Locating suitable sites for rainwater harvesting (RWH) in the central arid region of Iran

Rainwater harvesting is an encouraging instrument for augmenting surface and ground waters to overcome the inequality between water demand and supply, growing due to the rising need for water. This study offers an approach that can enable water managers to use the GIS to determine the most suitable location for rainwater harvesting by employing the TOPSIS multi-criteria decision analysis and applying its coefficients to zoning the area. To select the most effective indices for locating water harvesting in the region, 31 indices were determined, based on the studies done in this field in the world. For evaluating each index, four criteria, including suitability for purpose, ease and accuracy, cost, time and acceptance rate in local communities, were weighted by the Shannon entropy method. Then, using the TOPSIS ranking algorithm, the most effective indices were used to locate water harvesting. Using Geographic Information System (GIS), a map was developed for each index given a numerical value between 1 and 4. Finally, the map of rainwater harvesting locations was prepared in two ways: the geometric mean of eight indices and applying TOPSIS coefficients of the eight effective indices. Results showed that the time criterion with the weight of 0.306 was the most important. The ease and accuracy criterion with the value of 0.128 was the least important to select rainwater harvesting indices. Of the 31 indices, eight indices were selected as the most effective indices and classified into four classes: hydrology, soil, vegetation, and climate. Results of the rainwater harvesting potential map were classified into two categories of medium and high. In contrast, the TOPSIS coefficients’ application was classified into three high, high, and medium classes. Based on this map, 1.38% of the area located in a very high class was found very suitable for rainwater harvesting.