of this attributes, 5 spatial grou...

Rainfall in Iran is complex, with unpredictable fluctuations from year to year and from region to region. At-site frequency analysis is inadequate for regional planning. Thus, it is important to determine regional rainfall frequencies. Hierarchical cluster analysis and L-moments regional frequency analysis were used in this study to find homogeneou...

Fulltext available at: http://www.rezamodarres.iut.ac.ir/classification-spatio-temporal-pattern-rainfall-iran-using-hierarchical-and-divisive-cluster

Different time series analysis of daily air pollution of Isfahan city were performed in this study. Descriptive analysis showed different long-term variation of daily air pollution. High persistence in daily air pollution time series were identified using autocorrelation function except for SO2 which seemed to be short memory. Standardized air poll...

Multiplicative seasonal autoregressive integrated moving average models are appropriate for the monthly stream flow of the Zayandehrud River in western Isfahan province, Iran, through the Box and Jenkins time series modeling approach. Among the selected models interpreted from ACF and PACF, seasonal multiplicative ARIMA (1,1,0) × (0,1,1) satisfied...

Fulltext available at: http://www.rezamodarres.iut.ac.ir/daily-air-pollution-time-series-analysis-isfahan-city