جستجوی مقالات مرتبط با کلیدواژه « Drought monitoring » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Drought is one of the main natural causes in agricultural, economic and environmental sections. It is very difficult to quantify the characteristics of the severity, magnitude and duration of the drought objectively. Therefore, much effort has been made to monitor drought using a variety of indices. In order to investigate the meteorological drought on hydrological systems in the study area, were used from Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), SRI Standardized Runoff Index (SRI) and groundwater drought index (GRI). Then, the relationship between the indices, concurrence or non-concurrence of drought event was investigated. Finally, the best meteorological drought index for monitoring hydrological systems in the study region was selected. The results showed that comparing the correlation between the two meteorological indicators with SRI and GRI, SPEI is a priority in terms of drought warning, because it is able to show the occurrence of hydrological drought on a shorter time scale. There was no significant correlation at different time scales between the two SPI-GRI indices (cc = 0.18), which indicates the inadequacy of SPI to investigate the effects of climatic drought on groundwater level. Therefore, it is suggested to use SPEI instead of SPI to investigate the effect of precipitation changes on groundwater fluctuations.

The permanence of rainfall shortage compared with the long-term average of meteorological droughts, reduces river flow, groundwater level and hydrological droughts. To quantify the drought, several indexes has been defined. In this study, two drought indexes, including standardized precipitation index (SPI) and standardized streamflow index (SSI), were used for meteorological and hydrological drought monitoring. The aim of this study was the monitoring the drought in 5 stations in Tehran province during the period of (1985-2016), determining the most appropriate cumulative distribution function for calculating the SSI drought index and also a comparative study of meteorological and hydrological drought indicators in this province. The results show that the most suitable cumulative distribution function at the  Darake station is Gen-Loglogestic, at the Firuzkuh and Abali station is Gamma, at the Namrud station is Fatigue life and at the Sharifabad station is Beta. Among the stations with proper functions, Derek with the highest P-value (0.996) and the lowest RMSE (0.916) had the best fit with the Gen-Loglogestic distribution  function. Also, the similarity in the process of drought resulting from two different indicators, indicates that the meteorological and hydrological indicators are completely same, in other words, surface water resources in Tehran province are completely influenced by rainfall.

Drought management is an essential task to exploit water resources. In this study, the monthly rainfall of 35 synoptic stations in Qazvin province during 30-year were considered for drought monitoring. In this study two drought monitoring indices including modified standard Precipitation index (MSPI) and Standardized Precipitation Index (SPI) are accomplished and compared to the reports of four indices in the study area. The obtained results showed that the MSPI is more accurate than the SPI and other indices. Having the drought conditions in the stations, zoning of drought were calculated by Interpolation methods such as IDW, Kriging, GPI, and RBF.The obtained results demonstrated that IDW method with first power is the best method in terms of average error. Moreover, zoning of the precipitation is conducted using Kriging interpolation then the MSPI value for each cell is computed for monthly precipitation. The results show that if the precipitation interpolation is conducted firstly, the drought index is calculated more accurately than the method that drought index calculated in the stations. In order to assess the drought condition more accurately, the vegetation condition index (VCI) is computed using monthly NDVI product of MODIS. The correlation between VCI and MSPI was calculated that the results illustrated that MSPI confirms the results obtained by VCI. As a result, VCI can be used to monitor drought in the watersheds which suffer from sufficient ground stations.

One of the most important last century challenges in the world was drought and monitoring and assessing drought severity and duration to combat and mitigate its impacts is very necessary. In recent decades, with developing of remote sensing issues, satellite-based estimating drought with high spatial resolution and different time steps were widely used. Hence, the aim of this study was focused on the analyzing drought and error distribution of TRMM satellite data-based estimation with ground data over the period 1998 to 2014. In this regard, in order to assess the accuracy of meteorological drought index based on the TRMM satellite data, 41 synoptic stations were used in Iran. In this study, error assessment criteria were included NSE, RMSE, ME, Bias and correlation coefficient and also the IDW interpolation method in ArcGIS 10.3 was used for spatial analysis. Results of drought index showed that in terms of severity, Kerman, Bushehr, Kashmar, Ghazvin, Bojnurd, Kashan stations have suffered from at least one extreme status for 1998 to 2014 and in terms of frequency, the most frequent drought was in Karaj station. Results of spatial analysis of error criteria  showed that the drought index estimated of TRMM satellite had the lower error in northeast of Iran (around Mashhad and Kashmar stations) and southwest of Iran (around Shahrkord, Esfahan, Yasouj, and Shiraz stations) while the most error was in central region of Iran (around Biarjomand, Tabass stations), respectively. In most areas of the country, drought index estimated by TRMM data had acceptable agreement with ground stations data. Calibrating the TRMM data with ground stations can be used for drought monitoring in areas without stations for networks 0.25*0.25 latitude and longitude degrees.

Drought is recognized as a slow, creeping phenomenon that can accelerates the expansion of desertification in different regions especially in arid and semi-arid area with its effect on the agricultural sectors, water resources and vegetation cover. Positioning of Iran in the world arid and semi-arid belt is exposed to drought and water crisis and desertification. Drought monitoring and zoning with the goal of planning and water resources management are very important in different area especially in arid and semi-arid regions. One of the methods for drought study is monitoring and mapping of drought using meteorological indices and Geographic Information System techniques. In order to investigate and drought monitoring in present research during the period of 29 years (1989 to 2017) in Qoum-Kahak study region we used annual rainfall data from four stations (i.e. Qoume, Kahak, Koohsefid and Janatabad) which are located inside and around the Qoume-Kahak catchment. Then we applied meteorological indices such as Standard of Precipitation Index (SPI), Percent of Normal Index (PNi), Deciles Index (DI), Chinese Z Index (CZI) and Z-Score Index (ZSI) for drought monitoring during the study period. Afterward for drought mapping, four interpolation methods included Simple Kriging (SK), Ordinary Kriging (OK), Inverse Distance Weighting (IDW) and Radial Basis Functions (RBF) were used and compared. After determination of best method in each year, yearly drought map were produced based on the best interpolation methods in ArcGIS software environment. According to the result of meteorological indices the near-normal class occurred more than other classes in study stations. SPI results indicated that Jannatabad and Kahak stations have the highest and lowest frequency of extremely dry class during the study period, respectively. The most extremely dry class with the SPI of -2.35 was occurred in Janatabad station in the year of 1997-98. Based on the results of PNI and ZSI indexes there was no occurred extremely dry class in all stations. The result of PNI index indicated that Koohsefid station has the highest frequency of very dry class between all stations. According to the result of CZI index the extremely dry class was occurred only for Kahak and Janatabad stations in the water years of 2016-2017 and 1997-98 respectively. Extremely wet class was occurred also for Kahak and Janatabad stations during the water years of 2009-2010 and 1992-1993 respectively. The results of DI index illustrated that the class of very much below normal was occurred in Qoume and Koohsefid stations 4 times and in Kahak and Janatabad stations 3 times during the study period. We applied geostatistical analyst tools in ArcGIS software to produce zoning maps for rainfall and drought. Its result showed that ordinary kriging with RMSE of 28 mm is the best method to create rainfall map. Accordingly mean annual rainfall was 136 mm/year during the study period. We selected SPI index for drought monitoring and zoning because of according to the results of all meteorological indices,only for this index the extremely and severely drought classes for all stations have occurred Simultaneous with the minimal rainfall during the study period. Afterward we compared different interpolation methods to produce drought zoning maps for each year during the study period. Based on the results of RMSE ordinary kriging and simple kriging were the best methods for most years. The results of all meteorological indices suggested that in all stations the near-normal class has the most frequency during the study period. According to the results of SPI and CZI indices, the highest (7 years) and lowest (3 years) number of drought were occurred in Kahak and Jannatabad stations, respectively. While according to PN index the highest (9 years) and lowest (3 years) number of drought were observed in Qoum and Jannatabad stations, respectively. Also the results of PN index illustrated that there was no wet period during the study period. According to the ZSI Index, the extremely dry class did not occurred in the region and the ZSI results about the frequency of extremely wet class was similar to the SPI results. The results of drought zoning indicated that in the years of 1990, 1995 and 1997, most of the region has been in a state of extremely to slightly drought. In the years 2010 and 2017, slight to sever drought classes were occurred in most parts of the study area and the slight wet class was observed in the eastern part of region. While during the years of 1992, 1996 and 2009 whole of the study area has experienced moderate and severe wet conditions. In the year of 2011, half of the study area which is located in the eastern part of the region has been in a state of moderate wet condition.

Drought is a natural and climatic phenomenon that occurs in world wide areas every year and occurrence becomes an inevitable issue. This phenomenon is impaired in ecosystem. Arid rangeland ecosystems are a significant part of our land that is brittle systems that climatic changes are useful to simply unfounded destruction. Therefore, drought identifying and monitoring valid descriptive statistics indicators is the first step toward managing this phenomenon. Drought monitoring by using traditional systems is difficult. Remote sensing technology, coupled with geographic information systems, their ability in data performance has shown that in time of drought. This study was conducted at rangelands of Yazd Province to monitor of drought. In this study has been trying to research this index NDVI, EVI, NMDI, LST and TCI bands of MODIS images extracted from the data and precipitation data from climatology stations to use the range . Regarding the comparison between drought indices and indicators for climate satellite and satellite set performance indicators , to evaluate the climatic index SPI closest climatology stations to the monthly precipitation statistics for the period 2000-2008 types of rangeland in the study was used . To extract the parameters of satellite imagery resolution bands of MODIS images of 500 meters, the eight -day harvest interval for the period 2000 to 2012 and during the months of February through September, before and after it was prepared. Due to the different periods of precipitation data and satellite imagery, Joint Range Index Comparison between 2000 -2007 was considered. Data from other years was used to verify the accuracy of the results. Indices at intervals of three, six, nine, 12, 18 and 24 months showed that the volatility of short-term drought intervals greater than long-term intervals. But enjoying a bit of persistence. So in short periods of drought month intervals is greater than the other. Regarding the relationship between drought and precipitation, precipitation and meteorological drought index results showed that drought index ranged from three to nine months; with precipitation amounts of one percentage correlations are significant. In other words, changes in the amount of monthly precipitation index SPI is effective in short-term timeframe. Statistical comparison between results of calculation of satellite indicators and meteorological drought index showed that SPI index in short term with heat index and NMDI index has the highest correlation in one percent level.