interpolation methods

This study was conducted with the aim of understanding the temporal and spatial variations of groundwater levels in the Meshgin Plain Aquifer, located in Ardabil Province, with the application of spatial statistics and temporal regression and using groundwater depth data on an annual scale from 2007 to 2016. In order to achieve the optimal method of zoning spatial changes in groundwater level, a comparison of different interpolation methods including Radial Basis Functions (RBFs), Inverse Distance Weighted (IDW), and Kriging (KRG) based on cross-validation was used. In addition, regression relationships between groundwater level and the study years were fitted to determine how the data series ascended or descended. A comparison of interpolation methods based on cross-validation showed that the root mean square error (RMSE) of RBF, IDW, and KRG methods were 21.98, 22.85, 22.57 in 2007; and 23.45, 27.88, 26.25 in 2016, respectively. Therefore, the RBF method with the lowest estimation error due to the power applied to scattered data and low sampling points in both years was selected as the optimal method for estimation of groundwater level in the aquifer. The weighted average of groundwater table loss was calculated as equal to nine meters. Furthermore, the iso-decline map of groundwater level was indicative of a decrease in groundwater level in the western half and its increase in the eastern half of the aquifer which is related to anthropogenic factors (withdrawal of groundwater in agricultural lands). In general, it can be stated that the accuracy and efficiency of interpolation methods depend on the region and data characteristics. In the case of Meshgin Plain Aquifer, the discharge factor has been more effective than the recharge factor in annual fluctuations of groundwater level. Accordingly, it is necessary to establish a balance between the pattern of cultivation and irrigation and the pattern of spatio-temporal variations of groundwater level in managerial plans for Meshgin Plain Aquifer.

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.

As one of the most important natural disasters “drought” is a phenomenon, which has an important impact on water resources, natural ecosystems and human societies economic, social, political and cultural from the point of view. Therefore, it is essential and inevitable to create a proper management system based on the recognition of the drought characteristics including frequency, severity, continuity and spatial extend, and its monitoring to reduce the damages and its consequences. In this study, with the aim of better understanding of droughts in Jazmorian watershed and recognizing dry and wet periods, eight special characteristics of drought were studied using the SPI and CZI Meteorological drought indices and Geographic Information System (GIS). For this the rainfall data of 24 rain gauge stations were used over a 30year period of 1983-2013 and the drought condition were assessed. In order to interpolate and prepare the most suitable zoning map for the studied features, Kriging, Co-kriging and Inverse Distance Weighted (IDW) methods were selected and compared. To select the appropriate model for fitting on the experimental variogram, the ratio of Sill to Nugget was used. To choose the right interpolation method, the mean absolute error (MAE), mean bias error (MBE), root mean square error (RMSE), and general standard deviation (GSD) were calculated then selected with lower values indicating stronger spatial structures. The results showed that in studying the majority of drought features, the co-kriging method was better than the other two methods, and the SPI index evaluated the drought condition in more detail than the CZI index. On the other hand, the Jazmourian watershed, especially in the eastern part of the province of Sistan- Baluchestan, has a relatively high sensitivity to the drought phenomenon, in which increases the frequency, continuity and severity of droughts to the eastern and southeast regions, and affect the inhabitants of these areas heavily by the consequences of the drought. Therefore, it is suggested that in macro planning and drought management plans for Jazmorian watershed, studying drought in different monthly and annual time scales and providing a suitable strategy for the management of drought in the highlands and plains areas separately.

Groundwater is the main source of agricultural, drinking and industrial needs, especially in arid and semi-arid regions. The aim of this study was to investigate the relationship between groundwater quality and water level in Mashhad Plain. In this study, qualitative information of 41 underground water piezometer wells for months of feeding and evacuation was investigated in 2001-2015. The GS software and the GIS environment were used to map and Zonation using different interpolation methods. The results showed that the ordinary Kriging method with the lowest RMSe and the highest R2 had the best estimate in the region. The study of the predominant class of groundwater in Mashhad plain was classified as "good" and "moderate" for agricultural use, with Wilcox, C2-S1 and C3-S1 charts for drinking purposes. The results of the review of water quality parameters showed that, other than Mg, the rest of the parameters had incremental changes over the years, and among these parameters, electrical conductivity (EC) and the total dissolved solids (TDS) had a more significant increase, which reduced water quality during this It's been years. The average correlation between the spatial variation of the surface of the stand and the EC is -0.35 and -0.45, which indicates increased salinity by decreasing the aquifer's water level. The results of this research indicate that the main cause of water quality decline in Mashhad plain was the existence of industrial and residential areas and agricultural land development.

Geostatistical approaches have great importance because they include spatial correlation of geographic data. Present study evaluated the efficiency of geostatistical techniques and demonstrated their capabilities in studying the soil variables(soil texture (sand percent), EC and So4-2) in the important plant community of Nitraria schoberi in Meighan desert, Arak. A regular grid on the map comprising rectangular cells was designed and situated over the experimental area with 98 points for vegetation type. The grid was laid out in the field using the global positioning system. Soil samples were taken between 0-20 and 20-100 cm layers for each point. Analysis using the best view at semivariogram model were applied to select the Gaussian models of soil characteristics with R2 higher than 0.95. Among ordinary Kriging, simple Kriging and Inverse distance weighting methods, ordinary kriging method showed the best cross-validation criteria (mean square error and average error) and had higher prediction accuracy than others. Finally, spatial estimates of the soil characteristics were performed using ordinary kriging.

Rainfall erosivity is usually represented by indices based on rainfall characteristics. So far، many rainfall erosivity indices have been developed، out of which the R index (EI30 in the model of RUSLE) is the most acceptable one. By calculating the EI30 in various points، erosivity maps can be produced for the country، some provinces or any other parts of the country. In this study، erosivity map for Lorestan Province was produced using this index. In order to estimate this index for regions lacking data from recording rain gauges، regression analysis was used. Thus the EI30 index and a few easily obtainable rainfall erosivity indices were calculated for 13 recording rain gauges with long term and intensive rainfall data. A regression analysis was then carried out between EI30 index and other indices. The best regression equation was established using Modified Fournier index (MF) with determination coefficient and standard error of estimate of 0. 955 and 112، respectively. To mapping rainfall erosivity، all of rain gauges (both having rainfall intensity and daily rainfall depth records) existed in the province and that of the surrounding regions were then assessed، and 61 rain gauges having more than 15 year daily rainfall data were selected. The EI30 were then estimated for the selected ones using the regression equation. Mean، Maximum، Minimum and coefficient of variation of the rain gauges were 594. 94، 2257. 3، 98. 54 Mj-mm-ha-1hr-1year-1 and 66. 38 percent. For converting point erosivity data to a map، a number of common interpolation methods were assessed and in order to select the suitable one، cross- validatin method were used. from the interpolation methods، Co Kriging was found to be the most suitable in terms of low error measures based on cross validation. Therefore rainfall erosivity map were produced for Lorestan Province using Co Kriging.