This paper studies, through the principles of fuzzy set theory, groundwater response to meteorological drought in the case of an aquifer system located in the plains at the southeast of Xanthi, NE Greece. Meteorological drought is expressed through standardized Reconnaissance Drought Index (RDISt) and Standardized Precipitation Index (SPI), which are calculated for various reference periods. These drought indices are considered as independent variables in multiple fuzzy linear regression based on Tanaka's model, while the observed water table regarding two areas is used as a dependent variable. The fuzzy linear regression of Tanaka is characterized by the inclusion constraints where all the observed data must be included in the produced fuzzy band. Hence, each fuzzy output can get an interval of values where a membership degree corresponds to each of them. A modification of the Tanaka model by adding constraints is proposed in order to avoid irrational behavior. The results show that there was a significant influence of the meteorological drought of the previous hydrological year, while geology plays an important role. Furthermore, the use of RDISt improves the results of fuzzy linear regressions in all cases. Two suitability measures and a measure of comparison between fuzzy numbers are used.

This study proposes a hybrid fuzzy multi-criteria methodology for the selection of the most preferable site for applying managed aquifer recharge (MAR) systems by utilizing floodwaters. The use of MAR can increase water resources for later water utilization in case of drought. In this multi-criteria problem, seven recharge sites are under consideration, based on nine criteria, aiming to make a final list of their relative ranking. A fuzzy analytic hierarchy process (FAHP) based on the logarithmic fuzzy preference programming (LFFP) method is used to determine the weights of criteria. LFFP is an optimization-based method that produces a priority vector from a fuzzy pairwise comparison matrix. Furthermore, fuzzy inference systems (FIS) based on the Mamdani approach are used to estimate the rating of each alternative with respect to the criterion examined, and then the final evaluation of the alternatives is obtained. A FIS is a fuzzy if–then rule-based system where the experts’ qualitative knowledge is translated into numerical reasoning for each individual criterion. The proposed methodology is applied in the aquifer system of the agricultural plain located to the southeast of the city of Xanthi in the Prefecture of Xanthi, NE Greece.

Bottom-up management in a catchment scale is deemed the optimal way to avoid conflicts among water users through the participation of stakeholders, strategy co-shaping, and solutions co-creation. Water management cannot be one-dimensional; it demands cross sectoral cooperation. Usually, the difficulty lies in proper stakeholder training and inclusion of their opinions, which should be used in a quantifiable manner in water management. The Laspias River watershed occupies an area of 221.8 km² that includes the River Basin District of Thrace; it is characterized by intense agricultural and industrial activity. To comply with the augmented water needs and pollution loads this research aims to utilize a hybrid intuitionistic fuzzy multi-criteria-based methodology to address respectfully stakeholders’ opinion, this research aims to utilize a hybrid intuitionistic fuzzy multi-criteria-based methodology. It is often difficult to manage planning water management measures as the problems include multiple (conflicting) criteria that are based on stakeholder’s opinions, which are usually imprecise and in a rather qualitative form. This study provides the mathematical tools to reach comprehensive decisions with the public involvement offering a practical solution in an existing problem, that is the proper inclusion of stakeholders’ opinion. The weights are produced based on a stakeholder’s opinion. The alternatives’ ranking is achieved based on the fuzzified intuitionistic version of the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), and a hierarchy of mitigation problems is achieved via this novel approach.

Βottom-up management in catchment scale is deemed as the determinant way to avoid the conflict of the water users through the participation of stakeholders, strategy co-shaping and solutions co-creation. Water management cannot be one-dimensional but demands cross sectoral coop-eration. Usually, the difficulty lies in proper stakeholder training and their opinion inclusion, using a quantifiable manner in water management. The Laspias River watershed occupies an area of 221.8 km2, belonging to the River Basin District of Thrace and it is characterized by intense agricultural and industrial activity. Complying with the augmented water needs and pollution loads by respecting stakeholders’ opinion, this research aims to utilize a hybrid intuitionistic fuzzy multi-criteria-based methodology. It is a common difficulty to deal with supplier selection in resources management since it is a typically decision-making problem encompassing multiple (several conflicting) criteria, on which stakeholder’s opinions are usually imprecise and in a rather qualitative form. Therefore, the proposed method provides the mathematical tool to move into more comprehensive decisions with the public involvement. The weights are produced based on the stakeholder’s opinion. The alternatives’ ranking is achieved based on the fuzzified intuition-istic version of Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) and problems’ mitigation solutions’ hierarchy is achieved.

The consideration of a theoretical probability distribution regarding the annual cumulative discharge will provide a significant opportunity to characterize the intensity of the hydrological drought. However, the matching between the observed probabilities and the adopted theoretical probability distribution can not be identical. Hence, in this work this matching is achieved by using a fuzzy regression based methodology and the attributes of the log-normal distribution. Finally, an ascending procedure to classify the intensity of hydrological drought is proposed and it is applied in case of the Evros River.