Flood risk microzonation using IWPCA mathematical model, case stady: firoozabad Basin in Fars province, Iran

Flooding is a serious global problem, so as its intensity and frequency increase, global concerns in terms of loss of fatalities and economic losses associated with this phenomenon also increase..

Flood hazards are among the most important and frequent natural hazards in Iran and claim many lives and cause vast financial losses, annually (Chang, 2008). The extent and intensity of these hazards vary greatly. In this research the flood potential and the corresponding hazards due to Firouzabad watershed which is the Sub-basin of Mand River are studied. Due to violating the proper riparian zone rights, and as in Firouzabad watershed annually large amounts of water are lost due to floods caused by recent droughts, loss of vegetation, erosion and human made factors such is over-cultivation in the agricultural lands etc., thus attempt is made that by studying this topic a step is taken forward to solve the issue. Furthermore, by investigating the effective hydrological factors and recent climatic changes, the intensifying factors are identified. Considering the current shortage of water, it is possible that agricultural activity encounter water shortage and lack of efficiency. Therefore, through implementing proper solutions to prevent loss of water in the area such as control of surface waters and artificial recharge of groundwater tables etc. we could witness rich vegetation and cultivable agricultural lands in the watershed area in addition to increased water resources. Many research works have been done in terms of flood hazards among them the following could be mentioned:
The study area is located within the geographical area of southern Iran on the south west folded skirts of Zagros mountain ranges. Firouzabad area is limited to Mok and Mahkoyey Basin from north, Dehram Plain from south, Farashband from west and Meimand Plain from east. Firouzabad watershed is one of the appropriate areas for agricultural activity in Fars Province which is located within 100km distance from south east of Shiraz city. It is located within 52o 10' to 52o 38' E longitudes and 26o 36' to 36o 48' N latitudes. The watershed area is equal to 723 Km2 of which 240 Km2 is plain and 483 km2 is mountainous.
In this research use was made of ten effective parameters in order to investigate and create the flood hazard zones for Firouzabad watershed. For preparing the slope layer and its direction and topographic situation of the drainage density and distance from river use was made of DEM30 layer. Also for preparing the lithology layer use was made of geology layer with 1:1000000 scale. Also Landsat8 satellite images were used to create the land use and vegetation layer. Furthermore, the synoptic and rain-gage data corresponding to the existing station were utilized


After determining the effective variables on the flood, and preparing the corresponding maps of each variable in ArcGIS environment, a score is designated for each variable with respect to its importance. Next, using the AHP analysis, zoning of the flood potential for Firouzabad watershed was performed. At the next step, based on the importance and designated score, the combination of the mentioned ten variables layers was performed using the weighted linear combination (WLC) method, and the watershed was divided into five classes with flood occurrence probabilities ranging from high to low. Equation (1) shows the weight of each criterion for combining the layers and determining the flood potential of the watershed.
Accordingly, the flood potential zoning map was obtained by overlapping of the effective criteria


The results of weighting 10 effective parameters in flood occurrence of the Firouzabad watershed using IWPCA model showed that the slope and distance from river were the most significant parameters. In this case, the highest flood risk was in the central part of the basin. The results of zoning by IWPCA showed that the highest flood risk in the central part of the basin was about 248 km2, respectively.
Finally, the OLS method was used to evaluate the validity of the mentioned methods. The R2 coefficient in the IWPCA was about 0.76 and 0.41. The most important parameter in this output is R2 values, which indicate the appropriateness and accuracy of the used model. In a case, in which R2 is close to 1, the independent variables can exactly explain the changes in the dependent variables. Also, a P-value of at least 0.001 confirms the effectiveness of the IWPCA model in adapting to the dependent and independent variables.
Flood is a natural phenomenon which could occur with different return periods, based on the condition of the watersheds. In recent decades, by increase of population and overgrowth of cities and residential centers, humans by their aggressive behavior towards nature have exposed themselves to hazardous natural phenomena like floods. Considering the increased fatalities and financial outcomes in recent decades, the urban planners have sought new solutions and in locating new towns consider this issue. But concerning the old cities which are located near the rivers or where they overflow, other methods have been proposed. First there is need for further recognition of the situation and the flood potential and this has become possible by implementing new methods and tools developed by mankind. In this research, use has been made of ten effective criteria on flood potential. In this study and many similar research works both domestic and international studies performed in relation to the natural sciences, the geographic information system has been under focus of attention due to its various capabilities and tools and also tangible results. Also for enhancing the efficiency of these systems, use has been made of decision making techniques. Flood proneness in a watershed not only causes soil erosion but results in accumulation of runoffs in the main waterways, increased probability of formed gullies and flood occurrence downstream of watershed close to the exit point.
The results of weighting 10 effective parameters in flood occurrence of the Firouzabad watershed using IWPCA model showed that the slope and distance from river were the most significant parameters.
The results of zoning by IWPCA showed that the highest flood risk in the central part of the basin was about 248 km2, respectively