Drought as shortage of rainfall compared to its long- term mean in a period can be affected by climate change. Evaluationof drought changes can be useful tool for water resources management. In this study, to investigate the trend of drought in Iran, the monthly rainfall data of 119 meteorological stations in 1366-1390 are considered and SPI drought index are calculated based on these data. The Mann-Kendall and Pettitt tests are used for trend and change point analysis. Results of Pettitt test show change points for 42, 27, 35 and 16 stations in spring, summer, autumn and winter seasons respectively that demonstrates disregarding of change point analysis in trend test application can lead to non- negligible mistakes in results. The results of the trend analysis indicate that there are 4, 10, 8 and 9 increasing and 6, 1, 0 and 2 decreasing tren in stations in spring, summer, autumn and winter seasons respectively. Moreover, investigation of spatial distribution show most of stations with trend in SPI index in different seasons are located in west region of the country so that there are decreasing trend in spring and increasing trend in summer and winter while there is no specific spatial pattern in autumn.

Drought is one of the most complex and unknown natural phenomena that causes a periodic water crisis in the affected areas. Increasing water demand on the one hand and the experience of droughts in the province in recent years have led to the water crisis. Knowing the drought is one of the requirements for water crisis management. The purpose of this study was to analyze the trend of the SPI drought index in Isfahan province using nonparametric Sen’s slope test, Pettitt’s change point test and Man-Kendall test. From the monthly climatic data of 10 synoptic stations with a length of 27 years (1990-2017) for time series The results of applying Mann–Kendall and Sen’s slope tests based on SPI Index for 9, 12, 18, 24 and 48 month time periods, shows drought trend is significantly increasing for all stations out of Ardestan, Esfahan and Shahreza stations. In Ardestan station, the drought trend is significantly decreasing for 9, 12, 18, 24 and 48 month time periods and in Isahan station, the drought trend is significantly decreasing for only 48 month time period, and in Shahreza statition, the drought trend is significantly increasingonly for only 18 month time period. Despite all stations, the drought trend for one month time period, is significantly increasing just for Naein station. In addition, applying Mann–Kendall test on monthly rainfall for all station shows downward but not significant trend. Finally, applying Pettitt’s change point test based on SPI Index for 9, 12, 18, 24 and 48 month time periods indicates the existence of a significant change point. For same periods we observe no change point for the monthly rainfall in all stations. In summation, considering the SPI drought index, about 59% of all stations show significant downward trend bases on Mann-Kendall test and 60% of all stations show significant slope based on Sen's slope test and 75% of all stations show significant change point based on Pettitt's test. In general, for drought analysis using different time periods for the SPI index, in a short time period. (such as 6 months) drought is more frequent but shorter, and as the period increases the duration of drought also increases but frequency decreases. All together, we are facing a water crisis in Isfahan province and we must manage water demand very urgently.

Climate change and global warming are the greatest challenges that humanities have ever faced. Temperature variations, quantity and pattern of precipitation are the important potential impacts of climate change which may affect water resources and drought conditions. Mann-Kendall trend test and Pttitt homogeneous test were respectively used to detect trend variation and abrupt changes in the time series.The SPEI drought index which is based on precipitation and temperature data, is not only designed in a way to consider both precipitation and potential evapotranspiration (PET) but also has the capacity to include the effects of temperature variability on drought assessment. Therefore, the objet of this study is to investigate the trend and the detection of change points in seasonal series of SPEI drought index in Iran, and for this purpose the non-parametric Mann-Kendall and Pettitt statistical tests has been used. In the first step, the SPEI data, calculated based on monthly rainfall and evapotranspiration is extracted from those parts of the SPEI world database covering Iran, and are about 624 points of the 0.5° geographic network were separated from the entire data and stored in the Excel format. Then, the 50 years seasonal times series of SPEI data during the period of 1969-2018 were made for different seasons of the year. Finally, the nonparametric Mann-Kendall trend and Pettitt change point detection tests were performed on the data, and the results were analyzed. The results of using the Pettitt test in 624 points from Iran showed that in between the series of SPEI drought index in the spring, summer, autumn, and winter, 11, 31, 8, and 15 percent of points had significant change point, respectively, and their spatial location are the decreasing change points in the eastern and north-west in spring, northernwest, northern east, middle part and southern east in winter. Meanwhile in summer and autumn seasons the increasing and decreasing change points are in dispersed points from the southwest, and the south and northeast and the increasing change points in the middle parts of Iran, and parts of the south and north of the country, respectively. Also, the results of using Mann-kendall test showed a significant decreasing trend in 28 percent of points for spring, a significant increasing and decreasing trend in 5 and 25 percent of points for the summer season, a significant decreasing trend in 18 percent of points for the autumn, and also the existence of significant increasing and decreasing trends is in 1 and 15 percent of points, respectively in winter. The spatial location of these points for the four studied seasons was in the east, northwest and south of the country, half east, southwest and scattered parts from the south of the country, the central parts of the country, as well as the northeast and northwest, respectively. Result of using Mann-Kendall and Pettitt statistical tests indicated that climate change has occurred in parts of the country, varies from one season to another in such a way that in east and northwest parts of the country in spring and in north-west and south-east parts of the country in winter, more dry conditions are visible but in autumn, more humid condition were observed in central parts of the country. According to the fact that most of the country's precipitation is in winter and spring, this drying trend will cause a hazard in reducing water resources. The results also indicate that in most of the cases that a change-point exist in the drought index, a trend is also observed in data series based on Mann-Kendall trend test.

The most important impacts of climate change relate to temperature and precipitation. Precipitation is particularly important, because changes in precipitation patterns may lead to floods or droughts in different areas. Also, precipitation is a major factor in agriculture and in recent years interest has increased in learning about precipitation variability for periods of months to annual and seasonal trends and change points had been analyzed for 22 rainfall stations in Fars province during 1972 to 2011. Mann-Kendall non-parametric test and Sen’s method had been used to determine positive or negative trends; also Pettitt test, Standard normal homogeneity test, Buishand range test, Von Neumann ratio, for detection of change points in the time series had been implemented. The TFPW approach had been used in order to decline the effects of autocorrelation and serial correlation on Mann-Kendall test. The results of Mann-Kendall test and Sen’s Method showed decreasing trend for all rainfall stations except for the Monje station. But, no significant trends were observed in all stations. Also, the results indicated that the precipitation has not occurred nonhomogeneity; whereas all test indicated there is no change point on precipitation time series. No change and abrupt shift were visible in the precipitation time series except in winter for Ali Abad Khafr; and Ali Abad Khafr; Tangab and Ramjerd based on pettitt test and Standard normal homogeneity test, respectively.

Doroodzan Dam basin is one of the strategic agricultural areas in Fars province. Changes in time series of climatic parameters, especially temperature and precipitation parameters, can have a significant impact on the growth cycle of agricultural products, the status of water resources and the economy of the populations in the area. In the present study, rainfall and temperature trends were investigated in 13 rainfall stations and 4 thermometric stations. Initially, the change point pettitt test was used to assess the homogeneity and change point in the time series. Then, trends in the rainfall, average monthly and annual temperature time series were investigated using Mann-Kendall (MK), modified Mann-Kendall (MMK) and the sen’s slope methods. The results of the pettitt test showed that there is no significant change point in the monthly and annual rainfall and monthly temperature time series, only in the annual temperature of two stations, there is a significant change point at the 95% confidence level. The results of the trend analysis with all three abovementioned methods showed that the monthly precipitation in all stations and annual precipitation in most stations have a decreasing trend and the average monthly and annual temperature have an increasing trend; however, in none of the time series, the trend was significant in the confidence level of 95%. Based on the results, in the whole area, the mean annual temperature increased by 3.7 percent and precipitation decreased by 9.1 percent compared to the mean.

In this research, gradual and rapid changes of hydro-climatological variables, trends were analyzed for the Lighvanchai basin. Also, the natural (stationary) and impacted periods were identified. For this purpose, the traditional Mann-Kendall (MK1), modified (MK3) and Pettitt methods were used and for determination of the trend line slope the Senʼs estimator was used. Results showed that streamflow values of Lighvanchai River (in Hervy station) had a downward trend in the all time scales. In the spring, all precipitation related variables showed a decreasing trend. In the case of temperature variables, there was an increasing trend at the most of the studied time scales, which were significant from January to  May. Furthermore, the differences between Tmax and Tmin showed an increasing trend. On the other hand, air relative humidity time series showed a decreasing trend (specially in winter). It could be concluded that the combination of these changes led to decreasing trend in basin runoff. The result of Pettitt test showed that  the streamflow of  Lighvanchai (in Hervy) had a sudden change point, so that the average discharge in the recent period had been decreased about 35% compared to the first period. Most of studied climatic variables such as air temperature and RH, had a sudden change point that the date changes of these variables and the basin discharges (at Hervy station) were occurred in the mid-1990s. Regarding the discharges of Lighvan station (upstream of basin) the null hypothesis of abrupt change point were rejected. Therefore, along with the effects of climatic factors the effectiveness of the human factors on reducing the runoff in the basin outlet at Hervy station was confirmed.

This article aims to analyze the trend of monthly, seasonal and annual changes in the flow and sediment of the Mordaghchai. located in East-Azerbaijan province. In this regard, using non-parametric methods, discharge and sediment data of Gheshlagh-Amir hydrometric station have been analyzed in three time scales: annual, seasonal and monthly. The modified Mann-Kendall test was used to analyze the trend of gradual changes in discharge and sediment data. Also, the Sen's slope estimator was used to estimate the slope of the trend line and the non-parametric Pettitt test was used to investigate the abrupt changes in the discharge and sediment time series. The modified Mann-Kendall test was used to analyze the trend of gradual changes in discharge and sediment, and the Sen' slope estimator test was used to estimate the slope of trend line. Also, Pettit test was used to investigate abrupt changes in the river discharge and sediment time series. The results show that annual, monthly and spring, summer and winter discharges significantly decrease at the level of 5%. The annual and all-season sediment load data significantly decreased by 5%. There is a significant decrease in sediment load in all months except March, April and October. The results of the Pettitt test show that the average annual discharge in the period after the breaking point (1998) has decreased by 45% compared to the period before the breaking point. Also, the average annual sediment load after the breaking point (1996) has decreased by about 52% compared to the previous period.

Reference evapotranspiration as an important indicator of demand for air evaporation is an important factor for climatic and hydrological studies. Due to the occurrence of climate change and the occurrence of large fluctuations in precipitation and the occurrence of mild to severe droughts, it is important to study the evapotranspiration changes. In this study, to investigate the temporal-spatial changes of trend and change point in the reference evapotranspiration time series for different seasons in Mazandaran province, 40 years data (1981-2020) from satellite networks (with a resolution of about 5 km) were used. Non-parametric Mann-Kendall, Sen's slope, Pettitt's test (Non-Parametric Rank Test) and quantile regression were used to investigate the changes in the trend and to present the range of fracture point changes in the evapotranspiration. The correlation coefficient between network evaporation-transpiration data and ground station data was estimated to be more than 0.9 in most of the stations and the average value of BIAS was 0.24. The results of Pettitt's test showed the time of sudden changes in reference evapotranspiration in spring, autumn and winter seasons in 2013, 2007-2010 and 1999, respectively, in most cases. Very high values of evapotranspiration increased in spring in the eastern half, in summer in the northern half and in winter in the southern and western strips (with a seasonal slope percentage of 45, 75 and 120 percent, respectively), but they decreased in autumn in the north of the province (with a slope of -45 percent). In general, significantly increasing slope rates for high values of evapotranspiration were higher than average. A significant increase in high amounts of evapotranspiration, especially in the dry season, will reduce water resources and disrupt the agricultural sector. Therefore, scientific and practical methods for managing reference evapotranspiration in the province should be considered.

Revealing the contribution of each of the climatic and human factors can help the management of water resources. Firstly, trend analysis and change‐point tests were performed to determine the status of the parameters affecting the groundwater resources of the Mahidasht aquifer during the period from 1981 to 2019 by using statistical methods and the Pettitt test. The GMS model was calibrated as a tool to simulate the Mahidasht aquifer system. After determining the change point, modeling of the groundwater level before and after the change point was done using the GMS model. By removing the effect of human factors in the model, the contribution of the effects of climate variability and human activities on groundwater was obtained. The results showed that there was no significant trend in annual rainfall, but the annual runoff has a significantly decreasing trend at the confidence level of 99%, and the trend of the groundwater level is also significantly decreasing at the confidence level of 99%. Pettitt change point test showed precipitation without a change point, but the runoff in 1998 and the groundwater level in 2001 had a change point. Finally, the modeling of the aquifer showed that the contribution of human activities in the reduction of the groundwater level of the Mahidasht aquifer was 78 and climate variability is 22%.

Rainfall variation is a clear indicator of climate change. IPCC in its multiple assessment reports has raised concerns over the changing climate and rising global average temperatures which could lead to widespread and catastrophic impacts on natural and human systems. The study of long-term patterns is crucial in establishing evidence of shifting climate and informing policy decisions.This study examines the rainfall trend and variability of the semi-arid Agra district and assesses rainfall in the region. Annual rainfall for 101 years from 18 grid data points was statistically analysed for the same. For the projection and analysis of data points, a Thiessen network polygon was drawn using QGIS 3.28.4. Each grid data point was assigned a Thiessen polygon. According to the area each Thiessen polygon covers, it was assigned weights. Then according to the weight of each polygon, annual rain in that area was calculated. Next, the data were tested for homogeneity and breakpoints using the Standard Normal Homogeneity test, Buishand’s Range test, Buishand’s U test and Pettitt’s test. After this the trend of the data was identified using Mann-Kendall and the magnitude was calculated using Theil-Sen’s estimator. R-studio was used for all the statistical analysis and graph plotting. Upon conducting the Standard Normal Homogeneity test, Buishand’s Range test, Buishand’s U test and Pettitt’s test it was found that the data was non-homogeneous with the breakpoint in the year 1967. The Mann-Kendall test revealed a declining trend in the annual rainfall and the Theil-Sen estimator calculated the magnitude of this declining trend to be -1.63 for the last century. The findings suggest that climate change is having a significant impact on rainfall in the semi-arid Agra district. The declining trend in rainfall could have several negative consequences for the region, including water scarcity, crop failure, and increased risk of droughts.